breaking of coupling

[smitanuj]

we are having 3 turbine generators & 3 diesel generators running in synchronisation. one of the turbine tripped. Due to failure of load shedding the complete bus collapsed.Also the coupling ( shear pin )broke. As per the manufacturer the shear pin is rated for 19 MW load. My total power drawn from the synchronised bus is only 9 mw.
can anybody guide me the reasons of failure so that it can be avoided. we could not find out any.

 

[Alex68]

I think that it could be very difficult to answer without a deep study.
This is a tipical phenomena that could be studied with a program for electromagnetic analisys. Some of the results are the mechanical and electrical torque during the transient. The steady state torque is less than the limit of the shear pin but the transient torque could be much higher.

 

[electricpete]

I think Alex had a good plausible answer. When there is a transient, the machines angles and powers will swing, which certainly could be the cause.

 

[abeltio]

This is no more than some thoughts around what alex68 already stated...
when the turbine tripped, the whole rotating mass was deccelerating, if the generator breaker was still closed for some time (i.e. the gen breaker did not trip with the unit)you are actually feeding reverse power (motorizing) the generator.
If there was a spike in the motorizing power (an impact load) that could have caused the failure of the shear pin.
saludos.
a.

 

[jbartos]

Suggestion to smitanuj (Electrical) Aug 10, 2002 marked ///\\we are having 3 turbine generators & 3 diesel generators running in synchronisation. one of the turbine tripped.
///Do you have generator breakers?\\ Due to failure of load shedding the complete bus collapsed.
///What is the total Generating Capacity and what are individual generator ratings?\\Also the coupling ( shear pin )broke. As per the manufacturer the shear pin is rated for 19 MW load.
///What is the size of the Set?\\ My total power drawn from the synchronised bus is only 9 mw. can anybody guide me the reasons of failure so that it can be avoided. we could not find out any.
///Could you describe the power distribution system? Are all generators connected to one bus, or is there a ring bus?\\\

 

[busbar]

Have you carefully reviewed the dimensional conditions of the shaft and coupling before restart? It seems that scoring could be most undesirable, particularly at the stated power levels.