OBJECTIVE
• To roll and soak the turbine at rated speed.
• To synchronise the machine and achieve the block load.
PRE- REQUISITES & STATE OF PLANT
1. Work permit on various generator side equipments such as exciter, AVR, field breaker, generator transformers, unit auxiliary transformers, etc., cancelled and men, material are removed from these area.
2. The line up for the turbine rolling is done.
3. The switchyard 400 KV buses are charged with bus coupler close.
4. The main steam parameters are available and HP / LP bypass in service.
5. All the lockout relays in the generator protection panel are reset.
6. A minimum of three / four pulverisers are available to be taken into service.
7. Steam driven BFPs are also available.
8. Hydrogen pressure is adequate( 4.0 Kg/cm2 ) and spare bottles are available.
PRE-START CHECKS AND LINE UP
1. Check the excitation not blocked, signal is available in the control panel.
2. Check that the load limit is greater than 50 MW.
3. Check that hot reheat and cold reheat drain valves are open
4. Ensure that main generator voltmeter selector is not in off position.
5. Check the operation of Gen. Transformer tap position selector.
6. Close the 400 KV generator - 6 bay’ main bus -2 line isolator (SEM - 6004) from switch yard .
7. Ensure the Earthing switch ( SEM - 6008 ) is in open condition from switch yard .
8. Close the 400 KV generator -6 bay’ breaker, incoming isolator (SEM-6006).
9. Ensure all other isolators are in open condition.
10. Line up the G.T. cooling water circuit from local .
11. Switch on the generator transformer control supply for all the three phases from local Ensure that exciter air cooler isolating, hydrogen cooler isolating, stator water coolers are charged
12. Switch on the control supply for both the unit auxiliary transformers by changing the status
13. Ensure that GT/UAT cooler control system is in lined up condition 14. Ensure that speed reference set point is zero.
15. Ensure that turbine is kept on turbine follow mode with the minimum load limited about 100 MW on the coordinated control system insert.
16. Ensure that trip oil pressure and start up oil pressure values are normal OPERATIONAL STEPS
1. Raise the starting device slowly to about 42 % .
2. Ensure that start up oil pressure has decreased and at about 42 % of the starting device position the HP stop valves open.
3. Further raise the starting device position to open the hot reheat stop valves.
4. Checks the temperature of the turbine stop valves at 50 % depth and control valve temperature at 50 % and 100 % depth from TSE recorders.
5. Keep the warm-up controllers in auto mode. The output of the controller will modulate to maintain the TSE margin for stop valves.
6. Raise the starting device position to about 80 % and check that secondary oil pressure has build to open the control valves.
8. Ensure the pressure controller deviation is on positive side.
9. Ensure that drum level is on lower side to avoid sudden swing which may cause water carry over.
10. Raise the speed reference to about 360 RPM from UCB.
11. Check the uniform opening of control valves and turbine acceleration rate.
12. Ensure that gate valve gearing has closed when turbine speed exceeds 240 RPM.
13. Check that ‘Jacking oil pump’ has switch off at speed of about 540 RPM 14. Check all the bearing temperature rise and bearing vibrations to be normal.
15. Check the thrust bearing temperature and the differential expansions.
16. Soak the turbine at the soaking speed till the HP shaft temperature at 50 % depth (Calculated) reaches to about 1800C with respect to existing main steam temperature as per the X curves.
17. Check the TSE margin for various channels. First it will reduce and then gradually will increase once the difference between surface and mean temperature reduces.
18. Raise the speed reference to 3000 RPM in one stroke.
19. The turbine speed starts increasing opening of IP control valves can be seen at this stage.
20. At speed of about 2960 RPM the AOP should be switched off as main oil pump takes over (ensure that SLC for all the oil pumps are on).
21. Soak the turbine at 3000 RPM till IP shaft mean temperature (50 % depth) with respect hot reheat temperature as per the rolling X curves is satisfied.
22. Check that a minimum of about 30 K margin should be available before unit is to be synchronised.
23. Close the generator field breaker from AVR console.
24. Raise the AVR set point to build the Generator voltage to about 21.5 KV
25. Match the auto and manual set point of the AVR and transfer the AVR to auto mode.
26. Ensure that load controller is on with load gradient kept at 20 MW/min.
27. Turn on the synchroscope switch to check mode. All the meters showing incoming and running voltage and frequency energises. The synchroscope rate of rotation reflects the difference between incoming and running frequency.
28. Adjust the voltage so that incoming and running voltage values are same.
29. Adjust the turbine speed so that synchroscope is slowly rotating in clockwise direction showing incoming frequency is slightly higher than grid.
30. Check the breaker closing permissive green lamp glows once synchroscope is between 11 to 12 O’clock position.
31. Close the generator breaker when Gen. breaker closing permissive green lamp comes. The synchroscope indicator locks at the 12 O’clock position. The generator breaker closed red lamp comes on.
32. Immediately raise speed reference to pick up the load on the machine to avoid reverse power trip or low forward power trip.
33. Increase the load as per the TSE margin and at the earliest close HP/LP bypass valves.
34. Ensure that warm-up controllers have closed, otherwise close them manually.
35. Close all the drains which were opened during rolling.
36. Turn off the synchroscope switch to de-energise the synchroscope.
37. Check that Prlim value slowly increase. Also ensure that load reference set
38. Observed that change over from speed controller to load controller takes place once output of load controller is greater than that of speed controller. The load controller active facia glows on the insert.
39. Raise the starting device position to 100 %. Check the increase in auxiliary secondary oil pressure. Also ensure that tracking device is switched on.
40. Increase the load limiter value to about 150 MW from insert
41. Check the generator slot,core, exciter air and hydrogen cold gas temperatures 42. Check from the multipoint selector switches, generator stator core temperature.
43. Raise the HP bypass pressure set point to about 160 Kg/cm2 and temperature set point to about 3400 C to avoid HP bypass opening on auto.
44. Ensure that LP bypass stop valves and spray valves have closed fully.
* Unit synchronised with load controller in service *