transformer

[Guardiano]

Hi forum members,

I need some expert advices on the following. I'm using a 380 V / 220 V transformer to supply some single phase loads. The site where I'm using this transformer is rated at 415 V 50 Hz. Ideally I should have got around 240 V output on the transformer at no load taking into consideration the turn ratio of the transformer. However, I'm measuring 250 V on the secondary side of the transformer at no load. Four transformers at different locations on the same site are behaving similarly.
Could the harmonics in the network cause these variations?

Grundig

 

[JMatt]

It's likely that your 415V nominal system is actually operating around 432V.

 

[jghrist]

The site where I'm using this transformer is rated at 415 V

What is the measured voltage of the 415 V rated system? Is this a solidly grounded system? If so, why do you need a transformer to supply 220 V single phase loads? Can't you just run a neutral and a phase to the load?

 

[Guardiano]

Thanks for the comments. The system operates on the IN network that is with the neutral isolated and single phase load are provided through step down transformers. The voltage measured is 410 V.

Guardiano

 

[ScottyUK]

The small transformer will be designed to provide rated voltage at nominal conditions which are likely to be rated output and 0.8 lagging power factor. If you reduce the load you will see the voltage rise, and at zero load it's not surprising that the voltage is high.


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If we learn from our mistakes I'm getting a great education!

 

[ProtectionEngineer]

I believed your primary neutral is floating. The secondary no-load voltage is always higher than expected. This is normal. Is your transformer connections is Y-Y.
The measured voltage 250V at no-load is due to the third harmonic component.

The line-neutral voltage will be reduced to 240V once you started to add load.

Alex

 

[rickei]

If you measure 410V with transformer ratio you'll have about 237.5V and as ScottyUk says for let say range of 1000VA transformer have regulation of cca 5% so you got about 250V no load voltage

 

[waross]

Before I read rickei's post I assumed 5% regulation and calculated 249 Volts. Everything seems to be normal.

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

 

[rockman7892]

What are the primay and secondary connections of this transformer? Delta-Wye? Wye-Wye?

 

[RajeevCell]

I think the OP mentioned that it is a single phase 380/220 transformer. So, there's no issue of broken neutral or delta-wye connection.

Guardiano, the values you measured looks normal (unloaded condition) as others have pointed out, and doesn't pose any danger to your equipments.

Is it at a telecomm switch? Just being curious. You mentioned IN network.

Regards
Rahul