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CIRCUIT BREAKER FIRST TRIP TESTING
Michael McCraney
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Nameplate
capacity of
12,222
Megawatts
24 generating facilities
4,527 breakers 1,581 substations
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Southern Company Transmission System
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Some pics to use
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What is first trip testing?
Identifying lubrication problems in the mechanism.Identifying mechanical wear.
Identifying control circuit malfunctions.
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How does it work?
• The breaker is in service while the load is transferred.• It captures:
– Contact part / make time– DC supply current– DC supply voltage
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Test Equipment
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Typical Trip Shot
Trip coil plunger strikes latch
Auxiliary contact interrupts DC supply Voltage curve
Trip Coil Current curve
Main contact time
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General Times & Measurements
Main Contacts (Trip): < 50 ms or 3 cycle Main Contacts (Close): <200 ms or 12 cycle Voltage Drop: <10% Trip Latch: <5 ms between first & second shots Auxiliary Contacts: <5 ms between first & second shots
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What to look for…• Latch
– Increased latch time increases pole separation time.• Aux. contact interruption time
– Any delay in Acon time extends coil energizing time.• Maximum current
– High current could indicate wrong coil size or low current could show increased coil resistance.
• Voltage – Might indicate failing DC supply, insufficient wiring, or loose fuses.
• Main contact times– Could indicate worn mechanism or incorrect electrical wipe.
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Past Trip
Present Trip
Latch time difference
ACon
Increased Trip Latch Friction: FK-121-43000-5
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Decreased Operating Speed: HVB-121-40000
Second Trip
First Trip
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Defective Battery Bank: GM6A
Present First TripPast First Trip
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Faulty Auxiliary Contacts: 100-SFMT-40E
Close
Trip
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Close Coil Fire:72-PM-31-20
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