what is the max power of my generator ? 1

[emadshaaban1]

Hello
If you have got a 3phase generator and you've used it to supply a single phase load (you can not share the 1ph load into the 3 generator phases )
can you get the maximum power out of the generator or you can get 1/3 of full KVA ?

 

[waross]

The quick answer is that you can usually get 2/3 of the capacity on single phase.
However with the proper connection, and depending on the load, you may get up to 83% of the three phase rating.

Example;
Generator thermal capacities limit maximum KVA. Prime mover capabilities limit maximum kW
A set is rated for 50 KVA 40 KW, 0.8 PF.
For single phase use 2/3 of 50 KVA is 33.3 KVA, 2/3 of 40 kW is 27 kW, at 0.8 PF. so the quick answer is 27 kW.
BUT
Your prime mover still has enough power to produce 40 kW, so if your load has unity power factor or the load power factor has been corrected to unity, you may safely draw 33.3 kW.
33.3 kW from the original 40 kW is a maximum of 83% of the three phase rating on single phase service under favorable conditions.

When the generator is re-connected for true single phase operation, the highest voltage must be used for maximum capacity.
That is, the 240 Volt connection must be used for full capacity on a 120:240 Volt connected generator.
The common connection schemes for single phase conversion of 12 lead generators are:
The Double Delta connection,
The Zig-Zag connection, (Not to be confused with a Zig-Zag transformer connection.)
and
The Bar Delta or Collin connection. (Useful for 10 lead generator single phase connection but also possible with 12 lead generators.)
An exception is the Double Delta connection. This may be again connected with the two deltas in parallel for a maximum possible single phase capacity of 83% of the capacity of a three phase generator originally rated for 0.8 power factor.
Another possibility is a four lead generator where the load is connected across two line leads.
This would be a 208 Volt load on a 120/208 Volt generator. The quick answer is about 58% of three phase capacity.

Can you upload a good picture of the generator nameplate? What is your intended load?


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

 

[emadshaaban1]

Thank you for the perfect reply.
Would the unbalance load distributing over the 3 generator phases make any effects for the gen- ?

 

[waross]

In sizes of about 1000 KVA and larger unbalanced loading may lead to rotor heating and eventual damage. With smaller sizes the issue becomes progressively less. The worst case is single phase line to line loading. One phase is completely idle.
With the connections that I have mentioned, a 240 Volt load on a 120/240 Volt single phase connection will cause the same current to flow in all the windings. For a unity power factor load, The power factor in one phase winding will be unity, the PF in one phase winding will be leading at 50% and the PF in the third phase winding will be lagging at 50%.

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

 

[catserveng]

Bill has provided you with an excellent summary on this issue, if you need some additional info to help illustrate his descriptions, here are a couple of resources,

http://www.dieselserviceandsupply.com/Generator_Phase_Conversions.aspx

http://www.dieselserviceandsupply.com/Industrial_Generator_Phases_and_Voltage.aspx

http://www.steelsoldiers.com/showth...for-different-voltages-including-single-phase

http://www.google.com/url?sa=t&rct=...u4CwAg&usg=AFQjCNEtuC0tqL6ZJpRtxJo83idyZXoZXw

Bill, excellent descriptions, thank you!

MikeL

 

[waross]

I forgot to add that if the generator is prime power rated you may add 10% capacity for one hour out of twelve. You may add 10% capacity continuously for a prime power rated set if you are willing to void the warranty.

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