Abstract:
A compact and multi-functional power monitoring and circuit protection system is provided that is easily installed, used and modified, and internally derives all control and output power from the input voltages being monitored for abnormal power conditions. The functionality of all desired power monitoring and sensing devices is integrated into one unit controlled by a microprocessor. This substantially reduces the number of parts and control wiring required to achieve adequate power monitoring and circuit protection, and reduces the assembly and installation time. The integrated system uses only one set of voltage input wires, one set of current input wires, one set of blown fuse input wires and one output pair of wires to the power disconnect switch&#39;s shunt trip. Circuitry is provided to select one of the three power phases being monitored such that one of the three phases is always available to power the system. Control voltages for controlling the shunt trip and external circuits using output relays (to illuminate pilot lights, bell alarms, etc.) are also provided onboard the unit. A blown fuse detection circuit uses solid-state devices in lieu of replaceable trigger fuses. The unit can be instantly reset itself after a blown fuse condition in a power disconnect switch has been rectified.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims the benefit of U.S. Provisional Patent Application No. 60/565,891 filed Apr. 28, 2004, the disclosure of which is incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION  
       [0002]     This invention relates generally to a power monitoring and circuit protection system, and more particularly, to an integral system having multiple means for monitoring electrical power distribution systems and devices and protecting them against abnormal power conditions.  
       BACKGROUND OF THE INVENTION  
       [0003]     Electrical power distribution systems are used to bring electric service from a power utility into facilities such as residential, office and industrial buildings. Typically, the electric service provided by a power utility is in a three phase configuration. Each facility&#39;s distribution system includes a number of fused power disconnect switches, which switch power on and off, as well as protect against short circuits and overloads, including a main power disconnect switch and several branch power disconnect switches.  
         [0004]     With the rapid advancement of technology, electrical and electronic products used in such facilities have become quite sensitive to abnormal power conditions, which may cause interruption in use or failure of the products. Abnormal power conditions may arise, for example, from power utility failure in the form of under-voltages, over-voltages, voltage unbalances, phase reversals, phase angle errors or phase losses. Other abnormal power conditions may occur within a facility itself, such as blown fuses, over-currents, current unbalances or abnormal equipment operating temperature. It has therefore become necessary to protect power sensitive products from such abnormal power conditions.  
         [0005]     Many devices for sensing and protecting against abnormal power conditions are known. However, prior devices have various shortcomings in installation, operation and maintenance. Prior devices are typically available in individual packages or stand-alone units (e.g., one package to detect under-voltages, one package to detect blown fuses, one to generate a control power source, etc.), each comprising a sensing circuit or relay. To achieve the desired level of protection from a variety of abnormal power conditions, a series of prior individual packages must be manually wired together and to an external power supply to create a complete power monitoring and protection system for each power disconnect switch.  
         [0006]     For example, a wiring diagram for a typical prior art system for power monitoring and circuit protection is shown in  FIG. 1  (within the dashed border line), as wired to a facility&#39;s power disconnect switch  10 , which feeds power to a load. The power disconnect switch employs a separate fuse  12  for each of the three phases (labeled ØA, ØB, ØC) for basic over-current and short circuit protection. The switch  10  also employs a shunt trip solenoid  14 , which, when activated, opens the power disconnect switch  10  to disconnect power delivered to the load. A shunt-trip opens a power disconnect or circuit breaker with a low power electrical signal, rather than opening it manually.  
         [0007]     Under normal operating conditions, each of the main fuses  12  pass load current from the power source and permit that current to be fed to the load. Prior art blown fuse protection occurs when one of the main fuses  12  is blown and a smaller trigger fuse  16  (shown in  FIG. 7A ) attempts to carry the load current. The trigger fuse  16  is designed to burn under minimal current. Upon burning, the trigger fuse  16  extends an actuating arm  18  to actuate a micro-switch  20 . Using an external power source  34 , the micro-switch is wired to actuate the shunt trip solenoid  14 . This will open the power disconnect switch  10  and shut off all power to the load. To restore power, all of the blown fuses (main fuses and trigger fuses) must be manually replaced, imposing added costs and difficulties in maintaining the system.  
