synchronization of generators in parallel 1

[odlanor]

The powerplant has a transformer of 230kV-13.8-13.8kV
Each generator can absorb 1 / 4 of the reactive line.
The best sequence of operation to dispatch generation would be:
1 -starting and excitation the 1 generator-transformer unloaded.

2 - 13.8 kV synchronizing of the 3 generators.
obs: governors should have a speed droop 4 to 5% to allow parallel operation of generators to reduce circulating current between generators.

3-Synchronizing the transformer with the 230kV line.
obs: is it possible,with setpoints control of only 1 generator ?

5-dispatch generation using joint control of the power regulation of generators.

Anyone have any experience with this problem?

 

[waross]

Step one looks: OK.
Step two: In our small plant we used 3% droop, but 4 or 5 is probably acceptable when on the grid.
Step three: It may not be possible. With no or very light load, There may not be enough range of adjustment on just one generator. If you have your frequency very close to 60 Hz (or 50 Hz) you may be able to get a sync with just one governor.
If you get the speed settings very far apart on an unloaded group, you will be driving circulating currents betweeen the generators.
It may work well at one plant to sync with just the governor on one set and be very problematic at another plant.

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

 

[ScottyUK]

What kind of prime mover? A gas turbine behaves very differently to a steam turbine: the governor of a gas set at sync idle will be well open because of the huge internal load of the compressor, while the governor of a steam set will be barely cracked.

Regardless of the above, I'd be happier seeing each machine synchronise independently across its own generator breaker. Droop should be of no consequence because the machine will be in speed control (isochronous mode) until it closes onto the bars, at which point the governor should transfer into either load control for part-load operation or onto the thermal limiter for base load operation.


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

 

[odlanor]

scottyUK
it is a hydroelectric power plant.
If you synchronize each generator to the system , step by step, one generator cannot absorve reactive of line , in case of rejection.
Because of this we have to install shunt reactor at remote terminal of line.

 

[odlanor]

waross
... With no or very light load...
There is no load yet. You are trying to synchronize a set of 4 generators with 230kV system, commanded by one generator.

 

[rasevskii]

odlanor:

This sounds very familier: At a certain hydro plant in Africa about 30 years ago, two 33MVA hydro generators had to be connected first to the main transformer (about 66MVA 3 winding 11/220 KV) to be able to energize the single circuit 220kV line about 400Km to the next substation. The local operator there then synchronized with the main system there by hand. It was all a bit dicey with frequency and voltage wandering around at the local system end.

Perhaps your situation is similar. No real good reason why two or more generators cannot be syncd together at no load, already at that time we had the best full static excitation systems and electronic governors in service at that plant.

Where are you located?

rasevskii

 

[inpran]

Odlanor:

I'm from sub-stations background and don't have much experience with power plants. However, while commissioning a generator transformer bay for a thermal power plant, the client went in with the third method of your description. Three generators were synchronised with the 400 kV grid via the generator transformers.

 

[odlanor]

rasevskii
it is in Brazil. I believe 90% of generation in Brazil is hydraulic. I guess my problem is like you told.

inpran
That's like ScottyUK said: its depend of turbine type.
My power plant will operate with submerged generators with bubble turbines.

I give up!

 

[odlanor]

my god, this issue is not over yet!
let's summarize:
1-Excitation and starting the first generator-transformer unloaded.
2 - 13.8 kV synchronizing of the three generators.
3-Synchronizing the transformer with the 230kV line.
4-dispatch generation to 230 kV load.

We classify two types of load:

1 - intake load
system is operating at its rated frequency and power plant needs to replace the load of another power plant.
I believe there will be problems to address items 3 and 4.

2-load rejection
there was a blackout and your plant needs to make the restoration of the load is still connected.
I believe that there will be problems to address items 3 and 4.

What do you think?

 

[odlanor]

ERROR
2-load rejection there was a blackout and your plant needs to make the restoration of the load is still connected.
I believe that there will NOT be problems to address items 3 and 4.

 

[waross]

If the line is energized, the other end will be supplying the reactive demands until you raise your voltage enough to produce Kilo-VARs. You may be able to synchronize at a voltage equal to the line voltage. When all your generators are on-line increase the excitation to pick up the reactive demand. Not a complete solution, but a start.
If the line is not energized, sync your generators at a lower voltage until you have enough generators online to pick up the voltage and the reactive demand.

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

 

[odlanor]

waross ,
If the line is energized, ... refers to load 1.

If the line is not energized... refers to load 2.
Am I right?

 

[waross]

I am a little confused about load 1 and load 2.
I will restate.
If the line is energized from the other end, the other end will be supplying the reactive demands until you pick up the reactive load by increasing your excitation or voltage setting.

If the line is de-energized it may be possible to enegize and sync at a lower voltage and then ramp up the voltage of all four generators before the line is re-connected at the other end. However this may be one of those suggestions that is discussed and then discarded. The issues involved with ensuring that the far end of the line is not connected before you are ready, and with ramping up the voltage of four generators may be more problematic than the issues with sync'ing four unloaded generators.

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

 

[odlanor]

waross,
this condition refers to A-power plant of thread238-306333.
besides kVA ,remote A-load minimum is more than 3 generators.