Self-testing features of sensing and control electronics for a power grid protection system

Abstract

Systems and method for detecting potentially harmful harmonic and direct current signals at a transformer are disclosed. One system includes a protection circuit electrically connected to a transformer neutral, the transformer electrically connected to a power grid, the protection circuit including a DC blocking component positioned between the transformer neutral and ground and one or more switches selectively actuated to form a path between the transformer neutral and ground in the event of unwanted DC current at the transformer neutral. The system also includes a control circuit electrically connected to the protection circuit and positioned to selectively actuate the switches based on observed conditions within the protection circuit. The system further includes a plurality of test connections disposed within the protection circuit and useable to test electrical properties of the protection circuit.

The invention claimed is: 
     
       1. A system comprising:
 a protection circuit electrically connected to a transformer neutral, the transformer electrically connected to a power grid, the protection circuit including a DC blocking component positioned between the transformer neutral and ground and one or more switches selectively actuated to form a path between the transformer neutral and ground in the event of unwanted DC current at the transformer neutral; 
 a control circuit electrically connected to the protection circuit and positioned to selectively actuate the switches based on observed conditions within the protection circuit; 
 a plurality of test connections disposed within the protection circuit and useable to test electrical properties of the protection circuit; and 
 a plurality of detection components electrically connected to one or more electrical signal lines leading from one or more connection points on a power grid; 
 wherein the control circuit comprises a controller positioned within an interior volume of an electromagnetically shielded enclosure and receiving an output from each of the plurality of detection components, the controller including a plurality of test thresholds, and configured to drive at least one circuit component electrically connected to the transformer neutral in response to sensing a signal from one of the plurality of detection component of a detected harmonic or direct current signal above a respective one of the plurality of test thresholds. 
 
     
     
       2. The system of  claim 1 , wherein the protection circuit is electrically connected to a SCADA system remote from the protection circuit and control circuit, and wherein the SCADA system is electrically connected to the plurality of test connections for remote testing of electrical properties of the protection circuit. 
     
     
       3. The system of  claim 1 , wherein the plurality of detection components are selected from a group of detectors consisting of:
 a harmonic analyzer; 
 a shunt resistor electrically connected between the transformer neutral and a ground; 
 a Hall effect current sensor connected across a grounding line, the grounding line connected between the transformer neutral and a ground; and 
 an electromagnetic field detector. 
 
     
     
       4. The system of  claim 3 , further comprising:
 a shielded enclosure having an interior volume, the shielded enclosure configured to shield the interior volume from electromagnetic interference; 
 a plurality of filters positioned along a periphery of the shielded enclosure and connected to the electrical signal lines, the electrical signal lines extending into the interior volume from external to the shielded enclosure, the filters configured to prevent high frequency, high power electromagnetic signals from entering the shielded enclosure. 
 
     
     
       5. The system of  claim 4 , wherein the harmonic analyzer is positioned within the shielded enclosure. 
     
     
       6. The system of  claim 5 , wherein the shunt resistor is positioned external to the shielded enclosure. 
     
     
       7. The system of  claim 6 , wherein the Hall Effect current sensor is positioned external to the shielded enclosure. 
     
     
       8. The system of  claim 7 , wherein the electromagnetic field detector is positioned external to the shielded enclosure. 
     
     
       9. The system of  claim 1 , wherein the controller is configured to open a normally-closed switch connected between the transformer neutral and a ground connection. 
     
     
       10. The system of  claim 1 , wherein the controller is configured to open the normally-closed switch upon detection of a harmonic or direct current signal above a threshold on the transformer neutral. 
     
     
       11. The system of  claim 1 , wherein the indication received from at least one of the plurality of threshold detectors represents a detected harmonic, a direct current signal, or an electromagnetic pulse above a threshold associated with that threshold detector. 
     
     
       12. The system of  claim 11 , wherein the controller is configured to, during normal operation of the system, communicate status information regarding signals received from each of the detection components to the remote system. 
     
