Patent Publication Number: US-2023141386-A1

Title: Devices for overvoltage, overcurrent and arc flash protection

Description:
RELATED APPLICATIONS 
     The present application is a continuation of U.S. patent application Ser. No. 16/578,779, filed Sep. 23, 2019, which is a continuation of U.S. patent application Ser. No. 15/071,758, now U.S. Pat. No. 10,447,023 filed Mar. 16, 2016, which claims the benefit of and priority from U.S. Provisional Patent Application No. 62/135,284, filed Mar. 19, 2015, the disclosures of each are incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to circuit protection devices and, more particularly, to overvoltage, overcurrent and arc flash protection devices and methods. 
     BACKGROUND 
     Frequently, excessive voltage or current is applied across service lines that deliver power to residences and commercial and institutional facilities. Such excess voltage or current spikes (transient overvoltages and surge currents) may result from lightning strikes, for example. The above events may be of particular concern in telecommunications distribution centers, hospitals and other facilities where equipment damage caused by overvoltages and/or current surges and resulting down time may be very costly. 
     Typically, sensitive electronic equipment may be protected against transient overvoltages and surge currents using Surge Protective Devices (SPDs). For example, brief reference is made to  FIG.  1   , which is a system including conventional overvoltage and surge protection. An overvoltage protection device  10  may be installed at a power input of equipment to be protected  50 , which is typically protected against overcurrents. Typical failure mode of an SPD is a short circuit. The overcurrent protection typically employed is a combination of an internal thermal disconnector to protect the device from overheating due to increased leakage currents and an external fuse to protect the device from higher fault currents. Different SPD technologies may avoid the use of the internal thermal disconnector because, in the event of failure, they change their operation mode to a low ohmic resistance. In this manner, the device can withstand significant short circuit currents. In this regard, there may be no operational need for an internal thermal disconnector. Further to the above, some embodiments that exhibit even higher short circuit withstand capabilities may also be protected only by the main circuit breaker of the installation without the need for a dedicated branch fuse. 
     Brief reference is now made to  FIG.  2   , which is a block diagram of a system including conventional surge protection. As illustrated, a three phase line may be connected to and supply electrical energy to one or more transformers  66 , which may in turn supply three phase electrical power to a main circuit breaker  68 . The three phase electrical power may be provided to one or more distribution panels  62 . As illustrated, the three voltage lines of the three phase electrical power may designated as L 1 , L 2  and L 3  and a neutral line may be designated as N. In some embodiments, the neutral line N may be conductively coupled to an earth ground. 
     Some embodiments include surge protection devices (SPDs)  104 . As illustrated, each of the SPDs  104  may be connected between respective ones of L 1 , L 2  and L 3 , and neutral (N). The SPD  104  may protect other equipment in the installation such as the distribution panel among others. In addition, the SPDs may be used to protect all equipment in case of prolonged overvoltages. However, such a condition may force the SPD to conduct a limited current for a prolonged period of time, which may result in the overheating of the SPD and possibly its failure (depending on the energy withstand capabilities the SPD can absorb and the level and duration of the overvoltage condition). A typical operating voltage of an SPD  104  in the present example may be about 400V (for 690V L-L systems). In this regard, the SPDs  104  will each perform as an insulator and thus not conduct current during normal operating conditions. In some embodiments, the operating voltage of the SPD&#39;s  104  is sufficiently higher than the normal line-to-neutral voltage to ensure that the SPD  104  will continue to perform as an insulator even in cases in which the system voltage increases due to overvoltage conditions that might arise as a result of a loss of power or other power system issues. 
     In the event of a surge current in, for example, L 1 , protection of power system load devices may necessitate providing a current path to ground for the excess current of the surge current. The surge current may generate a transient overvoltage between L 1  and N. Since the transient overvoltage significantly exceeds that operating voltage of SPD  104 , the SPD  104  will become conductive, allowing the excess current to flow from L 1  through SPD  104  to the neutral N. Once the surge current has been conducted to N, the overvoltage condition ends and the SPD  104  may become non-conducting again. However, in some cases, one or more SPD&#39;s  104  may begin to allow a leakage current to be conducted even at voltages that are lower that the operating voltage of the SPD&#39;s  104 . 
     Additionally, within an electrical device cabinet there may be devices that may protect the equipment inside the cabinet and proximate personnel from arc flashes that could be generated inside the cabinet. An arc flash occurring within a cabinet may create severe damages and is considered to be a very serious safety hazard for the personnel. As such, detection of the arc flash and interruption of the corresponding current should be as fast as possible to minimize damages and/or risks. However, especially in high power systems, during an arc flash the fault current could be limited to a lower level than the current threshold required for the main circuit breaker to trip fast enough. Faster response times may be required to avoid damages and/or risk. One solution employed by many manufacturers includes an electronic system to force the external tripping of the circuit breaker. During an arc flash there may be a significant increase of the pressure inside the cabinet and a significant increase in the illumination. An electronic circuit may use pressure and/or optical sensors to detect the presence of an arc flash and trip the circuit breaker. Other more recent techniques use readings of the voltage and current of the power system and trip the circuit breaker when specific patterns of these readings are encountered. 
     However, the time that a circuit breaker may take to disconnect the system form the power source (after being externally tripped by the electronic circuit) may be in the order of 100 milliseconds or more. During this time, a short circuit current that may be in a range of about 10 kAmperes to about 100 kAmperes may cause damage to the internal portions of the equipment as well as expose proximate personnel to significant danger. 
     SUMMARY 
     Some embodiments of the present invention are directed to a circuit protection device that includes an arc flash, overcurrent, overvoltage and surge protection system that is connected between a plurality of phase lines and a neutral line that are between an incoming power supply line and an electrical load panel in an electrical equipment. 
     In some embodiments, the arc flash, overcurrent, overvoltage and surge protection system includes a crowbar device that is coupled to the plurality of phase lines and to the neutral line and is configured to prevent an overvoltage condition by generating a low resistance current path from the plurality of phase lines to the neutral line, a plurality of surge protection devices that are connected to the plurality of phase lines and to the neutral line and that are configured to protect the equipment during an overvoltage condition by conducting a limited amount of current that corresponds to the overvoltage condition, and a crowbar trigger circuit that is configured to cause the crowbar device to turn on and provide the low resistance current path from ones of the plurality of phase lines to the neutral line. 
     Some embodiments provide that the crowbar device includes a plurality of overvoltage protection modules that are coupled between respective ones of the plurality of phase lines and the neutral line. In some embodiments, ones of the plurality of overvoltage protection modules each include a bidirectional thyristor and an inductor that is connected in series with the bidirectional thyristor. Some embodiments provide that ones of the plurality of overvoltage protection modules each include two thyristors that are connected in antiparallel with one another and an inductor that is connected in series with the two thyristors. In some embodiments, the ones of the plurality of overvoltage modules further comprise a snubber circuit that is connected in parallel with the two thyristors. Some embodiments provide that the snubber circuit includes a resistor and a capacitor that are connected in series with one another. 
     In some embodiments, the arc flash, overcurrent, overvoltage and surge protection system further includes an arc flash detection system that is configured to detect an arc flash within the equipment and to generate and send an arc flash signal to the crowbar trigger circuit. 
     Some embodiments provide that the crowbar trigger circuit includes a plurality of thyristor trigger circuits that are configured to generate thyristor trigger signals that are received by the crowbar device. In some embodiments, the crowbar trigger circuit further includes a power supply and voltage hold-up circuit that is configured to receive electrical power for the trigger circuit and to provide power to the trigger circuit for a time period after the electrical power for the trigger circuit is lost, an interface circuit that is configured to receive inputs corresponding to voltages of the plurality of phase lines, current flow through the plurality of phase lines, an arc flash signal and/or temperatures or respective surge protection devices, and a microcontroller that is configured to receive data from the interface circuit, to process the received data and to generate and send trigger signals one or more of the plurality of thyristor trigger circuits, an alarm signal to a remote alerting device and/or a trip signal to a main circuit breaker. Some embodiments provide that the power supply and voltage holdup circuit includes a plurality of DC-DC converters that are each operable to provide voltages to ones of the plurality of thyristor trigger circuits and a holdup circuit that is configured to hold a voltage that is provided to the plurality of DC-dc converters. 
     Some embodiments provide that the crowbar device includes a plurality of pairs of antiparallel connected thyristors that are coupled between respective ones of the plurality of phase lines and the neutral line, a plurality of inductors that are connected in series respective ones of the plurality of pairs of antiparallel thyristors, and a plurality of surge protection devices that are connected between respective ones of the plurality of phase lines and the neutral line. 
     In some embodiments, the arc flash, overcurrent, overvoltage and surge protection system includes a crowbar device that is coupled to and between the plurality of phase lines and is configured to prevent an overvoltage condition by selectively generating a low resistance current path between the plurality of phase lines, a plurality of surge protection devices that are connected to and between the plurality of phase lines and that are configured to protect the equipment during an overvoltage condition by conducting a limited amount of current that corresponds to the overvoltage condition, and a crowbar trigger circuit that is configured to cause the crowbar device to turn on and provide the low resistance current path from ones of the plurality of phase lines to the neutral line. 
     Some embodiments provide that the arc flash, overcurrent, overvoltage and surge protection system includes a crowbar device that is coupled to the plurality of phase lines and to the neutral line and is configured to prevent an overvoltage condition by generating a low resistance current path from the plurality of phase lines to the neutral line, a plurality of surge protection devices that are connected to the plurality of phase lines and to the neutral line and that are configured to protect the equipment during an overvoltage condition by conducting a limited amount of current that corresponds to the overvoltage condition, and an arc flash trigger circuit that is configured to cause the crowbar device to turn on and provide the low resistance current path from ones of the plurality of phase lines to the neutral line. In some embodiments, the crowbar device includes a plurality of self-triggering crowbar modules that are connected to the neutral line and respective ones of the plurality of phase lines. 
     In some embodiments, the plurality of self-triggering crowbar modules each include two thyristors that are connected in antiparallel with one another, an inductor that is connected in series with the two thyristors, and a crowbar trigger circuit that is configured to receive a current signal from a current sensor on the corresponding one of the plurality of phase lines and to cause at least one of the two thyristors to provide a low resistance current path between the corresponding one of the plurality of phase lines and the neutral line responsive to the current signal exceeding a current threshold. 
     In some embodiments, the crowbar trigger circuit is configured to generate a trigger signal in the absence of any signal from the arc flash trigger circuit. Some embodiments provide that the crowbar trigger circuit is configured to provide self triggering of the corresponding one of the plurality of crowbar modules during a start-up period of the equipment. In some embodiments, the arc flash trigger circuit is configured to trigger the plurality of crowbar modules responsive to detecting an arc flash after the start-up period of the equipment. 
     Some embodiments provide that the ones of the plurality of crowbar modules further include a snubber circuit that is connected in parallel with the two thyristors and that the snubber circuit includes a resistor and a capacitor that are connected in series with one another. 
     In some embodiments, the arc flash, overcurrent, overvoltage and surge protection system further includes an arc flash detection system that is configured to detect an arc flash within the equipment and to generate and send an arc flash signal to the arc flash trigger circuit. 
     Some embodiments provide that the arc flash, overcurrent, overvoltage and surge protection system further includes a threshold selector that is connected to the arc flash trigger circuit and is configured to provide a threshold current selection signal corresponding to a current threshold value. In some embodiments, the threshold selector includes a user input device that receives a user input and that provides the threshold current selection signal to the arc flash trigger circuit. Some embodiments provide that the threshold current selection signal includes a discrete binary value, and wherein a lowest value of the discrete binary value corresponds to a default threshold current. 
     Some embodiments of the present invention are directed to an arc flash, overcurrent, overvoltage and surge protection system that includes a crowbar device that is coupled to and between a plurality of phase lines and is configured to prevent an overvoltage condition by selectively generating a low resistance current path between the plurality of phase lines and a plurality of surge protection devices that are connected to respective ones of the plurality of phase lines and to the crowbar device and that are configured to protect the equipment during an overvoltage condition by conducting a limited amount of current that corresponds to the overvoltage condition. 
     In some embodiments, ones of the plurality of surge protection devices each include a first terminal that is connected to a corresponding one of the plurality of phase lines and a second terminal that is connected to the crowbar device. Some embodiments provide that the crowbar device includes a plurality of phase terminals that are connected to the plurality of surge protection devices and a plurality of thyristors that are connected between different pairs of the phase terminals. 
     Some embodiments provide that the crowbar device further includes a crowbar trigger circuit that is operable to generate thyristor trigger signals to the plurality of thyristors responsive to detecting a fault condition on the phase lines. In some embodiments, the crowbar trigger circuit includes a rectification circuit that generates a direct current (DC) signal corresponding to the voltages between the plurality of phase lines, a comparator that compares the DC signal from the rectification circuit to a reference signal, and a plurality of isolation drivers that receive a comparator output, and, responsive to the comparator output indicating that the DC signal exceeds the reference signal, generates a trigger signal that turns on the plurality of thyristors. 
     In some embodiments, the surge protection devices comprise metal oxide varistors. 
