Abstract:
A system and method for protecting devices and equipment from lightning strikes is disclosed. The protection device provides real-time monitoring of local atmospheric conditions to protect sensitive power-supply and control equipment. Embodiments of the device may be triggered by the detection of an actual lightning strike or an abrupt change in atmospheric charging that could indicate the presence of lightning conditions. The device provides lightning protection by isolating control, power, and signal circuits from external conductors and placing them in safe operating conditions for the duration of lightning strike event. Embodiments of the device may include onboard surge suppression in addition to lightning detection and protection. The device may be integrated into customer control equipment and is fully automatic. Without requiring operator intervention, the system restores normal operation when lightning events are no longer detected.

Description:
TECHNICAL FIELD 
       [0001]    Embodiments of the invention are directed, in general, to lightning detectors and, more specifically, to a programmable lightning detector that provides customized protection to one or more devices. 
       BACKGROUND 
       [0002]    A typical lightning flash lass about a quarter of a second and consists of three or four separate discharges or strokes each individually lasting a few ten-thousandths of a second. It is well known that lightning strikes can cause extensive damage to buildings and equipment. A direct lightning strike can damage structures and equipment located on the roof or exterior buildings. The lightning current can be carried inside and through a building by power, telephone, or analog or digital data lines or cables. The direct injection of lightning current can cause immense damage to electrical and electronic circuits and equipment inside a building. The energy in a lightning stroke can also induce currents in the wires and cables inside a building if the lightning is carried by pipes, conduits, or reinforcing or structural steel. Surge currents are generally less intense than the direct injection lightning currents, but can easily damage integrated circuits and sensitive components in computers, modems, electronic control circuits and telephone systems. 
         [0003]    Lightning and surge damage can range from a temporary malfunction that does not cause any significant physical change to a permanent alteration in the physical properties of the equipment or its components, which may require repair or replacement of the equipment. Lightning damage in electrical and electronic equipment includes, for example, disabling motors or transformers so that equipment is no longer functional, vaporized transistors and integrated circuits on circuit boards, and blown fuses. Recovery from lightning damage can take time and can be expensive. Consequential damages from a lightning strike can also be expensive due to, for example, loss of business income while equipment is inoperative, cost of restoring data from backups and paper records, cost of replacing or repairing damaged equipment, cost of replacing damaged power and data cables, and the cost of replacing damaged structure. 
         [0004]    Electronic equipment is typically designed to operate in a well-controlled electrical environment. Users typically install lightning protection, such as electrical surge-protective devices, and/or power conditioning equipment to mitigate the effects of electrical disturbances and lightning. Protection against lightning can be much less expensive than the repair or replacement of damaged equipment. Lightning protection can take several different forms, such as lightning rods or arresters that are designed to divert the surge currents to earth. Low-energy surge-protective devices or suppressors may be installed on specific equipment that is either vulnerable to damage or susceptible to upset. These traditional lightning protection devices are not adapted for the particular equipment to which they are connected, but instead simply act to absorb or deflect lightning currents. 
       SUMMARY 
       [0005]    Embodiments of the invention are directed to an in-line protection device that integrates a high-capacity transient voltage surge suppressor with real-time monitoring of local atmospheric conditions to protect sensitive power-supply and control equipment. Embodiments of the device may be triggered by the detection of an actual lightning strike or an abrupt change in atmospheric charging that could indicate the presence of lightning conditions. The device provides lightning protection by isolating control, power, and signal circuits from external conductors and placing them in safe operating conditions for the duration of lightning strike event. Embodiments of the device may include onboard surge suppression in addition to lightning detection and protection. The device may be integrated into customer control equipment and is fully automatic. Without requiring operator intervention, the system restores normal operation when lightning events are no longer detected. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    Having thus described the invention in general terms, reference will now be made to the accompanying drawings, wherein: 
           [0007]      FIG. 1  is a high level block diagram illustrating lightning protection system  100  according to an exemplary embodiment; 
           [0008]      FIG. 2  is a high level block diagram illustrating the components of lightning protection circuit according to one embodiment; 
           [0009]      FIG. 3  is a schematic diagram of the components of a lightning protection circuit according to an exemplary embodiment; 
           [0010]      FIG. 4  is a flowchart illustrating an exemplary process  400  operating on a microcontroller for the lightning detection device; and 
           [0011]      FIG. 5  illustrates an exemplary lightning flash timeline. 
       
