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Accident of ABB Generator at Jamnagar, India
4

Accident of ABB Generator at Jamnagar, India

Accident of ABB Generator at Jamnagar, India

4
(OP)
STAY SAFE!!! TRAINING, TRAINING, AND MORE TRAINING!!!!!!!



Accident of ABB Generator (130.5MW) at Jamnagar, Reliance Industries Ltd,
India  

Please find an accident of ABB Generator (130.5MW).It is  good lesson to be
learn, what can go wrong if  isolation and normalization procedures are not
followed. Self isolation may lead to disaster.

Please find below an incident which has lead to the  complete damage of
Steam Turbine Unit.

The main reason for this incident is "CLOSING OF CONTROL OIL RETURN  LINE
MANUAL ISOLATION VALVES FOR SOME MAINTENANCE WORK  AND NOT OPENED AFTER
COMPLETION OF THE WORK".

The generator Exciter end and Turbine end Shaft was  found sheared off and
shaft thrown into pieces. The steam turbine got blasted and all high
pressure/temperature steam hot liquid poured into all  the cables and
auxiliary systems surrounding it. The  scene is entirely like a war Zone.

Findings:
In the control oil (Hydraulic skid) 4 fluid coolers  isolation valves (in
return line) in fluid side were  all found in closed condition. On
investigation, it is  understood that the mech. main. took permit to replace
hydraulic oil in the Control Oil Hydraulic Skid. The  mechanical maintenance
had done their self isolation  on the 4 fluid coolers isolation valves in
fluid side  without informing operation , without  reopening/normalization
(as required) they had cleared  the Permit.

When there was a turbine trip, the fluid could not  drain from hydraulic
operated servomotors. Thus,  obstructing the stop valve closure function.
Due to  pressure build-up in the return line the connector on  drain line
busted and  the stop valves remained  open  even after the trip request
(until the rupture of the  piping connection that acted as drain).Due to the
closed condition of 4 fluid coolers isolation valves  (in return line) the
problem was experienced even  during the  startup before accident. The
control valves  lost control and led to quick speedup (loss of control  and
fast speed up) this resulted in servo valve drain  port pressurization to
abnormal level, thus avoiding  the correct closure & movement of the control
valves.

As per inspection, and also after examination of event  recorder log
indicated all the trip requests were  present, so it was concluded that the
cause of the  accident is located on the hydraulic part of the  control
system, i.e. an improper status of the above  said isolation valves, left
without normalizing after  maintenance work. The defective closure of stop
and  control valves upon trip request has generated a  turbine/generator
over-speed situation (even it was  not possible to establish the speed value
accurately  as speed reached beyond sensing scale, but surely at  least
>4000 rpm) .

Photographs attached
 

RE: Accident of ABB Generator at Jamnagar, India

Thanks qc.  Impressive pics and valuable lesson.
 

RE: Accident of ABB Generator at Jamnagar, India

The Three Mile Island nuclear accident was also related to closing of cooling line valves for maintenance which violated regulation.

When can people learn?

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