     Some embodiments of the present invention are directed to a surge protection system that includes a plurality of crowbar modules that are coupled to a plurality of phase lines and that are configured to prevent an overvoltage condition by selectively generating a low resistance current path between the plurality of phase lines and a neutral line and a plurality of surge protection devices that are connected in series with respective ones of the plurality of crowbar modules to provide a plurality of series circuits that each include one of the plurality of crowbar modules and one of the plurality of surge protection devices, wherein each of series circuits is connected between a corresponding one of the plurality of phase lines and the neutral line. 
     In some embodiments, ones of the plurality of surge protection devices each include a first terminal that is connected to a corresponding one of the plurality of phase lines and a second terminal that is connected to a corresponding one of the plurality of crowbar modules. In some embodiments, ones of the plurality of crowbar modules each include a plurality of antiparallel thyristors that are connected between a corresponding one of the plurality of surge protection devices and the neutral line and a crowbar trigger circuit that is operable to generate thyristor trigger signals to the plurality of thyristors responsive to detecting a fault condition on the phase lines. 
     In some embodiments, the crowbar trigger circuit includes a rectification circuit that generates a direct current (DC) signal corresponding to a voltage on the corresponding one of the plurality of phase lines, a comparator that compares the DC signal from the rectification circuit to a reference signal, a driver that receives the comparator output, and, responsive to the comparator output indicating that the DC signal exceeds the reference signal, generates a thyristor drive signal, and an optical isolator that generates a thyristor trigger signal responsive to receiving the thyristor drive signal from the driver, wherein the thyristor trigger signal turns the pair of antiparallel thyristors on to provide a low resistance current path between the corresponding one of the surge protectors and the neutral line. 
     According to embodiments of the invention, a crowbar module includes first and second electrical terminals, a module housing, and first and second crowbar units. The first crowbar unit is disposed in the module housing and includes a first thyristor electrically connected between the first and second electrical terminals. The second crowbar unit is disposed in the module housing and includes a second thyristor electrically connected between the first and second electrical terminals in electrical parallel with the first crowbar unit. 
     In some embodiments, the first thyristor is connected in antiparallel to the second thyristor. 
     The crowbar module may include a snubber circuit disposed in the module housing and electrically connected between the first and second electrical terminals in electrical parallel with each of the first and second crowbar units. 
     The crowbar module may include a coil assembly connected electrically in series between the first terminal and each of the first and second crowbar units. In some embodiments, the crowbar module includes a snubber circuit disposed in the module housing and electrically connected between the first and second electrical terminals in electrical parallel with each of the first and second crowbar units. 
     In some embodiments, the coil assembly includes: an electrically conductive coil member, the coil member including a spirally extending coil strip defining a spiral coil channel; and an electrically insulating casing including a separator wall portion that fills the coil channel. 
     In some embodiments, the module housing includes a cover defining an enclosed cavity, the first and second crowbar units are contained in the enclosed cavity, and the crowbar module further includes a filler material that fills a volume in the enclosed cavity not occupied by the first and second crowbar units. In some embodiments, the filler material is an epoxy. 
     The crowbar module may include a metal-oxide varistor device disposed in the module housing and electrically connected between the first and second electrical terminals in parallel with each of the first and second crowbar units. 
     The crowbar module may include a trigger circuit disposed in the module housing and electrically connected to the first and second crowbar units. In some embodiments, the crowbar module includes an electrical connection to an external current sensor. 
     According to some embodiments, the first thyristor includes a first contact surface that is one of an anode and a cathode, and a second contact surface that is the other of an anode and a cathode, and the first crowbar unit includes an electrically conductive first electrode contacting the first contact surface, and an electrically conductive second electrode contacting the second contact surface. In some embodiments, the first electrode is a unitary metal unit housing member including an end wall and a side wall, the end wall and the side wall define a unit housing cavity, the thyristor is disposed in the unit housing cavity. The crowbar module may include a biasing device biasing at least one of the first and second electrode members against the first or second contact surface. 
     According to some embodiments, the first crowbar unit includes: a unit housing defining an enclosed chamber, the first thyristor being disposed in the enclosed chamber; a wire port defined in a wall of the unit housing between the enclosed chamber and an exterior of the unit housing; a cable gland mounted in the wire port; and an electrical lead extending through the cable gland from the exterior of the unit housing and electrically connected to the first thyristor. 
     The electrical lead wire may be terminated at a control terminal of the first thyristor. The crowbar module may include a second electrical lead wire extending through the cable gland from the exterior of the unit housing and electrically connected to a reference terminal of the first thyristor. 
     In some embodiments, the cable gland is bonded to the electrical lead wire. In some embodiments, the cable gland includes a resin that is bonded to the electrical lead wire. In some embodiments, the resin is an epoxy resin. 
     According to some embodiments, the cable gland includes: a tubular outer fitting secured in the wire port; and a sealing plug mounted in the outer fitting and surrounding the electrical lead wire; wherein the sealing plug fills the radial space between the electrical lead wire and the outer fitting. In some embodiments, the sealing plug is bonded to the electrical lead wire. In some embodiments, the outer fitting is formed of a polymeric material bonded to the unit housing. 
     According to some embodiments, the cable gland mechanically secures the electrical lead wire to the unit housing and hermetically seals the wire port. 
     According to embodiments of the invention, a crowbar unit includes a unit housing defining an enclosed chamber, a thyristor disposed in the enclosed chamber, a wire port defined in a wall of the unit housing between the enclosed chamber and an exterior of the unit housing, a cable gland mounted in the wire port, and an electrical lead extending through the cable gland from the exterior of the unit housing and electrically connected to the thyristor. 
     In some embodiments, the thyristor includes a first contact surface that is one of an anode and a cathode, and a second contact surface that is the other of an anode and a cathode, and the crowbar unit includes an electrically conductive first electrode contacting the first contact surface, and an electrically conductive second electrode contacting the second contact surface. 
     According to some embodiments, the first electrode is a unitary metal housing member including an end wall and a side wall, the housing member forms a part of the unit housing and defines a housing cavity, and the thyristor is disposed in the housing cavity. 
     The crowbar unit may include a biasing device biasing at least one of the first and second electrode members against the first or second contact surface. 
     In some embodiments, the electrical lead wire is terminated at a control terminal of the thyristor. The crowbar unit may include a second electrical lead wire extending through the cable gland from the exterior of the unit housing and electrically connected to a reference terminal of the thyristor. 
     According to some embodiments, the cable gland is bonded to the electrical lead wire. In some embodiments, the cable gland includes a resin that is bonded to the electrical lead wire. In some embodiments, the resin is an epoxy resin. 
     According to some embodiments, the cable gland includes a tubular outer fitting secured in the wire port, and a sealing plug mounted in the outer fitting and surrounding the electrical lead wire, wherein the sealing plug fills the radial space between the electrical lead wire and the outer fitting. In some embodiments, the sealing plug is bonded to the electrical lead wire. In some embodiments, the outer fitting is formed of a polymeric material bonded to the unit housing. 
     According to some embodiments, the cable gland mechanically secures the electrical lead wire to the unit housing and hermetically seals the wire port. 
     In some embodiments, the thyristor is a bi-directional thyristor. 
     According to method embodiments of the invention, a method for forming a crowbar unit includes: providing a unit housing defining an enclosed chamber and including a wire port defined in a wall of the unit housing between the enclosed chamber and an exterior of the unit housing; mounting a thyristor in the enclosed chamber; routing an electrical lead wire through the wire port; sealing the electrical lead wire in the wire port with a cable gland; and electrically connecting the electrical lead wire to the thyristor. 
     In some embodiments, sealing the electrical lead wire in the wire port with a cable gland includes: forming a cable gland, including inserting an electrical lead wire in a tubular outer fitting, introducing a liquid sealing material into the outer fitting about the electrical lead wire, and curing or hardening the liquid sealing material about the electrical lead wire to seal the electrical lead wire in the outer fitting; and mounting the electrical lead wire and the cable gland in the wire port. In some embodiments, the liquid sealing material is a resin. 
     According to embodiments of the invention, a crowbar device includes a device housing and a crowbar module and a current sensor disposed in the device housing. The crowbar module includes: a module housing; a thyristor disposed in the module housing; a self-trigger circuit disposed in the module housing; and a snubber circuit disposed in the module housing. 
     According to embodiments of the invention, a crowbar system includes a crowbar module and an external trigger and alarm interface circuit. The crowbar module includes: a module housing; a thyristor disposed in the module housing; a coil disposed in the module housing; a trigger circuit disposed in the module housing; and a snubber circuit disposed in the module housing. The external trigger and alarm interface circuit is electrically connected to the crowbar module. 
     It is noted that aspects of the invention described with respect to one embodiment, may be incorporated in a different embodiment although not specifically described relative thereto. That is, all embodiments and/or features of any embodiment can be combined in any way and/or combination. These and other objects and/or aspects of the present invention are explained in detail in the specification set forth below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying figures are included to provide a further understanding of the present invention, and are incorporated in and constitute a part of this specification. The drawings illustrate some embodiments of the present invention and, together with the description, serve to explain principles of the present invention. 
         FIG.  1    is a block diagram of a system including conventional surge protection. 
         FIG.  2    is a block diagram of a system including conventional surge protection. 
         FIG.  3    is a block diagram illustrating an arc flash and surge protection system according to some embodiments of the present invention. 
         FIG.  4    is a block diagram illustrating an arc flash and surge protection system according to some embodiments of the present invention. 
         FIG.  5    is a schematic diagram representing a circuit including an arc flash and surge protection system in a switchgear cabinet according to some embodiments of the present invention. 
         FIG.  6    is a schematic block diagram illustrating a trigger circuit as briefly described above regarding  FIG.  4   , according to some embodiments of the present invention. 
         FIG.  7    is a schematic block diagram illustrating a power supply and voltage hold-up circuit as discussed in reference to  FIG.  6   . 
         FIG.  8    is a block diagram illustrating a DC-DC isolated converter as discussed in reference to  FIG.  7   . 
         FIG.  9    is a schematic block diagram illustrating a thyristor trigger circuit as discussed in reference to  FIG.  6   . 
         FIG.  10    is a schematic diagram representing a circuit including an arc flash and surge protection system according to some embodiments of the present invention. 
         FIG.  11    is a schematic diagram representing a circuit including an arc flash and surge protection system according to some embodiments of the present invention. 
         FIG.  12    is a schematic diagram representing a circuit including an arc flash and surge protection system according to some embodiments of the present invention. 
         FIG.  13    is a top perspective view of a crowbar system and a trigger module according to some embodiments of the present invention. 
         FIG.  14    is a cross-sectional view of the crowbar system of  FIG.  13    taken along the line  14 - 14  of  FIG.  13   . 
         FIG.  15    is a top perspective view of a crowbar module forming a part of the crowbar system of  FIG.  13   . 
         FIG.  16    is a fragmentary, exploded, top perspective view of the crowbar module of  FIG.  15   . 
         FIG.  17    is an exploded, top perspective view of a coil assembly forming a part of the crowbar module of  FIG.  15   . 
         FIG.  18    is a cross-sectional, bottom perspective view of a casing forming a part of the coil assembly of  FIG.  17   . 
         FIG.  19    is an exploded, bottom perspective view of a crowbar unit forming a part of the crowbar module of  FIG.  15   . 
         FIG.  20    is a cross-sectional, top perspective view of the crowbar unit of  FIG.  19   . 
         FIG.  21    is an enlarged, fragmentary, cross-sectional view of the crowbar unit of  FIG.  19   . 
         FIG.  22    is a rear perspective view of the connector module of  FIG.  13   . 
         FIG.  23    is a fragmentary, perspective view of a crowbar module according to further embodiments of the invention. 
         FIG.  24    is a schematic diagram illustrating an arc flash and surge protection system used in protecting equipment according to some embodiments of the present invention. 
         FIG.  25    is a schematic block diagram illustrating a crowbar module as briefly described above regarding  FIG.  24   , according to some embodiments of the present invention. 
         FIG.  26    is a schematic block diagram illustrating a trigger circuit of the crowbar module as briefly described above regarding  FIG.  25   , according to some embodiments of the present invention. 
         FIG.  27    is a graph illustrating voltage and current values during an overvoltage condition according to some embodiments of the present invention. 
         FIG.  28    is a schematic block diagram illustrating an arc flash trigger circuit of the crowbar module as briefly described above regarding  FIG.  24   , according to some embodiments of the present invention. 
         FIG.  29    is a schematic block diagram illustrating a surge protection system used in protecting equipment according to some embodiments of the present invention. 
         FIG.  30    is a schematic block diagram illustrating a crowbar device as briefly described above regarding  FIG.  29   , according to some embodiments of the present invention. 
         FIG.  31    is a schematic block diagram illustrating a surge protection system used in protecting equipment according to some embodiments of the present invention. 
         FIG.  32    is a schematic block diagram illustrating a crowbar module as briefly described above regarding  FIG.  31   , according to some embodiments of the present invention. 
         FIG.  33    is a top perspective view of a crowbar system according to some embodiments of the present invention. 
         FIG.  34    is a top perspective view of a crowbar module forming a part of the crowbar system of  FIG.  33   . 
         FIG.  35    is a fragmentary, exploded, top perspective view of the crowbar module of  FIG.  33   . 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION 
     The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which illustrative embodiments of the invention are shown. In the drawings, the relative sizes of regions or features may be exaggerated for clarity. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. 
     It will be understood that when an element is referred to as being “coupled” or “connected” to another element, it can be directly coupled or connected to the other element or intervening elements may also be present. In contrast, when an element is referred to as being “directly coupled” or “directly connected” to another element, there are no intervening elements present. Like numbers refer to like elements throughout. 