         [0008]     The prior art system shown in  FIG. 1 , as an example, includes individual packages or relays for sensing phase failure  22 , under-voltage  24 , phase rotation  26 , over-current  28  and blown fuses  30  in the power service lines. Each of the three phases is tapped for voltage  42  and provided as a separate input to each of the individual relays, such that each sensing relay has at least three inputs. The over-current sensing relay  28  uses three-phase current inputs that are stepped down from the service operating current by current transformer  44  in the facility&#39;s power disconnect  10 . A typical current transformer has a 5 A secondary. For example, if the power disconnect switch is rated at 4000 amps, the current transformer used to step-down the current will have a 4000:5 amp ratio. A fourth current input is the ground reference point for the current transformers.  
         [0009]     Each of the individual sensing relays are typically provided with one, dry-type, Form ‘C’, output contact  32 , which is energized under normal conditions and drops out under a fault (dead-man&#39;s switch). However, these dry output contacts have no internal power source and require an external power source to make them functionally operative. Using an external power source, the dry contacts  32  may be used to illuminate pilot lights, sound an alarm, operate the shunt-trip feature of power disconnects, or drive additional relays if additional contacts are needed. In this prior art example, each of the output contacts  32  are wired directly to the shunt trip  14 , such that if any of the relays sense an abnormal power condition, the shunt trip is activated and the power disconnect switch  10  is opened to shut power off.  
         [0010]     In  FIG. 1 , the control power that enables each dry-type output contact  32  to activate the shunt trip must be derived by external means, e.g., transformer  34 . The control power is applied by additional wiring  36  to the dry contacts  32  of each of the individual sensing relays  22 ,  24 ,  26 ,  28 ,  30  to achieve functional output to operate the shunt trip  14 . If the system requires more output contacts, for example, to sound an alarm or illuminate a pilot light, additional stand-alone relays, such as auxiliary contacts  38 , must be connected in parallel with the relay contacts  32 . Each of these auxiliary contacts can only be associated with one of the sensing relays. If the auxiliary contacts  38  require power to perform a function (e.g., illuminate pilot lights, ring buzzers, etc.) an additional external power source, such as the control power transformer  34 , must be provided.  
         [0011]     Although prior systems are functionally effective, these systems require many different parts and extensive control wiring, which in turn require substantial assembly and installation time and expense. A protection system including several individual packages, like the system shown in  FIG. 1 , for example, requires hundreds of control wire terminations. Due to the complex wiring, the risk of mis-wiring any of the connections is great and troubleshooting the system is difficult. Existing systems also require a substantial amount of space due to the size of each individual package and the resulting required wiring. Further, existing systems are limited in function by the way they are installed. If contacts or relays are to be used for a different purpose, the system must be manually re-wired for each different application, which imposes added costs and reduces efficiency.  
       SUMMARY OF THE INVENTION  
       [0012]     In accordance with the present invention, a compact and multi-functional power monitoring and circuit protection system is provided that is easily installed, used and modified, and internally derives all control and output power from the input voltages being monitored, thereby overcoming the above-mentioned shortcomings of known power monitoring and circuit protection systems.  
         [0013]     In a preferred embodiment of the invention, the functionality of all of the desired power monitoring and sensing devices is integrated into one compact and integral unit controlled by a microprocessor. This substantially reduces the number of parts and control wiring required to achieve adequate power monitoring and circuit protection, and reduces the assembly and installation time. For example, the extensive control wiring shown in the prior art system of  FIG. 1  is virtually eliminated. Instead, the integrated system requires only one set of voltage input wires, one set of current input wires, one set of blown fuse input wires and one output pair of wires to the power disconnect switch&#39;s shunt trip. By eliminating the need for manual assembly of stand-alone devices, the possibility of any mis-wiring is also eliminated. Having all the required components in a single integral unit also eliminates certain liabilities and the time spent troubleshooting. Further, in many situations, space is at a premium. The apparatus of the present invention significantly reduces the space needed to protect electrical products from any abnormal power conditions.  
         [0014]     As a further aspect of the present invention, the control power required for powering all circuits in, and controlled by, the power protection system is derived from the voltage being monitored. For example, the voltage being monitored supplies power to the input circuits, the microprocessor, the output circuits and all relays for use in illuminating a pilot light or sounding a buzzer. Circuitry is provided to select one of the three power phases being monitored such that one of the three phases is always available to power the monitoring system. Control voltages for the shunt trip and external circuits using the output relays (to illuminate pilot lights, bell alarms, etc.) are also provided onboard the unit.  
