1. Electric Power Network Efficiency and Security (EPNES) 1 THE USE OF MICROMECHANICAL SWITCHES IN A POWER CIRCUIT BREAKER Esma Gel, Gerald T Heydt, Norma Faris Hubele, George G Karady 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 System Realization

17. Electric Power Network Efficiency and Security (EPNES) 17 lThe coil under the switch is energized lThe generated magnetic field moves the permanent magnet towards the base lThis closes the contact lThe problem is that the insulation has to withstand 7.2 kV between the contact and the magnet. lNo switch is available to meet with this requirement

18. Electric Power Network Efficiency and Security (EPNES) 18 lASU started to develop MEMS switches for this circuit breaker lA matrix contains 4 x 4 = 16 switches is being studied lSeveral sample has been built and tested lThis matrix permits the formation of 4 switching strings with 4 MEMS connected in series 1175  m 1328 μm 4 x 4 Matrix of switches using aluminum metalization

19. Electric Power Network Efficiency and Security (EPNES) 19 Reduced scale circuit breaker Control solenoid Switching string

20. Electric Power Network Efficiency and Security (EPNES) 20 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

21. Electric Power Network Efficiency and Security (EPNES) 21 Reliability Calculation

22. Electric Power Network Efficiency and Security (EPNES) 22 RELIABILITY ANALYSIS States of an individual switching unit Most probable failure mode is in closed condition

23. Electric Power Network Efficiency and Security (EPNES) 23 Lifetime distribution for q min = 0.001.

24. Electric Power Network Efficiency and Security (EPNES) 24 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.

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

26. Electric Power Network Efficiency and Security (EPNES) 26 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 PROBLEM lLack of suitable MEMS device in the market

27. Electric Power Network Efficiency and Security (EPNES) 27 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.