     In addition, spatially relative terms, such as “under”, “below”, “lower”, “over”, “upper” and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “under” or “beneath” other elements or features would then be oriented “over” the other elements or features. Thus, the exemplary term “under” can encompass both an orientation of over and under. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly. 
     Well-known functions or constructions may not be described in detail for brevity and/or clarity. 
     As used herein the expression “and/or” includes any and all combinations of one or more of the associated listed items. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
     Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. 
     According to embodiments described herein, an arc flash and surge protection system may protect electrical distribution and control equipment from arc flashes that may be generated inside an enclosure, such as an electrical switchgear cabinet. In the event of an arc in the absence of protections provided herein, a short circuit corresponding to the arc may cause the circuit breaker to trip and open the circuit within about 100 milliseconds. In the case of lower short circuit current due to, for example, circuit impedance, an arc flash detection system may trigger the circuit breaker to trip. However, during this period, the short circuit current, which may be between about 10 kA to about 100 kA, will damage internal equipment within the switchgear cabinet, and may present a serious safety hazard for personnel proximate the switchgear cabinet. 
     As disclosed herein, the above effects may be eliminated by using a crowbar device that has a very fast response time (e.g., less than about 5 milliseconds) and that may conduct the fault current to eliminate the arc until the circuit breaker trips and disconnects the switchgear cabinet from the power source. 
     The crowbar device may include two thyristors (one for each direction of AC current) that when triggered may create a short that will conduct the current and eliminate the arc flash. However, as provided herein, thyristors may be protected against damage from false triggers and/or overvoltages. False triggers may be protected against using circuit components described herein and overvoltage protection may be provided using surge protection devices that may be connected in parallel with the overvoltage protection device. The use of the surge protective device may protect the thyristors of the crowbar device from false trigger and other equipment in the installation. 
     In some embodiments, the crowbar device may protect the surge protection device in the event that the surge protection device has failed. For example, typical failure mode of such devices may be a short circuit that is interrupted by either an internal thermal disconnector and/or an external fuse/circuit breaker. In this manner, the crowbar device may further protect the surge protection device in case of its failure and therefore obviate a need for a thermal disconnector and/or a series fuse/circuit breaker. 
     Some embodiments provide that the crowbar device may be implemented in several different ways. A first example provides for a single operation in that the crowbar device is used only once and a replacement crowbar device is provided to replace the used crowbar device. A second example includes a crowbar device that can be used multiple times. In this example, the crowbar device may withstand the short circuit current until the circuit breaker trips. As such, the crowbar device may be restored after the fault event and allow a possible reclosure of the main circuit breaker that will permit the installation to resume normal operation (provided that the problem that caused the tripping of the crowbar system has been solved). 
     To trigger the crowbar device, a separate electronic circuit may be used. This circuit may receive the trigger signal from the arc flash detector circuit as an input and may trigger the crowbar device and/or the main circuit breaker. In some embodiments, this circuit may also receive voltage and current readings of the power lines and current readings of the surge protection devices as inputs. In this manner, the electronic system may indicate the presence of a short circuit anywhere downstream of the crowbar device, if there is an prolonged overvoltage condition and if the surge protective devices failed. In any of the above conditions (or any other condition that is required and can be detected by using these sensors or additional sensors) the electronic system may trigger the crowbar device and the main circuit breaker. 
     In addition, the electronic circuit may also provide an alarm signal to indicate the presence of and/or type of problem that caused the tripping of the crowbar device. Some embodiments provide that the crowbar device may be triggered responsive to one or more of the following conditions and/or events:
         Arc Flash inside the cabinet;   Failure of the surge protective device;   Prolonged overvoltage or overcurrent conditions;   Short circuit downstream the crowbar device;   Any other pattern of electrical disturbance in the system that can be detected using the existing sensors or by installing additional sensors for that reason; and   Remote manual trigger.       

     Reference is now made to  FIG.  3   , which is a block diagram illustrating an arc flash, overvoltage, overcurrent and surge protection system according to some embodiments of the present invention. Some embodiments of the present invention may be applicable to the protection of equipment corresponding to switchgear systems used in industrial installations including secondary distribution panels and/or a service entrance section of electrical generation facilities, including, for example, wind turbine generators. However, such embodiments are non-limiting. For example, arc flash and surge protection systems described herein may be applicable to many different types of systems that may be susceptible to overvoltage conditions, surge currents and/or arc flash faults. For example, medium and/or low voltage switchgear for controlling and distributing single or multiphase electrical power may use arc flash and surge protections systems as described herein. In some embodiments, a switchgear cabinet  60  may include an arc flash, overvoltage, over current and surge protection system  100  configured therein to protect the equipment  50 , the switchgear cabinet  60  and other components included thereon and/or personnel proximate the switchgear cabinet  60 . 
     Brief reference is now made to  FIG.  4   , which is a block diagram illustrating an arc flash, overvoltage, over current and surge protection system according to some embodiments of the present invention. As illustrated, a three phase line may be connected to and supply electrical energy to one or more transformers  66 , which may in turn supply three phase electrical power to a main circuit breaker  68 . The three phase electrical power may be provided to one or more distribution panels  62 . As illustrated, the three voltage lines of the three phase electrical power may designated as L 1 , L 2  and L 3  and a neutral line may be designated as N. In some embodiments, the neutral line N may be conductively coupled to an earth ground. 
     Some embodiments include an arc flash, overvoltage, overcurrent and surge protection system  100  connected between the phase lines L 1 , L 2  and L 3 , and neutral (N). The arc flash, overvoltage, overcurrent and surge protection system  100  may protect other equipment in the installation such as the distribution panel  62  among others. In some embodiments, the arc flash, overvoltage, over current and surge protection system  100  may be coupled to and/or receive one or more signals from an arc flash detection system  64  that may be in a distribution panel  62  and/or other equipment in the installation. 
     As discussed above, an arc flash, overvoltage, overcurrent and surge protection system  100  may implemented in a system corresponding to power distribution switchgear  60  that is configured to distribute multiphase electrical power. For example, reference is now made to  FIG.  5   , which is a schematic diagram representing a circuit including an arc flash and surge protection system in a three phase switchgear cabinet according to some embodiments of the present invention. As illustrated, a three phase line may be connected to and supply electrical energy to one or more transformers  66 , which may in turn supply three phase electrical power to a main circuit breaker  68  in the switchgear cabinet  60 . Within the switchgear cabinet  60 , the three phase electrical power may be provided to one or more distribution panels  62  that may or may not be within the switchgear cabinet  60 . As illustrated, the three voltage lines of the three phase electrical power may designated as L 1 , L 2  and L 3  and a neutral line may be designated as N. In some embodiments, the neutral line N may be conductively coupled to an earth ground. 
     In some embodiments, the arc flash, overvoltage, overcurrent and surge protection system  100  may include a crowbar device  102  that is operable to prevent an overvoltage condition by generating a low resistance path from the three voltage lines L 1 , L 2 , L 3  to the neutral line N. Although some embodiments are discussed herein with reference to an overvoltage condition, such embodiments may also refer to an overcurrent condition that may or may not be a result of an overvoltage condition. Some embodiments provide that the crowbar device may be triggered by a trigger circuit  106 . 
     As illustrated, the crowbar device  102  may include an overvoltage protection module  120  corresponding to each of the three phases L 1 , L 2  and L 3 . Each overvoltage protection module  120  may include two thyristors (e.g., TH 5  and TH 6 ) that are electrically coupled in parallel with one another, but with opposite polarities. Stated differently, an anode of a first thyristor (e.g., TH 5 ) of the pair of thyristors may be coupled to a cathode of the second thyristor (e.g., TH 6 ) of the pair of thyristors and a cathode of the first thyristor (TH 5 ) of the pair of thyristors may be coupled to the anode of the second thyristor (TH 6 ) of the pair of thyristors. In this manner, when the thyristors are triggered to be in a conductive state, each half of an alternating current waveform may be conducted from the phase to the neutral. 
     In some embodiments, an overvoltage protection module  120  may include a circuit of a resistor R and a capacitor C arranged in series with one another, such that the resistor-capacitor series RC is connected in parallel with the two thyristors (e.g., TH 5  and TH 6 ). Although described and illustrated as a single resistor R and capacitor C, embodiments may include more than one resistor and/or more than one capacitor to achieve the desired resistive and/or capacitive performance, but also to use extra R and C for redundancy, as the operation of this circuit may be important to prevent a false triggering of the thyristors. The snubber circuit may slow down a rate of change in voltage (dV/dt) that may otherwise result in falsely triggering the thyristor. For example, in the absence of the RC snubber circuit, the thyristor may be triggered by electrical noise that is unrelated to an actual overvoltage condition. The capacitor C may reduce the rate of change in voltage (dV/dt) together with the resistor R. The inductance L and the resistance R may limit the inrush of current of the high capacitance value of the capacitor C when the circuit is energized. 
     Some embodiments provide that an inductor L in arranged in series with the pair of antiparallel-connected thyristors. The inductor L may limit a rate of change in current (di/dt) through the thyristors, which might otherwise damage the thyristors. Also, L, combined with the RC snubber circuit, reduces the rate of change in voltage (dV/dt) at the thyristors in case of an overvoltage generated in the power system. In this manner, a self-trigger of thyristors may be prevented. 
     Some embodiments provide that in a three-phase power system, a crowbar device  102  includes three overvoltage protection modules  120  that may be coupled from respective phase conductors L 1 , L 2  and L 3  to a neutral N. In some embodiments, each of the overvoltage protection modules  120  is a modular component include all of the functional components therein in a single assembly. Some embodiments provide that multiple (e.g., three in a three-phase power system) overvoltage protection modules  120  may be configured as a single assembly including the components and functionality for overvoltage protection for all phases in a single assembly. 
     Some embodiments include surge protection devices (SPDs)  104 . As illustrated, each of the SPDs  104  may be connected between respective ones of L 1 , L 2  and L 3 , and neutral (N). The use of the SPD may protect the thyristors of the crowbar device during lightning events and/or transient overvoltage conditions, as well as protect other equipment in the installation. In addition, the SPDs may be used to protect all equipment in case of prolong overvoltages. However, such a condition may force the SPD to conduct a limited current for a prolonged period of time, which may result in the overheating of the SPD and possibly its failure (depending on the energy withstand capabilities the SPD can absorb and the level and duration of the overvoltage condition). Such event may be addressed by tripping the crowbar device. A typical operating voltage of an SPD  104  in the present example may be about 400V (for 690V L-L systems). In this regard, the SPDs  104  will each perform as an insulator and thus not conduct current during normal operating conditions. In some embodiments, the operating voltage of the SPD&#39;s  104  is sufficiently higher than the normal line-to-neutral voltage to ensure that the SPD  104  will continue to perform as an insulator even in cases in which the system voltage increases due to overvoltage conditions that might arise as a result of a loss of power or other power system issues. 
     In the event of a surge current in, for example, L 1 , protection of power system load devices may necessitate providing a current path to ground for the excess current of the surge current. The surge current may generate a transient overvoltage between L 1  and N. Since the transient overvoltage significantly exceeds the operating voltage of SPD  104 , the SPD  104  will become conductive, allowing the excess current to flow from L 1  through SPD  104  to the neutral N. 
     Once the surge current has been conducted to N, the overvoltage condition ends and the SPD  104  becomes non-conducting again. However, in some cases, one or more SPD&#39;s  104  may begin to allow a leakage current to be conducted even at voltages that are lower than the operating voltage of the SPD&#39;s  104 . Under such conditions, the leakage current may be measured using, for example, current transformers  105  that may provide leakage current values to the trigger circuit  106 . 
     An arc flash detection system  64  may be configured to detect an arc flash within the switchgear cabinet  60  using one or more sensors and/or sensor types including photosensors, pressure sensors and/or current transformers, among others. The arc flash detection system may provide an arc flash detection signal (AFD) to the trigger circuit  106 . 
     The trigger circuit  106  may receive inputs corresponding the line voltages L 1 , L 2 , L 3 , the line currents I 1 , I 2 , I 3 , the SPD leakage currents Is 1 , Is 2 , Is 3 , and the arc flash detection signal AFD. As described in more detail below, the trigger circuit  106  may, in response to a fault circumstance, cause the crowbar device  102  to turn on, thus providing a low resistance current path from the lines L 1 , L 2 , L 3  to the neutral N, cause the main circuit breaker  68  to trip, and/or cause the SPD&#39;s to begin conducting. In some embodiments, the trigger circuit  106  may further generate and/or transmit an alarm signal to one or more other types of monitoring, logging or alarm equipment. 
     Some embodiments provide that the trigger circuit  106  is powered through a trigger circuit power supply  65 , such as a single phase alternating current power source and/or a direct current power source. Some embodiments provide that the trigger circuit power supply  65  may be coupled to the trigger circuit  106  via one or more circuit interrupters or circuit breakers  67  and may be thus protected by the SPDs  104 . 
     Reference is now made to  FIG.  6   , which is a schematic block diagram illustrating a trigger circuit as briefly described above regarding  FIG.  5   , according to some embodiments of the present invention. In some embodiments, a trigger circuit  106  may include a power supply and voltage hold-up circuit  166 , which may receive single phase alternating current electrical power and/or direct current electrical power to power the trigger circuit. The power supply and voltage hold-up circuit  166  may include a voltage hold-up circuit that may provide power to the trigger circuit for at least 100 milliseconds after a condition which eliminates the availability of the electrical power received from the a trigger circuit power supply  65 . 
