CIRCUIT BREAKER FIRST TRIP TESTING

Michael McCraney

Nameplate

capacity of

12,222

Megawatts

24 generating facilities

4,527 breakers 1,581 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-121-43000-5

Decreased Operating Speed: HVB-121-40000

Second Trip

First Trip

Defective Battery Bank: GM6A

Present First TripPast First Trip

Faulty Auxiliary Contacts: 100-SFMT-40E

Close

Trip

Close Coil Fire:72-PM-31-20