     
       13. The system of  claim 12 , wherein the system is located at a power substation, and wherein the remote system is located at a central control station and includes the SCADA system. 
     
     
       14. The system of  claim 1 , wherein the controller is configured to execute one or more self-test procedures, the self-test procedures configured to confirm that the system operates as expected in the event of damaging of degrading events. 
     
     
       15. The system of  claim 14 , wherein the one or more self-test procedures are selected from a group of procedures consisting of:
 applying an alternating current signal at the transformer, the alternating current signal having a frequency different from that of the power system frequency; 
 applying a harmonic signal at a harmonic analyzer, the harmonic signal having an amplitude above the preset threshold defined by a threshold detector associated with the harmonic analyzer, the threshold defining a range of amplitudes; 
 applying a direct current (DC) voltage signal at the transformer neutral to simulate direct current received at the transformer neutral and 
 applying an electromagnetic (EM) detector signal, the EM signal having an amplitude above the preset threshold defined by a threshold detector, the threshold defining a range of amplitudes. 
 
     
     
       16. A method comprising:
 transmitting one or more electrical signals from a protection circuit to a remote system, the protection circuit electrically connected between a transformer neutral of a transformer in a power grid and ground, wherein the remote system periodically assesses operation of the protection circuit based on the one or more electrical signals; and 
 receiving at a control circuit electrically connected to the protection circuit one or more commands from the remote system to actuate one or more switches in the protection circuit, thereby testing an alternative configuration of the protection circuit; 
 receiving a plurality of detector signals at a controller forming a portion of the control circuit, the controller housed within an electromagnetically-shielded enclosure, and the detector signals including a harmonic detector signal and a direct current detector signal; 
 sampling each of the plurality of detector signals to detect a peak value over a predetermined period; 
 comparing each of the peak values to a corresponding remotely-set test threshold associated with that signal type, and, based on that comparison, generating one or more alarms if the remotely-set test threshold is exceeded; and 
 communicating at least the one or more alarms to the remote system. 
 
     
     
       17. The method of  claim 16 , further comprising communicating each of the peak values to the remote system. 
     
     
       18. The method of  claim 16 , further comprising periodically performing one or more self-test procedures, the self-test procedures configured to confirm that the controller and electrical protection circuit operate as expected in the event of damaging of degrading events. 
     
     
       19. A continuous grounding system for use in an alternating current system including a transformer, the system comprising:
 (a) a switch assembly connected between a transformer neutral of a transformer and a ground, the switch assembly having an open position and a closed position, the open position disrupting a path through the switch assembly between the transformer neutral and the ground, and the closed position establishing the path connecting the transformer neutral to the ground through the switch assembly, wherein in normal operation of the alternating current system the switch remains in a closed position; and   (b) a DC blocking component electrically connected in parallel with the switch assembly between the transformer neutral and the ground; and   (c) a control circuit configured to control the switch assembly, the control circuit configured to actuate the switch assembly to an open position in response to receipt of a signal indicative of an electromagnetic signal detected in proximity to the transformer that is indicative of an electromagnetic event capable of damaging the transformer.   
     
     
       20. A protection system comprising:
 (a) a switch assembly connected between a transformer neutral of a transformer and a ground, the switch assembly having an open position and a closed position, the open position disrupting a path through the switch assembly between the transformer neutral and the ground connection, and the closed position establishing the path connecting the electrical connection to the ground connection through the switch assembly, wherein in normal operation of the alternating current system including the transformer, the switch remains in a closed position; and   (b) a surge arrester electrically connected between the transformer neutral and the ground; and   (c) a control circuit configured to control the switch assembly, the control circuit configured to actuate the switch assembly to an open position in response to receipt of a signal indicative of an event potentially harmful to the alternating current system including the transformer.   
     