     In this manner, even with a loss of trigger circuit power due to a fault in another portion of the circuit, the power supply and voltage hold-up circuit  166  maintains sufficient voltage for the trigger circuit  106  to function until the circuit breaker is capable of tripping. For example, during this period, trigger signals to all of the thyristors may be maintained continually to keep the thyristors in a conducting state. Thus, the thyristors may be maintained in a conducting state until the main circuit breaker  68  has tripped. In the alternative, if a trigger signal to the thyristors is lost, the thyristors will only allow very limited current flow therethrough, which may result in the arc flash restarting. 
     Brief reference is now made to  FIG.  7   , which is a schematic block diagram illustrating a power supply and voltage hold-up circuit  166  as discussed in reference to  FIG.  6    above. In some embodiments, the power supply and voltage hold-up circuit  166  is configured to receive electrical power as a single phase alternating current (AC) power source including a voltage line L p  and a neutral line N p . In such embodiments, the received electrical power may be converted from AC to direct current (DC) using an AC-DC rectification unit  180 . The resulting DC power may be smoothed using a smoothing capacitor  182 . 
     The DC power may be provided to a voltage hold-up circuit  184  that may include a holding resistor Rh that is connected in parallel with a holding diode Dh. The parallel combination of the holding resistor Rh and the holding diode Dh may be connected in series with a holding capacitor Ch. Some embodiments provide that the Rh, Dh, Ch circuit is connected between the DC power line and the ground or neutral. In some embodiments, the anode of the holding diode Dh is connected to the DC power line and the cathode of the holding diode Dh is connected to the holding capacitor Ch, the other terminal of which is connected to the ground or neutral. 
     The power supply and voltage hold-up circuit  166  may include multiple different DC-DC isolated converters  186 . For example, in the context of a three phase system, a DC-DC isolated converter  186 - 1  may be provided to supply voltage (Vs, S) to a common driver in each of the three different thyristor trigger circuits  168 - 1 ,  2 ,  3 . Additionally, three DC-DC isolated converters  186 - 2 ,  3 ,  4  may be provided to supply voltage (Vs 1 , S 1 ; Vs 2 , S 2 ; Vs 3 , S 3 ) to respective ones of the thyristor trigger circuits  168 - 1 ,  2 ,  3 , respectively. 
     Brief reference is now made to  FIG.  8   , which is a block diagram illustrating a DC-DC isolated converter as discussed in reference to  FIG.  7    above. A DC-DC isolated converter  186  may receive an input DC voltage Vin to an inverter  191 , which is configured to convert the DC input voltage to an AC voltage. The AC voltage may be provided to an isolation transformer  192 , which may produce a corresponding AC output that is conductively isolated from the input AC voltage that is received from the inverter  191 . In some embodiments, the isolation transformer  192  may include a coil winding ratio that is 1:1 such that the AC output voltage is at a same voltage level as the AC input voltage received by the isolation transformer. Some embodiments provide that the isolation transformer  192  coil winding ratio is not 1.0 and thus the AC output voltage may have a different voltage level from the AC input voltage received by the isolation transformer  192 . The AC output voltage from the isolation transformer  192  may be received by a rectifier  193 , which is configured to convert the AC voltage to a DC output voltage. 
     Referring back to  FIG.  6   , in some embodiments, the trigger circuit  106  may include an interface circuit  164  that is configured to receive inputs from various sensors and provide the data corresponding to the received inputs to a microcontroller  162 . For example, the interface circuit  164  may receive inputs corresponding to: the voltages of the phase power lines L 1 , L 2 , L 3  and the neutral N; an arc flash alarm signal AFD from the arc flash detection system  64 ; current flow on the phase power lines I 1 , I 2 , I 3 ; current flow through the SPD&#39;s Is 1 , Is 2 , Is 3 ; and/or temperature of the SPDs Ts 1 , Ts 2 , Ts 3 , among others. 
     Some embodiments provide that the microcontroller  162  may process the received inputs and generate trigger signals to one or more thyristor triggers  168 - 1 ,  2 ,  3  to trigger the thyristors to a conduction mode. In some embodiments, the microcontroller may further generate a trip signal TCB to the main circuit breaker  68 . Some embodiments provide that the microcontroller generates an alarm signal that may be provided to local and/or remote locations that may be monitored and/or that may include supervisory control and data acquisition (SCADA). In some embodiments, the alarm signal is provided to a remote visual and/or audible annunciator. 
     The microcontroller  162  may trigger the thyristors based on a variety of causes and/or events. For example, an arc flash may trigger an arc flash signal to be sent to the microcontroller  162  from the arc flash detection system  64 . A system overvoltage condition corresponding one or more lines having a voltage that exceeds a predetermined threshold for a predetermined period of time may cause the microcontroller to trigger the thyristors. An overcurrent condition on one or more lines in which the current exceeds a predetermined current threshold for a predetermined period of time may cause the microcontroller to trigger the thyristors. 
     In some embodiments, overheating of the surge protection devices  104  in which a temperature of the SPDs exceeds a predetermined temperature threshold for a predetermined period of time may cause the microcontroller to trigger the thyristors. Additionally a short circuit may be detected when a voltage drop of any phase line and a corresponding current increase of that phase line may cause the microcontroller to trigger the thyristors. 
     Some embodiments provide that a detected end of life of an SPD may cause the microcontroller to trigger the thyristors. In some embodiments, such an SPD may include a metal oxide varistor (MOV) and/or combined MOV/GDT (gas discharge tube). Such a condition may be determined by a voltage drop in a phase line and a current rise in the corresponding SPD. 
     In some embodiments, the microcontroller may be configured to trigger the overvoltage protection device only when specific combinations of conditions and/or events are occurring with or without any constraints on the time interval between the conditions and/or events. 
     In some embodiments the thyristor triggers  168 - 1 ,  2 ,  3  may receive a trigger signal from the microcontroller  162  and provide control signals to corresponding thyristor pairs to cause the respective thyristors to switch from a substantially non-conducting state to a conducting state. For example, brief reference is now made to  FIG.  9   , which is a schematic block diagram illustrating a thyristor trigger circuit  168 - 1  as discussed above in reference to  FIG.  6   . 
     Each of the thyristor trigger circuits  168  may be the same and may be operable to trigger a pair of thyristors that correspond to a specific phase line. As such,  FIG.  9    is directed to one of the thyristor circuits of  FIG.  6   , namely  168 - 1 , which corresponds to the thyristors connected to phase line L 1 . The common driver  172  may be powered by voltage lines Vs and S that are provided from the power supply and voltage hold-up circuit  166  and that are provided to the common driver  172  of each of the other thyristor trigger circuits  168 - 2 ,  3 . The common driver  172  changes state to provide a thyristor trigger signal TH 1  responsive to trigger signal T 1  from the microcontroller  162 . Thyristor  1  changes to a conducting state responsive to the state change of TH 1  and remains in a conducting state as long as TH 1  is activated. In the case of thyristor  1 , the reference point C 1  is the neutral line N. 
     The opto driver  170  may be powered by voltage lines Vs 1  and S 1  that are provided from the power supply and voltage hold-up circuit  166 . In contrast with the DC voltage circuit Vs and S, the voltage lines Vs 1  and S 1  are not provided to other ones of the thyristor circuits  168 - 2 ,  3 . The opto driver  170  changes state to provide a thyristor trigger signal TH 2  responsive to trigger signal T 2  from the microcontroller  162 . Thyristor  2  changes to a conducting state responsive to the state change of TH 2  and remains in a conducting state as long as TH 2  is activated. In the case of thyristor  2 , the reference point C 2  is the phase line L 1 . The phase voltage reference point is a reason for using an opto driver to isolate the output. 
     Referring back to  FIG.  6   , the trigger circuit triggers all 6 of the thyristors at the same time and maintains the triggered state for at least 100 milliseconds while at the same time the power is supplied to the trigger circuit via the power supply and voltage hold-up circuit  166 . Additionally, while the thyristors are being triggered, the trigger circuit may provide a trigger signal to the main circuit breaker  68  and an alarm indicating the fault. In some embodiments, the alarm may also include data corresponding to a cause of the fault event. 
     Brief reference is now made to  FIG.  10   , which is a schematic diagram representing a circuit including an arc flash, overvoltage, overcurrent and surge protection system in a three phase switchgear cabinet according to some other embodiments of the present invention. As illustrated, embodiments according to  FIG.  10    differ from those described above regarding  FIG.  5    in that the crowbar device  102  includes a bidirectional thyristor for each phase to neutral instead of two unidirectional thyristors in a complementary arrangement for each phase. Some embodiments provide that the bidirectional thyristors each rely on four control wires for providing a trigger signal thereto. Other features of  FIG.  10    are substantially similar to those discussed above regarding  FIG.  5    and thus will not be repeated. 
     Reference is now made to  FIG.  11   , which is a schematic diagram representing a circuit including an arc flash, overvoltage, overcurrent and surge protection system in a three phase switchgear cabinet according to some other embodiments of the present invention. As illustrated, embodiments according to  FIG.  11    differ from those described above regarding  FIG.  5    in that the crowbar device  102  includes the thyristors and the SPDs  104 . In some embodiments, ones of the SPDs  104  are connected in the crowbar device  102  in parallel with the thyristor, RC and/or RLC circuits that are connected from each phase to the neutral. Some embodiments provide that the SPDs  104  are metal oxide varistors (MOVs) and/or combined MOV/GDT. In some embodiments, the MOVs may be thermally fused to prevent overheating of the MOV in the case of increased leakage currents, which may be a typical occurrence when an overvoltage condition exists in the power system. In this regard, the trigger circuit  106  may monitor the temperature rise and/or the thermal fuse and/or current through the MOV to indicate if the MOV has failed to short. Responsive to such conditions, the thyristors may be quickly triggered to prevent further damage of the whole device. Some embodiments provide that the thermal fuse may be sufficient to interrupt leakage currents when the MOV has not failed to short, to prevent overheating of the device. Other features of  FIG.  10    are substantially similar to those discussed above regarding  FIG.  5    and thus will not be repeated. To further reduce the overvoltage that could be applied to the thyristors, additional MOVs could be used in parallel to the snubber circuit (RC). 
     Reference is now made to  FIG.  12   , which is a schematic diagram representing a circuit including an arc flash, overvoltage, overcurrent and surge protection system in a three phase switchgear cabinet according to some other embodiments of the present invention. As illustrated, embodiments according to  FIG.  12    differ from those described above regarding  FIG.  5    in that the crowbar device  102  is configured to be connected from phase to phase instead of phase to neutral. Specifically, a thyristor and an RLC circuit is connected from each phase to another phase such that the crowbar device  102  may operate without conducting excess current to a neutral line N. Additionally, the SPDs  104  are connected from phase to phase to provide overvoltage protection for one phase relative to the other phases. In some embodiments, the crowbar device  100  include a single thyristor that may be a single directional thyristor. Other features of  FIG.  10    are substantially similar to those discussed above regarding  FIG.  5    and thus will not be repeated. 
     As used herein, “monolithic” means an object that is a single, unitary piece formed or composed of a material without joints or seams. 
     With reference to  FIGS.  13 - 23   , a crowbar system  200  and a connector module  290  according to embodiments of the invention are shown therein. The crowbar system  200  corresponds to and is an implementation of the crowbar system  102  of  FIG.  5   . The connector module  290  corresponds to and is an implementation of a connector that may be connected between the crowbar system  102  and the trigger circuit  106  as illustrated in  FIG.  3   . 
     With reference to  FIG.  13   , the system  200  includes three line conductors L 1 B, L 2 B, and L 3 B (electrically connected to the lines L 1 , L 2  and L 3 , respectively, of  FIG.  5   ), a neutral conductor NB (electrically connected to the neutral line N of  FIG.  5   ), and three crowbar modules  210 ( 1 ),  210 ( 2 ), and  210 ( 3 ) according to embodiments of the invention and each corresponding to a respective one of the modules  120  of  FIG.  3   . The conductors L 1 B, L 2 B, L 3 B, NB may be substantially rigid, metal plates or busbars, for example. The conductors L 1 B, L 2 B, L 3 B, NB may be mounted in an electrical switchgear cabinet  60 , for example. The crowbar modules  210 ( 1 ),  210 ( 2 ), and  210 ( 3 ) are electrically connected to the connector module  290 . Each of the crowbar modules  210 ( 1 ),  210 ( 2 ), and  210 ( 3 ) electrically and mechanically connects the neutral conductor NB with a respective one of the line conductors L 1 B, L 2 B, L 3 B. 
     In some embodiments, the conductors L 1 B, L 2 B, L 3 B, NB are rigid busbars and are rigidly affixed to and connected by the modules  210 ( 1 ),  210 ( 2 ),  210 ( 3 ) to collectively form a substantially rigid, unitary assembly or device  203  ( FIG.  13   ). 
     With reference to  FIGS.  14 - 21   , the crowbar module  210 ( 3 ) is shown therein. The crowbar modules  210 ( 1 ),  210 ( 2 ), and  210 ( 3 ) may be substantially identical in construction and therefore only the crowbar module  210 ( 3 ) will be described in detail below, it being understood that this description likewise applies to the other crowbar modules  210 ( 1 ),  210 ( 2 ). Herein, the numeral  210  is used to describe each of the three crowbar modules  210 ( 1 ),  210 ( 2 ),  210 ( 3 ) generally. 
