reduceing inrush current
reduceing inrush current
(OP)
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
we want to suppress the current when we connect it with "no load".
thank you






RE: reduceing inrush current
1> The inrush varies and may be up to 25 times FLC depending on the strength and direction of the residual magnetism and the point on the wave that the transformer is energized. There is a circuit which will reduce the residual magnetism when the transformer is de-energized.
2> The transformer may be energized at a reduced voltage through series resistor which are then shorted out.
3> Point on wave switching may be another option.
Bill
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"Why not the best?"
Jimmy Carter
RE: reduceing inrush current
Solcon is one of those that makes 15kV transformer inrush controllers, you might inquire on them about a 33kV if you are rich and desperate.
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RE: reduceing inrush current
Maloperetaion of protection? trip of generators?
RE: reduceing inrush current
the reason is the duration of the sag during the inrush
RE: reduceing inrush current
RE: reduceing inrush current
The pony transformer is much smaller, so it has little inrush. And the heating up from the pony is small because of the impedance of the pony.
Because the transformer is magnitized from the pony, closing the transformer breaker also required little or no inrush.
So just remember little pony transformers.
RE: reduceing inrush current
To reduce the inrush current, requirements are switch on when input voltage is at peak and reduce the residual flux in core from previous energisation.Residual flux will remain in core for several weeks or months.Reducing working flux density or using better core material grade etc will not change inrush current value.
Point of wave switching is quite common in EHV breakers( 400 Kv and above)-but in medium voltage it is first time that I see a device to limit inrush current.It looks like they are phase shifting to reduce input voltage. Another way is putting resitor in series in the first stage and then by pass contactor is closed to bring full voltage. It looks like that it must work for 33Kv also as vaccum switches are available at that voltage too.
I dont understand how heating the transformer will reduce inrush current.
RE: reduceing inrush current
RE: reduceing inrush current
http://www.joslynhivoltage.com/catPointonWave.htm
RE: reduceing inrush current
RE: reduceing inrush current
Being that Joslyn was apparently bought by T&B (which I didn't know), who was themselves just bought by ABB, I guess this makes it an ABB product. But since ABB already makes vacuum contactors of their own, I ponder the fate of Joslyn now. Unless of course Joslyn has always been making ABB's vacuum contactors, as they do for many others.
"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
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RE: reduceing inrush current
I had recently read about ABB/TB (T&D World?). Add another reason be be an engineer / historian.
On a similar topic, imagine keeping track of the Alstom / Areva / Alstom product line.
RE: reduceing inrush current
RE: reduceing inrush current
As a rotating equipment guy, I think of work as a torque acting through an angle. Since transformer does not move, it does no work.
Sorry for being a stickler. I think I know what was meant (pony transformer does not transform any significant amount of power for any significant time?).
My wife would probably say that I don't do any real work.
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(2B)+(2B)' ?
RE: reduceing inrush current
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If we learn from our mistakes I'm getting a great education!
RE: reduceing inrush current
2) Point of wave switching is known for many years and popular with EHV systems.
ht
Now it is being developed for MV systems too. Normally in MV system, transformer inrush current is not taken seriously,probably becuse the system impedance will cause sufficient voltage drop so as to limit the magnitude and duration of inrush current flow.In fact feeding system fault level is also a factor deciding the inrush current value.
3) Dear cranky , no offence was meant.We are from different parts of the world and when you write "pony transformer to heat up the transformer from the low side prior to closing the transformer breaker." I take it literally.We sometime heat the transformer by applying low voltgae to a transformer with shorted secondary.
I am still not clear how pony transformer will reduce inrush.If you energise transformer from HV or LV the inrush value as % will be same, may be slightly more for LV as air core inductance become less then.If you energise through another transformer, the only effect is inrush may come down little due to voltage drop through transformer impedance.It is not going to reduce the residual flux as it depends upon the point on voltgae wave at which the supply is switched off. Even if residual flux is zero at the time of Hv switching, still the inrush current will be there if switched when voltage is zero.Residual flux is adding up to the twice normal flux density that will happen when switched at voltage zero.
RE: reduceing inrush current
George Fotiou
www.Engineering-services.gr
RE: reduceing inrush current
Maybe the poles can be sequenced mechanically.
The ABB POW controllers I have seen provide individual closing signals for each phase. They can also stagger the trip signals to open each phase at the optimum point of the current waveform to minimize contact duty.
The optimum closing phase angle changed based on system conditions- whether the breaker was energizing the transmission line from the station bus or was energizing a station transformer from the line.
The extra complexity of monitoring the voltages, currents and closing times of the breaker poles makes the cost benefit ratio high for MV systems. Resistor closing is a lot simpler.
RE: reduceing inrush current
Let me make it clear I have never used a pony transformer, or this application. I had heard about this at an IEEE PES meeting just a few months ago.
Working on power systems, I don't haven't had the need to try this. So if you use this, let me know how it works.
RE: reduceing inrush current
Please find attached a paper on this matter.
Cheers!
Herivelto
RE: reduceing inrush current
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
www.gke.org
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Half full - Half empty? I don't mind. It's what in it that counts.
RE: reduceing inrush current
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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(2B)+(2B)' ?
RE: reduceing inrush current
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)' ?
RE: reduceing 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
RE: reduceing inrush current
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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(2B)+(2B)' ?