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Generators

Generators

Generators

(OP)
what would happen if you feed a busbar with two different supplies of 3 phase at 380volts, properly phased, same frequency 50hz but one supply is from a supply utility and the other from an emergency generator. I know this is not procedural to have the two supplies at the same time but say it so happens that you have the two alternative supplies at the same time

RE: Generators

The conditions you mention are not sufficient for paralleling. The voltage also need to be in sync and guaranteed to  remain so for the duration of the paralleing.  
If not a lot of bad thing can happen, worst being completely out of phase parallleing and creating a heavy short circuit.

At best the protective device on one of the sources can open in time and limit the damage. The worst could include injury or death of a person,  a blast, fire, smoke, twisted metals, generator off the pad..etc.. Something you do not want to experience or blamed for.

If properly synchronized nothing bad will happen. But the generator controls must be set up to share the load properly. If not it will either get overloaded or reverse powered and can shut down. Some undesirable outage can occur but nothing detrimental.

 

Rafiq Bulsara
http://www.srengineersct.com

RE: Generators

Assuming that you have a synchroscope and have successfully synchronized the generator with the utility:
With the set paralleled and the governor in droop control, the machine will take whatever load you set it for.
BUT:
If the utility voltage is not stable you need PF control or you may burn out the generator with reactive current even though the load is not excessive.
The switch gear beyond the point of common coupling must be capable of interrupting the combined fault current of both sources or the switchgear may explode rather than clear a fault.
In the event of a utility failure, the generator may backfeed the utility lines. This may be fatal to utility repair crews.
This is not to say that it can't be done. But you must involve the utility engineering department and install all protective equipment that they require.
You should also use some type of power factor control to avoid excessive reactive currents due to variations in the supply voltage.
Warning. We are trained professionals. Don't try this at home without expert supervision.

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

RE: Generators

"Warning. We are trained professionals."

Some of you are... the rest of us just muddle along as best we can. wink
  

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

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