    
    
     DETAILED DESCRIPTION 
       [0012]    The invention now will be described more fully hereinafter with reference to the accompanying drawings. 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. One skilled in the art may be able to use the various embodiments of the invention. 
         [0013]      FIG. 1  is a high level block diagram illustrating lightning protection system  100  according to an exemplary embodiment. Electrical and/or electronic equipment  101  receives electrical power from source  102 . Surge protector  103  protects equipment  101  from current and voltage surges that are carried on power supply line  104  from source  102  or any other origin, such as lightning strikes on cable  104 . Relay  105  and lightning detector  106  provide additional protection for equipment  101  specifically in response to lightning detection. In one embodiment, lightning detector  106  includes a lightning detection circuit that detects a charge imbalance that matches a lightning profile and commands relay  105  to open. The lightning detection circuit may detect radio frequency (RF) energy generated by lightning and/or may detect any change in atmospheric charge. When relay  105  is open, equipment  101  is disconnected from power source  102  and power supply line  104 . Accordingly, if lightning has occurred within detectable range, then lightning detector  106  protects equipment  101  from any current or voltage surges that would otherwise propagate along supply line  104 . 
         [0014]    It will be understood the source  102  and cable  104  are not limited to electricity distribution systems, but may be any power or data connection between equipment  101  and an external device. For example, cable  104  may be a telephone line, Ethernet or data cable, cable or closed-circuit television cable, or any other electrically conductive connection. 
         [0015]      FIG. 2  is a high level block diagram illustrating the components of lightning protection circuit  201  according to one embodiment. The lightning protection circuit  201  comprises lightning detector circuit  202 , which is coupled to microcontroller  203  through isolation circuit  204 . Large electromagnetic pulses, such as those caused by lightning, are detected in circuit  202 , which generates a signal at output  205  corresponding to the lightning&#39;s electromagnetic pulse. Lightning is comprised of a series of separate discharges or strokes. Lightning detector  202  generates a detection signal corresponding to each discharge or stroke. In one embodiment, the output signal at  205  is proportional in amplitude to the electromagnetic pulse created by the lightning. The duration of the detection signal corresponds to the duration of each discharge or stroke in the lightning. 
         [0016]    Lightning detector circuit  202  is a charge balance monitoring system that detects a charge imbalance. Lightning detector  202  may detects broadband RF signals and can be tuned to specific frequencies associated with lightning. 
         [0017]    Isolation circuit  204  isolates lightning detector  202  from microcontroller  203  to protect controller  203  from being damaged by the signals output from detector  202 . In one embodiment, isolation circuit  204  optically isolates controller  203  from detector  202  so that there is no direct current path between those components. 
         [0018]    Controller  203  receives and analyzes the output signals from detector  202 . Controller  202  evaluates whether the detector output signals correlate to lightning. For example, controller  202  may analyze the relative strength, duration, and repetition interval of the detector  202  output signals and compare those parameters to one or more lightning profiles. The lightning profiles may be generated based upon observations of actual lightning as described in more detail below. Detector  202  generates a detection output signal whenever it receives an electromagnetic pulse in a certain frequency range. Interference from other devices that emit electromagnetic pulses, such as large electronic equipment, appliances, fluorescent lights and car engines, may cause detector  202  to output a detection signal that is not associated with lightning. In one embodiment, controller  203  prevents lightning protection circuit  201  from generating false lightning detections by comparing the detector output both to known lightning profiles and other known electromagnetic pulse emitters. Detector output signals that match other known, non-lightning emitters can be eliminated and not further processed by lightning detector  201 . 
