Generator Problem

[sjvanhecke]

I have a Steam Turbine generator at a garbage burner that is having load fluctuation problems it fluctuates from 16MW to 1 MW for what appears to be no reason at all. This occurs about every minute. The generator is about thrity years old and the stator has been rewound. Any input on this problem would be helpful.

 

[RRaghunath]

This appears to be Turbine governor problem (nothing to do with generator).

 

[ScottyUK]

I'd concur with rraghunath. Most likely source is an unstable governor valve controller. If the swings are as severe as you say, you should be able to see the governor valve moving, or see surging on the steam flow instruments.



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

 

[xabproject]

What kind of load are you connected with - type, magnitude of load with respect to the Gen rating, in-parallel with utility or islanded?
Your Gen is ofcourse old. But is your turbine also that old?

 

[sjvanhecke]

The swings are actually between 1MW and 600kw every minute. The steam pressure valve does not seem to be moving at the time output changes. The governor has been checked, the exciter has been checked and the mainline steam pressure does not seem to change. It baffles the mind. Again any help would be good.

 

[rbulsara]

Although I am not a turbine expert, the clarifications to the following questions may help others to post more helpful responses:

Is this unit running in parallel with other units or the utility grid?

Is the 1MW-600kW amount of the swing in power (deviation) or the total load on the turbine? I read your post as it is the total load.

If in paralllel with other system, many other items such as load share module, AVR etc. may play a role.

What was the steady load before this fluctuations started happening?

How old is the installation?

 

[ScottyUK]

Can you confirm the magnitude of the load swing: your initial post refers to swings of 16MW (sixteen megawatts) to 1MW (one megawatt), and now we are discussing swings of 400kW? I'm somewhat lost!

Please post a bit more info on the nature of the load on your generating set, the grid connection if present, and the rating of the generating set in terms of voltage , power, etc.



------------------------------

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

 

[Rodmcm]

It is possible that the droop on the governor is not set wide enough. External swings of load would cause a movement in the power delivered by the generator
What sort of system are you connected to?

 

[sjvanhecke]

To answer some of the questions. This is a small power plant, so they are tied directly to the grid. The installation was originally installed in the fifties, but ther have been upgrades since then. The output goes from 4MW to about 3MW all at once and takes about a day to recover. The voltage remains constant. The unit is rated for 5MW at 12470 volts line to line. I hope this helps.

 

[ScottyUK]

Rodmcm may have found the problem: does your governor have a droop characteristic? Is it enabled?

If the unit is running without a droop characteristic enabled i.e. it is configured as an isochronous machine for islanded operation even though it is tied to the grid, this would account for the load variation you are seeing.



------------------------------

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

 

[Sackeyfio]

I agree with Rodmcm and ScottyUK. The droop setting is responsible for load sharing in a grid.
If your droop setting is lower compared to other generators on the grid, then your gen will take proportionally a bigger chunck of any load change on the grid.

If it has no droop setting then it is isochronous and for that matter it should not be tied to the grid but rather be isolated to feed its own load.

 

[abeltio]

if the load is swinging like you describe... there are several items to look at:
1. grid frequency. is it stable? this is a very small generator so if the grid frequency is swinging it may be the dog wagging the tail.
2. control valves: are they following the load?
3. steam vacuum? is it constant?

the only way to troubleshoot load swings in a feedback system like a steam turbine control... is to open the loop.
one way to do that is to open the line breaker (house load or "island" operation) and see what happens.
HTH



saludos.
a.

 

[marada93]

If you have a control valve or governor malfunction, and load is truly swinging as you say, then this would have a ripple effect over other plant systems. Steam flow/pressure swings would be apparent, as would drum level swings. For instance, I've experienced a broken valve stem that caused rapid load swings on an Alstom turbine-generator, but load wasn't the only thing swinging.

If boiler pressures, steam flow, and drum level seem unaffected, then I suspect instumentation. If you are experiencing boiler transients as well, look for a broken valve stem. You'd need to be on the turbine deck when the transient is happening.

 

[sjvanhecke]

Thanks for your help everyone, I have a few more notes concerning this problem. The plant has 3 generators, (2) 13.5MW units, and this 25MW unit (I dropped the 2 and accidentally put 5MW earlier). The twin 13.5MW units are stable, but the 25MW unit is constantly moving about 1 MW every minute. The 25MW unit swings even if the two 13.5MW units are offline. All 3 generators are, ofcourse connected to the grid, and they all individually sustain their own load (their boiler feed pumps, ID & FD Fans, etc.). I hope this helps, I appreciate the feedback.

 

[Rodmcm]

I would still think that it is a governor problem.