Transformer Inrush
Transformer Inrush
(OP)
Has anyone ever used any transformer inrush elimination techniques?
I think in the past I have read about preflux circuits and also maybe zero current crossing circuit breakers (not sure if I dreamt the last one though!).
If anyone has any experience or weblinks I'd appreciate it.
Application = 31.5MVA 15kV (primary)
I think in the past I have read about preflux circuits and also maybe zero current crossing circuit breakers (not sure if I dreamt the last one though!).
If anyone has any experience or weblinks I'd appreciate it.
Application = 31.5MVA 15kV (primary)






RE: Transformer Inrush
The website is here: http://www.joslynhivoltage.com/
I tried to find the Point on Wave product, but I got tired of navigating the site. Perhaps you could call them?
------------------------------------------------------------------------
If it is broken, fix it. If it isn't broken, I'll soon fix that.
RE: Transformer Inrush
Forgive me if I am wrong, but I am assuming you want to know about any techniques to block protections from tripping during transformer energization (due to in rush currents)?
the method I am familiar with is to detect a 2nd harmonic and block the protections when it is present.
RE: Transformer Inrush
Nope, I think he is talking about eliminating the actual inrush. If you can close each breaker pole at precisely the right phase angle (near peak voltage), there is no inrush.
But at 15 kV, I've never heard of it being done.
RE: Transformer Inrush
thread238-205768: Breaker sometimes trips on transformer inrush current
thread238-205964: Inrush current based on XFMR rating
thread238-151176: POWER TRANSFORMER PEAK CURRENT
Keith Cress
kcress - http://www.flaminsystems.com
RE: Transformer Inrush
Is it really possible to fully eliminate inrush for a 3-phase transformer (i.e. one three limbed core) by point-on-wave switching? The Alstom Network Protection & Automation guide claims that it isn't. I haven't thought about it too carefully, but it doesn't look simple.
Note also that due to core remanence, your next switch-on points-on-wave depend on your last switch-off points on wave.
Hmm!
RE: Transformer Inrush
On a slightly different topic, isn't it desired for other reasons to switch elements on during the zero crossing point?
RE: Transformer Inrush
Yep. it's possible. I haven't any expereince with this issue.
You can see attached intresting document:
http
RE: Transformer Inrush
Anyway why do you need to limit the inrush on transformers? If u have diff protection, than marks has to answer in his 22 jan 09 13:50 post.
"Throughout space there is energy. Is this energy static or kinetic! If static our hopes are in vain; if kinetic — and this we know it is, for certain — then it is a mere question of time when men will succeed in attaching their machinery to the very wheelwork of nature". – Nikola Tesla
RE: Transformer Inrush
Consider the easiest case: A single phase transformer.
The flux in the core is the integral of the applied voltage.
It is helpful to consider two cases:
Case A:
If you begin integrating sin(wt) from a zero crossing, you end up with another sinusoid which is fully offset (i.e. oscillates from 0 to 2).
Case B:
If you begin integrating sin(wt) from a peak, you end up with another sinusoid with no offset (i.e. oscillates from -1 to +1)
The steel in a transformer core can be magnetised "forwards" to +Bmax, and "backwards" to -Bmax. Total allowable change in flux before saturation is 2*Bmax.
A transformer is designed for minimum core steel, so 2*Bmax corresponds to integrating one half-cycle of applied voltage. The core flux moves from -Bmax (at a voltage zero crossing) to +Bmax (at the next zero crossing).
Suppose you switch your transformer on at a voltage zero-crossing, and the core flux with the transformer de-energised was 0. Case A occurs and you attempt to magnetise the transformer core "forwards" to 2*Bmax. The core will saturate at roughly Bmax, and Bmax worth of flux is forced through the air. The result is a high inrush.
Suppose you switch your transformer on at a positive voltage peak, and the core flux with the transformer de-energised was 0. Case B occurs. The first 1/4 cycle magnetises the core forwards to +Bmax, the second (negative) 1/4 cycle brings the core back to 0, the third magnetises the core to -Bmax and so on. The result is no inrush.
The above explanation does not include effect of remanence.
Real transformer cores have memory, and do not always contain zero flux with the transformer de-energised. Hopefully you can see how remanence would affect the two examples above.
RE: Transformer Inrush
At higher voltages, perhaps pre-insertion resistors or reactors could be used.
RE: Transformer Inrush
RE: Transformer Inrush
RE: Transformer Inrush
DPC is correct I want to eliminate (ideally!) but otherwise reduce the transformer inrush current on a island power system. There may be a case where we need to energise a 30MVA transformer from a 35MVA gas turbine alternator. I was worried about transient voltage drop out of tolerance on the system.
RE: Transformer Inrush
Please, find attached a paper on transformer controlled switching in which it is shown that inrush currents can be reduced to values less than the transformer nominal current.
I hope this information will help you.
Best regards,
Herivelto Bronzeado
RE: Transformer Inrush
After several operations and adjustments we were able to get inrush currents reduced from 3600+ amps to about 200 amps on 240 MVA, 230 kv transformers. The transformers were unloaded which made things simpler. The breakers were 350 kV class GIS breakers with single pole operating capability.
We're writing a paper about the results and the problems.
Biggest problem is a small change in timing makes a large change in inrush. After the breaker is operated 2-3 times, it closes a little faster. Supposedly, the adaptive relay accounts for this. The relay was making setting changes the same time as the test engineer so it took a while to get the optimum setting installed.
The relay can also be set to open the breaker poles at current zero's. We did not implement that feature.
Settings are more complicated if there is a load or the transformer bank is three single phase units.
If inrush is a problem - use closing resistors.
RE: Transformer Inrush
As soon your paper is ready, I would appreciate if you send a copy to me. Thank you!
Regards,
Herivelto
RE: Transformer Inrush
RE: Transformer Inrush
I've never heard of this being done at 15 kV.
I think the pre-insertion resistors may be your best option.
RE: Transformer Inrush