     The module  210 ( 3 ) includes a plastic cover  212 , a metal base busbar  214 , fasteners  215 , a coil assembly  220 , an internal circuit board assembly  230 , a signal cable  232 , and two thyristor assemblies or units  201 ,  202 . 
     Each of the thyristor units  201  and  202  includes a thyristor  270 . The thyristor  270  of the unit  201  corresponds to the thyristor TH 6  of  FIG.  5    and the thyristor  270  of the unit  202  corresponds to the thyristor TH 5 . 
     A center through hole  214 B and outer through holes  214 A are defined in the busbar  214  ( FIG.  16   ). The holes  214 A may be countersunk or recessed to fully receive the heads of bolts  217 . According to some embodiments, the busbar  214  is formed of aluminum. According to some embodiments, the busbar  214  is unitary and, in some embodiments, monolithic. 
     The cover  212  and the busbar  214  form a module housing that defines an enclosed cavity  212 A within which the coil assembly  220 , the internal circuit board assembly  230 , the signal cable  232 , and the crowbar units  201 ,  202  are contained. The signal cable  232  extends out of the cover  212  through a hole  212 B and to the connection module  290 . 
     The cover  212  may be formed of a dielectric or electrically insulating material having high melting and combustion temperatures. In some embodiments, the cover  212  is formed of a material that provides good moisture resistance. In some embodiments, the cover  212  is formed of a polymeric material and, in some embodiments, a silicone compound or polybutylene terephthalate (PBT). 
     A filler material  218  ( FIG.  14   ) fills the volume within the cavity not occupied by the components  220 ,  230 ,  232 ,  201 ,  202 . The filler material  218  may be a dielectric or electrically insulating material having high melting and combustion temperatures. In some embodiments, the filler material is formed of a polymeric material and, in some embodiments, includes a material selected from the group consisting of epoxy cast resin. 
     The coil assembly  220  ( FIGS.  14  and  16 - 18   ) includes an electrically conductive coil member  222 , an electrically conductive busbar  224 , an electrically conductive terminal member  226 , an electrical insulator sheet  227 , an electrically insulating casing  228 , coupling screws  229 A and coupling bolts  229 B. 
     The coil member  220  corresponds to the coil L ( FIG.  5   ). The coil member  220  includes a coil body  222 A, a spirally extending coil strip  222 C defining a spiral coil channel  222 B, and a coupling extension  222 D. Threaded bores  222 E extend axially through the extension  222 D and through holes  222 F extend axially through the body  222 A. 
     According to some embodiments, the coil member  220  is formed of metal and, in some embodiments, is formed of aluminum. According to some embodiments, the coil member  220  is unitary and, in some embodiments, monolithic. 
     The terminal member  226  includes a body  226 A, a coupling extension  226 B, and a terminal post  226 C. Holes  226 E extend axially through the extension  226 B. A threaded bore  226 D extends axially into the post  226 C. The terminal member  226  is electrically and mechanically connected to the coil member  220  by the bolts  229 B, which extend through the bores  222 E,  226 E. The insulator sheet  227  is interposed between the body  226 A and the body  222 A to prevent or inhibit direct flow of electrical current therebetween. 
     According to some embodiments, the terminal member  226  is formed of metal and, in some embodiments, is formed of aluminum. According to some embodiments, the terminal member  226  is unitary and, in some embodiments, monolithic. 
     The busbar  224  includes a body  224 A that is substantially planar on its upper side and has standoffs  224 B projecting from its lower side. Bolt holes  224 C extend axially through the body  224 A and the standoffs  224 B. Fasteners  229 A extend through holes  224 D and into the coil body  222 A to secure the upper face of the busbar  224  in mechanical and electrical contact with the coil body  222 A. 
     According to some embodiments, the busbar  224  is formed of metal and, in some embodiments, is formed of aluminum. According to some embodiments, the busbar  224  is unitary and, in some embodiments, monolithic. 
     The casing  228  includes an outer shell portion  228 A and a separator wall portion  228 B. The outer shell portion  228 A partially surrounds and encases the components  222 ,  224 ,  226 ,  227 . Bolt holes  228 C are defined in the portion  228 A in alignment with the holes  222 F. The terminal post  226 C projects through a post hole  228 D and above the casing  228 . The separator wall portion  228 B fills the coil channel  222 B between the adjacent windings of the coil strip  222 C. 
     The casing  228  may be formed of a dielectric or electrically insulating material having high melting and combustion temperatures. In some embodiments, the casing  228  is formed of a polymeric material. In some embodiments, the casing  228  includes an epoxy. In some embodiments, the casing  228  includes a material selected from the group consisting of epoxy adhesive and/or epoxy cast resin or silicone elastomer. In some embodiments, the casing  228  is monolithic. In some embodiments, the casing  228  includes a material selected from the group consisting of epoxy adhesive and/or epoxy cast resin that is itself covered by an outer layer of a different material. 
     The outer casing layer  223  may be formed of a different material that the casing  228  in order to provide complementary properties. In some embodiments, the outer casing layer  223  is formed of a material that provides enhanced moisture resistance as compared to the material of the casing  228 . In some embodiments, the outer casing layer  223  is formed of a silicone compound or PBT. The O-rings  223 A (made of the same or similar material as the O-rings  265 A,  265 B) prevent leakage of the epoxy used in liquid form (initially) to form the casing  228 . 
     The circuit board assembly  230  includes a substrate  230 A (e.g., a PCB) and a capacitor  230 B, a pair of resistors  230 C,  230 D, a lead wire  230 E, and a lead bracket  230 F mounted thereon. The capacitor  230 B corresponds to the capacitor C ( FIG.  5   ). The resistors  230 C,  230 D correspond to the resistor(s) R ( FIG.  5   ). The capacitor  230 B is electrically connected to the busbar  224  by the wire  230 E and the resistors  230 C,  230 D is electrically connected to the busbar  214  by the lead bracket  230 F. The resistors  230 C,  230 D and the capacitor from a snubber circuit as discussed in more detail below. 
     With reference to  FIGS.  16  and  19 - 21   , the crowbar unit  201  is shown therein. The crowbar units  201 ,  202  may be substantially identical in construction and therefore only the crowbar unit  201  will be described in detail below, it being understood that this description likewise applies to the crowbar unit  202 . 
     The crowbar unit  201  has a lengthwise axis A-A ( FIG.  20   ). The crowbar unit  201  includes a first electrode or housing  240 , a piston-shaped second electrode  250 , a thyristor  270  between the housing  240  and the electrode  250 , and other components as discussed in more detail below. 
     With reference to  FIGS.  19  and  20   , the housing  240  has an end electrode wall  242  and a cylindrical sidewall  244  extending from the electrode wall  242 . The sidewall  244  and the electrode wall  242  form a chamber or cavity  241  communicating with an opening  246 . A threaded bore  249  extends axially into the electrode wall  242 . A wire aperture or port  248  extends through the side wall  244  and has an enlarged recess  248 A at its outer opening. 
     The electrode  250  has a head  252  disposed in the cavity  241  and an integral shaft  254  that projects outwardly through the opening  246 . The thyristor  270  is disposed in the cavity  241  between and in contact with each of the electrode wall  242  and the head  252 . 
     Turning to the construction of the crowbar unit  201  in greater detail, the crowbar unit  201  further includes spring washers  262 , flat washers  264 , an insulating member  266 , an end cap  268 , a retention clip  267 , O-rings  265 A,  265 B, and a cable gland  280 . 
     The electrode wall  242  of the housing  240  has an inwardly facing, substantially planar contact surface  242 A. A locator feature or post  247  projects upwardly from the contact surface  242 A. An annular slot  243  is formed in the inner surface of the sidewall  244 . According to some embodiments, the housing  240  is formed of aluminum. However, any suitable electrically conductive metal may be used. According to some embodiments, the housing  240  is unitary and, in some embodiments, monolithic. The housing  240  as illustrated is cylindrically shaped, but may be shaped differently. 
     As best seen in  FIG.  20   , the head  252  of the electrode  250  has a substantially planar contact surface  252 A that faces the contact surface  242 A of the electrode wall  242 . A threaded bore  255  is formed in the end of the shaft  254  to receive the bolt  215  for securing the busbar L 3 B to the electrode  250 . An annular, sidewardly opening groove  254 D is defined in the shaft  254 . 
     According to some embodiments, the electrode  250  is formed of aluminum and, in some embodiments, the housing sidewall  244  and the electrode  250  are both formed of aluminum. However, any suitable electrically conductive metal may be used. According to some embodiments, the electrode  250  is unitary and, in some embodiments, monolithic. 
     An annular gap G 1  is defined radially between the head  252  and the nearest adjacent surface of the sidewall  244 . According to some embodiments, the gap G 1  has a radial width in the range of from about 5 to 15 mm. 
     The housing  240 , the insulating member  266  and the end cap  268  collectively define an enclosed chamber  245  containing the thyristor  270 . 
     The thyristor  270  includes a body  272  and an anode  274  and a cathode  276  on axially opposed ends of the body  272 . It will be appreciated that in  FIG.  14    the internal structure and components of the thyristors are not shown in detail. The anode  274  and cathode  276  have substantially planar contact surfaces  274 A and  276 A, respectively. The thyristor  270  is interposed between the contact surfaces  242 A and  252 A such that the contact surface  274 A mates with the contact surface  242 A and the contact surface  276 A mates with the contact surface  252 A. As described below, the head  252  and the wall  242  are mechanically loaded against the thyristor  270  to ensure firm and uniform engagement between the mating contact surfaces. The locator post  247  of the housing  240  is seated in a complementary locator socket  277  formed in the contact surface  276 A. 
     The thyristor  270  further includes a gate or control terminal  278 A and a reference terminal  278 B. For example, as illustrated in  FIG.  5   , an input to the gate or control terminal  278 A of the thyristor labeled therein as TH 5  may correspond to signal TH 5  from the trigger circuit  106 . Similarly, a reference connection to a reference terminal  278 B of the thyristor TH 5  may correspond to the reference C 5  from the trigger circuit  106 . 
     With reference to  FIG.  20   , the cable gland  280  is affixed in the wire port  248  and two signal wires  232 A,  232 B extend through the wire port  248  and the cable gland  280  and into the chamber  245 . The wire  232 A is electrically terminated at the control terminal  278 A and the wire  232 B is electrically terminated at the reference terminal  278 B. 
     The cable gland  280  includes a fitting  282  that is secured in the wire port  248 . The fitting  282  has a cylindrical body  282 A, a flange  282 B and a through bore  282 C. The body  282 A is seated in the wire port  248  and the flange  282 B is seated in the recess  248 A. The fitting  282  may be secured in place by adhesive  284 , for example. In some embodiments, the adhesive  284  bonds the body  282 A and the flange  282 B directly to the wall of the wire port  248 . 
     The cable gland  280  further includes a sealing plug  286  in the bore  282 C. The sealing plug  286  surrounds the wires  232 A,  232 B, bonds to the wires  232 A,  232 B and the fitting  282 , and continuously fills the radial space between the wires  232 A,  232 B and the fitting  282  and seals about the wires  232 A,  232 B. In this manner, the sealing plug  286  serves to mechanically retain or secure the wires  232 A,  232 B in the port  282 C (providing strain relief) and to fully seal, plug or close the bore  282 C (e.g., hermetically). 
     The sealing plug  286  may be formed of a rigid material having high melting and combustion temperatures. In some embodiments, the sealing plug  286  is formed of a polymeric material. In some embodiments, the sealing plug  286  is a hardened or cured resin. In some embodiments, the sealing plug  286  includes an epoxy. In some embodiments, the sealing plug  286  includes an epoxy adhesive or an epoxy cast resin. 
     The fitting  282  may be formed of a rigid material having high melting and combustion temperatures. In some embodiments, the fitting  282  is formed of a polymeric material. In some embodiments, the fitting  282  is formed of Nylon-66 (PA-66), or equivalent. 
     A cable gland  280  can also be provided for sealing and penetration of the cable  232  through the cover  212  ( FIG.  15   ). 
     The spring washers  262  surround the shaft  254 . Each spring washer  262  includes a hole that receives the shaft  254 . The lowermost spring washer  262  abuts the top face of the head  252 . According to some embodiments, the clearance between the spring washer hole and the shaft  254  is in the range of from about 0.015 to 0.035 inch. The spring washers  262  may be formed of a resilient material. According to some embodiments and as illustrated, the spring washers  262  are Belleville washers formed of spring steel. While two spring washers  262  are shown, more or fewer may be used. The springs may be provided in a different stack arrangement such as in series, parallel, or series and parallel. 
     The flat metal washers  264  are interposed between the spring washer  262  and the insulator ring  266  with the shaft  254  extending through holes formed in the washers  264 . The washers  264  serve to distribute the mechanical load of the upper spring washer  262  to prevent the spring washer  262  from cutting into the insulator ring  266 . 
