Voltage surge and overvoltage protection by distributed clamping device dissipation

• US 9,071,048 B2
• Filed: 11/05/2013
• Issued: 06/30/2015
• Est. Priority Date: 04/05/2007
• Status: Active Grant

• Current Assignee: I-EWM Acquisation, LLC
• Original Assignee: Georgia Tech Research Corporation (University System of Georgia)
• Inventors: Divan, Deepakraj M.
• Primary Examiner(s): Jackson, Stephen W
• Application Number:
  US14/072,362
• Publication Number:
  US 20140055895A1
• Time in Patent Office: 602 Days
• Field of Search: 361/118
• US Class Current: 1/1
• CPC Class Codes: H02H 3/207 also responsive to under-voltage window comparators for indication G01R19/165
• CPC Class Codes: H02H 9/002 limiting inrush current on switching on of inductive loads subjected to remanence, e.g. transformers
• CPC Class Codes: H02H 9/04 responsive to excess voltage lightning arrestors H01C7/12, H01C8/04, H01G9/18, H01T
• CPC Class Codes: H02H 9/042 comprising means to limit the absorbed power or indicate damaged over-voltage protection device
• CPC Class Codes: H02H 9/044 Physical layout, materials not provided for elsewhere varistors H01C7/12; spark-gaps H01T; Ovshinsky devices H10N70/00

Abstract

Disclosed are various embodiments of voltage protectors that include a first voltage clamping device configured to clamp a voltage of an input power applied to an electrical load, and a second voltage clamping device configured to clamp the voltage applied to the electrical load. A series inductance separates the first and second voltage clamping devices. Also, a switching element is employed to selectively establish a direct coupling of the input power to the electrical load, where a circuit is employed to control the operation of the switching element.

Claims

1. A voltage surge and overvoltage protection system, comprising:

at least one first voltage clamping device configured to clamp a voltage of an input power voltage applied to an electrical load to a predetermined first voltage clamping level;

at least one second voltage clamping device configured to clamp the voltage applied to the electrical load to a predetermined second voltage clamping level;

a selectably actuatable switch connected between the first voltage clamping device and the second voltage clamping device for disconnecting power from the second voltage clamping device and the electrical load; and

a switch control circuit that controls actuation of the switch in response to detection that the input power voltage has exceeded a predetermined voltage level for a predetermined time.

2. The system of claim 1, wherein the at least one first voltage clamping device comprises a metal-oxide varistor.

3. The system of claim 1, wherein the at least one second voltage clamping device further comprises a metal-oxide varistor.

4. The system of claim 1, wherein the selectively actuatable switch comprises a relay.

5. The system of claim 1, wherein a clamping voltage of the at least one first voltage clamping device is substantially higher than a clamping voltage of the at least one second voltage clamping device.

6. The system of claim 1, wherein the switch is actuatable between a first state in which the switch establishes a direct coupling of the input power to the electrical load;

and a second state in which the direct coupling is opened.

7. The system of claim 6, further comprising a series impedance coupled in parallel with the switch, where the switch presents a path of least resistance that bypasses the series impedance when the switch is in the first state.

8. The system of claim 6, where the switch further couples a shunt resistance across the electrical load in the second state.

9. The system of claim 6, further comprising an impedance switch configured to add an impedance to the electrical load, where the switch control circuit further controls the operation of the impedance switch.

10. The system claim 9, where the switch is in parallel with the impedance switch, where the impedance is configured to minimize a voltage across the switch when added to the electrical load;

and the switch control circuit is configured to sequence a manipulation of the switch and the impedance switch in order to open the direct coupling so as to minimize a potential tier physical damage to the switch due to sparking.

18. The system of claim 5, wherein a clamping voltage of the at least one first voltage clamping device is at least twice as high as a clamping voltage of the at least one second voltage clamping device.

32. The apparatus of claim 4, wherein the relay comprises a double pole relay.

33. The apparatus of claim 32, wherein the double pole relay is a double pole, double throw (DPDT) relay, and wherein the first pole of the relay is used for disconnecting power from the second voltage clamping device and the electrical load, and the second pole is used to impose an impedance between the first clamping device and the second clamping device and electrical load in response to the switch control circuit.

34. The apparatus of claim 33, wherein the switch control circuit controls actuation of the first pole of the relay independently of the second pole of the relay.

38. The apparatus of claim 1, wherein the switch control circuit is a programmed microprocessor.

11. A method for providing voltage surge and overvoltage protection to an electrical load, comprising the steps of:

applying an input power voltage to the electrical load;

providing a first parallel clamping device and a second parallel clamping device between the input power voltage and the electrical load;

distributing a dissipation of an overvoltage experienced in the input power voltage among the first parallel clamping device and the second parallel clamping device

monitoring the voltage of the input power voltage for an overvoltage having a magnitude and duration exceeding a predetermined voltage-time threshold;

maintaining a direct coupling of the input power voltage to the electrical load through the first and second clamping devices so long as the magnitude and a diaration of the overvoltage are less than said voltage-time threshold; and

disconnecting the direct coupling of the input power voltage to the electrical load by opening a switch connected between the first parallel clamping device and the second parallel clamping device in response to detection that the magnitude and duration of the overvoltage are greater than said voltage-time threshold.

