Generator Synchronization

Most of the electricity consumed today is produced by three phase synchronous  generator.Since a huge amount of electricity is consumed every day,AC power networks are generally made up of a large number of synchronous generator all operating in the same frequency.

When the power demand increase,additional generator are connected to the AC power network.Before connecting a three phase synchronous generator to an AC power network,the following conditions are to be observed :-

What is generator synchronization?

Important parameter

• Frequency ( Hz ) : The frequency of the voltages produced by the generator must be equal  to ac power network frequency.
• Voltage ( Volt ) : The value of voltages produced by the generator must be equal to the AC power network voltage.
• Phase Sequence : The phase sequence of the voltage must be same at that of the AC power network.
• Phase ( R,Y,B ) : The voltage produced by the generator must be in phase with the AC power network voltages

Generator Synchronize precaution

A generator is said to be synchronized when all these condition are met.A synchronous generator must never be connected to an AC power network before verifying synchronization.

Connecting a non-synchronized generator to an AC power network could cause severe damages to the generator because of the high torque that would be applied to the generator shaft and huge currents that flow in the generator windings at connection.

Once a synchronous generator is connected to an AC power network,no current flows between the generator and the AC power network because they produce voltages having the same amplitude and phase.As a result,the generator supplier neither active or reactive power to AC power network.

In this case,the generator is said to be “floating” on the AC power network.Furthermore,its frequency can no longer be changed by adjusting the tourqe applied to the generator shaft.This is because the AC power network is so powerful that it imposes it own frequency.

However,adjusting the torque applied to the generator’s shaft allows changing the amount of active power that is exchanged between the generator an the ac power.Increasing or decreasing can make the torque increases or decrease the power active to ac power network.

The generator could even receive active power from the AC power network an thus operate as a synchronous motor if the torque applied to the generator’s shaft were decrease to zero

As in three phase synchronous motors,the amount of reactive power that is exchanged between a synchronous generator and the AC power network can be changed by adjusting the field of current.It usually adjusted so that no reactive power is exchanged between the generator and the AC power network.

So that the power factor of the generator is UNITY.This minimizes the line currents and allows the size of the conductor connecting the generator to the AC power network to be reduced to minimum.