INTRODUCTION TO HP LP BYPASS SYSTEM, ITS COMPONENTS AND OPERATION PROCEDURE HAVE BEEN STUDIED IN THIS KNOWLEDGE SHARING SESSION

1. HP LP
BYPASS SYSTEM
NTPC TANDA STAGE-1
RAVI PAL SINGH
OPERATION GROUP-D

2. LAYOUT
1. Introduction
2. Components
3. Operation
DISCLAIMER
Only HP LP Bypass system has been studied here. Due to time constraint and for sake of simplification, all other
operation activities to be performed are not discussed here.

3. HP LP
BYPASS SYSTEM
INTRODUCTION

4. WHY BY PASS SYSTEM IS REQUIRED ?
BOILER TURBINESTEAM
HOT HOT
NORMAL RUNNING

5. BOILER TURBINECOLD STEAM
WHY BY PASS SYSTEM IS REQUIRED ?
COLD HOT
LIGHT UP AFTER SHUT DOWN
BYPASS SYSTEM REQUIRED FOR MATCHING LIVE STEAM AND TURBINE METAL
TEMPERATURE. ITS MAIN JOB COMPRISES TO ROUTE STEAM FROM THE MAIN STEAM LINE
TO THE COLD REHEAT LINE OR FROM THE HOT REHEAT LINE TO THE CONDENSER.

6. HP LP BYPASS SYSTEM
REHEATER
MAIN STEAM
CRH HRH
HP
BYPASS
CONDENSER
LP
BYPASS
HP
TURBINE
IP
TURBINE
TURBINELP

7. WHEN BYPASS SYSTEM IS REQUIRED ?
1. DURING START UP OF BOILER (COLD, WARM, HOT START UP): The Bypass system valves
keeps the pressure and temperature of steam supplied to turbine within permissible limits.
2. WHEN FLOW IS NECESSARY THROUGH REHEATER: During startups flow through Reheater
coils is necessary to prevent damage due to high temperatures(>4500) in Goose neck area.
3. DURING START UP OF TURBINE: The rolling of turbine when the turbine control valves are
only partially opened, bypass system valves facilitate circulation of remaining steam from
boiler directly to condenser.
4. DURING NORMAL OPERATION: The Bypass system valve ensures that the steam pressure
inside the boiler as well as inside the main stream line does not exceed the maximum
permissible value. It dissipates the excess steam in case of abrupt changes in output, which
might be due to sudden tripping of turbine or load shedding, and also absorbs pressure
peaks.

8. FUNCTIONS OF BYPASS SYSTEM
FUNCTIONS OF HP BY PASS SYSTEM
1. To establish flow at the outlet of super heater for raising boiler parameters during
startup.
2. To maintain or control steam pressure at preset valve in main steam line during startup.
3. To warm up steam lines.
4. To control steam temperature down steam of HP By Pass at the preset value.
5. To dump steam from boiler into condenser in case the generator circuit breaker opens.
FUNCTIONS OF LP BY PASS SYSTEM
1. Control of steam after Reheater.
2. Establish flow of steam from reheat line to condenser by its opening, proportional to the
opening of by pass valve.
3. Release of stem entrapped in HP and Reheater circuit in case generator circuit breaker
opens.

9. HP LP
BYPASS SYSTEM
COMPONENTS

10. TEMPERATURE CONTROL
SPRAY VALVES
TEMPERATURE CONTROL
SPRAY VALVES
HP BYPASS SYSTEM AT NTPC TANDA STAGE 1
MOTORISED ISOLATING VALVE
PRESSURE CONTROL
VALVE

11. HP BYPASS SYSTEM AT NTPC TANDA STAGE 1
HP BYPASS MOTORISED
ISOLATING VALVE
HP BYPASS PRESSURE
CONTROL VALVE
HP BYPASS TEMEPRATURE
CONTROL SPRAY VALVES
LOCATED NEAR BFP#A AT 06 METER ELEVATION

12. HP BYPASS PRESSURE CONTROL VALVE
Model : ARS 80
Pressure : 139 ksc
Temperature : 540 degrees
Pressure Drop : 128 ksc
Steady Flow : 130 TPH

13. HP BYPASS TEMPERATURE CONTROL VALVE
Model : E 22 S BD
Pressure : 180 ksc
Temperature : 170 degrees
Pressure Drop : 57 ksc
Steady Flow : 19 TPH
Model : E 22S
Pressure : 123 ksc
Temperature : 170 degrees
Pressure Drop : 26.5 ksc
Steady Flow : 19 TPH

