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synchronization of 4-generators in parallel

synchronization of 4-generators in parallel

synchronization of 4-generators in parallel

(OP)
A typical transformer unit of a power plant comprises:
 - A step-up transformer with 3 windings 230 kV (star grounding) -13, 8 kV (delta) -13, 8 kV (delta)
 - Two bus generation directly connected to 13.8 kV low voltage side of step-up transformer
 - Each two hidrogenerators are connected to the bus generation through circuit breaker.
The high side of transformer  is connected to SF6-substation through circuit breaker.

The ideal procedure for synchronizing the power plant to the 230kV system would be:
 - Synchronize the four generators at the  LV transformer by bus generation.
 - Synchronize HV transformer to SF6-substation by controlling the set of four generators.

People of regulation and governor do not agree , because of circulating current between generators. Generators should be connected one by one.  
Someone could explain the problem?
 

RE: synchronization of 4-generators in parallel

It is very difficult to have four unloaded generators operating in parallel without some circulating current.

As far as I'm concerned, the ideal order would be energize the transformer from the 230kV side and then parallel each generator one at a time across its own 13.8kV breaker.

Obviously that wouldn't work for black start if that is a concern.

RE: synchronization of 4-generators in parallel

(OP)
my problem is black start!

RE: synchronization of 4-generators in parallel

Then bring up one generator, add some load.  Bring up a second generator, add more load.  Repeat as necessary.

RE: synchronization of 4-generators in parallel

(OP)
I am understanding that for 230kV enrgization will be:
...from the 230kV side and then parallel and add load each generator one at a time across its own 13.8kV breaker.

RE: synchronization of 4-generators in parallel

If you connect the transformer to the first generator before the generator is started and ramp the transformer up with the generator it may be the friendliest method of energizing the transformer. Then synchronize with the substation or grid. The pick up some load and proceed to sync and load the other generators one by one.
You could energize the transformer from the 230 kV side but bringing it up with the first generator avoids inrush issues.

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

RE: synchronization of 4-generators in parallel

(OP)
correction:

 ...Then synchronize(at 230kV) with the substation or grid. The pick up some load and proceed to sync(at 13,8kV) and load the other generators one by one.

  

RE: synchronization of 4-generators in parallel

davidbeach has good (lps) answers

RE: synchronization of 4-generators in parallel

(OP)
I think this would be the sequence of switching:

1- normal synchronization
 the ideal order would be energize the transformer from the 230kV side and then synchronize and add load each generator one at a time across its own 13.8kV breaker.

2- black start:
-connect the transformer to the first generator before the generator is started and ramp the transformer up with the generator and connect to substation 230kV ( previously desenergized)
-Connect 230kV transmission line up to remote busbar substation.
- Add some load.
- For other generators synchronize and add load each generator one at a time across its own 13.8kV breaker.

My concern is the inrush current of transformer in black-start over generator:- If we assume a value of 10 times rated current transformer, this will be 40 times rated current generator.

RE: synchronization of 4-generators in parallel

There is no transformer inrush when you bring the transformer up with the generator. That's the whole point of starting the first generator with the transformer already connected.  

RE: synchronization of 4-generators in parallel

Further to David's last post. Bringing the transformer up with a generator will avoid inrush issues on the grid as opposed to energizing the transformer from the 230 kV side.

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

RE: synchronization of 4-generators in parallel

(OP)
....Bringing the transformer up with a generator will avoid inrush issues on the grid..


At another power plant with a similar case, they should modify  the ramp of automatic starting of AVR and other precautions.
I do not know how the energization sequence  of the this power plant.
In what case , could that happened?

RE: synchronization of 4-generators in parallel

There are two methods for transformers.
The frequency and the voltage may be ramped up together to maintain the Volts/Hertz ratio.
The generator may be brought up to speed and then the voltage may be ramped up.
The second method is not suitable for starting relatively large motors.  

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

RE: synchronization of 4-generators in parallel

(OP)
Transformer energization of a single generator could be done without causing any inrush current with manual starting;
- could increase tension in the generator very slowly to the rated value.

Manual starting  is only for maintenance.

The automatic starting by regulators is the operating procedure.
In this case there is the risk of inrush current.
 

RE: synchronization of 4-generators in parallel

Start the generator with the transformer connected.  Ramp to speed.  Let the regulator bring the voltage up.  No inrush.

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