What he dod was tie the x0/h0 to gnd
not the source x0
Step Up transformer Installation
- Thread starter MFRichardson16
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not the source x0
No they wouldn't
any imbalance would flow in the neut
it's done all the time
but I would have gone
wye-delta-wye to begin with
not wye-wye-wye
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
It is done all the time by utilities which employ a MGN at voltages above 600V.
Phil Corso
Senior Member
- Location
- Boca Raton, Fl, USA
Mike...
Some detail (especially damage photos) covering extent of damage may reveal type of fault! How is step-up xfmr connected to supply... UG or OH? Any lightning-arresters, or surge-capacitors involved?
Phil
Some detail (especially damage photos) covering extent of damage may reveal type of fault! How is step-up xfmr connected to supply... UG or OH? Any lightning-arresters, or surge-capacitors involved?
Phil
That's what I said... just using different words. :slaphead:
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
They are only isolated if you remove the jumper shown on the nameplate.
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Bugman1400
Senior Member
- Location
- Charlotte, NC
Perhaps the breaker failed from severe overvoltage.....either from a floating neutral that went L-L or from resonance. If the local end has the neutral adequately grounded or if the breaker is, in fact, rated at L-L then, my money is on resonance.
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And that was the suggestion I agreed with
I would like see the bonding
was the 150 kva h0 or x0 bonded to the frame?
was the feed xfmr x0 bonded to frame?
Phil Corso
Senior Member
- Location
- Boca Raton, Fl, USA
Not enough detail for guesstimates about cause. Did the fault occur during commissioning?
Or it could have been the breaker itself. I recall a ground-fault occurring in the draw-out carriage of a breaker! Unfortunately, there was no “bus stab” for ground, so, the fault-current had to travel thru the wheels on the carriage! The result was loss of 20-30 ft of (approved) LV switchgear!
Phil
OP mentions the system has been up and running with power fluctuations once or twice a month... which is a fairly good indication by my understanding (which is not very good btw
) of a resonance problem.Phil Corso
Senior Member
- Location
- Boca Raton, Fl, USA
OP mentions the system has been up and running with power fluctuations once or twice a month... which is a fairly good indication by my understanding (which is not very good btw
Xfmr certainly fits the "L" component of Resonance phenomenon, but to date no evidence of the "C" component! OP said 15 ft between step-up xfmr and open HV disconnect. No word yet of other "resonance" markers!
Phil
You're just looking at the failed breaker. The grounding was revised after that mishap.Xfmr certainly fits the "L" component of Resonance, but to date no evidence of the "C" component! OP said 15 ft between step-up xfmr and open HV disconnect. No word yet on"resonance" markers!
Phil
The HV disconnect has to have been closed for the system to be getting power fluctuations once or twice a month. :slaphead:
Any chance the resonance problem stems from the primary side of this transformer?
Phil Corso
Senior Member
- Location
- Boca Raton, Fl, USA
@ Smart $...
1) You’re right about present fluctuations being caused by resonance! V & I excursions are resonance markers!
2) Fault occurred with HV-side switch open! Thus, HV-side capacitance is nil!
3) Yes! Fault, in the form of a switching transient, or HV reflection could be influenced by LV-side configuration!
Phil
1) You’re right about present fluctuations being caused by resonance! V & I excursions are resonance markers!
2) Fault occurred with HV-side switch open! Thus, HV-side capacitance is nil!
3) Yes! Fault, in the form of a switching transient, or HV reflection could be influenced by LV-side configuration!
Phil
Bugman1400
Senior Member
- Location
- Charlotte, NC
My "money" was on the 4160 having the resonance issue. With the 4160 UG cables to the single phase pad mounts via 1200? feet, that could serve as your C that Phil was referring to.
I doubt a reflected wave from the transformer could generate enough current to blow the breaker
even if we assume at the 150 kva transformer:
-incident 20 x 150000/(1.732 x 480) = 3600 A
-0% transmitted/refracted
-100% (opposite sign) reflected ~ 3600 + whatever the feed was putting out (even if very short lines and still supplying 3600 inrush)
but it would be opposite sign and sum to ~0
it was a cb rated at aic 65 ka
my wag, by grounding both h0/x0 he some how completed a ground loop thru earth and possibly in parallel with the egc's
ground fault from feeder phase to ground thru the 150 kva xfmr winding
even if we assume at the 150 kva transformer:
-incident 20 x 150000/(1.732 x 480) = 3600 A
-0% transmitted/refracted
-100% (opposite sign) reflected ~ 3600 + whatever the feed was putting out (even if very short lines and still supplying 3600 inrush)
but it would be opposite sign and sum to ~0
it was a cb rated at aic 65 ka
my wag, by grounding both h0/x0 he some how completed a ground loop thru earth and possibly in parallel with the egc's
ground fault from feeder phase to ground thru the 150 kva xfmr winding
Phil Corso
Senior Member
- Location
- Boca Raton, Fl, USA
Gentlepeople...
Here we go, again! Another trip into La-La land... all without data and OP!
Phil
Here we go, again! Another trip into La-La land... all without data and OP!
Phil
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