         [0015]     As a further aspect of the invention, the device can be used for any number of operating voltages, up to 600V AC. A programmable gain amplifier, embedded in the microprocessor, enhances the digital resolution of lower voltage levels.  
         [0016]     As a further aspect of the invention, the blown fuse detection circuit is non-destructive (no parts to replace). This is achieved using solid-state devices in lieu of replaceable trigger fuses. The unit can instantly reset itself after a blown fuse condition in the facility&#39;s power disconnect switch has been rectified.  
         [0017]     As a further aspect of the invention, the integral unit has the ability to assign more than one output relay to a specific sensing circuit or more than one sensing circuit to a specific output relay, eliminating the restriction of having just one Form ‘C’ contact per sensing circuit. For the purpose of functional output (shunt trip, pilot lights, audible alarms, etc.), the circuits of the present invention also provide an onboard voltage source, eliminating the need for external control voltage sources.  
         [0018]     Other objects, features and advantages of the present invention will be apparent when the detailed description of the preferred embodiments of the invention is considered in conjunction with the drawings, which should be construed in an illustrative and not limiting sense as follows: 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]      FIG. 1  is a wiring schematic of a typical prior art power protection system wired to a typical power disconnect switch.  
         [0020]      FIG. 2  is a wiring schematic of a power protection system in accordance with the invention wired to a typical power disconnect switch.  
         [0021]      FIG. 3  is a circuit diagram of a phase selection circuit for selecting a phase of the power being monitored to use for energizing the power protection system of the invention.  
         [0022]      FIG. 4  is a circuit diagram of a shunt trip circuit for the power protection system of the invention.  
         [0023]      FIG. 5  is a representation of an LCD Setup Menu for use with the power protection system of the invention.  
         [0024]      FIG. 6  is a block diagram showing the current and voltage flow of the power protection system of the invention.  
         [0025]      FIG. 7A  is a wiring diagram showing a prior art blown fuse detector for use in a typical prior art power protection system.  
         [0026]      FIG. 7B  is a wiring diagram showing a blown fuse detector for use in the power protection system of the invention.  
         [0027]      FIG. 7C  is a schematic of the blown fuse detection circuit for use in the power protection system of the invention.  
         [0028]      FIG. 8  is a schematic of the pin out arrangement of a microprocessor for use in the power protection system of the invention.  
         [0029]      FIG. 9  is a schematic of a voltage input circuit prior to entering the microprocessor.  
         [0030]      FIG. 10  is a schematic of a current input circuit prior to entering the microprocessor.  
         [0031]      FIG. 11  is a schematic of the pin out arrangement of an output relay driver for use in the power protection system of the invention. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0032]     A preferred embodiment of the invention is herein described in detail, and is sometimes referred to as a “power protection system”. It is to be understood that while a particular system configuration, circuit layouts, and modes of operation are described, other modifications and variations may be made thereto in accordance with the general principles of the invention disclosed herein.  
         [0033]     The power protection system is an integrated electronic system used to monitor the power utilized in a facility for abnormal power conditions and causing a power disconnect switch to open when certain abnormal power conditions are detected. The system may be used to control any of the power disconnect switches in a facility, including the main power disconnect switch and any of the branch disconnect switches. The system includes the functionality of the existing stand-alone power sensing packages described above, as well as other types of power regulation, power monitoring and fault detection circuits, the required wiring (circuitry) and control power to make them function as a whole. All of the power monitoring and circuit protection devices are combined onto a single printed circuit board and controlled by a microprocessor. The circuit board and all necessary input/output ports are placed in a single enclosure having an LCD screen or other type of user interface for a user to select the desired power monitoring features. Thus, the power protection system is readily portable, and easily installed, maintained and modified. If a facility has more than one power service line that requires monitoring, a second power protection system may be installed and both systems can be synchronized together.  
