Voltage surge and overvoltage protection with sequenced component switching

• US 8,335,067 B2
• Filed: 04/29/2011
• Issued: 12/18/2012
• 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 M.
• Primary Examiner(s): Jackson, Stephen W
• Application Number:
  US13/098,169
• Publication Number:
  US 20110205675A1
• Time in Patent Office: 599 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 claiming level;

a series inductance coupled between the first and second voltage clamping devices;

a first selectable actuatable switch connected between the series inductance and the electrical load;

a second selectively actuatable switch in parallel with the first switch for connecting an impedance component between the series inductance and the electrical load; and

a switch control circuit that controls actuation of the first switch and the second switch in a plurality of predetermined sequences, each of the plurality of predetermined sequences corresponding to one of a plurality of predetermined operating conditions on the input power voltage.

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 first and second selectively actuatable switches comprise relays.

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 first 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, wherein the first switch presents a path of least resistance that bypasses the impedance when the first switch is in the first state, and wherein the second switch is actuatable between a first state in which the second switch is opened and a second state in which the second switch couples the impedance component between the series inductance and the electrical load.

8. The system of claim 6, further comprising a shunt resistance coupled from the connection of the impedance component and the second voltage clamping device, and wherein the first 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 impedance component comprises a negative temperature coefficient resistor 6.

10. The system of claim 9, wherein the impedance component is configured to minimize a voltage across the first switch when added to the electrical load;

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

21. The system of claim 1, wherein the switch control circuit controls the actuation of the first switch and the second 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 second switch on in response to detection of a voltage sag and turns the second switch off after the input power voltage has returned to nominal after the voltage sag.

23. The system of claim 22, wherein the switch control circuit turns the second 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.

41. The system of claim 1, wherein the plurality of predetermined operating conditions is selected from the group comprising:

(1) a power up condition, (2) a voltage sag condition, (3) a moderate overvoltage condition, and (4) a severe overvoltage condition.

42. The system of claim 1, wherein the switch control circuit comprises a microprocessor including a memory for storing a control program and a plurality of voltage-time curves for use in timing the operation of the first switch and the second switch.

43. The system of claim 42, wherein the plurality of voltage time curves includes at least one severe overvoltage time curve and one or more moderate overvoltage time curves.

44. The system of claim 1, wherein the switch control circuit operates as a finite state machine comprising a power off state, a nominal state, an isolation state, and a voltage sag state.

45. The system of claim 1, further comprising a voltage detection interface circuit for detecting the predetermined operating conditions on the input power voltage and providing corresponding signals to the switch control circuit.

46. The system of claim 1, wherein one of the predetermined operating conditions is a power up condition, and wherein a corresponding one of the predetermined sequences of switch actuation comprises:

(a) initially configuring the first switch and the second switch in an off position;

(b) in response to power appearing on the input power voltage, turning on the second switch to connect the impedance to limit inrush current during power up of the load;

(c) initiating a timer for timing a predetermined time period;

(d) upon expiration of the predetermined time period, turning on the first switch to bypass the impedance; and

(e) turning off the second switch to disconnect the impedance.

47. The system of claim 1, wherein one of the predetermined operating conditions is a voltage sag condition, and wherein a corresponding one of the predetermined sequences of switch actuation comprises:

(a) in response to detection of a voltage sag on the input power voltage, turning on the second switch to connect the impedance and turning off the first switch;

(b) in response to detection that the voltage sag is over and that the voltage has returned to a predetermined nominal voltage level, turning on the first switch at an optimal point in the power voltage cycle; and

(c) turning off the second switch to disconnect the impedance.

48. The system of claim 1, wherein one of the predetermined operating conditions is a moderate overvoltage condition, and wherein a corresponding one of the predetermined sequences of switch actuation comprises:

(a) in response to detection of a moderate overvoltage condition, initiating a timer of a first predetermined time period corresponding to predetermined risk of damage to components of the system;

(b) in response to expiration of the first predetermined time period, turning on the second switch to connect the impedance component between the input power voltage and the electrical load;

(c) initiating a second timer of a second predetermined time period corresponding to a risk of damage to components of the system; and

(d) in response to expiration of the second predetermined time period, turning off the first switch to disconnect the input power from the electrical load.

49. The system of claim 48, further comprising a shunt resistance coupled between the “

off”

terminal of the first switch and a phase neutral of the input power voltage, so that the shunt resistance is in parallel with the electrical load when the first switch is off.

50. The system of claim 48, wherein a corresponding one of the predetermined sequences of switch actuation further comprises:

(e) initiating a third timer of a third predetermined time period corresponding to a risk of damage of the impedance component; and

(f) in response to expiration of the third predetermined time period, turning off the second switch to disconnect the impedance component from the electrical load, thereby isolating the electrical load completely from the input power voltage.

51. The system of claim 50, wherein the first predetermined time period corresponds to a time associated with one of a plurality of moderate overvoltage voltage-time curves stored in a memory in the switch control circuit.

52. The system of claim 51, wherein the memory in the switch control circuit stores a plurality of moderate overvoltage voltage-time curves, each corresponding to a different time period associated with a different moderate overvoltage condition.

