power station synchronization requirement
power station synchronization requirement
(OP)
Hi everybody
very good morning
I have a question regarding the synchronization of two power station to grid
we say voltage should be equal but i would like to know what is the % practical voltage difference (tolerance) that can exist between the two system just before the synchronization .
I know other requirements of phase sequence and frequency should also be met. I just want to share the practical experiences of other engineers they have observed.
very good morning
I have a question regarding the synchronization of two power station to grid
we say voltage should be equal but i would like to know what is the % practical voltage difference (tolerance) that can exist between the two system just before the synchronization .
I know other requirements of phase sequence and frequency should also be met. I just want to share the practical experiences of other engineers they have observed.






RE: power station synchronization requirement
Why is there a voltage difference?
If is a phase angle difference, the voltage may be off by 30% or more. Not a good idea but it will quickly correct itself. As long as it doesn't correct so fast that it trips the main breaker, blows a coupling or shears a drive key. I have seen small (350 KVA) machines synchronized with a calculated phase angle voltage difference of 50%. Possible but not recomended.
If the voltage difference is a difference in RMS voltages, there will be a reactive current driven by the voltage difference.
Up to a megawatt or so, if your voltmeters appear to show the same voltage you are good to go. Your voltage error will probably be less than 5%. Close the breaker and then trim the power factor. (By adjusting the voltage setting.)
Frequency. You want the synchroscope needle to be moving slower than the second hand on a clock. The second hand moves at 1 RPM. 1/4 to 1/2 RPM is better for synchronizing.
On 60 Hz that's a frequency error of 0.4% to 0.8%.
Phase sequence must be the same.
Phase angle difference should be within plus or minus 12 degrees. That's between 2 minutes before the hour to 2 minutes after the hour on a clock face. If you close when the synchroscope is at 5 minutes to the hour, you have a 30 degree phase angle and a voltage difference of 50%.
We have a regular who has extensive experience with much larger sets. He will recommend different tolerances. The big sets are less tolerant of errors than the small sets.
Bill
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"Why not the best?"
Jimmy Carter
RE: power station synchronization requirement
10% voltage difference is not uncommon.
It is the frequency difference / phase angle that you want to closely monitor when it comes to generator synchronising with the grid.
In any case, it is important to see that the generator voltage is more than the grid voltage to ensure there won't be pole slipping protection operation the moment you close the circuit breaker (because the generator field is weak)
RE: power station synchronization requirement
If you want to read the whole thread it is here: thread238-233765: Synchronizing Torque.
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If we learn from our mistakes I'm getting a great education!
RE: power station synchronization requirement
Generally I set the phase angle to 3 degrees for a nice stable deisel machine and up to 8 degrees for a gas machine (I'm talking reciprocating machines, not turbines).
Voltage difference, normally I would use a 5% window maximum.
Most modern voltage matching equipment will match within a volt or so (if given enough time and the engine is reasonably stable).
What is just as important as voltage and phase angle is the dwell time.
This is how long the generator output is within the "phase window" before breaker close. Set this too short and a possible crash synch can happen if the engine is unstable.
Stable deisels, can be set anything up to 0.5 seconds, Gas machines usually around 0.3 seconds.
I have used these parameters on dozens of machines with no problems.
RE: power station synchronization requirement
RE: power station synchronization requirement