         [0034]     A wiring diagram of a power protection system  100  in accordance with the invention is shown in  FIG. 2  as wired to a facility&#39;s power disconnect switch  10 . Referring to the input/output flow diagram of  FIG. 6 , the power protection system  100  includes power sensing software for monitoring and sensing under-voltage, over-voltage, phase rotation, voltage unbalance (between phases), current unbalance (between phases), over-current, blown fuse detection, temperature and generator synchronization, all within the microprocessor  200 . A control panel  104  is mounted in the surface of the power protection system&#39;s enclosure to provide a user interface for initial system setup, monitoring current system status and to provide easy modification of the system parameters and functions. For example, the control panel may include an LCD display  106  or other visual interface, and a control knob  108  or keypad for selecting certain system parameters or entering system information. The control panel  104  may also display or indicate which abnormal condition has occurred, when an abnormal condition has occurred.  
         [0035]     The power protection system has four sets of input terminals (for voltage  110 , current  120 , thermistor input  130  and blown fuse detection  140 ) and one output  150  to the main power disconnect switch&#39;s shunt trip coil. Thus, installation of the power protection system of the invention requires substantially fewer wire connections than prior systems.  
         [0036]     The voltage input block  110  accepts one tap from each of the main power service&#39;s three phases (A, B, C) and the neutral. The voltage input at this one block  110  is used for monitoring and sensing all of the potential voltage abnormalities, including under-voltage, over-voltage, phase rotation and voltage unbalance. This input voltage also provides power to the voltage regulators  112  ( FIG. 6 ) that provide control power within the system.  
         [0037]     Many prior protection systems cannot maintain system power that is derived from a three-phase AC system when one or two of the phases go offline. This is because the system uses one of the three phases exclusively to power the device. If that one phase is lost, the other two, regardless of condition, will not be used. Therefore, the system will be dead. Thus, prior systems use a “dead man&#39;s” switch that drops out when there is a fault or the critical phase is lost, potentially providing a false alarm.  
         [0038]     The power protection system of the present invention remains operational even when one or two of the phases are lost. Referring to  FIG. 3 , a phase selection circuit is used to select any of the three phases, as long as one of the phases is active, and to output the selected phase to a voltage regulator circuit  112  for use in the system and to a Shunt Trip Circuit ( FIG. 4 ). Under normal three phase conditions (all three phases active), voltages A, B &amp; C enter the phase selection circuit at points V 1 , V 2  &amp; V 3 . Three triac switching circuits control the phase that continues to V 4 . Under normal conditions, Triac Q 8  is on while Q 9  and Q 10  are off. This allows the power from V 1  to continue to Vout. In this mode of operation, Triacs Q 9  and Q 10  are turned off when current passes through diodes D 20  and D 23  and saturate transistors Q 6  and Q 7 . Turning on transistors Q 6  and Q 7  removes current flow to opto-isolators U 29  and U 30 , which subsequently turn off Triacs Q 9  and Q 10 . In the event power is lost from V 1 , transistor Q 6  would turn off, causing Triac Q 9  to turn on and allow V 2  to continue to V 4 . This type of logic is used to provide power to the voltage regulators  112  and shunt trip circuit ( FIG. 4 ) as long as there is at least one phase active. Table I, below, illustrates the logic of the circuit.  
                                                           TABLE I                       V1   V2   V3   Q6   Q7   U28   U29   U30   Q8   Q9   Q10   V4                   ON   ON   ON   ON   ON   ON   OFF   OFF   ON   OFF   OFF   A       OFF   ON   ON   OFF   ON   OFF   ON   OFF   OFF   ON   OFF   B       ON   OFF   ON   ON   ON   ON   OFF   OFF   ON   OFF   OFF   A       ON   ON   OFF   ON   ON   ON   OFF   OFF   ON   OFF   OFF   A       OFF   OFF   ON   OFF   OFF   OFF   OFF   ON   OFF   OFF   ON   C       ON   OFF   OFF   ON   ON   ON   OFF   OFF   ON   OFF   OFF   A       OFF   ON   OFF   OFF   ON   OFF   ON   OFF   OFF   ON   OFF   B                  
 
         [0039]     The selected phase is output to the voltage regulators  112  for converting the raw input voltage to a lower voltage usable by the system. The regulated voltage is used for powering the components of the power protection system. Regulator circuits of these types are commonly known in the industry and are therefore not shown or described in any further detail herein.  
