Parallel generator sets connected in Delta. 2

[Federico_]

First at all I wanna say thanks to the person who can give me guidance. I have a project to connect two gensets in parallel, delta configuration. Is it possible that the synchronism is unstable due to the third harmonic? Or what other problem can arise from this, I know that in Wye connection there is not this kind of inconvenience, but they require it in Delta Connection. Thank you in advance if any ad.

 

[waross]

No problem. You will probably find delta connection diagrams on the sets.
Of more concern than harmonics is grounding.
There is a condition known as a "Discontinuous Ground Fault". That is a fancy term for an arcing ground fault.
An arcing ground fault on an ungrounded system may develop high frequency, high voltage potentials.
This may cause motor and transformer failures throughout the plant.
You have three options.
1: An artificial neutral or grounding transformer(s).
2. Corner grounding.
3: If you are running the windings in series for the higher voltage, ground one of the center points.
This was standard grounding practice for decades when 120/240 V, wild leg delta systems were common.


--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[Federico_]

Thank you for your prompt response, could you please let me know if a configuration like the one in the diagram would work without problem? Thank you very much.

 

[waross]

Yes. That is the old "Wild Leg" circuit of years past. The neutral should be grounded.
If your customer wants to run ungrounded, you should use a good ground detector system.
Alternately use a high impedance ground.

100 years ago, motor and transformer windings were insulated by being wound with cotton threads.
There was "Single Cotton Covered", SCC and "Double Cotton Covered", DCC.
Transformer burnouts were frequent, and an ungrounded delta system allowed a plant to run on open delta at reduced capacity in the event of a transformer failure.
50 Years ago, enamel insulations were in use for windings and burnouts were relatively rare.
As well, many three phase transformers were in use.
If any one winding in a three phase transformer or generator burned out, it acted as a short circuit on the other phases and so was not suitable to use in open delta.


--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[edison123]

Don't see any paralleling issues with delta connected generators as long as if you follow standard synch procedures. Triplen harmonics do not appear on the line side in delta connection.

Muthu

http://www.edison.co.in