         [0019]    Upon detection of lightning, controller  203  generates a control signal  206  for multiple-channel controller  207 . Control signal  206  indicates to channel controller  207  that some action should be taken for one or more controlled channels. In one embodiment, multi-channel controller  207  provides control over eight different channels. However, it will be understood that controller  207  may control any number of channels, including one. In addition to indicating that lightning has been detected, control signal  206  may designate one or more particular channels for which channel controller  207  should take action. In one embodiment, channel controller  207  controls one or more relays  208  or other interfaces  209 . Channel controller  207  opens or closes relays  208  or activates interface  209  upon receipt of control signal  206 . 
         [0020]    Relays  208  and interface  209  may operate to control connects between equipment  210 - 212  and a power line or other wire, cable, or connection. For example, relay  208   a  may act as a switch that couples device  210  to a power source  213 , relay  208   b  may act as a switch that connects device  211  to a telephone line or cable television line, and interface  209  may connect device  212  to a computer or packet network  215 . Typically, such switches  208 - 209  are closed to allow power, data, signals, or other information to flow to equipment  210 - 212  during normal operation. When activated by channel controller  207 , relays  208  and/or interface  209  open to disconnect equipment  210 - 212  from power source  213  and other lines and networks  214 ,  215 . Once disconnected, equipment  210 - 212  is protected from current surges caused by a lightning strike. It will be understood that equipment  210 - 212  may be any electrical or electronic equipment or other device that is vulnerable to lightning surge currents. It will be further understood that relay  208  and interface  209  may couple such equipment to any conductive structure. 
         [0021]    Microcontroller  203  and/or channel controller  207  also regulate how long equipment  210 - 212  remains disconnected or off-line. Each individual device  210 - 212  can be reconnected after an independently selected duration so that the equipment can be reconnected and/or rebooted in any particular sequence or after any desired delay. Equipment  210 - 212  may correspond to different devices in the same system, such as different boards in an equipment rack or different components of a computer system or server. It may be necessary or preferred to reconnect, power-up, and/or reboot the components of the same system in a particular order, such as reconnecting a power supply, then reconnecting internal buses, and finally reconnecting external interfaces. 
         [0022]    Microcontroller  203  and/or channel controller  207  may be programmed to perform such an ordered reconnection following a lightning detection disconnect. Microcontroller  203  may provide separate disconnect and connection commands to channel controller  207  for each channel or for groups of channels. A first control signal from microcontroller  203  may indicate which channel should be disconnected from a conductive element. A second control signal may indicate that the channel should be reconnected to the conductive element. Microcontroller  203  may determine when to transmit the second control signal based upon the duration of a lightning event. Alternatively, commands or signals sent from microcontroller  203  may comprise both disconnection and connection, or activation and deactivation, information. The control signals from microcontroller  203  may indicate which channel should be disconnected from a conductive element, and for how long the disconnection should last. 
         [0023]    In one embodiment, channel controller  207  can control up to sixteen separate channels. Each channel may be coupled to a separate device, and a unique action can be designated for each device. For example, separate timing, sequential logic, delay, sensitivity, and routines may be applied to each channel. 
         [0024]    In some embodiments, surge suppressor  217 , which may be part of lightning protection circuit  201  or a separate device, provides additional protection beyond lightning protection. Surge suppressor  217  may comprise fast-acting, ceramic fuses and thermal overload metal oxide varistors (TMOV) that provide protection to equipment  210  for any current surge on line  218 . Accordingly, if line  218  or power supply  213  were hit by lightning, then lightning protection circuit  201  will protect equipment  210  both by blocking the current surge at surge suppressor  217  and by disconnecting equipment  210  from line  218  using relay  208   a . Alternatively, if a current surge originates at power source  213 , lightning detector  202  will not observe an electromagnetic pulse and lightning protection circuit  201  will not open relay  208   a . However, surge suppressor  217  will still protect equipment  210  from a current surge on line  218  even though relay  208   a  is not triggered. 
         [0025]    Although only three relays/interface devices ( 208 ,  209 ) are shown in  FIG. 2 , it will be understood that any number of such devices may be controlled by lightning protection device  201 . The number of relays and other interfaces that can be controlled is limited only by the capabilities of microcontroller  203  and the number of channels available on channel controller  207 . 
