Pre reclose current on HV breaker 2

[bacon4life]

In the attached waveform of a successful 115 kV circuit breaker reclose, what accounts for the 2 cycles of current before the inrush from time 1.3 to 1.347? During this time the digital fault recorder shows about 35 amps with no harmonics. At time 1.347, the current jumps to around 300 amps with significant harmonic distortion indicating transformer inrush. Prior to the fault, the PCB had about 50 amps of load.

This line only recloses from one end, which explains the difference increased load after reclosing. Previous reclose events captured by this DFR also show the same pattern. Unfortunately the relays are not set to create records of successful recloses.

 

[magoo2]

Is it possibly a closing resistor in the circuit breaker?

I'd really have to know a little more about the breaker and the system equivalent to speculate beyond that.

 

[bacon4life]

No closing resistor showing on the prints. It is a Westinghouse AA-10 oil breaker.

What details would you need about the system? This substation has several 115 kV subtransmission lines feeding it, along with a large 115 kV capacitor bank. The re-closed line is one of a parallel set that runs to a hydro generating plant 40 miles away. Along the line are several tapped distribution substations. When the trip occurred the plant end opened and stayed open, shifting all the generation to the parallel line.

 

[TLCPA]

The AA-10 is a pneumatic operator on the oil circuit breaker (OCB). This is not the type/model of the circuit breaker. You are seeing the pre-insertion resistor in the 115 kV OCB.

 

[bacon4life]

Oh, I had not realized pre-insertion resistors were standard on OCB's, rather than as an add on component for capacitor switching like they are for SF6 breakers. The maintenance manual for the GMB shows a 700 ohm resistor across each of the two interrupters to reduce TRV during low current interruptions.