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Differences Between Droop Base Load & Isochronous?
What is the different between Droop Base Load & Isochronous Base Load system?

What is the different between Droop Base Load & Isochronous Base Load system?

When should we apply for Droop Base Load?

2 out of 2 members thought this post was helpful...

There are *lots* of posts and responses on about Droop Speed Control and Isochronous Speed Control. The search function of is second to none, as has been noted many times before. It takes multiple words, when most site search functions will not.

When you load a unit operating in Droop Speed Control to Base Load, or select Base Load and let the control system load itself to Base Load, it will accept some of the load of the grid to which it is connected up to the rated output of the unit. It will just sit there at Base Load as long as you leave it there. The key thing is that the unit is *NOT* controlling the frequency of its output, the grid is doing that. It's fat, dumb and happy just to put out as much power as it can while not having to worry about the frequency of its output.

Now, a unit operating in Isochronous Speed Control *MUST AND WILL* adjust its fuel in order to make the frequency of its output equal to the frequency setpoint in response to load changes. As people start motors, or turn lights on or off, or start or stop their computers, the load will vary and unless some unit is adjusting its output to put out more or less power *WHILE MAINTAINING CONSTANT FREQUENCY* the frequency will vary all over the place. A unit being operated in Isochronous Speed Control *CANNOT* have it's load adjusted by the operator or any other means; its load is a function of the amount of power required to maintain frequency. So, one cannot select Base Load while a unit is operating in Isochronous Load Control, or even Pre-selected Load. The load of an Isochronous unit will vary in response the number or motors, lights, and computers which are requiring power; it's not something the operator or control system can dictate.

I've never seen this analogy used here before, and it's kind of odd that it hasn't been so let's give it a try. Isochronous Speed Control is like driving a car with cruise control enabled to maintain a constant speed. As the car climbs a hill and then goes down the other side the cruise control mechanism will increase the fuel and decrease the fuel, respectively, to maintain the speed. If the car has several passengers and a load of luggage in the boot and approaches a long, steep hill it might be possible that the output of the car's engine won't be able to maintain speed. The cruise control mechanism is the "frequency" control, and as the load changes the cruise control will respond to try to maintain the speed setpoint. If you were driving that car, how would you increase the output of the engine to maximum (rated) without exceeding the speed setpoint? It's the same for a combustion turbine.

If a unit being operated in Isochronous Speed Control reaches Base Load, then some operator somewhere isn't paying attention to the grid and hasn't started and synchronized enough generators. A unit being operated in Isoch Speed Control should never be allowed to reach its rated power output, because if more motors or lights or computers are started the frequency is going to start decreasing because the unit can't produce any more than rated power (without some special logic and sequencing).

Enjoy your searching! If you have more questions about something you read in the numerous posts, well, that's what we're here for!

This is to inquire that in isochronous mode, will the unit run at rated frequency/speed or will maintain the grid frequency which may be higher/lower than rated?

1 out of 1 members thought this post was helpful...


This is to ask what the load on the Isochronous machine is?

The prime mover of an Isochronous machine (I'm referring to one Isochronous machine on a grid--not multiple Isochronous machines being controlled by some kind of Isochronous load sharing scheme) can only produce rated power output. So, if that's 25 MW and the load on the Isochronous machine has been allowed to exceed 25 MW then it will not be able to maintain rated frequency. By the same token, if the load on the Isochronous machine has been allowed to decrease below 0 MW then the Isochronous machine will not be allowed to maintain rated frequency.

When operating in Isochronous mode, the reference for the prime mover is speed, which is directly proportional to frequency. The speed reference (frequency reference) can be changed, but that usually isn't desirable since, on an AC (Alternating Current) system, frequency regulation is pretty important in order to ensure efficient transmission and distribution and use of the power being developed by the synchronous generator prime movers.

If a machine is somehow being operated in Isochronous mode when connected to a grid with MANY other generators and their prime movers and it's operating stably (the prime mover energy input flow-rate and the generator output are not oscillating wildly or hunting) then if the load on the grid increases to the point that the prime mover of the Isochronous machine has reached its maximum power output then the frequency will start to decrease. It just can't put out any more power to support frequency. The Droop machines will automatically increase their power output--but only as frequency decreases. Operators can increase the power output of one or more Droop machines (presuming they're not already operating at their maximum output) which will help to increase the grid frequency, including the speed of the Isochronous machine.

