Traditional Hydro-mechanical Governer Load and Speed Motors and Automatic AVR Operation Mode


Thread Starter


Dear all readers

Recently I've encountered a mechanical-hydraulic governor load and speed adjusters (motors), as an vague operation system that made me confused very much.

This governor is a traditional fly-ball governor that has to (load & speed) motors on it.

What do these motors actually do?

How does governor adjust the speed of power plant unit constantly (from no load to full load) for example (200 rpm) and what are the rules of (load and speed)'s motors in this process?

Also I see the Operators after paralleling the generator to the power network with (speed and load selectors on Control Board) try to put load on the generator. They say, they open speed to 100% using speed selector and limit the generator load (P out_real power) and adjust it by load selector. I asked what's the different between load and speed. They say there is no different and do the same things, just two motors on Governor!! Why?

I've found Speed of unit was constant and the Pout generator was constant too.

Now there are question. How does the governor keep the speed and out put Power (real power) of the generator constant while unit is parallel to the network? I see the governor command to the servo motor that opens and close wicket gates.

In no load condition and full load condition what do the load and speed motors do in order to keep the unit speed (from no load to full load) and load (real power) be constant and the philosophy of what do Operators do get load from Generators?

Speed no load = Constant 200 rpm
Speed full load = Constant 200 rpm
Speed constant from no load to full load

Real power of Generator (P out) no load = 0 MW
Real power of Generator (P out) full load = Constant 30 MW

Imag power of Generator (Q out) no load = 0 MW
Imag power of Generator (Q out) full load = [-2 Mvar +12Mvar]

V terminal : [12.2 14] Kv

Also I've found that Operators adjust the reactive power and terminal voltage of generator using AVR selector time to time while AVR was on automatic condition, and it should correct the voltage to the 13.8 KV.
It's my question why do they this? Why doesn't AVR correct it automatically while it's on automatic mode?

Best regards
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Welcome to the world of synchronous generators and control systems! It seems you are new to the industry and to methods which have been employed for decades (more than a century) for control and protection of prime movers (hydro turbines; reciprocating engines; steam- and gas turbines; etc.) and synchronous generators.

The fly-ball governor is the classic governor, and one of the first control "systems" ever used on prime movers. In AC power generation speed control is critical--because frequency is directly related to speed. So, if the speed control of a prime mover is unstable the generator frequency will be unstable. You can find videos of fly-ball governors, and LOTS of explanations of how they work--which is basically by balancing centrifugal forces which change when speed changes against spring tension.

Two topics you have mentioned have been covered MANY times before on speed control, specifically droop speed control, and VAr control. There is a 'Search' field cleverly hidden at the far right of the Menu bar of every webpage. It's suggested you use the Search 'Help' function the first couple of times you use the feature as the syntax is different than most other search engines. But, again, these topics have been covered ad nauseum before and there's not much sense in covering the same territory again.

If you have questions, we have answers. Doubts? That's not our specialty (see the definition of 'doubt' in your Oxford's English Dictionary).

There is one formula you need to remember: F = (P *N)/120. The frequency of a synchronous generator is proportional to the number of poles of the generator (a value which doesn't change when the unit is operating) times the speed of the rotor (to which the poles are attached), divided by 120. When multiple synchronous generators are connected together on a network/grid, they all operate at speeds that are directly related to the number of their poles and the frequency of the grid. That is, ALL generators must be spinning at the proper speed to produce the same frequency--and they are. They are said to be synchronized together. At magnetic forces at work inside the generator keep them all locked in to synchronism together. (Of course, transient conditions can occur when frequency is unstable and other conditions can allow some variations--but they don't usually last long and are out of the norm.)

So, you can investigate synchronous generators, droop speed control, and VAr control for more information. Both in and on the World Wide Web, where you'll find lots of information and videos. Be very, very wary of droop speed control descriptions that talk about speed variations during load changes--they are NOT fully explaining the circumstances and assumptions when making those statements. And, they are not descriptive of real-world operation of generators.

Hope this helps! Remember, we're here to clarify and answer questions; doubts are best dealt with somewhere else.