Dear All,

I have a problem with one of my SGT-300 Turbine.

The Turbine is equipped with the old MK II Control Racks and is synchronized with other Generators at 11KV Bus.

When one of the Generators tripped, all the load went to the SGT-300 and caused a trip. The varistors also got burned at the exciter of the generator side.

We replaced the varistors, started the turbine, and we confirmed that the generator can produce 11KV by providing directly 12VDC Excitation Voltage to the Exciter.

Then we connected back the excitation wires. We noticed that the excitation voltage is not coming out. The Protection Relay has NO Alarm and the AVR NO Alarm either. As per drawing, the excitation to come out, the relays KA5 (Excitation Permissive) has to close. However this is not happening.

We checked that there is a contact command named SS4 (Excitation Permit) from the MK II (SOM module Slot5, Plug 4, Output 3 out of 4), that is not activating.

The question is what is preventing this SS4 command to activate.
Thanks and regards,

George Kaimenopoulos
FMN plc, Lagos, Nigeria
Phone: +2348172115573

 

You may check the speed of prime mover. Usually SS4 is a speed switch and when unit speed reached 95% then SS4 will activate.