If I haven't described your situation and answered your questions--please, feel free to explain the circumstances at your site and clarify your question and we'll be happy to try to provide more information. This isn't a simple subject to begin with, and many times the correct answer depends on the circumstances and situation at the site.

i ask about running three power stations on droop mode. each power station has different speed and power of engine. how can do it?


AC power generation occurs at a particular frequency--50 Hz or 60 Hz, depending on which part of the world, or country, you are referring. However, on an AC power distribution and transmission system (a "grid") to which multiple prime movers are generators are synchronized (that's a very important word: synchronized--it's MUCH more than just being connected to a grid with other generators and their prime movers!) EVERY generator operates at the SAME frequency. And the frequency of a generator is dictated by the following formula:

     F = (P*N)/120
F=Frequency (in Hz)
P=The number of poles of the generator
N=Speed of the generator rotor (in RPM)
Now, prime movers (turbines of all types (wind; hydro; steam; combustion (gas)); reciprocation engines; etc.) all run best at a particular speed--which is NOT always the same speed as the generator requires to run at a particular frequency. So, in that case, some kind of gear box is employed to change the prime mover speed to the speed required per the formula above to make the generator run at the frequency necessary to synchronize the prime mover and generator to the grid with other prime movers and generators.

Once synchronized, very great magnetic forces at work inside the generator (I'm referring to synchronous generators) work to keep the generator spinning at the frequency which is proportional to the grid frequency--regardless of how much energy the prime mover is applying to the generator rotor.

If the prime mover is applying only enough energy (torque) to the generator rotor to keep it spinning at synchronous speed (the speed proportional to the grid frequency) the generator output will be zero.

If the generator applies more torque to the generator rotor than is required to keep the generator spinning at synchronous speed (in other words, the prime mover would be trying to increase the generator rotor speed), the generator--which is locked into synchronous speed and can't speed up (or slow down)--converts the extra torque into amperes which is how the generator output increases.

If, the prime mover does NOT apply sufficient torque to the generator rotor to keep it spinning at synchronous speed (in effect, trying to slow the generator rotor) the generator will become a motor and will apply torque to the prime mover in order to keep the generator rotor spinning at synchronous speed. Again--once the prime mover and generator is synchronized to a grid with other prime movers it is locked into synchronous speed--it has to be. No single generator, or group of generators, can operate at any other speed than the speed that is proportional to grid frequency and the number of poles of that generator. A two-pole generator has to turn at 3000 RPM when connected to a 50 Hz grid; a four-pole generator has to turn at 1500 RPM when connected to a 50 Hz grid. And no single generator--once synchronized to the grid--can spin at 50.7 Hz if the grid frequency is 50.0 Hz, nor can it run at 48.2 Hz if the grid frequency is at 50.0 Hz. The formula above determines the synchronous speed of every generator synchronized to a grid. Full stop. Period.

Now, as to how generators of different capacity can connect to a grid with other generators of different capacities--that is accomplished by Droop Speed Control. It is the prime mover mode of operation that allows a generator to be synchronized to a grid with other prime movers and generators and stably contribute to powering the loads (motors and lights and televisions and computers and computer monitors, etc.) connected to the grid. Droop speed control is often said to allow generators to "share" load--and that is a true statement.

Droop Speed Control is how the prime mover governor (control system) controls the energy flow-rate into the prime mover, be it water (for a hydro turbine), or fuel (for a reciprocating engine or a combustion turbine)--and that controls the amount of torque being produced by the prime mover and applied to the generator rotor. And, since the generator converts torque into amperes if the torque being applied to the generator rotor from the prime mover increases the generator will produce more amperes, and the power output of the generator will increase. By controlling the amount of energy flowing into the prime mover the amount of power being produced by the generator can be controlled.

That's the theory in a nutshell. It's no more complicated than that at it's very base. By keeping the energy flow-rate into the generator's prime mover stable the amount of torque being applied to the generator's rotor will remain stable and the generator's output will be (remain) stable. Change the energy flow-rate, the generator's output will change. And that's what Droop Speed Control does--works to maintain a constant energy flow-rate into the generator's prime mover. Plain and simple. The grid is controlling the speed of the generator rotor, and the prime mover is controlling the energy flow-rate into the prime mover.

Hope this helps!