reduceing inrush current 5

[furm]

does someone know about "soft start" for 20MVA transformer 33kv.
we want to suppress the current when we connect it with "no load".
thank you

 

[Bronzeado]

Hi folks,

Please find attached a paper on this matter.

Cheers!

Herivelto

 

[Skogsgurra]

Very fine, Bronzo!

I was involved with a 130 kV breaker (BBC, I think - or Oerlikon) with a common shaft and where the pole actuators could be adjusted so the poles closed in sequence. The technology at that time (sixties) wasn't mature and we never got it right. The poles wore out and the utility lost interest in a project that never left ground. Looks like the problem has been solved now. Thanks for the paper!

Gunnar Englund

http://www.gke.org

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Half full - Half empty? I don't mind. It's what in it that counts.

 

[electricpete]

Why would a resistor reduce inrush any more than a reactor?

Just a thought: the dc component (which causes the saturation and resulting high magnetizing currents) decays with R/L time constant. Adding resistance to the circuit would make the dc decay faster and the magnetizing transient disappear faster.

I see the linked article was prepared by Mr. Bronzeado as well as several of the listed references on subjects such as sympathetic inrush.


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[electricpete]

Picky self-correction.
decays with R/L time constant
should have been
decays with L/R time constant
or
decays with R/L decay constant



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(2B)+(2B)' ?

 

[Bronzeado]

Regarding the resistor question, it is important to observe that a series pre-insertion resistor in a circuit-braker gives a voltage drop when the inrush current starts. This voltage drop reduces the magnetic flux on the transformer which in turn reduces the inrush current.

Note that this voltage drop occurs only during the first semi-cycle of the inrush current but it is sufficient to reduce the magnetic flux on the transformer. As a consequence, the first peak of the inrush current is reduced and so on.

In the company I used to work for, the maintenance people was abandon the use of the pre-insertion resistor as it is very expensive and difficult to replace.

Herivelto

Best regards,

Herivelto S. Bronzeado
Ministério de Minas e Energia - MME, Brasília, Brazil

 

[electricpete]

Good point.
I was forgetting that preinsertion resistor is only in the circuit alone for brief period of time before main contacts close.

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