14. LP BYPASS SYSTEM AT NTPC TANDA STAGE 1
MOTORISED ISOLATING VALVE
PRESSURE CONTROL
VALVE
TEMPERATURE CONTROL
SPRAY VALVE
MOTORISED SPRAY
ISOLATING VALVE

15. LP BYPASS SYSTEM AT NTPC TANDA STAGE 1
LP BYPASS MOTORISED
ISOLATING VALVE
LP BYPASS PRESSURE
CONTROL VALVE
LP BYPASS TEMEPRATURE
CONTROL SPRAY VALVES
LOCATED NEAR HP
TURBINE AT 09 METER
ELEVATION
LOCATED NEAR MOT
COOLERS AT 05 METER
ELEVATION
LP BYPASS MOTORISED
SPRAY ISOLATING VALVE
LOCATED NEAR CW#A2
O/L PIPE AT 05 METER
ELEVATION

16. LP BYPASS PRESSURE CONTROL VALVE
Model : NR 64 300
Pressure : 13.75 ksc
Temperature : 540 degrees
Pressure Drop : 4.35 ksc
Steady Flow : 150 TPH

17. LP BYPASS TEMPERATURE CONTROL VALVE
Model : NR 100 80
Pressure : 24 ksc
Temperature : 45 degrees
Pressure Drop : 1 ksc
Steady Flow : 44 TPH

18. HP LP BYPASS OIL SUPPLY UNIT

19. HP LP BYPASS OIL SUPPLY UNIT
LOCATED BETWEEN MOT COOLER AND CENTRIFUGE MACHINE AT 00 METER ELEVATION

20. HP-LP BYPASS OIL SUPPLY UNIT PANEL
IN UCB
OPERATE THIS TO
SWITCH ON HP LP
BYPASS OIL SUPPLY
UNIT MOTOR
MOTOR IS ON
OIL PRESSURE
ADEQUATE FOR
OPERATION OF
VALVES

21. HP-LP BYPASS CONSOLE AT NTPC TANDA STAGE 1

22. HP LP
BYPASS SYSTEM
OPERATION

23. PREREQUISITES
1. Boiler is lit up.
2. Drum pressure is at least ~20 ksc and in rising trend.
• During cold startup use Oil firing to steadily raise drum pressure upto 20 ksc and when it is
in rising trend HP LP Bypass can be operated.
• During warm and hot startup use oil firing and if drum pressure is equal to or more than 20
ksc and in rising trend HP LP bypass can be operated.
3. Boiler Stop valves MSM 1A and MSM 1B are open and MS line is charged.
4. Turbine is on barring.
5. CW lines of condenser is charged.
6. HP sealing is charged from PRDS and maintain pressure at 500 mmwcl and temperature 260°C.
7. LP sealing is charged from PRDS and maintain pressure at 1000 mmwcl and temperature 160°C.
8. Vacuum puling is complete and condenser vacuum is steady at less than -0.850 ksc.
9. LP Exhaust hood spray is charged.

24. HP-LP BYASS CONSOLE OPERATION
1. Start HP/LP bypass oil supply unit pump.
2. Wait for Adequate Oil pressure indicator to be ON. Thereafter proceed to next step.
3. Open HP Bypass motorized isolating valve HPBM-17.
4. Open LP Bypass motorized isolating valve LPB-16.
5. Open manual isolating valves of LP Bypass temperature control spray valve.
6. Open LP Bypass temperature control motorized isolating valve LPB-12.
7. Now operate HP Bypass, LP Bypass pressure control valves and LP bypass temperature
control valve from HP LP Console in OPSTN.
8. LP bypass temperature control valve is fully opened.

