Voltage Control in Power Plants

Hello everyone

I have some questions regarding voltage control at the level of power plants. Please let me know if anyone has any information about this.

1- How is voltage control done in power plants? Does this happen only by excitation control or voltage regulation, or by changing the tap of the transformer, or by synchronous condenser?

2- In the issue of voltage control in power plants, which is the priority between changing the reactive power of the power plant and changing the tap of the power plant transformer?

Most situations are different, and while many do not require transformers with tap changers some do. In my personal experience, it seems tap changers provide a wider range of adjustment/response to grid conditions, or to captive power plant operation (where the power plant supplies power to a single facility, usually some kind of industrial facility like a steel or aluminium mill or large refinery, etc.).

So, when to change transformer taps is mostly a function of operating conditions and circumstances.

Note that some tap changers can change taps under load (when current is flowing through the transformer). Other tap changers cannot and the transformer cannot have any appreciable current flow when the taps are being changed.

But, in general voltage modulation (variation of or the maintenance of a particular voltage--or reactive current setpoint) is accomplished with the synchronous generator excitation system (often called the AVR, or Automatic Voltage Regulator), or sometimes just the "voltage regulator" or the "exciter." There are plants that operate with a fixed excitation system setting and change taps as the situation requires (though I suspect those are unusual, there are some that do--and, again, the situation dictates that decision/choice).

Lastly, when you talk about "power plants" you must recognize that there are MANY types of power plants. There are large utility power plants, there are small utility power plants (often called "peaking plants"); there are independent power producers (which sell electricty into a market (such as a region of a nation or group of nations); there are combined cycle power plants (which produce electricity and steam for a nearby facility or for heating neighborhoods, etc.). There are all kinds of power plants, hydro-electric power plants, nuclear power plants, fossil-fuel fired power plants, etc. There are also photo-voltaic power plants, and even large wind farms, which have been "described" in some media articles and postings as "power plants." The location and primary purpose of a power plant can have none or many circumstances and scenarios which it may be required to respond to (some parts of the world have very unstable power systems and some power plants primarily try to limit those unstable periods). Synchronous condensers are used when current is not required in an area but some kind of voltage or VAr support is required because of the nature of the load in the area, or the area is remote and not served by any nearby utility power plants.