     The insulator ring  266  overlies and abuts the washer  264 . The insulator ring  266  has a main body ring  266 A and a cylindrical upper flange or collar  266 B extending upwardly from the main body ring  266 A. A hole  266 C receives the shaft  254 . According to some embodiments, the clearance between the hole  266 C and the shaft  254  is in range of from about 0.025 to 0.065 inch. An upwardly and outwardly opening peripheral groove  266 D is formed in the top corner of the main body ring  266 A. 
     The insulator ring  266  is preferably formed of a dielectric or electrically insulating material having high melting and combustion temperatures. The insulator ring  266  may be formed of polycarbonate, ceramic or a high temperature polymer, for example. 
     The end cap  268  overlies and abuts the insulator ring  266 . The end cap  268  has a hole  268 A that receives the shaft  254 . According to some embodiments, the clearance between the hole  268 A and the shaft  254  is in the range of from about 0.1 to 0.2 inch. The end cap  268  may be formed of aluminum, for example. 
     The clip  267  is resilient and truncated ring shaped. The clip  267  is partly received in the slot  243  and partly extends radially inwardly from the inner wall of the housing  240  to limit outward axial displacement of the end cap  268 . The clip  267  may be formed of spring steel. 
     The O-ring  265 A is positioned in the groove  254  so that it is captured between the shaft  254  and the insulator ring  266 . The O-ring  265 B is positioned in the groove  266 D such that it is captured between the insulating member  266  and the sidewall  244 . When installed, the O-rings  265 A,  265 B are compressed so that they are biased against and form a seal between the adjacent interfacing surfaces. In an overvoltage event, byproducts such as hot gases and fragments from the thyristor  270  may fill or scatter into the cavity chamber  245 . These byproducts may be constrained or prevented by the O-rings  265 A,  265 B from escaping the crowbar unit  201  through the housing opening  246 . 
     The O-rings  265 A,  265 B may be formed of the same or different materials. According to some embodiments, the O-rings  265 A,  265 B are formed of a resilient material, such as an elastomer. According to some embodiments, the O-rings  265 A,  265 B are formed of rubber. The O-rings  265 A,  265 B may be formed of a fluorocarbon rubber such as VITON™ available from DuPont. Other rubbers such as butyl rubber may also be used. According to some embodiments, the rubber has a durometer of between about 60 and 100 Shore A. 
     The electrode head  252  and the housing wall  242  are persistently biased or loaded against the thyristor  270  along a load or clamping axis C-C ( FIG.  20   ) to ensure firm and uniform engagement between the thyristor contact surfaces  276 A,  274 A and the surfaces  242 A,  252 A. This aspect of the unit  201  may be appreciated by considering a method according to the present invention for assembling the unit  201 , as described below. 
     The wires  232 A,  232 B are secured in the bore  282 A of the fitting  282  using the sealing plug  286 . In some embodiments, the wires  278 A,  278 B are inserted into the bore  282 A, a liquid sealing material is introduced (e.g., poured or injected) into the bore about the wires  232 A,  232 B, and the sealing material is cured to form the rigid sealing plug  286  on the wires  232 A,  232 B. 
     The fitting  282  is secured in the wire port  248  using the adhesive  284 . The wires  232 A,  232 B are connected to the terminals  274 A,  276 A. In some embodiments, the wires  232 A,  232 B are secured by the sealing plug  286  before the step of securing the fitting  282  in the wire port  248 . 
     The O-rings  265 A,  265 B are installed in the grooves  254 ,  266 D. The thyristor  270  is placed in the cavity  241  such that the contact surface  276 A engages the contact surface  242 A. The electrode  250  is inserted into the cavity  241  such that the contact surface  252 A engages the contact surface  274 A. The spring washers  262  are slid down the shaft  254 . The washers  264 , the insulator ring  266 , and the end cap  268  are slid down the shaft  254  and over the spring washers  262 . A jig (not shown) or other suitable device is used to force the end cap  268  down, in turn deflecting the spring washers  262 . While the end cap  268  is still under the load of the jig, the clip  267  is compressed and inserted into the slot  243 . The clip  267  is then released and allowed to return to its original diameter, whereupon it partly fills the slot and partly extends radially inward into the cavity  241  from the slot  243 . The clip  267  and the slot  243  thereby serve to maintain the load on the end cap  268  to partially deflect the spring washers  262 . The loading of the end cap  268  onto the insulator ring  266  and from the insulator ring onto the spring washers  262  is in turn transferred to the head  252 . In this way, the thyristor  270  is sandwiched (clamped) between the head  252  and the electrode wall  242 . 
     When the crowbar unit  201  is assembled, the housing  240 , the electrode  250 , the insulating member  266 , the end cap  268 , the clip  267 , the O-rings  265 A,  265 B and the cable gland  280  collectively form a unit housing or housing assembly  249  containing the thyristor  270 . 
     The crowbar module  210  may be assembled as follows in accordance with methods of the invention. 
     In order to construct the coil assembly  220 , the busbar  224  is secured to the coil member  222  using the bolts  229 A. The terminal member  226  is secured to the coil member  222  using the bolts  229 B with the insulator sheet  227  captured between the terminal member  226  and the coil member  222 . The casing  228  is thereafter molded about and through this subassembly. For example, in some embodiments, the subassembly is placed in a mold, the mold is then filled with liquid casing material (e.g., a liquid resin), and the material is then cooled or cured to form the rigid casing  228 . The regions of the holes  228 C,  228 D,  222 F,  226 D may be temporarily filled or plugged with mold features or the like to prevent the liquid casing material from filling these regions. The casing  223  is molding or fitted about the casing  228 . For example, the casing  223  may be molded or co-molded around the casing  228 . Elastomeric O-rings  223 A may be fitted about the terminal post  226 C and the busbar standoffs  224 B. 
     The coil assembly  220  is secured to the electrode  240  of the crowbar unit  201  by a bolt  217  and to the electrode  250  of the crowbar unit  202  by a bolt  217 . The heads of the bolts  217  are seated in the holes  228 C of the casing  228  to provide a low, flat profile. The base busbar  214  is secured to the electrode  250  of the crowbar unit  201  by a bolt  217  and to the electrode  240  of the crowbar unit  201  by a bolt  217 . The heads of the bolts  217  are seated in the holes  214 A of the base busbar  214  to provide a low, flat profile. The lead wires  230 E and  230 F are secured to the busbar  224  and the base busbar  214 , respectively, by screws. 
     The cover  212  is installed over the foregoing subassembly and secured to the base busbar  214  by fasteners (e.g., screws), adhesive, and/or interlock features, for example. The cable  232  (which includes the wire pairs  232 A,  232 B from each of the crowbar units  201 ,  202 ) is routed through the opening  212 B in the cover  212 . The remaining volume of the cavity  212 A is filled with the filler material  218 . In some embodiments, a liquid filler material is introduced (e.g., poured or injected through the hole  214 B) into the cavity  212 A, and then cured to form the rigid filler material  218 . 
     The connection module  290  ( FIGS.  13  and  22   ) includes a circuit or circuits corresponding to an interconnection between the crowbar system  102  and the trigger circuit  106 . For example, some embodiments provide that the crowbar system  102  includes three crowbar modules  210 ( 1 ),  210 ( 2 ) and  210 ( 3 ) (schematically illustrated as crowbar module  120  in  FIG.  5   ) that include connections to trigger circuit  106 . Specifically, for example, each of cables  232  may correspond to a respective one of the crowbar modules  210  and may correspond to thyristor trigger signals for each of the two crowbar units  201  within each crowbar module  210  and reference signals for each of the two crowbar units within each crowbar module  210 . The connection module  290  may include a surrounding enclosure  292 , and multiple electrical contacts that are configured to provide connections to contacts in a mating connector (not shown). In this manner, the crowbar system  102  may be connected to the trigger circuit  106 . 
     In order to connect the crowbar modules  210 ( 1 ),  210 ( 2 ),  210 ( 3 ) to the conductors L 1 B, L 2 B, L 3 B, NB, each of the line conductors L 1 B, L 2 B, L 3 B is mechanically and electrically connected to the terminal member  226  of a respective one of the crowbar modules  210 ( 1 ),  210 ( 2 ),  210 ( 3 ) by a bolt  215 , and the neutral conductor NB is mechanically and electrically connected to the base busbars  214  of the crowbar modules  210 ( 1 ),  210 ( 2 ),  210 ( 3 ) by bolts  215 . 
     In use, the crowbar system  200  and the crowbar modules  210 ( 1 ),  210 ( 2 ),  210 ( 3 ) perform as described above for the system  102  and the three modules  120 , respectively ( FIG.  5   ). 
     When a triggering event occurs, and the thyristors  270  of a module  210  conduct current between the lines the module  210  bridges (i.e., the neutral line N and the associated one of the lines L 1 , L 2 , L 3 ). As discussed above, the crowbar units  201 ,  202 , and therefore the thyristors  270  thereof, are oriented in opposite directions in order to conduct current in respective ones of the AC current directions. In the case of the crowbar unit  202  of the module  210 , the current flows sequentially through the terminal post  226 C, the terminal extension  226 B, the coil member extension  222 D, the coil strip  222 C, the coil body  222 A, the busbar  224 , the electrode  250  mated to the busbar  224 , the thyristor  270 , the electrode  240  mated to the busbar  214 , and the busbar  214 . In the case of the crowbar unit  201 , the current flows sequentially through the busbar  214 , the electrode  250 , the thyristor  270 , the electrode  240 , the busbar  224 , the coil body  222 A, the coil strip  222 C, the extension  222 D, the extension  226 B, and the terminal post  226 C. 
     The construction and configuration of the crowbar modules  210  provides a compact, modular, unitarily packaged device that can be efficiently integrated into existing electrical equipment cabinets. The packaging provides a simple and convenient arrangement and features for connecting the modules  210  to the lines L 1 , L 2 , L 3 , N (e.g., via conductor busbars L 1 B, L 2 B, L 3 B, NB). 
     Moreover, the construction and configuration of the crowbar modules  210  can provide the crowbar modules  210  with increased strength and durability to withstand the physical effect (electromagnetic forces generated) of fault currents over a prolonged period of time, and other electrical and mechanical stresses in service. Therefore, it can safely withstand the short circuit event (avoid any safety issues to the personnel and any damages ti the equipment of the installation as well as the whole installation itself) when it is triggered. 
     The crowbar module  210  can operate when triggered in two distinct ways: one to withstand the fault current for the period of time required to trip the upstream main circuit breaker and a second (a different design than the first) that the thyristors  270  cannot withstand the fault current and fail in short. The second option is attractive due to the lower energy withstand capabilities of the thyristors employed in the design. However, in such case, the crowbar system  200  typically can only be triggered once, as after it is triggered, the system  200  is not recoverable and it has to be replaced. In the case where the thyristors  270  can withstand the fault current, two additional provisions are typically required. One is that the inductance of the added coil  222  is used to eliminate the possibility of damaging the thyristors due to high di/dt during the conduction of the fault currents (creates a hot spot on the internal surface of the thyristor disk). The impedance of the coil is also useful to allow the snubber circuit  230 B,  230 C,  230 D to prevent thyristor self-trigger due to excessive dv/dt (reduce the dV/dt, that requires a certain impedance in the circuit—in some applications this could be part of the existing impedance of the system and allow the omission of the coil). The second is that even in this case there should be provisions using the same construction for the crowbar module  210  to withstand the damage in case the thyristor fails short—typical failure mode of the thyristor. Therefore the configuration of the crowbar module  210  is highly beneficial, and in some cases mandatory, for both design implementations (withstand and failure of the crowbar module  210 ). 
     For example, when a module  210  is activated, a thyristor  270  thereof may be damaged (e.g., as a result of carrying all of the fault current). However, the associated housing assembly  241  contains the damage (e.g., debris, gases and immediate heat) within the crowbar unit  201 ,  202 , so that the module  210  fails safely. Moreover, the components of the module  210  surrounding the unit  201 ,  202  can also contain any or buffer any heat or damage products that escape the unit  201 ,  202 . In this way, the module  210  can prevent or reduce any damage to adjacent equipment (e.g., switch gear equipment in the cabinet) and harm to personnel. In this manner, the module  210  can enhance the safety of equipment and personnel. This can be a very important feature as the main reason for using a crowbar system as discussed herein is the protection of equipment and personnel from arc flash hazards that are typically caused by breaking the insulation between bus bars or by failures on semiconductive devices (like thyristors, IGBTs, etc). So, such a system may be of limited or no significant value if it creates the same damaging effects that it is employed to solve (hazardous failure of semiconductive devices). 
     The construction of the coil assembly  220 , and in particular the casing  228 , provide a robust, unitary component. The enhanced strength of the coil assembly  220  is beneficial to withstand the stresses that may be experienced and exerted by the coil member  222 , which is located in series across lines. 
     The filler material  218  can provide the module  210  with improved strength. The filler material  218  can help to contain byproducts from destruction of the thyristor. The filler material  218  can thermal insulate as well as electrically insulate electrical components of the module  210  from the environment (e.g., personnel and other equipment in the switch cabinet). The filler material  218  can also provide tamper resistance. 
     The cable gland  280  provides strain relief for the wires  232 A,  232 B, and also serves to seal the wire port  248  to prevent or inhibit expulsion of byproducts from destruction of the thyristor through the wire port  248 . 
