Synchronous Compensators

Synchronous Compensators are synchronous motors which are run without any load.  These motors are used to generate or absorb reactive power from the system.  Generally located near large loads, these motors, running in the overexcited condition provide reactive power according the the load demand. 

In large transmission lines, the line capacitances generate excessive capacitive line charging current which can lead to a rise of voltage in the system. In such a scenario, the synchronous compensator can run underexcited and absorb the excess reactive power.  This is particularly true in EHV (Extra high voltage systems) where the capacitive line charging is higher than the magnetizing power of the load even during loaded conditions. 

While static reactors and capacitors can be used in reactive power regulation in lines, sychronous compensators have the advantage of quick responses and fine control depending on the excitation. 

In newer installations, static compensators with thyristor controls have replaced synchronous compensators owing to their low maintenance and running costs.

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