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4
- #1
qcrobert
Industrial
- Jun 24, 2010
- 229
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
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