Governor Control

Hi,

if you are having high amp draws and poor power factor, then you need better droop current compensation installed on each unit's AVR (automatic voltage regulator). Besides speed control, generators require voltage control. Like the other authors suggest having one generator operate in isochronous mode (frequency control) and the other gens in droop speed control (followers) The voltage regulators must be set up in the same way. One of the four 2MW generators should have the voltage droop mode off (this unit sets the voltage of the system grid). The other 3 2MW units should operate in voltage droop mode (following). Using this method you will not get circulating current between generators because the three units paralleled in droop mode will not "push" the voltage up or pull it down. A simple current droop compensation circuit requires a CT (current transformer), a resistor (a load which builds a voltage when current is passed through it, and a transformer (basically an amplifier) to boost that ac voltage formed on the resistor. This circuit is installed on each generator and a switch can short the CT current effectively disabling droop compensation. Also the output of the transformer is connected in series with the voltage sensing of the AVR voltage regulator. Depending upon the direction of the current the voltage sign either adds or subtracts from the nominal sense voltage. Thus this negative feed back circuit protects each generator against high circulating current (over current tripping)and poor PF power factor etc.

Hope this helps.
Len Howe AET Avionics.
My e mail is lenhowe at cintek dot com.
 
Regarding droop/ischo..

When 3 generators are running in parallel and if we adjust the droop setting for one particular generator, what are the changes occurs in this situation?

I mean does it applies to all running generators or to that particular unit only?

thanks for the elaborate description about droop and isocho that was really helpful.
 
arun,

Okay, ....

Under your scenario with three gen-sets operating in parallel, one in Isoch and the remaining two in Droop, if you change the Droop setpoint of one of the Droop machines the load of that Droop machine will change <b>AND</b> the load of the Isoch machine will also change by an amount equal and opposite to the load change on the Droop machine.

Let's say this is the configuration:

Unit 1: 10 MW machine, operating in Isoch control at 5.0 MW
Unit 2: 4 MW machine, operating in Droop control with 4% Droop, at 2.0 MW
Unit 3: 5 MW machine, operating in Droop control with 5% Droop, at 5 MW

So, the total load on the system is (5+2+5) 12 MW and the load is relatively stable at this time.

Now, this means that the Droop speed reference for Unit 2 is 102%, and the Droop speed reference for Unit 3 is 105%. (Unit 2 is operating at half of rated capacity, so the Droop setpoint is half of rated, which is half of the possible 4% Droop, or 102%. Unit 3 is operating at full rated capacity, which is the full 5%, or 105%.) the Isoch machine, Unit 1, is operating at 50% of rated capacity but the speed reference is 100.0% because it is controlling frequency.

Now, if the operator lowers the speed reference of Unit 3 by 1%, from 105% to 104%, the load of Unit 3 will drop to 4.0 MW. Unit 1's governor, sensing the drop in frequency as the load of Unit 3 is lowered will <b>Increase</b> its output to 6.0 MW, and the frequency will remain stable at rated. Unit 2 will remain unchanged at 2.0 MW. The load on the system is unchanged at 12.0 MW, but now Unit 1 is supplying 6.0 MW, Unit 2 is supplying 2.0 MW, and Unit 3 is supplying 4.0 MW.

If the operator then increased the Droop setpoint of Unit 2 to 103%, the load of Unit 2 would <b>increase</b> to 3.0 MW, and the load of Unit 1 would <b>decrease</b> to 5.0 MW. The load of Unit 3 would be unchanged at 4.0 MW, and the total load on the system would still be 12.0 MW at rated frequency.

Does this help?
 
Very useful and clearly explained information on this thread. Now I have a question: how this theory applies in the case we have inverters (powered by photovoltaic panels or by batteries) in parallel with diesel and/or steam generators?

The concept of frequency control in droop and isochronous mode is the same? What about the isochronous load sharing? Can 2 inverters be in parallel and do load sharing (the same as 2 generators in parallel both in isochronous mode)?

Thanks in advance!
 
R

Ramon Villasana

Hi Markvguy.

I have been following your statements, replies and comments on queries about generation plants control practice and it seems to me that you are a perfect teacher, making thing and statements as clear and simpler as posible, without loosing depth.

<b>Moderator's Note:</b> Markvguy no longer posts on this forum. We do however have some great people who post here.

I am a Spanish speaking teacher (Venezuelan) on electric power systems and I am sure any electric power engineering student can follow your explanations without too much effort. Than you. If you have a blog, or a webpage where you post your experience and knowledge on various issues on Power Systems or power plants I will like to have access to it and I am sure my students, too. Please send any information.

Thank you
 
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