Possible Transient Recovery Voltage Issues
Possible Transient Recovery Voltage Issues
(OP)
I have recently been introduced to Transient Recovery Voltage issues when a vacuum contactor clears a fault. We had a failure of some lightning arresters in the field and some of the engineers think that it is a TRV issue. I have a basic understanding of what occurs when a vacuum contactor clears a fault and how this causes problems. My question is this: Can a TRV travel from a 4160V secondary on a XFMR to a 995V secondary on the same XFMR? The 4160V secondary has its own lightning arresters at the XFMRs terminals and so does the 13,800V primary. The 4160V secondary has several heavy inductive loads controlled by vacuum contactors. When the fault occured, the 995V circuits were energized to the line side of the MCCBs but they weren't closed. We had 3 lightning arresters (each phase to ground on a high resistance grounded system)these were installed on the line side of the 995V MCCBs within a couple of feet. There is also a reactor on each phase of the 995V circuits between the XFMR and the MCCBs. These arresters failed very violently and caused a subsequent 3 phase to ground fault on the line side of the MCCBs. I would also be grateful if any of you could share any other ideas as to what may have caused this. Thanks in advance.
I am an engineer, so the glass is twice as big as it needs to be.






RE: Possible Transient Recovery Voltage Issues
The fast dv/dt couples easily through winding-winding capacitances and can probably find other ways as well.
To me, it sounds like your arresters are not ready to absorb the energy in the surge caused by the cleared fault. Did the designer really calculate with maximum stored magnetic energy during a worst case fault? I think not.
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: Possible Transient Recovery Voltage Issues
I am an engineer, so the glass is twice as big as it needs to be.
RE: Possible Transient Recovery Voltage Issues
Also what was the voltage rating of the failed arresters?
RE: Possible Transient Recovery Voltage Issues
I am an engineer, so the glass is twice as big as it needs to be.
RE: Possible Transient Recovery Voltage Issues
Does the capacitive coupling mean that the voltage on the 995 Volt winding may approach the voltage on the 4160 winding?
Does the transformer ratio become less important than the voltage division of the inter-winding capacitance any any other impedances to ground?
If such is the case then the surge may have been a non-issue on the 13.8kV side.
Bill
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"Why not the best?"
Jimmy Carter
RE: Possible Transient Recovery Voltage Issues
There's a difference between lightning and clearing a fault with a vacuum contactor. The lightning is usually less powerful (if it isn't a direct hit) than an overvoltage from a fault. Especially if there are inductive components involved.
I do not think that the arresters on the 13.8 kV side has any influence in this particular case.
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: Possible Transient Recovery Voltage Issues
My point is that given the very high dv/dt of the transient there may be little current through the transformer winding and as a result, little transformer action.
I am thinking that the worst case for winding configuration may be when the winding end that takes the worst hit from the surge is closest physically to a winding end serving the 995 Volt loads.
I am thinking that in this case the EMF on the end of the 995 volt winding may approach the voltage of the surge. The actual surge voltage on the 995 Volt terminal would be reduced more or less by the other factors you mentioned,
Other winding configurations may be more conducive to insulation failure to ground of one or both windings.
I agree with you.
I suspect that a surge caused by a very fast dv/dt may cause voltages on the secondary in excess of the greatest voltage possible due to transformer action.
This may explain the 995V Volt arresters failing before the 4160 Volt arresters.
Gunnar; Please, if you think that I am off base then RF my entire post to avoid confusion. If my question/suggestion has merit then please RF this message.
Bill
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"Why not the best?"
Jimmy Carter
RE: Possible Transient Recovery Voltage Issues
RE: Possible Transient Recovery Voltage Issues
Yours
Bill
Bill
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"Why not the best?"
Jimmy Carter
RE: Possible Transient Recovery Voltage Issues
"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: Possible Transient Recovery Voltage Issues