         [0026]      FIG. 3  is a schematic diagram of the components of a lightning protection circuit according to an exemplary embodiment. The components in section  301  form a charge balance monitoring system that operates as a lightning detector. A surface mount antenna biased by resistor R 1  detects charge imbalance, such as changes in atmospheric charge caused by lightning, and generates an input pulse to the base of transistor Q 1 , which operates with transistor Q 2  to amplify the received pulse. 
         [0027]    The detector  301  is triggered whenever a positive charge is applied to the base of transistor Q 1 . The antenna may also receive RF signals that correspond to electromagnetic pulses caused by lightning. Sufficiently strong RF signals will cause a charge imbalance at the base of transistor Q 1  thereby creating an output signal from the detector  301 . In one embodiment, an active tuning circuit can be added to detector  301  between resistor R 1  and transistor Q 1 . The active tuning circuit may be tuned to RF energy generated by lightning. 
         [0028]    The electromagnetic pulses received by detector  301  are provided to microcontroller section  302  through isolation device  303 , which may be an opto-isolator that prevents high currents or rapidly changing voltages in detector  301  from damaging the microcontroller  304 . Isolation device  303  also adds a further level of protection to the equipment and devices  307  that are being protected. In addition to blocking current surges that are output by detector  301 , isolation circuit  303  also blocks current surges that result from a direct lightning strike on the lightning protection circuit. 
         [0029]    Section  302  includes the power supply, biasing and clock circuits for microcontroller  304 , which receives and analyzes the electromagnetic pulse signals. If the signals from detector  301  correlate to a lightning pattern or signature, then microcontroller  304  outputs a signal to channel controller  305 . Based upon the input signals from microcontroller  304 , channel controller  305  controls relay  306 , which regulates connections between equipment  307  and external lines  308 . 
         [0030]    Microcontroller  304  may also output serial data in response to lightning detection. For example, upon detection of lightning, microcontroller  304  generates serial output data on line  309 . Serial driver  310  provides an interface for the serial data to external equipment or device  311 , which may be network components. The serial data may provide specialized information to device  311 , such as information concerning the distance, strength, or duration of detected lightning. For example, device  311  may be a processor, chip or ASIC on a network server, blade, card or interface. Instead of just disconnecting device  311  from an external connection using a relay, microcontroller  304  can “talk” directly to device  311  to notify it that a disconnection or lightning strike is imminent. This allows the protected device  311  to store data, halt or pause current processes, and/or enter a shutdown, sleep, or hibernation state to minimize the effects of potential lightning damage. 
         [0031]    The construction and composition of the lightning detection, isolation, microcontroller, and channel controller sections are not limited to any particular embodiment, but may be constructed using generally available components. For example, in one embodiment, the following components may be used. Transistors Q 1  and Q 2  may be 2N3904 NPN General Purpose Amplifier devices available from Fairchild Semiconductor Corporation. Diodes D 1  and D 2  may be 1N914 high conductance fast diodes available from Fairchild Semiconductor Corporation. Isolation device  303  may be a MCT6 8-pin DIP dual-channel phototransistor output optocoupler available from Fairchild Semiconductor Corporation. Microcontroller  304  may be a peripheral interface controller (PIC) available from Microchip Technology Inc. A 4 MHz crystal may be used to provide a clock input for the microcontroller. Channel controller  305  may be a ULN2003AN high-voltage high-current Darlington transistor array available from Texas Instruments Incorporated. The components may be mounted in any form, such as surface mount, SOT, DIP, etc. 
         [0032]    Some embodiments of the lightning detection and protection device may include built-in high-capacity surge suppression in addition to a high-speed circuit isolation during lightning strikes. High capacity Metal Oxide Varistors (MOV) with Thermal Overload Isolation for fire protection during surge events as well as in-line ceramic fuses to prevent over-current conditions may be used to provide surge suppression. 
