Questions and Answers
What is the purpose of the additional 50 NB drain provided at the PRDS floor?
Why does the seal steam supply control valve close on interlock?
How often should the steam traps on drains of Aux.PRDS/HT Header/Station HT header/Aux.seal steam line be serviced?
What is the purpose of the continuous draining through the warm up orifice in the Auxiliary Seal steam supply line?
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What should be done if the DP across the jacking oil filter is more than 5-10 KSC even after cleaning?
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What is the minimum temperature of the piping near the orifice in the Turbine seal steam header?
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Why should the orifice size be increased by at least 25 % in the Auxiliary Seal steam supply line?
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What should be done after restarting the unit?
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What action should be taken to ensure the auxiliary seal steam temperature is maintained when the machine is on load?
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During a grid failure, which action is appropriate regarding seal steam supply?
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What should be ensured if the direct source of auxiliary seal steam from CRH is closed?
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What is a critical observation during shutdown when the turbine is on barring gear?
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What should be the rated pressure for auxiliary seal steam when charged through the unit HT aux. steam header?
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During initial start-up when the aux. steam system is unavailable, which alternative is mentioned?
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What happens at higher main steam pressures and temperatures concerning seal steam parameters?
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What should be done during post-barring stalling?
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Study Notes
Actions Needed Under Various Operating Conditions
- Actions required when machine is on load, coasting down, during grid failure/total AC failure, during shutdown, and during startup
- Vacuum killing required in cases where no other unit is available for seal steam supply or when seal steam supply is available from another unit
- Shutdown of unit required when turbine speed slowdown is observed during barring gear operation or when turbine rotor comes to a standstill
When Machine is on Load
- Ensure condensate-free auxiliary seal steam with temperature above 290°C
- Maintain auxiliary seal steam temperature using motorized drain valve MAW-10-A0 41, opening/closing at 285°C/300°C
- If direct source of auxiliary seal steam from CRH is closed/not provided, use Unit HT Aux.steam header and maintain rated pressure (16 kg/cm²) and temperature (320°C)
Initial Start-up and Seal Steam Parameter Maintenance
- During initial start-up, if Aux steam system is not available from other units, use Main steam to charge Aux PRDS and maintain required seal steam parameters
- However, at higher MS steam pressure and temperature, it's difficult to maintain required Aux PRDS and seal steam parameters
- In such cases, CRH Source is to be lined up for HT header and auxiliary seal steam supply (or direct source of seal steam from CRH)
Additional Precautions
- Ensure seal steam supply control valve closes on interlock if seal steam temperature < 250°C or HP shaft temperature > 300°C and seal steam temperature < 280°C
- Ensure all steam traps on drains of Aux.PRDS/HT Header/Station HT header/ Aux.seal steam line are functional and serviced annually
- Check steam traps jointly with TMD & Operation and create a joint protocol
- Ensure continuous draining through warm-up orifice provided in Auxiliary Seal steam supply line, upstream of seal steam control valve
- Ensure orifice size is increased by at least 25% if continuous draining is not effective
Turbine Seal Steam Header
- Ensure continuous warm-up flow through given orifice (Parallel to MAL-81) in Turbine seal steam header
- Use Non-contact thermometer to ensure temperature of piping near orifice is at least 100°C+
- Investigate and correct reasons for low temperature/flow through this line (e.g. line/orifice choked)
After Restart of Unit
- Ensure Jacking oil pump discharge filter has been cleaned
- Ensure DP across jacking oil filter is not more than 5-10 KSC; replace filter element if necessary
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Description
This quiz covers the necessary actions to take when operating a turbine under different conditions, including during load, coasting down, grid failure, and shutdown.