Dear gentlemen:

Actually I am working in a private power plant (steam turbine Generator) which produced power and steam to petrochemical plant
Generator load max = 120MW
Frequency = 60Hz
GIS 110Kv

We are connected to the grid with two line 110Kv.

During the last three months we observed that there is something strange, our Steam turbine generator are in Load limiter mode and we faced some perturbation that the of the five STG changed around 4MW each that is mean 16MW total and this change only fluctuation for a couple of seconds and then it normalized.

After investigation I found that only the excitation current of all STG’s changed in the same time and then we have this fluctuation in load but there was no changes in steam flow or Governor valves opening or also frequency.

For your information, the partner have a synchronous motor which consume around 20MW, and during changeover of mol sieve bed there was also changes in the (MAC) synchronous motor load but not a big fluctuation.

My question is why all generators load changed for a short period of time while we are on load limiter mode, and what are the causes.

Thanks

 

Is the MVA remaining constant with the VARS and MWs changing?

 

There is a small changes in VAR (from 45MVAR to 44.86MVAR) and the Apparent power There is a changes, but The excitation current was decreased for all generators.

 

Dear

I checked the excitation current it was decreased a little bit decreased during MW increase which is for me strange and also power factor is the same

 

What was happening to the frequency during this event?

The power produced by a generator is directly proportional to the amount of torque being applied to the generator by the prime mover driving the generator.

However, if the frequency is fluctuating when load control is selected that could be causing a problem. You say a very large motor was changing load at the same time. If the grid frequency was also unstable at the same time, and if the load limiter was active that could explain the problems you are describing.

But, really, there's a lot of information we don't know about your site and how it's controlled and operated so it's very difficult to say for sure exactly what happened.

 

What is the THD (total harmonic distortion)?