     In some embodiments, the cable gland  280  is constructed to permit breach or failure of the cable gland  248  in response to pressure in the chamber exceeding a threshold pressure in a prescribed range. That is, the cable gland  280  can serve as a pressure dependent valve. This may be very important feature in case for some reason the crowbar module  210  is overexposed to fault currents—above its specifications—and the cable gland  280  operates as a pressure relief inside the module  210  without generating significant hazards (i.e., it is a controlled way to relieve the internal pressure by allowing a smoke emission in a specific direction that could be externally controlled by guiding the smoke emissions to a vent. 
     A failure of the cable gland  280  can be observed without disassembling the crowbar unit  201 ,  202 . The valve function the gland  280  can be advantageously employed to determine the maximum fault current and duration that the crowbar module  210  can withstand, having as an indication only when the valve will open when the crowbar unit  201 ,  202  is being tested or rated (used as a first indication that the fault current withstand capability of the crowbar module  210  is close to its limits, instead of experiencing a full damage of the whole module). 
     Electrical protection devices according to embodiments of the present invention (e.g., the device  210 ) may provide a number of advantages in addition to those mentioned above. The devices may be formed so to have a relatively compact form factor. The devices may be retrofittable for installation in place of similar type crowbar devices not having a thyristor as described herein. In particular, the present devices may have the same length dimension, as such previous devices. That depends on the fault current rating of the crowbar system, the duration of the fault current and the mode of operation during trigger (withstand or failure). That determines the size of the thyristors  270  employed and therefore the size and construction details of the crowbar modules  210  and of the whole system. 
     According to some embodiments, the areas of engagement between each of the electrode contact surfaces (e.g., the contact surfaces  242 A,  252 A) and the thyristor contact surfaces (e.g., the contact surfaces  274 A,  276 A) is at least one square inch. 
     According to some embodiments, the biased electrodes  240 ,  250  apply a load to the thyristor  270  along the axis C-C in the range of from 2000 lbf and 26000 lbf depending on its surface area. 
     According to some embodiments, the combined thermal mass of the housing  240  and the electrode  250  is substantially greater than the thermal mass of the thyristor  270 . As used herein, the term “thermal mass” means the product of the specific heat of the material or materials of the object (e.g., the thyristor  270 ) multiplied by the mass or masses of the material or materials of the object. That is, the thermal mass is the quantity of energy required to raise one gram of the material or materials of the object by one degree centigrade times the mass or masses of the material or materials in the object. According to some embodiments, the thermal mass of at least one of the electrode head  252  and the electrode wall  242  is substantially greater than the thermal mass of the thyristor  270 . According to some embodiments, the thermal mass of at least one of the electrode head  252  and the electrode wall  242  is at least two times the thermal mass of the thyristor  270 , and, according to some embodiments, at least ten times as great. According to some embodiments, the combined thermal masses of the head  252  and the wall  242  are substantially greater than the thermal mass of the thyristor  270 , according to some embodiments at least two times the thermal mass of the thyristor  270  and, according to some embodiments, at least ten times as great. 
     As discussed above, the spring washers  262  are Belleville washers. Belleville washers may be used to apply relatively high loading without requiring substantial axial space. However, other types of biasing means may be used in addition to or in place of the Belleville washer or washers. Suitable alternative biasing means include one or more coil springs, wave washers or spiral washers. 
     According to further embodiments of the invention, the crowbar module  210  may be constructed with only one crowbar unit  201  or  202  (i.e., the other crowbar unit  202  or  201  is omitted), so that the crowbar module so formed electrically conducts only in one direction. Such modified crowbar modules may be used in matched, inverted pairs to provide the functionality of the crowbar module  210 . 
     According to further embodiments of the invention, the crowbar module  210  may be constructed with only one crowbar unit  201  or  202  (i.e., the other crowbar unit  202  or  201  is omitted), but such that the remaining single crowbar unit  201 ,  202  includes, in place of the thyristor  270 , a bi-directional thyristor that can operate in both directions. That is, when triggered, the bi-directional thyristor will conduct current in both directions of the AC current. This crowbar module may be reduced in size and/or cost as compared to the dual thyristor crowbar module. 
     According to further embodiments of the invention, the crowbar module  210  may be constructed without the coil  222 . 
     With reference to  FIG.  23   , a crowbar module  310  according to further embodiments of the invention is shown therein. The crowbar module  310  corresponds to the crowbar module  210 , except as described below. In  FIG.  23   , the cover  212 , the filler material  218 , and the crowbar unit  201  are not shown, in order to provide clearer view for the purpose of explanation. The crowbar unit  201  in the crowbar module  310  is electrically connected to the base busbar  214  and the coil member  222  by the bolts  217 A and  217 B as in the crowbar module  210 . 
     The crowbar module  310  includes an integral metal-oxide varistor (MOV) device  288 . The integrated MOV device  288  is electrically connected to the terminal member  226  by a lead  289 A (bypassing the coil  222 C), and to the base busbar  214  by a lead  289 B. The MOV device  288  is mounted on an electrically insulating substrate  288 C between the leads  289 A,  289 B. The MOV device  288  includes a first pin type lead electrically contacting the lead  289 A and a second pin type lead electrically contacting the lead  289 B. The MOV internally includes a thermal link (thermal disconnector or thermal fuse) between the lead  288 A and the one electrode of the MOV. The other electrode of the MOV is connected to lead  288 B. In addition, the connection between the  226  and the MOV lead  288 A, as well as the connection between the busbar  214  and the lead  288 B, is done using a bus bar to enable the connections to the power line and the ground to withstand the forces generated form the conducted current when the MOV conducts surge/lightning currents or fault currents from the power source. The crowbar module  310  may be used as a crowbar module in the crowbar device  102  of the system described above with reference to  FIG.  11    for example. An additional MOV could also be used—integrated in the PCB  288 C—and connected in parallel to the two thyristors to reduce the overvoltage at their ends and to prevent the maximum expected overvoltage which could lead to the false trigger of the thyristor. 
     Reference is now made to  FIG.  24   , which is a schematic diagram illustrating an arc flash, overvoltage, overcurrent and surge protection system according to some embodiments of the present invention.  FIG.  24    may include elements that are described above regarding at least  FIG.  5    and thus additional description thereof may be omitted. In some embodiments, the arc flash, overvoltage, overcurrent and surge protection system  500  may protect the electrical system of a wind turbine generator from arc flash, overcurrent and/or surge or lightning events. Some embodiments provide that arc flash, overvoltage, overcurrent and surge protection system  500  includes a crowbar device  502  that is operable to prevent an overvoltage condition by generating a low resistance path from the phase voltage lines L 1 , L 2 , L 3  to the neutral line N. Some embodiments provide that the crowbar device  502  includes crowbar modules  520  that are each connected between the corresponding phase voltage line L 1 , L 2 , L 3  and the neutral line N. 
     Some embodiments provide that each of the crowbar modules  520  maybe connected to a current sensor  505  that may monitor the current flow of the corresponding phase line. In some embodiments, the current sensor  505  may be separate from the crowbar module  520  and/or the crowbar device  502  while in some other embodiments the current sensor  505  may be integrated into the crowbar module  520  and/or the crowbar device  502 . 
     Some embodiments include surge protection devices (SPDs)  104 . As illustrated, each of the SPDs  104  may be connected between respective ones of L 1 , L 2  and L 3 , and neutral (N). The use of the SPD  104  may protect the thyristors of the crowbar device  502  during lightning events and/or transient overvoltage conditions, as well as protect other equipment in the installation. 
     In some embodiments, the crowbar device  502  may be triggered by an arc flash trigger circuit  506 . As described above, an arc flash detection system  64  may be configured to detect an arc flash within the switchgear cabinet  60  and provide an arc flash detection signal (AFD) to the arc flash trigger circuit  506 . In some embodiments, the arc flash trigger circuit  506  may manage trigger and alarm signals from the crowbar modules  520  and provide the trigger outputs to one or more circuit breakers  68 . Some embodiments provide that the arc flash trigger circuit  506  may also provide indications corresponding to the condition of each crowbar module  520  and a cause of triggering ones of the crowbar modules  520 . 
     The arc flash, overvoltage, overcurrent and surge protection system  500  may also include a threshold selector  510  that provides a signal to the arc flash trigger circuit  506  to set the current threshold at which the arc flash trigger circuit  506  causes the crowbar module  520  to actuate. 
     In use and function, under normal operating conditions, a crowbar module  520  may remain inactive and thus not conduct current between phase lines L 1 , L 2 , L 3  and the neutral line N. Normal operating conditions may include those in which a phase line voltage is less than a specific threshold. For example, in some embodiments, the specific threshold may be about 1800 V peak, however, such embodiments are non-limiting as the threshold voltage may be more or less than 1800 V. 
     A crowbar module  520  may be triggered in different ways depending on when a fault condition is detected. For example, the crowbar module  520  may be triggered in a first manner during a start-up period and a second manner during steady state operation. 
     During a start-up period, such as within about 2 seconds or less from the start of a wind turbine or other generating device, the crowbar module  520  may operate without a power supply from the arc flash trigger circuit  506 . In this regard, the crowbar module  520  cannot be triggered by an alarm signal from the arc flash detection system  64  as such system is generally unavailable for operation during a start-up period. In this manner, the crowbar module  520  may be self triggered during the start-up period. 
     Reference is now made to  FIG.  25   , which is a schematic block diagram illustrating a crowbar module as briefly described above regarding  FIG.  24   , according to some embodiments of the present invention. The crowbar module  520  may include two thyristors TH 1 , TH 2  that are connected anti-parallel to one another and in series with an inductor L. As used herein, the term “anti-parallel” may refer to a configuration in which components are connected in parallel with one another, but in a complementary arrangement relative to one another. For example, an anode terminal of a first component may be connected to a cathode terminal of a second component while the cathode terminal of the first component is connected to the anode terminal of the second component. In some embodiments, a resistor R and a capacitor C may be connected in series with one another and in parallel with the thyristors TH 1 , TH 2 . The crowbar module  520  may further include the crowbar trigger circuit  530  that is configured to provide a self triggering function within the crowbar module  520 . During a start-up period, the crowbar trigger circuit  530  may be powered by current received from the current sensor  505 . For example, the crowbar module  520  may be self triggered once the current through the phase line is above the threshold current (I TH ) for a period of more than 2 ms. In such cases only the crowbar module  520  that is connected to the corresponding phase line may be triggered. 
     Brief reference is now made to  FIG.  27   , which is a graph illustrating voltage and current values during a fault condition according to some embodiments of the present invention. Continuing with the example above, at time t 1  a fault current I reaches the threshold current I TH . At time t 2 , responsive to the fault current I exceeding the threshold current I TH  for a specific period of time, crowbar module  520  begins to conduct the fault current thus reducing the voltage for the remaining portion of that cycle at time t 3  to about zero volts. If the fault is still present during the second half of the cycle, then the crowbar module  520  again conducts the fault current thus reducing the voltage for the remaining portion that cycle. 
     Referring back to  FIG.  25   , some embodiments provide that every time the crowbar module  520  is triggered a trigger signal will be provided to the arc flash trigger circuit  506 . In some embodiments, the response time of the crowbar module  520 , from the time the overcurrent is detected, may be less than about 1 ms. In some embodiments, the response time may be less than about 500 μs. Some embodiments provide that the response time may be about 300 μs 
     Reference is now made to  FIG.  26   , which is a schematic block diagram illustrating a crowbar trigger circuit of the crowbar module as briefly described above regarding  FIG.  25   , according to some embodiments of the present invention. The crowbar trigger circuit  530  may receive a current signal from current sensor  505  into one or more step up transformers  510 ,  512 . Since the current signal and the output from the step up transformers  510 ,  512  may be an alternating current (AC) signal, the outputs from the step up transformers  510 ,  512  may be received by rectifiers  520 ,  522 , respectively. The rectifiers  520 ,  522  may generate direct current (DC) signals that correspond to the current signal from the current sensor  505 . 
     The crowbar trigger circuit  530  may also include variable reference signal generators  530 ,  532  which provide reference signals corresponding to the selected value of I TH . Comparators  540 ,  542  may be configured to receive the DC signals from the rectifiers  520 ,  522 , respectively and reference signals from the variable reference generators  532 ,  530 . Responsive to the one of DC signals from the rectifier exceeding the reference signal, the output state of the comparator changes from high to low, or vice versa. The crowbar trigger circuit  530  may include delay circuits  550 ,  552  that are configured to receive output signals from the comparators  540 ,  542 . Responsive to receiving a changed output from the comparators  540 ,  542 , the output of the delay circuits  550 ,  552  will change after a given time delay. By providing the time delay, a false triggering of the thyristors may be prevented and/or reduced. The output from the delay circuits  550 ,  552  may provide thyristor trigger signals via diodes  588 ,  582  that cause corresponding ones of the thyristors to turn on into a conducting state. 
     In some embodiments, the delay circuits  550 ,  552  may provide different reference voltage signals relative to one another. For example, delay circuit  550  may provide a positive voltage relative to the neutral line for triggering thyristor TH 1 . Similarly, delay circuit  552  may provide a positive voltage relative to the inductor bottom terminal L TH . 
     While the above describes the self-triggering operation of the crowbar trigger circuit  530  during a start-up period, once the start-up period is over the normal operation of the crowbar module  520  is responsive to the arc flash trigger circuit  506 . The crowbar trigger circuit  530  may receive a control voltage Vcc and ground into DC-DC converters  570 ,  572 . In some embodiments, a first DC-DC converter  572  may provide a DC voltage that is capable of triggering the first thyristor TH 1  and a second DC-DC converter  570  may provide a DC voltage that is capable of triggering the second thyristor TH 2 . The crowbar trigger circuit  530  may also receive an arc flash detection signal into a driver  580 . In response, the driver  580  may energize optical switches  560  and  562 , causing the DC voltages to be applied to the thyristors TH 1 , TH 2  via diodes  584 ,  588 . 