12. The method of claim 11, where the at least one predefined voltage-time threshold further comprises a plurality of predefined voltage-time thresholds, the method further comprising the steps of:

storing the predefined voltage-time thresholds in a memory;

monitoring the power voltage to identify the over voltaae; and

timing a duration of the overvoltage.

13. The method of claim 11, wherein the switch is an isolation relay, and wherein the step of disconnecting the direct coupling of the power voltage to the electrical load comprises the step of switching the isolation relay from a first state to a second state, where the relay couples the power voltage directly to the electrical load in the first state.

14. The method of claim 13, further comprising the step of completely isolating the electrical load from the input power when the isolation relay is in the second state.

15. The method of claim 13, where the electrical load is partially isolated from the input power when the isolation relay is in the second state, where the isolation relay is coupled in parallel to an impedance.

16. The method of claim 11, further comprising the step of adding an impedance to the electrical load when the power voltage experiences a voltage sag during a steady-state operation of the electrical load.

17. The method of claim 16, further comprising the step of removing the impedance from the electrical load when the power voltage has reached a predefined point in the power voltage cycle after the power voltage has returned to a nominal state.

19. The method of claim 11, wherein a clamping voltage of the first parallel clamping device is substantially higher than a clamping voltage of he second parallel clamping device.

20. The method of claim 19, wherein a clamping voltage of the first parallel clamping device is at least twice as high as a clamping voltage of the second parallel clamping device.

35. The method of claim 13, wherein the isolation relay comprises a double pole relay.

36. The method of claim 35, wherein the doable pole relay is a doable pole, double throw (DPDT) relay, and further comprising the steps of:

disconnecting power from the second voltage clamping device and the electrical load using the first pole of the relay in the first state, and

imposing an impedance between the first clamping device and the second clamping device and electrical load using the second pole of the relay.

37. The method of claim 35, further comprising the step of imposing an impedance between the first clamping device and the second clamping device to limit inrush current during power up of the load.

21. An apparatus for protecting an electrical load from transient voltage surges and overvoltages when connected to an input power voltage, comprising:

at least one first voltage clamping device connected to the input power voltage configured to clamp the voltage of the input power voltage to a first predetermined clamping level;

at least one second voltage clamping device connected to the electrical load configured to clamp the voltage applied to the electrical load to a second predetermined clamping level lower than said first predetermined clamping level, in parallel arrangement with said first clamping device;

a voltage detector circuit that provides a control signal representing tle input power voltage;

a processor circuit operative to provide a switching signal in response to a determination that the control signal from the voltage detector circuit indicates that the input power voltage exceeds a predetermined threshold for a predetermined duration of time;

a switch responsive to the switching signal from the processor circuit to switch between (i) a first state in which the input power voltage is directly coupled to the electrical load and first clamping device and (ii) a second state in which the direct coupling is opened and a shunt resistance is connected in parallel with the load and the second clamping device.

22. The apparatus of claim 21, wherein the voltage detector is connected to measure the input power voltage at a point prior to a terminal of the switch.

23. The apparatus of claim 21, wherein the clamping level of the first voltage clamping device is approxi ately five nes the nominal input power voltage.

24. The apparatus of claim 21, wherein the clamping level he first voltage clamping device is substantially higher than the clamping level of the second voltage clamping device.

25. The apparatus of claim 24, wherein in the clamping level of the first voltage clamping device is approximately twice as high as the clamping level of the second voltage clamping device.

26. The apparatus of claim 21, Therein the processor stores a plurality of voltage-time curves representing predefined voltage-time thresholds utilized for controlling the operation of the switch.

27. The apparatus of claim 21, wherein the processor is a programmed microprocessor.

28. The apparatus of claim 21, wherein the first voltage clamping device is a metal-oxide varistor.

29. The apparatus of claim 21, wherein the second voltage clamping device is a metal-oxide varistor.

30. The apparatus of claim 21, wherein the switch is a first switch, and further comprising a second switch responsive to a second switching signal from the processor circuit, the second switch coupling an impedance between the input power voltage and the electrical load, the second switch operative to switch between (i) a first state in which the input power voltage is coupled to the electrical load through the impedance and (ii) a second state in which the impedance is not connected to the electrical load.

31. The apparatus of claim 21, wherein the processor circuit provides the second switching signal to place the second switch into the first state in response to detection of a voltage sag of a predetermined voltage and duration, so as to couple the impedance between the input power voltage and the electrical load to reduce inrush current when the input power voltage returns to a nominal level.