1. Electric Power Network Efficiency and Security (EPNES) 1 CONCEPTUAL DESIGN OF POWER CIRCUIT BREAKER USING MICROMECHANICAL SWITCHES George G Karady, Gerald T Heydt, Neil Shah Arizona State University, Tempe, AZ, USA PSERC

2. Electric Power Network Efficiency and Security (EPNES) 2 MOTIVATION lNo major change in CB design in many years lLarge moving components and size lNeed for vacuum or SF 6 enclosure lNo synchronous switching Application of electronics components and MEMS switches allow miniaturization and zero current switching

3. Electric Power Network Efficiency and Security (EPNES) 3 Micro-switch based Circuit Breaker Concept

4. Electric Power Network Efficiency and Security (EPNES) 4 Conceptual circuit diagram for an ac circuit breaker Circuit breaker contains two switches Positive switch operates in the positive cycle Negative switch operates in the negative cycle

5. Electric Power Network Efficiency and Security (EPNES) 5 Switching string assembly with several strings connected in parallel. (Positive switch only ) lVoltage rating is increased by switching additional units in series lCurrent rating is increased by switching additional units in series

6. Electric Power Network Efficiency and Security (EPNES) 6 Switching string operation

7. Electric Power Network Efficiency and Security (EPNES) 7 Illustration of circuit breaker closing.

8. Electric Power Network Efficiency and Security (EPNES) 8 Illustration of current interruption.

9. Electric Power Network Efficiency and Security (EPNES) 9 Operation of Switching Strings Connected in Parallel

10. Electric Power Network Efficiency and Security (EPNES) 10 PSPICE simulation of circuit interruption

11. Electric Power Network Efficiency and Security (EPNES) 11 Equivalent circuit of a switching string lClosed switches equivalent is the contact resistance lOpen switches equivalent is the diode voltage

12. Electric Power Network Efficiency and Security (EPNES) 12 Equivalent circuit modeling the non- simultaneous operation of the switches.

13. Electric Power Network Efficiency and Security (EPNES) 13 lCurrent distributions when all string except one is turned on with one millisecond delay. lA. Inductive load current lB. The closing of all switches in string 1 eliminated the diodes and inserted the contact resistances lC. Simultaneously the current of the other two strings reduced to zero, because the diodes become reverse biased. Simulation of switch closing

14. Electric Power Network Efficiency and Security (EPNES) 14 lCurrent distribution during current interruption. lA). String current when one string is turned off with 1 msec delay. lB) String current when all strings except one is turned off with 1 msec delay. lThe short circuit current is interrupted with a half cycle Simulation of switch opening

15. Electric Power Network Efficiency and Security (EPNES) 15 Current injection circuit for interruption of DC current. DC current interruption requires current injection : Charge capacitor produces current oscillation. During the negative cycle the switches are opened At zero crossing the diodes interrupts the current

16. Electric Power Network Efficiency and Security (EPNES) 16 Circuit with MEMS switch

17. Electric Power Network Efficiency and Security (EPNES) 17 MEMS Switch

18. Electric Power Network Efficiency and Security (EPNES) 18 MEMS Switch

19. Electric Power Network Efficiency and Security (EPNES) 19 lNew latching type switch become available lThe switch has two position “ON” or “OFF” lThe switch has an operating coil lShort positive or negative pulse change switch position lThe problem is that the insulation has to withstand 7.2 kV between the contact and the magnet. Voltage: 400V Current : 100mA Resistance 0.5 ohm Insulation 400V Operating coil current: 100mA, 500 usec

20. Electric Power Network Efficiency and Security (EPNES) 20 l lA diode and grading resistance is connected in parallel with the switch l lThe switching coil is supplied by a microwave power supply l lA antenna provided short duration 945Mz signal is rectified by the tunnel diode and capacitor l lThe obtained DC signal operates the switch l lThe 95kV BIL is achieved by a distance of 30 inches

21. Electric Power Network Efficiency and Security (EPNES) 21 l l Five building blocks are connected in series to form a switching unit l lThe operating coils are connected in series to meet with the 400V insulation level l lA microwave power supply provides dc operating current for the series connected coils l lA high power (1W) microwave transmitter provides the short duration square wave signal l lThe antenna picks up the signal l lThe signal is rectified. This provides dc current to the operating coil

22. Electric Power Network Efficiency and Security (EPNES) 22 Switching chain assembly

23. Electric Power Network Efficiency and Security (EPNES) 23 Circuit breaker arrangement Positive switch Negative switch

24. Electric Power Network Efficiency and Security (EPNES) 24 AC circuit breaker concept

25. Electric Power Network Efficiency and Security (EPNES) 25 System Realization

26. Electric Power Network Efficiency and Security (EPNES) 26 Reduced scale circuit breaker Control solenoid Switching string

27. Electric Power Network Efficiency and Security (EPNES) 27 The technical data of the developed small scale circuit breaker Rated current:8 A steady state Interruption current:50 A for a half cycle Rated voltage:4000 V BIL:95 kV Number of switches in series in a single string:10 Number of strings in parallel:8

28. Electric Power Network Efficiency and Security (EPNES) 28 Research work needed lAnalysis of distribution in a large swathing string assembly using equivalent circuit lAnalysis of steady state current distribution in a large swathing string assembly using equivalent circuit lAnalysis of transient current distribution during turn on using SPICE lAnalysis of transient current distribution during turn off using SPICE lAnalysis of turn on and off overvoltages lReliability analyses: Safe operation time? Required number of units ?

29. Electric Power Network Efficiency and Security (EPNES) 29 Research work needed l lBuilding and testing MEMS switch assembly 5 x 6 matrix l lDevelopment of Microwave pulse generation for turn on and off. l lDevelopment of circuit breaker control (on and off signal generation using and or logic components) l lBuilding and testing of a MEMS based circuit breaker l lDevelopment and analysis of DC current interruption concept using current injection l lTesting the DC injection method using the mechanical switch assembly l lTesting the mechanical circuit breaker

30. Electric Power Network Efficiency and Security (EPNES) 30 Conclusions l The study proved that the micro- switched based medium voltage circuit breaker is feasible. lIt offers small size, zero current switching and interruption of short circuit current within a half cycle.

31. Electric Power Network Efficiency and Security (EPNES) 31 The specific results are: lDevelopment of novel concept for CB’s using switching matrix and switching string. lDevelopment of a method to analyze the effect of none simultaneous operation of switches in a switching string assembly. lReliability analysis of switching matrix. lBuilding of a proof of principles switching string assembly to experimentally proof the validity of the concept. lProposal for development of a new type of MEMS device and the specification of the new device. lDevelopment of a novel analytical model for the reliability analysis of the switching matrix.

32. Electric Power Network Efficiency and Security (EPNES) 32 FUTURE WORK lFinalization the analytical technique for operation of large switching matrixes, l Improvement of reliability analysis and lTesting the proof of principle switching assembly. lDetailed design of the MEMS based switch lImplementation of the educational objective

33. Electric Power Network Efficiency and Security (EPNES) 33 Acknowledgement l The authors would like to acknowledge the support of NSF and the Navy. l The authors thank to Prof B. Kim of ASU and l Graduate students: Mr. Neil Shah, Daniel S. James II and Rahim Kasim for their contribution.