Voltage surge and overvoltage protection with RC snubber current limiter

• US 8,325,455 B2
• Filed: 04/29/2011
• Issued: 12/04/2012
• 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 Malhar
• Primary Examiner(s): Jackson, Stephen W
• Application Number:
  US13/098,105
• Publication Number:
  US 20110205674A1
• Time in Patent Office: 585 Days
• Field of Search: 361/118
• US Class Current: 361/118
• 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 series inductance coupled between the first and second voltage clamping devices;

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

an high impedance component coupled between the series inductance and the second voltage clamping device in parallel with the switch for providing isolation between the input power voltage to the electrical load when the switch is off; 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 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 and the electrical load is coupled to the input power through the high impedance component.

7. The system of claim 6, wherein the switch presents a path of least resistance that bypasses the high impedance component when the switch is in the first state.

8. The system of claim 6, further comprising a shunt resistance coupled from the connection of the high impedance component and the second voltage clamping device, and wherein the switch couples the shunt resistance across the electrical load from phase to neutral in the second state.

9. The system of claim 1, wherein the high impedance component is an RC snubber.

10. The system of claim 1, wherein the switch control circuit turns the switch off in response to a high magnitude overvoltage or a long duration overvoltage reaches a point where the first and second voltage clamping devices may be damaged.

21. The system of claim 1, wherein the switch control circuit controls the actuation of the switch in response to overvoltages and voltage sags experienced in the input power voltage.

22. The system of claim 21, wherein the switch control circuit turns the switch back on after the input power voltage has returned to nominal after a voltage sag.

23. The system of claim 22, wherein the switch control circuit turns the switch on at an optimal time during the cycle of the input power voltage so as to minimize an inrush current to the electrical load.

24. 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.

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 by separating the first and second parallel clamping devices with a series inductance;

providing a high impedance component between the series inductance 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 duration 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 series inductance 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 and coupling the high impedance component between the input power voltage and the electrical load.

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 overvoltage; 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, and the relay permits the connection of the high impedance component to the electrical load in the second state.

14. The method of claim 13, further comprising the step of connecting a shunt resistance across the electrical load 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 the high impedance component.

16. The method of claim 11, further comprising the step of disconnecting the direct coupling of the input power voltage 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 high impedance component 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.

25. The method of claim 11, wherein the high impedance component is an RC snubber.

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

27. The method of claim 26, 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.

18. A system for conditioning an input power voltage applied to an electrical load, comprising:

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

means for maintaining a direct coupling of the input power voltage to the electrical load unless a magnitude and a duration of the overvoltage are less than at least one predefined voltage-time threshold;

means for disconnecting the direct coupling of the input power voltage by breaking the connection between the first parallel clamping device in response to detection that the magnitude and duration of the overvoltage are greater than said at least one predefined voltage-time threshold; and

means for providing a high impedance between the first parallel clamping device and the second parallel clamping device in response to the disconnecting of the direct coupling of the input power voltage to the electrical load by the disconnecting means.

19. The system of claim 18, further comprising means for providing the high impedance to the electrical load when the power voltage experiences a voltage sag during a steady-state operation of the electrical load.

20. The system of claim 19, further comprising means for removing the high 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.

28. The system of claim 18, wherein the means for providing a high impedance comprises an RC snubber.

29. The system of claim 18, wherein a clamping voltage of the first parallel clamping device is substantially higher than a clamping voltage of the second parallel clamping device.

30. The method of claim 29, 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.

31. 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 the 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 high impedance component is coupled between the input power voltage and the electrical load prior to the second clamping device; and

a series inductance connected in between the first clamping device and the switch to distribute dissipation of overvoltage across the first and second voltage clamping devices when the switch is in the first state.

32. The apparatus of claim 31, wherein the high impedance component is an RC snubber.

33. The apparatus of claim 31, wherein the voltage detector is connected to measure the input power voltage at a point prior to a terminal of the switch.

34. The apparatus of claim 31, wherein the clamping level of the first voltage clamping device is approximately five times the nominal input power voltage.

35. The apparatus of claim 31, wherein the clamping level of the first voltage clamping device is substantially higher than the clamping level of the second voltage clamping device.

36. The apparatus of claim 35, wherein the clamping level of the first voltage clamping device is approximately twice as high as the clamping level of the second voltage clamping device.

37. The apparatus of claim 31, wherein the processor stores a plurality of voltage-time curves representing predefined voltage-time thresholds utilized for controlling the operation of the switch.

38. The apparatus of claim 31, wherein the processor is a programmed microprocessor.

39. The apparatus of claim 31, wherein the first voltage clamping device is a metal-oxide varistor.

40. The apparatus of claim 31, wherein the second voltage clamping device is a metal-oxide varistor.

41. The apparatus of claim 31, further comprising a shunt resistance connected in parallel with the load and the second clamping device when the switch is in the second state.

42. The apparatus of claim 31, wherein the processor circuit provides the switching signal to place the 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.