Generator AVR control mode 2

[NickParker]

P.F control mode is a popular control mode at a power plant when connected to the grid.

why not constant voltage or MVAR control? what happens if constant voltage or MVAR control mode is applied?

Thanks!

 

[edison123]

Once connected to grid, the voltage is dictated by the grid, not by the generator. PF control is sorta MVAR control.

Muthu

http://www.edison.co.in

 

[wcaseyharman]

Constant voltage is required in the US for large generators connected to the transmission system. It’s classified as Automatic Voltage Control (AVR). It effectively controls the generator voltage to a setpoint and the VAR output varies with the system voltage. It’s used in transmission to allow generators to respond by increasing VAR output to system low/high voltage events.

VAR control is similar to PF control but can be problematic as the VAR output doesn’t generally vary with load. This can cause low or high voltage issues with the generator when the load is low and the VAR setpoint is high. In most cases PF control makes more sense as it avoids these issues.

 

[Kiribanda]

In my opinion it depends on how much MW & MVARS that I have to export (push) to the grid. It is mentioned in the contract agreement with the Utility.
I can install a 500MW generator tomorrow, but can I export all the 500MW?
If my generator is not supposed to provide any VAR support at the point of common coupling, then I can simply run on the PF=100% mode.
Finally this mode of operation (Constant voltage mode or PF mode) is given by the PSSE studies after connecting the generator to the Utility system.

 

[dpc]

A key factor is the relative size of the generator compared to the grid. Large generators generally run in some type of voltage control mode to help supply vars to the grid and regulate voltage. But for small cogeneration systems, the generator too small to appreciably influence the grid voltage so running in voltage control mode can be problematic. The AVR will alternate between max and min excitation settings for small grid voltage changes. For these smaller units, some type of power factor or VAR control mode is generally used. This is often a point of friction between merchant power plants and grid operators and requirements are often spelled out interconnection agreements.

In island mode, the generator needs to be in voltage control (or at least one of them for multiple units).

 

[waross]

why not constant voltage or MVAR control?

With constant voltage control, the MVAR production will vary as the grid voltage varies.
MVAR control is related to PF control.
Both MVAR control and PF control are implemented by adjusting the AVR output.
In the one case, excitation is controlled by the MVAR output.
In the other case, excitation is controlled by the PF.
MW output is controlled by varying the fuel supply or steam flow and is not related to the AVR setting or output.
Power out plus losses equals power in.

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

 

[RRaghunath]

NickParker,
You are referring to a captive power plant that is meant to supply power specifically to an industrial plant.
Such power plants are operated in PF control mode as the intent is to avoid PF based penalties (by grid authority) for going below the stipulated power factor at the point of interconnection.
Voltage control is typically followed by all large power plants that supply to grid.
MVAR control mode has an advantage that a positive MVAR flow out of the generator is always maintained irrespective of the load / grid and that ensures the generator field is strong. This helps avoid machine going out of step while recovering from an external fault in the system.
MVAR control mode is beneficial when the generator is exclusively supplying a network of distribution lines in an area (it is known faults in overhead distribution lines is more common).