HV phase lost, strange voltages on LV side

[UKMeterman]

Hi,
Storme Katie dislodged one of the HV jumpers on the DNO 11 KV network, so the local 11KV 415 transformer was single phasing. I expected to get 240, or 120V but there were some people getting 150V and I got about 70 volts and it was indepenent of load. I am trying to work out why not 120V?
Thanks

 

[Pete999]

11KV Delta 415V Star

 

[Simonslimline]

11KV Delta 415V Star

A Dyn11 i expect.

HV Delta

LV star with neutral brought out.

LV leads HV with 30°

 

[UKMeterman]

11KV Delta 415V Star

Hi I would expect the standard winding arrangements

 

[Pete999]

Hi I would expect the standard winding arrangements

In my experience HV / LV 11KV / 415V Delta / Star is a standard configuration!

 

[Pete999]

Doesn't anyone have anymore input?

 

[Simonslimline]

Doesn't anyone have anymore input?

I expect Lucien Nunes will have an answer.

 

[Pete999]

I expect Lucien Nunes will have an answer.

I,m sure he will, but I was thinking more along the lines of the original poster

 

[Pete999]

Delta-Star Transformer Connection Overview | EEP

 

[Pete999]

Where has the OP gone? this topic would have been really interesting, I was involved in HV years ago, and it's not discussed much on this forum, pity it would a good topic to discuss, still never mind.

 

[UKMeterman]

Hi,
The OP is here, the DNO have been and tided up the supply to the village (hot glove job) and everything is now working correctly.

 

[Pete999]

Hi,
The OP is here, the DNO have been and tided up the supply to the village (hot glove job) and everything is now working correctly.

Hi Mate nice to hear from you again, thanks for getting back to us, did the DNO come up with a reason for the strange voltages you were getting?

I know I had some weird voltages in Cyprus when I was AP HV at an RAF base, never did get to the reason why it was normally a case of "just get it fixed, we will discuss later) but we never did, had to keep the planes in the air.

 

[sunray]

I know this is 6 months old but in my experience three phase transformers are wired without a neutral on the primary.
If it were wired as star and one phase is lost, the centre point moves away from zero volts to 3.1Kv. The most likely result would be your 3 240v star secondaries would be 210, 210 & 0.
Now the biggy, if the star of the primary and the secondary are connected to a common earth point and that earth fails at the same time as losing a HV phase, suddenly the star point (neutral) of the 240v secondary sits at 3.1Kv, as could any other earth wiring connected to the earth point.

With a delta primary they'd be 240, 120 & 120 relative to the floating star secondary point and being isolated from the HV primary the most likely fault voltage, anywhere on the secondary will not excede 240v under these circumstances (compared to 3.1Kv).

Sorry I'm still talking old money, these figures are off the top of my head for 11Kv primary from 30 years back. Out training was done with 110v (63.5v) primary and 24v secondary.

(E&OE)

 

[sunray]

I know this is 6 months old but in my experience three phase transformers are wired without a neutral on the primary.
If it were wired as star and one phase is lost, the centre point moves away from zero volts to 3.1Kv. The most likely result would be your 3 240v star secondaries would be 210, 210 & 0.
Now the biggy, if the star of the primary and the secondary are connected to a common earth point and that earth fails at the same time as losing a HV phase, suddenly the star point (neutral) of the 240v secondary sits at 3.1Kv, as could any other earth wiring connected to the earth point.

With a delta primary they'd be 240, 120 & 120 relative to the floating star secondary point and being isolated from the HV primary the most likely fault voltage, anywhere on the secondary will not excede 240v under these circumstances (compared to 3.1Kv).

Sorry I'm still talking old money, these figures are off the top of my head for 11Kv primary from 30 years back. Out training was done with 110v (63.5v) primary and 24v secondary.

(E&OE)

Following on; If the two low voltage phases have significantly different loads, the phase with the heavier load will be at less than 120v and the lighter loaded phase will be sitting above 120v, your figures of 70v and 150v don't surprise me at all but I'd have liked them to equal your regular voltage when added.
After sitting there for a week playing during training, I could have quoted hook line and sinker, but sadly 30 odd years on I'd have to start calculating.