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fluctuation in secondary voltage of transformer

fluctuation in secondary voltage of transformer

fluctuation in secondary voltage of transformer

(OP)
we have a problem during testing the transformer the
data is 1600kva,delta/star 11kv/380v while we are testing the secondary side we found the voltage is fluctuated from 400V to 500V or 600V or 700V in a (ms)seconds then return back to 400V.

RE: fluctuation in secondary voltage of transformer

Is that transformer connected? Is there a load?

Regarding the millisecond variation. As you know, the voltage of a 380 V grid changes between -537 and +537 V fifty times every second. Or once every 20 ms.

On top of that there are usually transients caused mostly by load changes. Those transients are normally in the 700 V range (peak) and not to worry about.

What measurement equipment do you use? And why are you testing this? Did you have a problem?

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: fluctuation in secondary voltage of transformer

If this trafo connect to load?
If the star earthed now?
If the RMS or peak meas?
Regards.
Slava

RE: fluctuation in secondary voltage of transformer

(OP)
btw it`s no load

RE: fluctuation in secondary voltage of transformer

(OP)
1-it`s no load.
2-the star is earthed.
3-the measurement is rms.

RE: fluctuation in secondary voltage of transformer

Do you really see RMS over milliseconds?

Please tell us what instrument you are using.

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: fluctuation in secondary voltage of transformer

(OP)
we use avo meter  

RE: fluctuation in secondary voltage of transformer

(OP)
not milliseconds but it appear for while then return back to 400Volt

RE: fluctuation in secondary voltage of transformer

Hi Tarek.
Few steps for to be sure.
1. Please provide fixing contact of AVO meter, maybe is contact.
2. Please for second phase use another AVO meter.
Are you have this on all phases.
For first, it's seems as bad meas or AVO meter problem.
Slava

RE: fluctuation in secondary voltage of transformer

(OP)
only in one phase.

RE: fluctuation in secondary voltage of transformer

Stop, stop.
380V it's phase to phase voltages.
Please check again all meas:
R-N
S-N
T-N
R-S
S-T
T-R
and back to us with results.
 

RE: fluctuation in secondary voltage of transformer

(OP)
R-S= GIVE VERY HIGH VALUE.
S-T=GIVE VERY HIGH VALUE.
T-R=GIVE VERY HIGH VALUE
IT GIVE A VERY HIGH VALUE IN THE SECONDARY SIDE THEN RETURN BACK TO 400V,SOMETIMES IT REACHED 1000 VOLT IN THE SECONDARY SIDE.

RE: fluctuation in secondary voltage of transformer

Something crazy.
I strongly recommend stop test and check this trafo again.
Megger, transmission ratio, etc.
Phase to phase voltages are very high and phase to earth/ground are OK????
I haven't any idea on this moment, 3 times voltages and back to the normal??? Earthed star w/o any load, maybe some capacitors are connected on the bus???

RE: fluctuation in secondary voltage of transformer

(OP)
we removed all the capacitors.

RE: fluctuation in secondary voltage of transformer

Is this a test you do routinely? Or is it the first time you do it?

Why do you do it? Did you have some kind of problem with this transformer?

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: fluctuation in secondary voltage of transformer

Your transformer could be failing, turn to turn in a primary winding. It may well be an arcing or intermittent fault.
Is this a dry type or oil filled transformer?
Is this a new transformer or one that has been in service and is developing a problem?
Are there any current transformers in the primary circuit that you may use to compare primary phase currents?
In another thread, you asked about a short circuit test.
A short circuit test on a failing transformer may lead to a catastrophic failure with property damage, fire, injury and death. At least one of our regulars here has lost friends who died when a transformer exploded.
 

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: fluctuation in secondary voltage of transformer

(OP)
this is a new one,an oil filled transformer.

RE: fluctuation in secondary voltage of transformer

Does this transformer have automatic tap changers?

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: fluctuation in secondary voltage of transformer

Hi.
It seems as turn to turn problem.
But what about some Buhholtz relay?
Best Regards.
Slava

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