         [0040]     The selected raw voltage is also input to the shunt trip circuit shown in  FIG. 4 , where it is regulated by zener diode Q 3 . When the shunt trip circuit receives a drive signal  202  from the microprocessor  200 , derived from any of the abnormal power sensing algorithms, opto-isolator U 18  is turned on, which turns on triac Q 5  and delivers power to the shunt trip output  150 . This activates the shunt trip solenoid  14  in the facility&#39;s power disconnect. In the event of a total power loss, a user may want to open (shunt trip) the power disconnect. If all three phases are lost, however, there is no input power at V 4  to deliver to the shunt trip  14 . Therefore, a stored energy capacitor C 52  stores the energy to power the shunt trip  14  under these conditions. During normal conditions, energy from V 4  is stored in capacitor C 52 . This energy will be used in the event there is no voltage at V 4  to deliver to the shunt trip output  150 . Thus, the shunt trip  14  may be activated even when none of the three phases are active. For safety, LED D 7  in  FIG. 4 , will illuminate when there is a charge present in capacitor C 52 . A bleed resistor R 46  is provided in the circuit to discharge capacitor C 52  when the system is powered down and no charge is required in capacitor C 52 .  
         [0041]     Referring to  FIG. 2 , the voltage input block  110  receives raw input voltages from the system being monitored via wire taps  68 . The present invention monitors these voltages for abnormalities as well as uses them to power the system and any other external loads. For the purpose of voltage monitoring, the system is auto-ranging for any system voltage up to 600V. However, the transformers and voltage regulator circuits of the power protection system may be readily modified to increase the voltage operating range. This method is used to maintain optimal resolution at lower operating voltages. The input voltages are converted to digital using a 12-bit analog to digital (A-D) converter  114  embedded in the microprocessor  200 . Shown in  FIG. 9 , prior to entering the A-D converter, the raw voltage is adjusted to yield 3VDC at full input voltage. An isolation transformer  208  is used to step-down the input voltage and well as isolate the circuit from external voltage spikes. A full wave rectifier D 27  and low pass filter (C 35 , R 35 , C 46 ) converts the AC signal to DC. The resistor divider (R 35  &amp; R 36 ) in conjunction with isolation transformer  208  is calibrated to output 3VDC at full input voltage at input block  110 . Using a 12-bit A-D converter there are 4095 possible digital values for voltage. With full-scale input voltage, plus 150%, at inputs  110 , the A-D converter  114  will register  4095 . At zero volts it will register  0000 . Upon system startup, the CPU samples the digital input voltage values. If the value is below half scale (2048), the microprocessor is programmed to engage a 2× programmable gain amplifier  204  at the input of the A-D converter  114 . This will increase the analog input voltage to the A-D converter and thus increase the resolution of the samples.  
         [0042]     After the appropriate amplification has been determined, a reference voltage is sampled and stored by the microprocessor  200 . The abnormality range percentage settings shown in  FIG. 5  will be based on this reference voltage. Having established that the reference voltage is a 12-bit digital value, all range settings  206  shown in  FIG. 5  are percentages of the stored reference value. If the monitored voltage, and subsequent digital value, deviate in excess of the range settings  206 , the microprocessor will react in accordance with the additional settings shown in  FIG. 5 . When a range setting has been exceeded, a user may want to delay the alarm, assign specific output relays  158  to close, operate the shunt trip of a power disconnect, etc.  
         [0043]     The current input block  120  receives a transformed current from the secondary side of the current transformer  44  in the facility&#39;s power disconnect switch  10 . For example, using a current transformer with a 4000:5 amp ratio, if the operating current of the disconnect switch is 4000 amps, the secondary output is 5 amps. Using the same current transformers  44 , if the disconnect switch operates at 2000 amps, the secondary output is 2.5 amps. Referring to  FIG. 10 , resistor R 41  is used to establish a voltage from the current source of current transformers  44 . This AC voltage at R 41  is then converted to 3VDC in a similar manner as the voltage input circuit described above and illustrated in  FIG. 3 . The converted current signal is then input to the embedded A-D converter  122 . The microprocessor  200 , uses software algorithms to sense current abnormalities in the same way it senses voltage abnormalities. Auto-ranging is not required when using current transformers. The current input to the power protection system is always 0-5 amps, regardless of the switch&#39;s operating current.  