25. HP LP BYPASS CONSOLE OPERATION
RAISE COMMAND WILL REDUCE MS PRESSURE AND INCREASE RH PRESSURE

26. HP LP BYPASS CONSOLE OPERATION
RAISE COMMAND WILL REDUCE RH PRESSURE AND INCREASE LPBE TEMPERATURE

27. HP LP BYPASS CONSOLE OPERATION
RAISE COMMAND WILL REDUCE LP BE TEMPERATURE

28. HP LP BYPASS CONSOLE OPERATION
OPERATE BP AND L-BP TO MAINTAIN MS AND RH PRESSURE AND TEMPERARUTERS

29. HP LP BYPASS CONSOLE OPERATION
MP TOP
TEMPERATURE
MS
TEMPERATURE
HRH
TEMPERATURE
MS PRESSURE HRH PRESSURE
<2000C 300-3200C 260-2800C 35KSC 5-10KSC
200-2700C 320-3600C 280-3400C 35KSC 5-10KSC
270-3500C 360-4300C 340-4100C 35KSC 5-10KSC
350-4000C 430-4700C 410-4500C 50KSC 5-10KSC
400-4300C 470-4900C 450-4700C 80KSC 5-10KSC
430-4500C 490-5000C 470-4900C 90KSC 5-10KSC
1. Operate HP Bypass, LP Bypass pressure control valves and LP bypass temperature
control valve from HP LP Console in OPSTN to gradually reach MS HRH Pressure upto
mentioned in table below.
2. By maintaining flow in HP LP Bypass gradually reach MS and RH Temperatures as
mentioned in table below.
3. If MS and HRH temperature rise is fast or more then as given in table below, control
temperature by using fuel firing and Burner tilt. This will cause delay in rolling.
4. When all parameters have become stable prepare Turbine for rolling.

30. SKODA TURBINE CONTROL CONSOLE

31. SKODA TURBINE CONTROL CONSOLE

32. HP LP BYPASS CONSOLE OPERATION WITH
ROLLING
1. Ensure turbine is in speed control mode in Skoda OPSTN.
2. Reset the turbine.
3. Press Latch button on Skoda OPSTN to open the stop valves.
4. Ensure Turbine speed remain steady 63-64 RPM.
5. Roll the turbine up to 1200 rpm by pressing Auto Button on Skoda OPSTN Speed control
Block. During this control valves will open, hence accordingly increase fuel firing or
operate HP Bypass, LP Bypass pressure control valves to maintain MS and HRH
pressures.
6. Closely monitor turbine bearing vibrations and eccentricities for any abrupt spikes.
Monitor differential expansion of turbine to be within limit as below:
• HP DE : +3.5 MM TO -1.5 MM (control by MS Temperature)
• MP DE : +3.5MM TO -1.5 MM (control by HRH Temperature)
• LP DE : +4 MM TO -2 MM (control by condenser vaccum)

33. HP LP BYPASS CONSOLE OPERATION WITH
ROLLING
7. Keep rolling on 1200 RPM to until HP/MP turbine expansion stabilizes. Required values are for
rolling to 3000 rpm are as below:
8. Roll the turbine up to 2998 by pressing the Auto button once again on Skoda OPSTN Speed
control Block. Once again control valves will open, accordingly increase fuel firing or operate
HP Bypass, LP Bypass pressure control valves to maintain MS and HRH pressures.
9. Closely monitor turbine bearing vibrations and eccentricities for any abrupt spikes.
10. Keep rolling on 2998 RPM to until HP/MP turbine expansion stabilizes. Required values for
synchronization are as below:
11. When all parameters have become stable prepare to synchronize the machine.
TYPE OF STARTUP HPOE MPOE
COLD STARTUP 10 MM 04 MM
HOT/WARM STARTUP 20 MM 10 MM
TYPE OF STARTUP HPOE MPOE
COLD STARTUP 14 MM 07 MM
HOT/WARM STARTUP 20 MM 10 MM

34. HP LP BYPASS CONSOLE OPERATION WITH
SYNCRONIZATION
As soon the machine is synchronized Turbine control valves will be opened rapidly, to
raise load around 15~20 MW. Hence operate the HP LP bypass as below:
1. Just after synchronization immediately close LPBP pressure control valve and there
after LPBP motorized isolating valve.
2. Close LPBP spray control valve, its motorized isolating valve, LP Bypass spray and
exhaust hood spray manual valves in local.
3. Gradually close HPBP control valve keeping MS Pressure, load constant. When the HP
BP control valve is closed fully then close its motorized valve.
4. Switch off HP LP Bypass Oil Supply Unit Panel.

35. MERITS OF HP LP BYPASS SYSTEM
1. It cuts down unit startup time.
2. It allows boiler operation during short turbine trips.
3. It gives smooth warm up of boiler components, including Reheater. A most rapid
boiler run-up may be possible. It saves fuel.
4. It enables the boiler to take up heavy rejection trip to house load operation
advantageously.
5. It allow better matching of boiler and turbine parameters.
6. DM Water loss during startup is minimized during start up and sudden load shedding.
7. Independent operation of boiler is achievable.
8. To prevents frequent flowing of safety valves.

36. THANK YOU