         [0033]    In other embodiments, a light, buzzer or horn may be activated by the lightning detection circuit to provide a visual and/or audible warning to a user when lightning is detected. Alternatively or additionally, a light or some other indication may provide notice to the user whether a particular circuit has been disconnected due to lightning detection. Referring to  FIG. 2 , user interface  216  may be a light, LED, buzzer, gauge, horn, vibrator or shaker that provides visual, audible or tactile feedback to the user indicating whether one or more circuits are connected/disconnected or active/inactive. In one embodiment, based upon the strength of received signals, the user interface may indicate that a local lightning event has been detected or is imminent or that lightning has been detected at a distance. User interface  216  may provide different levels of warning based upon a perceived distance of a lightning event. 
         [0034]      FIG. 4  is a flowchart illustrating an exemplary process  400  operating on a microcontroller for the lightning detection device. Process  400  may be embodied as software instructions running on a PIC. The software instructions may be compiled using the PICBASIC PRO complier available from microEngineering Labs, Inc. The compiled routines may run at a default clock speed, such as 4 MHz, or at faster speeds if external oscillators or clock inputs are provided to the PIC. The software instructions may be stored in the on-board flash memory of the PIC. 
         [0035]    In step  401 , the PIC powers-up and loads software instructions into on-board flash memory. In step  402 , the PIC begins a filtering sub-routine during which it receives and analyzes signals from a lightning detector circuit. The filtering sub-routine compares the signals received from the lightning detector, which corresponds to electromagnetic pulses, to known lightning profiles. If the received signals match a known or expected lightning pattern, then the process moves to step  403  and begins a sub-control routine sequence. The control sub-routine regulates the channel controller to trigger relays or other interfaces to disconnect protected equipment from conductive lines. The process then moves to a reset sub-routine in step  404  in which the relays and other interfaces operate to reconnect the protected equipment to the conductive lines. The reset sub-routine may control the order and timing by which the protected equipment is reconnected to the conductive lines. For example, components of a system may be reconnected in a particular sequence and/or after a predetermined delay. The reconnection delay may be selected based upon an off/on cycle time requirement in which the protected equipment is left in a disconnected or off condition for a set period to allow components to stabilize before being reenergized. 
         [0036]    After resetting and reconnecting the protected equipment in step  404 , the process returns to step  402  where the microcontroller continues to monitor signals from the lightning detector to identify additional lightning events. Process  400  is intended to be an outline of the process for detecting lightning events and protecting equipment and devices and is not exclusive of other steps, routines, or processes that may be running concurrently with process  400 . For example, diagnostics and maintenance routines may also be run by the microcontroller. 
         [0037]      FIG. 5  illustrates an exemplary lightning flash timeline. A lightning strike comprises a series of individual discharges or strokes. Each of the strokes, which propagate from the ground up to a cloud, are preceded by a leader that propagates from the cloud to ground. The first discharge begins with a stepped leader  501  that propagates at a relatively slower rate compared to the later components of the lightning strike. A return stroke  502  follows the stepped leader  501 . The stepped leader lasts approximately 20 ms, and the return stroke takes 60 μs. The subsequent strokes are separated by approximately 40 ms and are preceded by a dart leader  503 . The dart leader  503  follows the path of the previous return stroke  502  and is about ten times faster than the first stroke  501 . Each dart leader  503  is followed by a return stroke  504 . Information concerning the composition of lightning can be found in many sources, including, for example, Martin A. Uman “Lightning,” Dover Publications, Inc. New York, 1984, the disclosure of which is hereby incorporated by reference herein. Representative values as well as a range of typical values for normal cloud to ground lightning discharges are given in Table 1 based upon information in the cited reference. It will be understood that the lightning characteristics listed herein are merely representative of typical lightning values and are not intended to represent or limit relevant lightning parameters. Typical or expected ranges for lightning parameters can be exceeded by a considerable percentage in a powerful lightning strike. 
         [0000]    
       