     
       21. A protection circuit for an alternating current system including a transformer, the protection circuit comprising:
 a DC blocking component electrically connected between a neutral of the transformer and a ground;   a switching assembly electrically connected in parallel with the DC blocking component, the switching assembly being designed to break or interrupt DC current;   an overvoltage protection device electrically connected in parallel with the DC blocking component and the switching assembly between the neutral and the ground;   a controller, including a processing device, configured to:
 (i) detect the presence of a fault current between the neutral of the transformer and the ground that is above a predetermined threshold; and 
 (ii) upon determining that the fault current is above the predetermined threshold, close the switch assembly, forming an electrical path between a neutral of the transformer and a ground. 
   
     
     
       22. The protection circuit of claim 21, wherein the controller is further configured to generate an alarm. 
     
     
       23. A protection circuit for an alternating current system including a transformer, the protection circuit comprising:
 a DC blocking component electrically connected between a neutral of the transformer and a ground;   a switching assembly electrically connected in parallel with the DC blocking component, the switching assembly being capable of breaking or interrupting DC current;   an overvoltage protection device electrically connected in parallel with the DC blocking component and the switching assembly between the neutral and the ground;   a current measuring device configured to measure a current through the overvoltage protection device; and   a controller, including a processing device, configured to:
 (i) monitor a measurement from the current measuring device to detect a current through the overvoltage protection device; and 
 (ii) upon detecting current through the overvoltage protection device, close the switch assembly, thereby forming an electrical path between a neutral of the transformer and a ground. 
   
     
     
       24. The protection device of claim 23, wherein the controller is further configured to deactivate the protection mode based upon determining that the overvoltage protection device has triggered. 
     
     
       25. The protection circuit of claim 23, wherein the switching assembly includes a switch operated using a default open position. 
     
     
       26. The protection circuit of claim 25, wherein the switch comprises an AC switch. 
     
     
       27. The protection circuit of claim 26, wherein the switching assembly further includes a DC switch operated using a default closed position. 
     
     
       28. A protection circuit for an alternating current system including a transformer, the protection circuit comprising:
 a DC blocking component electrically connected between a neutral of the transformer and a ground;   a switching assembly electrically connected in parallel with the DC blocking component, the switching assembly being capable of breaking or interrupting DC current, the switching assembly including an AC switch and a DC switch, the AC switch being in a default open position;   an overvoltage protection device electrically connected in parallel with the DC blocking component and the switching assembly between the neutral and the ground;   a controller, including a processing device, configured to actuate the switching assembly in response to detecting an electrical condition at the transformer neutral.   
     
     
       29. The protection circuit of claim 28, further comprising a voltage probe connected between the transformer neutral and ground and configured to monitor a voltage level at the transformer neutral. 
     
     
       30. The protection circuit of claim 28, wherein the DC blocking component comprises a capacitor. 
     
     
       31. The protection circuit of claim 28, wherein the DC blocking component comprises a resistor. 
     
     
       32. The protection circuit of claim 28, further comprising a surge arrester electrically connected in parallel with the DC blocking component, the switching assembly, and the overvoltage protection device between the neutral and the ground. 
     
     
       33. The protection circuit of claim 32, wherein the surge arrester comprises a metal oxide varistor. 
     
     
       34. The protection system of claim 20, further comprising a DC blocking component electrically connected in parallel with the surge arrester and the switch assembly between the transformer neutral and the ground. 
     
     
       35. The continuous grounding system of claim 19, further comprising a control input communicatively connected to the control circuit from a remote system, wherein the control circuit is configured to drive the at least one external component in response to receipt of a remote triggering signal. 
     
     
       36. The system of claim 20, further comprising a control input electrically connected to the control circuit to provide remote control of actuation of the switch assembly. 
     
     
       37. The protection circuit of claim 21, further comprising a control input electrically connected to the controller to provide remote control of actuation of the switch assembly. 
     
     
       38. The protection circuit of claim 23, further comprising a control input electrically connected to the controller to provide remote control of actuation of the switching assembly.