THE USE OF MICROMECHANICAL SWITCHES IN A POWER CIRCUIT BREAKER

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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

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• Micro-switch based
• Circuit Breaker Concept

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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

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• Switching string assembly with several strings
  connected in parallel. (Positive switch only)
• Voltage rating is increased by switching
  additional units in series
• Current rating is increased by switching
  additional units in series

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• Switching string operation

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Illustration of circuit breaker closing.
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Illustration of current interruption.
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• Progress
• October 2003- February 2004
• Karady

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• Proof of concept experiment

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Reduced scale circuit breaker
Control solenoid
Switching string
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The technical data of the developed small scale
circuit breakerRated current 8 A steady
stateInterruption current 50 A for a half
cycleRated voltage 4000 VBIL 95
kVNumber of switches in series in a single
string 10Number of strings in parallel 8
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Automatic turn off

• Comparator checks whether current is above
  threshold
• If the current is above threshold, a signal is
  sent to latch a D Flip-Flop
• Turn off signal is sent to positive cycle
  switch if fault is initiated in positive cycle of
  line current.
• Turn-off signal is sent to the negative cycle
  switch soon after current zero.

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Manual turn off the switch

• A positive pulse is sent to the latch using
  push button
• The output of the latch is sent to the
  positive and negative cycle logic blocks
• Turn-off signal is sent to the positive cycle
  switch if the switching is initiated in the
  positive cycle
• Turn off signal is sent to the negative cycle
  switch after current zero

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Turn on the switch

• Using push button, a signal is sent to the
  positive and negative logic blocks to
  start/restart the circuit
• Logic blocks check for positive/negative cycle
  using voltage signal from source
• Turn on signal is sent to the positive cycle
  switch, if the turning on starts in positive
  cycle
• Turn on signal is sent to the negative cycle
  switch after current zero.

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Block diagram of the control circuit
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PSpice simulation of the control circuit
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Waveforms showing the working of the control
circuit
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• Realization of MEMS base circuit breaker

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• Received 6 MEMS switches
• Developed circuit diagram for operation of MEMS
  switches when operating coils are connected in
  series
• Developed circuit diagram for operation of MEMS
  switches when operating coils are connected in
  parallel
• Developed control concept

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• MEMS Switch
• Rating 100V, 100mA
• Insulation 400V Positive coil current pulse
  close the switchNegative coil current pulse open
  the switchOperation requires coil current of
  5V, 100mA

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• New latching type switch become available
• The switch has two position ON or OFF
• The switch has an operating coil
• Short positive or negative pulse change switch
  position
• The 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

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• A diode and grading resistance is connected in
  parallel with the switch
• The switching coil is supplied by a microwave
  power supply
• A antenna provided short duration 945Mz signal is
  rectified by the tunnel diode and capacitor
• The obtained DC signal operates the switch
• The 95kV BIL is achieved by a distance of 30
  inches

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Switching Unit Operation coils are connected in
parallel
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Switching Unit Realization
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• FUTURE WORK
• Finalization the analytical technique for
  operation of large switching matrixes,
• Improvement of reliability analysis and
• Testing the proof of principle switching
  assembly.
• Detailed design of the MEMS based switch
• Implementation of the educational objective
• PROBLEM
• Need for 25 more switches
• Surface mounting of MEMS switches