     Reference is now made to  FIG.  28   , which is a schematic block diagram illustrating an arc flash trigger circuit of the crowbar module as briefly described above regarding  FIG.  24   , according to some embodiments of the present invention. The arc flash trigger circuit  506  may receive a ground and an operating voltage Vcc, such as, for example, 24 V DC. A latch circuit  546  may receive and latch an alerted state of an arc flash signal received from an arc flash detection system  64 . Some embodiments provide that the arc flash trigger circuit  506  includes a plurality of output triggers  544  that may be used to provide a trip signal to one or more circuit breakers and/or alarms. 
     In some embodiments, the arc flash trigger circuit  506  include a matrix  548  that is configured to receive a discrete digital input from a threshold selector  510  and to generate a current threshold value based on the value of the received digital input signal. Some embodiments provide that the threshold selector  510  may be a rotary switch that provides a discrete digital signal, such as a two bit binary signal. In such embodiments, different outputs of the threshold selector  510  may be 00, 01, 10 and 11. In some embodiments, the 00 may correspond to a default threshold current value that is used in the self-triggering operation of the crowbar module  520 . In this manner, the absence of a signal during a start-up period may correspond to the 00 binary value. By way of example, current threshold values corresponding to the different binary signals may include 6.3 kA, 500 A, 8 kA and 10 kA. 
     The arc flash trigger circuit  506  may provide a reliable voltage (V CC ) to the three crowbar modules  520  after the first  2   s  from the start-up and may transfer the alarm signal from the arc flash detection system  64  to the three crowbar modules  520  without introducing any delay after the first  2   s  from the start-up. 
     In some example embodiments, the crowbar module  520  may be triggered when the current through the power line is above I TH  peak for a period of more than 2 ms. In that case, only the crowbar module  520  that is connected to the corresponding power line is self triggered each time the current goes above I TH . In some embodiments, the response time of the crowbar module  520  once triggered is around 300 μs. 
     Some embodiments provide that the crowbar module  520  may also be triggered when there is an alarm signal from the arc flash detection system  64 . In that case, all three crowbar modules  520  are triggered until the main circuit breaker  68  is tripped. Some embodiments provide that the response time of the crowbar module  520  once triggered, is less than 2 ms, and may typically be around 300 μs. Then, the crowbar module  520  will be in continuous trigger for a period of 100 ms. 
     Some embodiments provide that an arc flash and surge protection system may include a crowbar module as an electronic switch that is connected in series with an energy absorber. In such applications, there TOV (overvoltages) in the system that could damage the equipment. In this regard, a solution to direct part of the energy to a device that will absorb it may be advantageous. Some embodiments include an energy absorber that may be based on multiple metal oxide varistors (MOVs) that are connected in parallel to absorb the TOV event. For example, the voltage may be clamped during such an event by turning on the MOVs to conduct some current when the voltage is increased. 
     For example, for a 240V system, the peak voltage is 336V. The use of an MOV with a Maximum Continuous Operating Voltage (MCOV) of 250 VAC as close as possible to the nominal voltage may be used such that during normal conditions the MOV will not conduct any current. The MOV may conduct a very small leakage current (˜1 mA) at 336V. However, as the voltage is increased, the MOV may start conducting heavily in an effort to limit the voltage. In this case, the voltage cannot exceed the value of 1000V peak. 
     However, there are power systems that may need protection at much lower voltage levels, for example 700V instead of 1000V. In such cases, to reduce the protection level, MOVs with lower MCOV, i.e. thinner MOV disks, may be used. For example, the MOV may have a MCOV of 150 VAC instead of 250 VAC. In such cases, under normal operation the MOV may conduct a significant current (above a few Amps) that will force it to failure within a limited period of time (depending on the exact level of the conducted current). In this regard, an energy absorber may be used with an MOV having an MCOV of 150 VAC in series with one another. 
     For example, reference is now made to  FIG.  29   , which is a schematic block diagram illustrating a surge protection system used in protecting equipment according to some embodiments of the present invention. As illustrated, the arc flash, overvoltage, overcurrent and surge protection system  600  may include a crowbar device  602  that is connected between the different phase lines L 1 , L 2 , L 3 . The crowbar device  602  may be connected in series with multiple MOVs  605  that are connected to respective ones of the plurality of phase lines L 1 , L 2 , L 3 . 
     The crowbar device  602  may function as a switch that will connect the MOVs  605  that function as energy absorbers to the phase lines only when the voltage exceeds a given threshold. In some embodiments, the given threshold is about 600V, however, this is merely a non-limiting example. The MOVs  605  may conduct as much current as necessary to keep the voltage below 700 V. By way of example, based on the voltage-current curve of a 150 VAC MOV, at 700 V, the MOV  605  may conduct 10 kA of current, which exceeds the current that can be produced by the TOV. As such, the phase lines L 1 , L 2 , L 3  cannot reach the 700V level. 
     Additionally, when the sinusoidal system voltage declines to cross the zero level, the impedance of the MOV will increase and will limit the current through the thyristor in the crowbar module  602 . Then when the current through thyristor in the crowbar device  602  goes below 200 mA, the thyristor will disconnect the energy absorber from the system. This may occur as soon as the system voltage drops below 280V peak approximately. 
     Brief reference is now made to  FIG.  30   , which is a schematic block diagram illustrating a crowbar device as briefly described above regarding  FIG.  29   , according to some embodiments of the present invention. The crowbar device  602  may include a plurality of thyristors TH 1 , TH 2 , TH 3  that are connected between the different pairs of the plurality of phase lines L 1 , L 2 , L 3 . A crowbar device trigger circuit  630  may include a rectification circuit  632  that receives three phase AC current from the plurality of phase lines L 1 , L 2 , L 3  and generates a corresponding DC signal. The crowbar device trigger circuit  630  may include a comparator  634  that receives the DC signal and a reference voltage Vr and compares the two signals. If the DC signal exceeds the reference voltage Vr, then the comparator  634  generates an output to a plurality of trigger drivers  636  that are configured to trigger the thyristors into a conduction mode responsive thereto. Once the DC signal drops below the reference voltage Vr, then the comparator  634  output changes state and the trigger drivers  636  turn off the thyristors. 
     Reference is now made to  FIG.  31   , which is a schematic block diagram illustrating a surge protection system  60  used in protecting equipment according to some embodiments of the present invention. Instead of the line to line connection described above regarding  FIGS.  29  and  30   , the arc flash, overvoltage, overcurrent and surge protection system may include a crowbar device  700  that includes MOVs  705  that are series connected with crowbar modules  720  from each phase line L 1 , L 2 , L 3  to neutral N. Since each phase line includes an independent MOV  705 /crowbar  720  module combination, then a fault at an individual phase line may be addressed without triggering the MOV  705 /crowbar module  720  combination of the other phase lines. Brief reference is now made to  FIG.  32   , which is a schematic block diagram illustrating a crowbar module as briefly described above regarding  FIG.  31   , according to some embodiments of the present invention. A crowbar device trigger circuit  730  may include a rectification circuit  732  that receives an AC phase current from a corresponding phase line and generates a corresponding DC signal. The crowbar device trigger circuit  730  may include a comparator  734  that receives the DC signal and a reference voltage Vr signal and compares the two received signals. If the DC signal exceeds the reference voltage Vr, then the comparator  734  generates an output to a trigger driver  736  that then activates an optical isolator  738 . The output from the optical isolator  738  is configured to trigger the thyristors TH 1 , TH 2  into a conduction mode responsive thereto. Once the DC signal drops below the reference voltage Vr, then the comparator  734  output changes state and the trigger driver  736  turns off the thyristors TH 1 , TH 2 . 
     With reference to  FIGS.  33 - 35   , a crowbar system  800  according to further embodiments of the invention is shown therein. The crowbar system  800  includes a crowbar device  802  (corresponding to the crowbar device  502  of  FIG.  24   ), a trigger and alarm interface circuit unit  806  (corresponding to the trigger circuit  506  of  FIG.  24   ), and a remote threshold selector switch  807  (corresponding to the threshold selector  510  of  FIG.  24   ). 
     With reference to  FIG.  33   , the crowbar device  800  includes three crowbar modules  810 , three SPDs  804 , a neutral conductor NB, line conductors L 1 B, L 2 B, L 3 B, and three current sensors  805 . The crowbar device  800  further includes a crowbar device housing  860  (shown in dashed lines) within which the crowbar modules  810 , SPDs  804 , conductors NB, L 1 B, L 2 B, L 3 B, and current sensors  805  are mounted, disposed and encased. 
     In some embodiments, the trigger and alarm interface circuit unit  806  and the remote selector switch  807  are located outside of the crowbar device housing  860 . For example, the trigger and alarm interface circuit unit  806  may be located elsewhere in an electrical service cabinet containing the crowbar device  802  and the lines L 1 , L 2 , L 3  so that the trigger and alarm interface circuit unit  806  is better positioned for operator access or to detect activity in the cabinet. The remote selector switch  807  may be located a substantial distance (e.g., at least 20 feet) from the crowbar device  802 . For example, the crowbar device  802  may be located high above the ground on a tower while the remote selector switch  807  is mounted near ground level to enable convenient access by an operator. 
     The crowbar modules  810  correspond to the crowbar modules  520  of  FIG.  24   . Each of the crowbar modules  810  is electrically and mechanically coupled to the neutral conductor NB (corresponding to neutral line N) and a respective one of the line conductors L 1 B, L 2 B, L 3 B (corresponding to the lines L 1 , L 2 , L 3 ). 
     A respective SPD  804  (corresponding to the SPDs  104  of  FIG.  24   ; e.g., an MOV-based SPD) is mounted between and electrically connects the associated line conductor L 1 B, L 2 B, L 3 B and the neutral conductor NB in parallel to the associated crowbar module  810 . 
     The current sensors  805  correspond to the current sensors  505 . Each of the current sensors  805  is operatively mounted on a respective one of the line conductors L 1 B, L 2 B, L 3 B and has an output signal wire  805 A connected to the associated crowbar module  810 . 
     Each crowbar module  810  is also electrically connected by an electrical cable  806 A to the trigger and alarm interface circuit unit  806 . The remote selector switch  807  is in turn electrically connected to the interface circuit unit  806  by an electrical cable  807 A. 
     The crowbar modules  810  may be constructed and operate generally as described herein with regard to the crowbar module  210 , except as described below. Each module  810  may include a filler material corresponding to the filler material  218 ; however, this filler material is not shown in  FIG.  35   . 
     With reference to  FIGS.  34  and  35   , the crowbar module  810  includes a module housing  811  defining an enclosed chamber  811 A. The module housing  811  includes an outer cover  812 , a removable cover or back plate  813 , and a base plate  815 . The outer cover  812  is provided with a rear side opening  812 A. The opening  812 A is closed and environmentally sealed by a removable cover or back plate  813 . The interface between the back plate  813  and the cover  812  about the opening may be hermetically sealed by a rubber seal  813 A. In some embodiments, the chamber  811 A is hermetically sealed or moisture sealed. 
     With reference to  FIG.  35   , crowbar units  801 ,  803  corresponding to the crowbar units  201 ,  202  and a circuit board assembly  830  corresponding to the circuit board assembly  230  are disposed in the chamber  811 A between a coil assembly  820  (corresponding to coil assembly  220 ) and a base busbar  814 . 
     The circuit board assembly  830  may include a snubber circuit corresponding to the snubber circuit of the circuit board assembly  230 . 
     An internal circuit board assembly  833  is secured to the back plate  813  in the chamber  811 A. The internal circuit board assembly  833  may include the crowbar self trigger circuit  530  of the crowbar module  520  of  FIGS.  25  and  26   . Advantageously, placing the trigger circuit  530  in the crowbar module housing  811  in close proximity to the thyristors TH 1 , TH 2  can reduce or prevent induced noise on the cables that might otherwise trigger the thyristors TH 1 , TH 2  accidentally. 
     An electrical connector  813 B is mounted on the back plate  813  to electrically connect the wires  805 A,  806 A to the circuit board assembly  830 , the circuit board assembly  833 , and the thyristors of the crowbar units  801 ,  803 . The electrical connector  813 B may be environmentally sealed. 
     Various inventive aspects as disclosed herein may be used independently of one another. For example, a crowbar unit  201  including a cable gland  280  as described may be used without the unitarily assembling the crowbar unit  201  with a coil, busbars, a snubber circuit, and or another crowbar unit. 
     Many alterations and modifications may be made by those having ordinary skill in the art, given the benefit of present disclosure, without departing from the spirit and scope of the invention. Therefore, it must be understood that the illustrated embodiments have been set forth only for the purposes of example, and that it should not be taken as limiting the invention as defined by the following claims. The following claims, therefore, are to be read to include not only the combination of elements which are literally set forth but all equivalent elements for performing substantially the same function in substantially the same way to obtain substantially the same result. The claims are thus to be understood to include what is specifically illustrated and described above, what is conceptually equivalent, and also what incorporates the essential idea of the invention.