FREQUENCY-POWER CHARACTERISTICS OF SYNCHRONOUS GENERATOR. FREQUENCY-POWER CHARACTERISTICS OF SYNCHRONOUS GENERATOR
Before considering the requirements for paralleling generators, it is useful to review the frequency-power and voltage-VAR relationships observed with stand alone machines. These relationships hold for all fixed-speed synchronous machines.
Frequency - Power relationship
In order to understand the frequency-power relationship, it is important to try to understand the mechanical system that drives the generator. At no-load, the mechanical system is rotating at the no-load speed, nnlnnl and results in the generation of voltages at no load frequency nflnfl. The speed and frequency are related by the equation for synchronous speed:
When the generator is loaded, power is drawn from the mechanical system and the generator applies a torque which opposes the direction of motion of the mechanical system. As a result, the generator tends to slow down the mechanical system. (In the same way that when you are driving on a flat road and then start to go up a hill, the car slows down).
In a synchronous generator, changing mechanical speed is undesirable, as it results in a change in the frequency of the induced voltages. For this reason, a "governor" is applied to the mechanical system to make the change in speed predictable with power changes. The mechanical governor sets the no-load speed and controls the reduction in speed so that the speed-power relationship is linear:
Tags: FREQUENCY-POWER CHARACTERISTICS OF SYNCHRONOUS GENERATOR, FREQUENCY-POWER CHARACTERISTICS, SYNCHRONOUS GENERATOR, Frequency - Power relationship, governor, mechanical governor