Operation modes of Alternator or generator – Grid mode & Island mode

An alternator or generator generates power might be used to supply either two purpose. The first is to supply power directly to the load or to consumer. The second one is to supply power to the grid. As example in case of power plant or power station several alternator supplies power to the grid, there is no direct consumer.

Operation modes of Alternator

When the alternator supplies power to the load or consumer directly, the criteria of the load affects the alternator. We cannot control the load (KW or MW) and power factor but the terminal voltage and frequency can be controlled. This is called ISLAND mode.

When the alternator is connected to the Grid, in fact synchronized with the grid- alternator swings with the grid. The frequency, voltage we cannot control but the load in KW or MW supply we can control. This is called GRID mode.

So the operation mode of alternators primarily divided in to two general group. One is Island mode and the second is grid mode.

How to control power factor output of an alternator in Power Plant

We can control power factor in a power plant easily. In a power plant the alternator set is supplying power to the grid independent of load. Thus in this case there is no load connected to make the power factor lagging or leading, we are left to control the power factor.

Modern power plant control system has automatic system of changing the power factor by just a command. But how this happens internally is fact to think about.

  

Say an alternator in a power plant is generating 8.5 MW active power and 6.5 MVAr under .85 power factor. The power factor is the ratio of two power active and reactive. Low power factor means reactive power is high & high power factor means active power is high.

Basic of Power Plant Automation System

Power plant Automation system is the complete solution of safe and efficient operation. In a power plant there are lots of complex system required to work and more complication is that this system are inter related. Not only interrelated, they are required to follow exact time sequence in operation. Say in a heavy oil power plant- the engine run by HFO, at the same time there are at least dozens of direct process need to smoothly operate.

The recognized facts & parameters are – pressure of fuel supply, temperature of fuel, engine cylinder temperature, engine lube oil temperature & pressure, cooling water temperature in different location, engine speed etc.