GE generator Power system stabilizer

[stratford]

Dear all
On site we have one Ge generator 325MVA 4-pole hydrogen cooled with static excitation system EX2100. One of the features of the excitation system is the Power System Stabilizer. Unfortunately this is not tuned yet. Is it possible to tell me some more theoretical or practical data fro this feature? On the other generator of our CCGT(CCPP) the Steam turbine generator brushless excitation system has its power system stabilizer feature energized.

 

[rmw]

The grid has to furnish to you the tuning parameters that they want your PSS to have for you unit size and location and characteristic(s).

rmw

 

[davidbeach]

I doubt that "the grid" will furnish tuning parameters. The local coordinating council, the WECC in the Western United States, will provide boundary conditions within which the generator must operate. The generator owner will need to perform/hire out the studies necessary to determine the PSS settings.

 

[ScottyUK]

I agree with David - the grid operator will provide a 'must comply with' minimum specification but the actual tuning is pretty specialised. Usually the OEM will have a fairly accurate transfer function to describe both the turbine-generator behaviour and the PSS and can tune the PSS to optimise the overall behaviour of the unit. Somewhere I have some data on older Westinghouse PSS which gives a reasonable if quite mathematical explanation of the PSS operation. It uses discrete op-amps so it is possible to follow the signal path and circuit behaviour. If it would be of use I will try to find it and scan it.


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Sometimes I only open my mouth to swap feet...

 

[rcw retired EE]

GE usually tests and tunes the PSS remotely using a phone or internet link to the EX2000. With the generator on liine, some small step changes are activated. The data is dumped to their engineering offices, number crunched and the optimum settings are calculated.

But if you didn't buy that service, they are very hard to work with.

 

[cuky2000]

PSS could be helpfull to minimize the risk of subsynchronous resonance cause by the system changing impedance such as remote series compensation of interconnected transmission line. In general the PSS could improve the generator transfer power limit if properly adjusted. To be more effective, the PSS should be tuned after complete the setting in the generator excitation control system.

The enclosed link may provide a general overview in this subject

http://www.pge.com/includes/docs/pd...vices/contracts_tariffs/wi_handbook/app_h.pdf

 

[rmw]

Excuse me all to hell for leaving off the word 'operator'. I assumed it would be intuitively clear to the initiated.

rmw

 

[ScottyUK]

Hi rmw,

Was clear to me - we know National Grid plc as 'The Grid' anyway! They still don't tell us what tuning parameters to use, only what they expect the behaviour of the machine to be after we set up the PSS.


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Sometimes I only open my mouth to swap feet...

 

[davidbeach]

I agree with ScottyUK, my point was that the system operator would not provide the tuning parameters, but would only provide operating requirements and it would be up to the generator operator to tune the PSS to meet the operating requirements. The tuning parameters will be different for every prime mover/generator combination but the system operating requirements can be the same across the entire system.

 

[tlr7616]

Tuning of a Power System Stabilizer is something that requires a fair amount of studying, and then some testing of the generator. Typically you will need to simulate the proper PSS model in a transient stability program like PTI or GE's transient stability programs. This presumes you have a proper mathematical model suitable for use by the appropriate software. You adjust the various gains and time constants (etc) in the simulation until you get adequate performance. Basically you model your excitation system with and without the PSS. The PSS should improve damping, etc when compared to the no PSS simulation.

As David points out the transmission system operator you are plugged into should have some guidance for how the PSS behaves--normally it says something like it should be on and properly tuned, probably not terribly helpful! The tuning of a PSS is usually part of the commissioning program for a generator.

As noted by others this service is available from the generator manufacturer as well as consulting firms. It is a non trival thing to do properly, be prepared to pay a fair amount of money for such a study. The software tools required to simulate this are rather costly, both in money and in staying proficient in their use (never mind learning how to use them to begin with).

Given that it is a GE generator I would suggest you contact GE's study folks, they write the PSLF/PSDS software and will certainly be able to help you given that it is a GE machine. Their senior staff can probably suggest PSS settings that will be nearly right on, experience counts for something in this case. By the way, I am in no way affiliated with GE, I just know that gray haired folks are often really helpful. One of those seen it, done it, got the T-shirt things....

 

[Rodmcm]

Our experience is that the transmission system operators are becoming more cagey about supplying settings and are requiring the owner to provide his own transient stability studies. This is expensive, a recent simulation and setting of the pss exceeded $65K from the vendor. The transmission authority monitored the settings, approved them, and then monitored them through the testing phase. This was a very difficult exercise when that the governor tuning characheristics changed during the commissioning which then upset the PSS model which then upset the transmission authority which then etc etc etc.