11 kv/400 v transformer phase problem !!

[eleceng85]

we faced a problem in power plant consisted of 4 diesel generators 400 v synchronise togather and every generator connected to 400v/11kv delta/wye Transformer the synchronisation in low voltage side (400v) when we turn on the first generator it's transformer rise up the voltage to 11kv and this voltage delivered to all transformers in the high voltage side (11kv) but in each low voltage sides of each transformer there's only two phases live and the other one have 0 voltage ( we tested by voltmeter ) we tried by starting from other generator but it's the same problem. all the for transformers act like that (when we feed it from low voltage side it work perfectly but when we feed it from high voltage side there's missing phase in the other side (400)!! ... could u help me plzzz ???

 

[Skogsgurra]

You do have an insulated N, I assume. Are you testing voltage from that N or from Ground?

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[davidbeach]

Assuming that the 400V is on the delta side of the transformers, the only meaningful voltage measurements are from phase to phase.

 

[eleceng85]

i tested it according to the ground and according to the other phase even i touch it by bare hand and bare feet !!! it's voltage 0 zero... that's really make me sick

 

[jghrist]

i tested it according to the ground and according to the other phase even i touch it by bare hand and bare feet !!! it's voltage 0 zero... that's really make me sick

First of all, touching with your bare hands is liable to make you dead, not just sick!!

As David said, measuring from phase to ground without the generators running is not meaningful. The generators provide the only ground source, so when they are not running, there is no defined voltage from phase to ground. Measure the phase-to-phase voltages.

 

[eleceng85]

as well as every generator sensing missed phase .... low voltage side for every transformer is delta

 

[alehman]

It's possible that one phase of your generators are intentionally grounded, although that would be unusual.

As others have said, you you measured phase to phase with a volt meter? (not your fingers!)

Alan
“The engineer's first problem in any design situation is to discover what the problem really is.” Unk.

 

[waross]

I would be checking the connections on the synchroscope.
It is possible that someone used 240:120 PTs, phase to ground for the synchroscope rather than 400:120 PTs phase to phase.
That would probably give the symptoms as I understand them on an ungrounded delta system.

Bill
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"Why not the best?"
Jimmy Carter

 

[eleceng85]

actually the terberg "synch. module" phase voltages was L1=0,L2=680,L3=400 but i measured it by voltmeter: L1L2=400,L2L3=400,L1L3=400 .... and according to ground
L1=0,L2=400,L3=400 !!! does any one tell me y this transformer act like that ??!!

 

[jghrist]

does any one tell me y this transformer act like that ??!!

Several respondents have already - there is no ground source.

 

[davidbeach]

Actually, it sounds like a corner grounded delta system. Don't use any voltages other than phase-phase, none of the rest mean anything.

 

[waross]

One phase has a connection to ground in each transformer. Probably a PT for the synchroscope connected to ground.
Other than that, look for some device that each transformer LV side has that is connected to ground in each instance.

Bill
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"Why not the best?"
Jimmy Carter