53. The system of claim 1, wherein one of the predetermined operating conditions is a severe overvoltage condition, and wherein a corresponding one of the predetermined sequences of switch actuation comprises:

(a) in response to detection of a severe overvoltage condition, initiating a timer of a predetermined severe overvoltage time period corresponding to predetermined risk of damage to components of the system; and

(b) in response to expiration of the predetermined time period, turning off the first switch and the second switch to isolate the input power voltage from the electrical load.

54. The system of claim 53, wherein the second switch is normally in the off position with the impedance component not connected to the electrical load, and the second switch is maintained in the off position during such a severe overvoltage condition.

55. The system of claim 53, wherein the predetermined severe overvoltage time period corresponds to a time associated with a severe overvoltage voltage-time curve stored in a memory in the switch control circuit.

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;

providing a series inductance between the first and second voltage clamping devices;

providing a first selectably actuatable switch connected between the series inductance and the electrical load;

providing second selectively actuatable switch in parallel with the first switch for connecting an impedance component between the series inductance and the electrical load; and

controlling the actuation of the first switch and the second switch in a plurality of predetermined sequences, each of the plurality of predetermined sequences corresponding to one of a plurality of predetermined operating conditions on the input power voltage.

12. The method of claim 11, further comprising the steps of:

providing a plurality of predefined voltage-time curves stored in a memory;

monitoring the power voltage to identify an overvoltage;

timing a duration of the overvoltage; and

providing a particular predetermined sequence for actuation of the first switch and the second switch in accordance with each of the plurality of predefined voltage-time curves.

13. The method of claim 11, further comprising the step of switching the first switch from a first state to a second state, where the first switch couples the input power voltage directly to the electrical load in the first state, and the first switch imposes a shunt resistance across the electrical load in the second state.

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

15. The method of claim 13, where the electrical load is partially isolated from the input power voltage when the first switch is in the second state, where the first switch is coupled in parallel to the impedance component.

16. The method of claim 11, wherein one of the predetermined plurality of sequences comprises the step of adding the impedance component 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 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 a clamping voltage of the first parallel clamping device is substantially higher than a clamping voltage of the second parallel clamping device.

26. The method of claim 25, 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.

56. The method of claim 11, wherein an overvoltage experienced in the input power voltage is distributively dissipated between the first parallel clamping device and the second parallel clamping device in conjunction with the series inductance.

57. The method of claim 11, further comprising the steps of:

providing an 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 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 the first switch connected in response to detection that the magnitude and duration of the overvoltage are greater than said voltage-time threshold.

58. The method of claim 57, further comprising the step of closing the second switch to couple the impedance component between the input power voltage and the electrical load in response to detection of a voltage sag condition as one of the predetermined operating conditions on the input power voltage.

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

a first selectively actuatable switch connected between the input power voltage and the electrical load for maintaining a direct connection between the input power voltage and the electrical load unless turned off;

a second selectively actuatable switch connected in parallel with the first switch for connecting an impedance component between the input power voltage and the electrical load;

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; and

means for providing a plurality of operating sequences of the first switch and the second switch in response to detection of a corresponding one of a plurality of predetermined operating conditions on the input power voltage.

19. The system of claim 18, wherein at least one of the plurality of predetermined operating conditions is a voltage sag on the input power voltage, and wherein the impedance component is added 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 impedance component from the electrical load when the input power voltage has reached a predefined point in the power voltage cycle after the power voltage has returned to a nominal state.

27. 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.

28. The system of claim 27, 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.

29. 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 first switch responsive to a first switching signal 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;

a second switch in parallel with the first switch and responsive to a second switching signal to switch between (i) a first state in which an impedance component is coupled between the input power voltage and the electrical load prior to the second clamping device and (ii) a second state in which the impedance component is disconnected;

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

a processor circuit responsive to the control signal from the voltage detector circuit operative to provide the first switching signal and the second switching signal in a plurality of predetermined sequences, each of the plurality of predetermined sequences corresponding to one of a plurality of predetermined operating conditions on the input power voltage; and

a memory associated with the processor circuit for storing a control program for providing the plurality of predetermined sequences and for storing data for use in determining the plurality of predetermined operating conditions on the input power voltage.

30. The apparatus of claim 29, further comprising a series inductance connected in between the first clamping device and the second clamping device to distribute dissipation of overvoltage across the first and second voltage clamping devices when the first switch is in the first state.

31. The apparatus of claim 29, wherein the impedance component is a negative temperature coefficient (NTC) resistor.

32. The apparatus of claim 29, wherein the voltage detector is connected to measure the input power voltage at a point prior to a terminal of the switches.

33. The apparatus of claim 29, wherein the clamping level of the first voltage clamping device is approximately five times the nominal input power voltage.

34. The apparatus of claim 29, wherein the clamping level of the first voltage clamping device is substantially higher than the clamping level of the second voltage clamping device.

35. The apparatus of claim 34, 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.

36. The apparatus of claim 29, wherein the voltage-time curves represent predefined voltage-time thresholds utilized for determining the predetermined sequences.

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

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

39. The apparatus of claim 29, further comprising a shunt resistance connected in parallel with the load and the second clamping device when the first switch is in the second state.

40. The apparatus of claim 29, 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.