         [0044]     The thermistor input block  130  receives a signal indicative of the temperature of the surface to which the temperature probe is attached. An industry standard thermistor circuit is provided in a separate package wired to thermistor inputs  130 . The circuit will output 0-3VDC for a temperature range of 0-150 degrees Celsius. This is input to the microprocessor, via embedded A-D converter  116 , which may be programmed to set off an alarm or activate the shunt trip circuit if the temperature exceeds the temperature setting in the user setup menu.  
         [0045]     The blown fuse detector inputs are used for detecting if one or more of the power disconnect switch&#39;s main fuses  12  have blown. As shown in  FIG. 7B , a tap is placed on the line side  210  and the load side  212  of the main fuse  12 . This is wired to the corresponding blown fuse detector input  140  for each phase (for example, A 1  and A 2 ). A resistor  142  in the blown fuse detection circuitry ( FIG. 7C ) is wired between each of the taps for each main fuse  12  (for example, between A 1  and A 2 ), as shown in  FIG. 7B .  FIG. 7C  shows that when there is a blown fuse, there is a current flow through R 12 , which activates opto-isolator U 6 . This grounds the output FUSE_ 1  and sends a logic low to the microprocessor  200 . Under normal conditions, there is no current flow through R 12  and the output FUSE_ 1  sends a logic high to the microprocessor. The microprocessor  200  will react to the logic low based on the user settings detailed in  FIG. 5 . This may be the activation of the shunt trip, switching output relays, etc.  
         [0046]     The power monitoring features of the invention is performed by the software based abnormal power sensing algorithms (or PSAs). As set forth above, analog to digital converters are used to quantize the raw power inputs for use in the microprocessor. Within the microprocessor, the PSAs monitor the digital inputs for voltage, current, temperature and blown fuses status, with respect to the menu settings shown in  FIG. 5 . Other PSAs may be added by modifying the software in the microprocessor. Terminals are provided for field modification of the software ( FIG. 8 , pins  21  &amp;  22 ).  
         [0047]     Referring to  FIG. 2 , the power protection system preferably includes 16 output relays  158 . However, more output relays could easily be added. The output relays are simply Form ‘C’ contacts that are controlled by signals sent from the microprocessor. The microprocessor  200  sends a 3-bit address ( FIG. 8 , Pins  23 ,  57 ,  58 ) to the integrated circuit (IC) shown in  FIG. 11 . Along with the 3-bit address, a chip select bit ( FIG. 8 , Pins  25 ,  26 ) and a data bit ( FIG. 8 , Pin  24 ) are sent to the IC. The chip select bit is used to select between the two IC&#39;s required to drive  16  output relays  158 . Each IC can control up to 8 output relays. The data bit is a logic high (3.3V) to turn the relay on, or a logic low (0V) to turn the relay off.  
         [0048]     The output relays  158  function as user outputs that can be used for a variety of operations. Typically they are used as dry contacts for building management systems. However, the output relays can also be used to control items such as pilot lights, bell alarms, etc. Control power for the output relays  158  is available and assignable on the circuit board by pin jumpers  166 . This could also be achieved by software control through the setup menu. This control power is being derived from the voltage input  110  via voltage regulators  112 . This eliminates the need for separate control power transformers and external power supplies, as required by prior art systems. An industry standard 24VDC voltage regulator  112  is fed from the phase selection circuit  220  and tied to pin jumpers  166  on the PCB  102 . The output relays  158  are user assignable to any of the sensing algorithms through the setup menu. Additionally, more than one output relay  158  can be assigned to a particular PSA. Conversely, more than one PSA can be assigned to a particular output relay. Terminal blocks  162  are used for connecting the output relays to lights, buzzers, alarms, building management systems or other external devices.  
         [0049]     A shunt trip output contact is also integral to the power protection system of the invention. A preferred type of shunt trip contact is a solid state, SCR type, output contact U 18  ( FIG. 4 ). The contact delivers a control signal to a shunt trip  14  should the microprocessor  200  detect an abnormal condition. In accordance with the present invention, shunt trip functionality is reduced to a single contact because all of the sensing algorithms are software based and selectable via the setup menu and the shunt tripping voltage is derived on the device itself. In prior systems, such as the system shown in  FIG. 1 , shunt trip control power was derived from an external power source (such as a transformer  34 ), wired to several dry contacts of multiple sensing devices, which were then wired to the shunt trip coil  14 . The power protection system of the present invention internally regulates the system&#39;s voltage to the required shunt tripping voltage without the need for an external transformer, again reducing parts and assembly time. See  FIGS. 3 &amp; 4 . An operational block diagram of a power protection system in accordance with the invention is shown in  FIG. 6 .  
