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Excitation Supply of Sync. Motors

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Kiribanda

Electrical
May 6, 2003
697
Hello gentleman,

This question is about the excitation system of MV/HV synchronous motors.

Usually ( what I have seen ) a sync. motor has got

1) A main circuit breaker, which switches the 3-phase a.c. power supply from the bus bars to the motor terminals. This breaker is usually tripped by motor stator protective relay scheme.
2) The second circuit breaker, which takes the same bus bar power supply and gives to the excitation system (brushless or with brushes). This breaker is usually tripped by the excitation protective relay system (e.g. Out of step, Low field current etc).

As a result in any MV/HV switchgear panel two separate breakers are used side by side for this purpose.

Is it absolutely necessary for these two power supply channels to be independent and separate? Is it not possible to use the main breaker as the common switching device to switch both power supply channels at the start and open during a stator or excitation fault?

Regards!:)

Kiribanda
 
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