Transformer energization harmonics 2

[KJLRSA]

I have a customer asking us to directly connect a 11kV 5MVAR capacitor bank with filter reactor tuned to 4.8pu to a 20MVA transformer breaker. The transformer is feeding a submerged arc furnace. The capacitor bank will therefore energize at the same time as the transformer.

They don't want to fork out the extra money for the additional capacitor bank breaker and control. I have a feeling the transformer energization harmonics will cause the tuned filter to amplify the harmonics below the 5th to a point where they damage the capacitors.

I have suggested another breaker so when the transformer is switched on the cap bank only comes in after 1 min to negate the first few cycles harmonics on the Tx, but as stated before money is a problem.

Has anyone had any experience with this sort of problem and can anyone tell me what the expected harmonic magnitudes are on transformer magnetization?

 

[rcw retired EE]

We used the ABB Point-On-Wave controller (CAT Controller) with good success on three 230 kV, 240 MVA transformers. The 230 kV GIS breakers had single pole operation capability. Each phase had to be adjusted to close at the appropriate time. Phase A would close first, then B&C would follow together. Timing of the close signal was adjusted by the controller to account for variations in ambient conditions that might affect breaker closing time (time since last operation, hydraulic pressure, oil temperature, control power voltage level, etc.)

I'm not sure that this technology can be applied to a standard 3-pole breaker that has one operating mechanism for all three phases. It also was quite expensive in technician time to get all the settings correct.

 

[Bronzeado]

rcwilson,

In the case of a standard 3-pole breaker that has just one operating mechanism for all three phases, I think it will be possible to adjust it, mechanically, to "simulate" a single phase mechanism, giving the necessary closing delay.

best regards,

Herivelto Bronzeado