Fluctuation of MW on 2 turbo-alternators

[SA07]

Hi
We noticed from time to time rapid fluctuations of MW on both our turbo-alternators (45 MW each) which are exporting power on the utility grid. Any idea what may be the cause? Please see attached printscreen on scada. Thanks

 

[LittleInch]

SA07,

You've been here a long time so you must know you need to supply a whole heap more information than one camera phone picture....

for starters what exactly are the different coloured lines?
What are their units?
Powered by?
What have the utility company said?
Did some other large load or generator on the grid trip?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[9wearSuave]

If I am interpreting the units in question being the green and teal plots, it appears the responses are opposing each other. Seems like teal is fighting green Their governor control systems should be tuned by trained professionals to operate in parallel. But like LittleInch mentioned, can't really make any suggestions based on such little information.
Are they sharing a GSU transformer?

 

[waross]

Add a small percentage to the proportional band of the governors?

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[SA07]

Green line = MW unit 2
Pale blue = MW unit 1
Each unit are powered by steam turbine
We are investigating on our side first before contacting the Utility company.
We do not know whether a large load or generator tripped at same time.
Both units are in operation since 2007.
This is a new phenomenon we are observing.
We have just entered summer. Yesterday this phenomenon occurred around 13.30. In the morning, it was sunny. During the day, there were dark clouds. A few days back same phenomenon occurred during the day.
Can this phenomenon be related to photovoltaic?
Our country is a small island MW load 500-600 MW.

 

[waross]

Apart from the noticeable upset, the pale blue line looks pretty rough.
I suspect a problem in your prime mover control.
It may be a governor issue, or it may be a steam valve issue.
Something in the system is developing stiction.
Possibly the packing on a steam valve stem is too tight.
The fluctuations loosen it and it works freely for awhile.
You will probably see the steam valves jittering as this happens.
It could be a lack of lubrication somewhere in some linkage, anywhere from inside the governor to the steam valve.
Not knowing what hardware is in place, I am giving my best guess.
In a diesel engine, a fuel valve controlled by an electrical signal with a spring return will show this action if the valve needs lubrication.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[TugboatEng]

If the thrust washer for the governor weights gets grooves it can become sticky as well. This was a common problem on Cat D398 and 399 engines. I don't know what it was endemic to those engines because they used the same Woodward governors everybody else used.

 

[LittleInch]

What are the units though?

How much does it vary? 1%? 10%?

What happens to the frequency?

What are the the other lines?

Solar drop off can be very dramatic. What sort of percent is solar?

The two seem to start off in opposite directions but then diverge.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[crshears]

Do you have traces of the vectorial power flow sum for all export lines that you can add to the other traces?

This information will be diagnostic in determining whether any power flow bump is being caused by external circumstances.

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[SA07]

Frequency does not change
Other lines are other process parameters which the operators display permanently on their scada screen and monitor them closely. They are not related to power.

Solar production is approx. 5%

Each turbo-alternator exports on each transformer and each transmission line. They enter a utility substation and then each one goes to a different utility substation. That may explain the difference in the curves.

However all the utility substations are connected in a ring. Also the utility company many interconnect both lines so that both units export on a common busbar.

We do not have vectorial power flow.

 

[wcaseyharman]

I can’t provide an answer, but maybe some ideas where to look.
If this were my unit I would be attempting to plot control valve servo current, control valve position, and control valve command. Also would be checking steam pressure and flow.
Electrically I’d look at voltage and frequency /unit speed.

I’d also look at the unit configuration- do these turbines come off a common header or are they totally independent?

We’ve had control valve servos fail that caused MW oscillations or sudden changes in output. We’ve also had CT issues that looked like MW changes but were just bad connections. Lots of possibilities that make us hard to troubleshoot via the internet. Good luck!

 

[doehl1]

We've had units that were at or near a temperature or pressure limit(er) and a faulty sensor, thermocouple, etc was causing the PID control and subsequently the fuel valve to start hunting.

 

[SA07]

There is no permanent fault on our machines. But from time to time we got this disturbance which seems to be due to the utility network.