We have Alstom Steam turbine with H2 cooled generator with capacity of 400MW with 02 9HA.01 Gas Turbines in CCPP operation.
Problem Statement:
During ST seal oil AC pump change over, DP for ST seal oil system becomes 0 and then returns back after few sec while seal oil pump is running.
For change over both pumps are kept in running and then when one pump is stopped, DP drops to 0 and after few seconds it gets back to normal.
If DP is not maintained at 0.5bars within 15sec then ST trips on Safety of H2 gas leakage.
System Description:
Steam Turbine Generator is H2 cooled and its sealing is ensured by Seal Oil system.
As per design, Seal oil pressure should be 0.5bar above the pressure of H2 inside the generator and to ensure this 02EA self-operated pressure regulators are installed that routes the extra flow back to seal oil tank and ensure 0.5bar DP. There are 02 AC pumps and 01 DC pump (Emergency Pump) installed for the seal oil system.
Some more system details are as follows
Concerns:
1. Is change over method we used is OK since it is not mentioned in OEM manual?
For pump change over activity we perform following steps
2. We have doubts on 02EA pressure regulators slow response. Is there any check recommended. (Please note: During normal running condition, DP is maintained as recommended by OEM at 0.51bars)
I have attached the trend of DP vs Pumps changeover activity.
Problem Statement:
During ST seal oil AC pump change over, DP for ST seal oil system becomes 0 and then returns back after few sec while seal oil pump is running.
For change over both pumps are kept in running and then when one pump is stopped, DP drops to 0 and after few seconds it gets back to normal.
If DP is not maintained at 0.5bars within 15sec then ST trips on Safety of H2 gas leakage.
System Description:
Steam Turbine Generator is H2 cooled and its sealing is ensured by Seal Oil system.
As per design, Seal oil pressure should be 0.5bar above the pressure of H2 inside the generator and to ensure this 02EA self-operated pressure regulators are installed that routes the extra flow back to seal oil tank and ensure 0.5bar DP. There are 02 AC pumps and 01 DC pump (Emergency Pump) installed for the seal oil system.
Some more system details are as follows
- Seal oil pressure DP to be maintained at 0.5bars
- Seal oil temperature to be maintained between 25- 39 Deg C
- If DP reduces to 0.2bars then standby AC pump cuts in and if it is not increased within 5 sec then DC seal oil pump cuts in and if still not increased then ST trips after 15 sec
- If DP increased above 0.8bars, the extra flow is transferred back to either seal oil tank or suction of seal oil pipe via self-operated pressure regulators
- System can handle flow from both pumps because of flow adjusting valves
- IF seal oil system fails, then H2 will be purged from generator and through air extraction ports to air extraction tank to atmosphere
Concerns:
1. Is change over method we used is OK since it is not mentioned in OEM manual?
For pump change over activity we perform following steps
- Both AC pumps in running mode on "Manual"
- One pump is turned "Off" and kept on manual and DP drops to 0.
- DP remains zero while one AC pump is in service.
2. We have doubts on 02EA pressure regulators slow response. Is there any check recommended. (Please note: During normal running condition, DP is maintained as recommended by OEM at 0.51bars)
I have attached the trend of DP vs Pumps changeover activity.
Attachments
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