         
               
               
               
             
               
             
               
               
               
               
               
             
               
             
               
               
               
               
               
             
               
             
               
               
               
               
               
             
               
             
               
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Representative 
                 Potential Range 
               
               
                   
                 Values 
                 of Values 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 Stepped Leader 
               
             
          
           
               
                 Time interval between steps 
                 50 
                 μs 
                 30-125 
                 μs 
               
               
                 Charge deposited on stepped-leader 
                 5 
                 C 
                 3-20 
                 C 
               
               
                 channel 
               
             
          
           
               
                 Dart Leader 
               
             
          
           
               
                 Charge deposited on dart-leader 
                 1 
                 C 
                 0.2-6 
                 C 
               
               
                 channel 
               
             
          
           
               
                 Return Stroke 
               
             
          
           
               
                 Current rate of increase 
                 10 
                 kA/μs 
                 &lt;1-&gt;80 
                 kA/μs 
               
               
                 Time to peak current 
                 2 
                 μs 
                 &lt;1-30 
                 μs 
               
               
                 Peak Current 
                 10-20 
                 kA 
                 −110 
                 kA 
               
               
                 Time to half of peak current 
                 40 
                 μs 
                 10-250 
                 μs 
               
               
                 Charge transferred (excluding 
                 2.5 
                 C 
                 0.2-20 
                 C 
               
               
                 continuing current) 
               
               
                 Energy dissipated 
                 100 
                 kJ/meter 
               
             
          
           
               
                 Lightning Flash 
               
             
          
           
               
                 Number of strokes per flash 
                 3-4 
                 1-26 
               
             
          
           
               
                 Time interval between strokes 
                 40 
                 ms 
                 3-100 
                 ms 
               
               
                 Time duration of flash 
                 0.2 
                 sec 
                 0.01-2 
                 s 
               
               
                 Charge transferred including 
                 25 
                 C 
                 3-90 
                 C 
               
               
                 continuing current 
               
               
                   
               
             
          
         
       
     
         [0038]    Using the information in Table 1, or any other source of information regarding the characteristics of a lightning stroke, one or more profiles can be developed for use by the microcontroller to identify lightning and to distinguish electromagnetic pulses generated by other sources. For example, an arc welder may generate an electromagnetic pulse when it is turned on. The lightning detector may receive the electromagnetic pulse from the arc welder and send an output signal to a microcontroller. The arc welder can be distinguished from a lightning strike because it does not have the same characteristics, such as a series of very rapidly occurring pulses. Instead, the arc welder would generate a single, long electromagnetic pulse. The microcontroller would reject that pulse and would not trigger the relays or other interfaces. 
         [0039]    The microcontroller may be programmed to recognize specific characteristics of a lightning event using, for example, one or more profiles requiring a series of electromagnetic pulses having specified frequency, pulse duration, pulse interval and/or number of pulses. Additionally, the relative strength of received electromagnetic pulses may be measured or characterized to estimate a distance of the lightning event from the detector. 
         [0040]    The lightning detector and protection circuit described herein can be applied for use in buildings or static locations to protect against current surges that may enter equipment via fixed lines, wires or cables. In another embodiment, the lightning detector and protection circuit may be used in a mobile environment, such as in a commercial vehicle or trunk. The mobile lightning detector and protection device would give warnings to a user, such as a driver or workman at a field location. Upon detection of a lightning event, the device may also prevent operation of certain equipment on the vehicle. For example, if the vehicle was a bucket truck or scissors lift, the device may trigger a relay, interface or interlock that prevents or disables the operation of the bucket, lift, ladder or other extension apparatus. It is well known that higher objects are more exposed to lightning. This would prevent the user from being exposed to dangerous lightning conditions. In other embodiments, the device may cause a relay or other interface to lower the bucket or lift under certain high lightning threat levels conditions. 
         [0041]    In another embodiment, the lightning detection device may be used to evaluate environmental conditions. For example, the device may be located in a remote area, such as a forest. When lightning events are detected, the device may evaluate other environmental factors, such as the temperature, humidity, and wind conditions to determine a risk of forest fire. The microcontroller may also receive such environmental data and may generate an output signal to the channel controller to trigger a warning or alert when such forest fire conditions are observed during the occurrence of a lightning event. 
         [0042]    Many modifications and other embodiments of the invention will come to mind to one skilled in the art to which this invention pertains having the benefit of the teachings presented in the foregoing descriptions, and the associated drawings. Therefore, it is to be understood that the invention is not to be limited to the specific embodiments disclosed. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.