Sparking from transformer floating neutral (LV side) when connected to load

[veera1257]

We have 33kV/330V transformer in our solar plant and it's LV side is connected to INVERTER. As per inverter manual we connected its 3 phases to INVERTER and Neutral is left opened and untouched (Floating neutral). We needed cooling for our inverter hence we used Air-conditioner for INVERTER room cooling, for that we took supply from transformer LV side and we connected neutral of air-conditioner to the Floating neutral of transformer and when checked meter showing 190V and we installed a stabilizer and gave stabilizer out put to AC.

AC worked for 4 days properly and later we found that sparking is coming from the Neutral joint though there is no loose connection.

What could be the reason for this and let us know how to resolve this issue.

Thanks in advance.:angel:

 

[ggunn]

We have 33kV/330V transformer in our solar plant and it's LV side is connected to INVERTER. As per inverter manual we connected its 3 phases to INVERTER and Neutral is left opened and untouched (Floating neutral). We needed cooling for our inverter hence we used Air-conditioner for INVERTER room cooling, for that we took supply from transformer LV side and we connected neutral of air-conditioner to the Floating neutral of transformer and when checked meter showing 190V and we installed a stabilizer and gave stabilizer out put to AC.

AC worked for 4 days properly and later we found that sparking is coming from the Neutral joint though there is no loose connection.

What could be the reason for this and let us know how to resolve this issue.

Thanks in advance.:angel:

I believe you need to bond X0 to a ground rod at the transformer if you want any loads to connect to it.

 

[veera1257]

Thank you for your reply.

But as far as guidelines and inverter manual is concerned we should not connect neutral of transformer to earth weather solidly or by any means.It should be floating with respect to PV array.If we do so there might be harmonic problem.

Also requesting you to let me know the exact reason so as to why should we maintain T/F neutral as floating for Solar inverters..

 

[ggunn]

Thank you for your reply.

But as far as guidelines and inverter manual is concerned we should not connect neutral of transformer to earth weather solidly or by any means.It should be floating with respect to PV array.If we do so there might be harmonic problem.

Also requesting you to let me know the exact reason so as to why should we maintain T/F neutral as floating for Solar inverters..

If you ground the neutral of the transformer but the inverter does not connect to it, the inverter still has a floating neutral.

 

[winnie]

Without understanding the specific circuit and grounding of the inverter and solar array, there really is no way to answer your question.

If your system is grounded someplace else (say in the inverter, or the solar array itself), then the neutral of the transformer is very likely being driven to a voltage that is not ground potential. Grounding the neutral in this case would cause a large short circuit, because your system would now have two grounds are different voltage.

You will need to research and provide more information about the rest of the circuit. It is quite likely that you will need another transformer to provide power for the cooling system.

-Jon

 

[AdrianWint]

Is the air conditioner single phase or three phase?

 

[StarCat]

Clarification of Field Wiring

Clarification of Field Wiring

Maybe I am missing something here, but the transformer mentioned appears to be upstream from the inverter on the DC side of the system and the live leg of power for the AC unit must be coming from the inverter???
Please tell this American exactly what a stabilizer is.
I'd like a diagram for where things are landed and also see the HVAC machine nameplate.
Its implied that the AC unit is dead now.
I think it will be found that the unit may have run, but most likely it did not run correctly and now has a ground fault, most likely from a failed compressor.
This looks like a most unusual situation with the HVAC power source being classed as separately derived.

 

[ggunn]

Maybe I am missing something here, but the transformer mentioned appears to be upstream from the inverter on the DC side of the system...

Transformer on the DC side? Surely that isn't what you mean.

And don't call me Shirley.

 

[SolarPro]

Hard saying what the design standards are in India, but you can find basic schematics for ac collection systems, which integrate PV inverters and pad-mounted distribution transformers for interconnection at medium voltage in this article:

"Basics of Medium-Voltage Wiring for PV Power Plan AC Collection Systems"

 

[Smart $]

"Sparking" may be [electric] corona, given you have a 33kV primary. What measures were taken to reduce voltage stress on primary connections? Does the transformer have separate termination compartments for primary and secondary? Is the transformer enclosure and frame bonded to ground?