         [0050]     An additional feature of the power protection system  100  is its ability to be synchronized with additional power protection systems. Certain situations may require two or more power sources to be on a common bus. This can only occur if both power sources are operating at the same voltage and phase rotation. In situations where there are two or more power disconnect switches  10 , a power protection system  100  can be installed on each power disconnect switch  10  to permit monitoring of voltage and phase in each power disconnect switch. The power monitoring systems  100  are then wired together via the generator sync  160  (see  FIG. 2 ). If the voltage and/or phase angle detected in one of the systems are different than the voltage and/or phase angle in the other system, an alarm signal is generated by the microprocessor  200 . This is achieved by digitizing the input voltages of the individual power sources, as described hereinbefore, and comparing the values of the separate units using the generator sync PSA.  
         [0051]     Using the setup menu shown in  FIG. 5 , the alarm signals generated by the PSAs in the microprocessor  200  can be routed to either activate the shunt trip contact  150 , actuate one or more of the output relays  158 , or both. A preferred, simplified, setup menu for several power sensing algorithms is shown in  FIG. 5 . Other power sensing circuits may be added by software modification if desired. Column 1 shows the type of sensing algorithm. Columns 2-7 show the various options for each sensing algorithm shown in Column 1.  
         [0052]     Column 2 allows a user to activate or deactivate the sensing algorithm. Column 3 allows the user to set the detection threshold. For example, in the under-voltage sensing algorithm, a user can set the detection threshold anywhere between 50-100% of the reference voltage. Column 4 allows a user to set the time delay for a specific sensing circuit to prevent, for example, nuisance tripping. This is useful to avoid tripping when, the system senses a temporary abnormal power condition, which is remedied without user intervention. Column 5 allows a user to assign one or more output relays  158  to a sensing algorithm (to operate, e.g., an alarm or illuminate a light) in addition to the shunt trip circuit  150 . In certain situations, it is not desirable to activate the shunt-trip  14 . Instead, it may only be desirable to sound an alarm or illuminate a light. Thus, Column 6 allows a user to decide whether the shunt-tripping capability is assigned to each sensing algorithm. Column 7 allows a user to select whether each power sensing algorithm alarm can automatically reset, or requires a manual reset. This is useful when an abnormal power condition is temporary and remedies, such as overnight power sag that nobody witnesses. The setup menu may also be used to set certain system operating voltages, for example, for the shunt trip output.  
         [0053]     A further advantage of the power protection system is its ambient temperature operating range of 0° C. to 105° C. Most prior stand-alone power monitors have a maximum operating temperature of 55° C. These devices are often located in areas where the ambient temperature can exceed its designed operating temperatures (electrical switchgear rooms, boiler rooms, machine rooms, etc.), which may cause undesirable operation of the electronic circuits. The present invention does not have this problem.  
         [0054]     Although the invention has been described with reference to preferred embodiments, which should be construed in an illustrative and not limiting sense, it will be appreciated by one of ordinary skill in the art that numerous modifications are possible in light of the above disclosure. For example, a non-microprocessor based circuit may be employed using analog devices, the output display may be larger (e.g., seven segments) or it may include a color, touch-screen interface for menu programming and monitoring. Further, the present device may be configured to control more than 16 output relays, may possess a real-time clock event logging, the apparatus may be integrated with workstations, workstation software and programmable logic controllers (PLCs), the printed circuit boards may be fabricated to have multiple layers, and multiple temperature sensing inputs could be used for monitoring the temperature at more than one location. Further still, the device may be configured to switch power disconnects or circuit breakers on as well as off. Additionally, a battery backup (UPS), or alternate power source may be used to provide power if all primary input power is lost. The system may also be configured to operate on other than three-phase AC systems. The system may be modified to sense ground fault currents, line harmonics and transients. Further, the transformers and voltage regulator circuits of the power protection system may be readily modified to increase the voltage operating range of the power protection system. All such variations and modifications are intended to be within the scope and spirit of the invention, as defined in the following claims: