CIRCUIT BREAKER FIRST TRIP TESTING Michael McCraney

Nameplate capacity of 12,222 Megawatts 24 generating facilities 4,527 breakers1,581 substations

Southern Company Transmission System

Some pics to use

What is first trip testing? Identifying lubrication problems in the mechanism. Identifying mechanical wear. Identifying control circuit malfunctions.

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

Test Equipment

Typical Trip Shot Trip coil plunger strikes latch Auxiliary contact interrupts DC supply Voltage curve Trip Coil Current curve Main contact time

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

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.

Past Trip Present Trip Latch time difference ACon Increased Trip Latch Friction: FK

Decreased Operating Speed: HVB Second Trip First Trip

Defective Battery Bank: GM6A Present First Trip Past First Trip

Faulty Auxiliary Contacts: 100-SFMT-40E Close Trip

Close Coil Fire:72-PM-31-20