HPLP bypass HPLP bypass HPLP bypass ET 2010

1. HP LP BYPASS SYSTEM
Presented by
A S GUPTA BE,MBA,BOE,EA,IPMA-D
Supdt(O)

2. HP & LP BYPASS SYSTEM
Purpose
 Primarily meant to enable Boiler operation independent of
the turbine
 Opening o HPBP & LPBP Valves ensures minimum steam
flow through superheater & reheater tubes during start-ups,
low load operation & sudden unloading of unit
 Utilized or building up of steam parameters quickly before
starting of the turbine online
 Avoiding the boiler trip on Reheat protection
 No steam flow through Boiler steam tubes will lead to
starvation & thereby overheating and lead to premature
failure of tubes

3. HP & LP BYPASS SYSTEM

4. HP & LP BYPASS SYSTEM
 Provides the alternative path for boiler operation
 HP Bypass dumps steam into CRH inlet of reheater
 LP Bypass bypasses IPT & LPT and dumps steam into
condenser
 The capacity of HPLP bypass is 60% of full load turbine
steam flow
 Reduces chances of opening of Boiler safety valves at
raised steam pressures

5. REHEAT PROTECTION
RH protection (delay=10 sec) will act if
 TURBINE HP V/V & HPBP CLOSED [ either turbine
HP stop v/v or HP CV in both HP line closed ] & [
both HP BP <2%] OR
 TURBINE IP V/V & LP BP closed [ Either IP stop
v/v or IP CV v/v in both IP line closed ] & [ Either LP
BP stop v/v or LP BP C/V in both LP line is closed]
OR
 Generator ckt bkr open & [both HP BP closed OR
both LP BP closed

6. HP BYPASS SYSTEM
Benefits
 Boiler start-up without starving superheater & reheater
tubes, till the opening of turbine steam control valves
 Raising the steam parameters (press& temp) quickly, to a
level acceptable for the starting of the turbine at an optimum
rate
 Continued Boiler operation while tripping of turbine provided
boiler load <60%
 Avoiding Reheat protection
 Conservation of DM water, during start-up or Shut down (by
dumping steam into condenser instead of atmosphere)
 Maintain sufficient steam pressure in the CRH line for
auxiliary steam supply purpose during low load condition

7. HP BYPASS SYSTEM

8. HP BYPASS SYSTEM
HP Bypass consists of:
 Bypass Valves BP1 & BP2
 Spray water pressure controller BD valve
 Spray water temp. controller BPE1, BPE2 valves
 2 nos Hydraulic Oil Supply units
MS press. ahead of HPT is maintained by proper
adjustment of BP valves
Steam temp in CRH line controlled by BPE valves

9. OIL SUPPLY UNIT
 OSU provides Energy for operation of steam valves
 Consists of Filters, Axial piston pump, Relief valve, NRV, Oil
Accumulator, Press reducing valve, Ball Cocks
 Axial Pump maintains Contant oil press. in the accumulator
by automatic operation
 Gas filled bladder to retain oil press in accumulator or fairly
long duration
 A safety valve protects the system from excessive pressure

10. HP BP HYDRAULIC SYSTEM

11. OIL SUPPLY UNIT INTERLOCKS
 Pump Auto off Oil Press high >160ksc
 Pump Auto on Oil Press Low <120ksc
 Pump Auto off Oil Temp high >70 DegC
 Pump Auto off Oil Level low <18 Lit
 Alarm Oil Press too high >170ksc
 Alarm Oil Press too Low <90ksc

12. TEMPERATURE CONTROL

13. HP BP PROTECTION
BP Valve Priority Close Conditions
 Condenser Vacuum Low (<-0.6 ksc)
 Bypass Downstream Temp very high (>380 degC)
 Loss of Oil Pressure in Safety System Accumulator
<100 ksc (stage-1)
Under these conditions
 Steam Press Controller Switches to Manual from
Auto
 spray water valve will close
 This protection will override the Fast opening signal
& open push button operation

14. HP BP PROTECTION
HP Bypass Fast Opening Conditions
 Generator Circuit Breaker Opening & Boiler on
& no priority close
 Turbine Trip & Boiler on & no priority close
 Turbine Load Shedding Relay Operation
 HP BP Pressure Controller Deviation > 8 ksc
 Pressing the Fast Opening Button

15. HP BP PROTECTION
BP Valve Auto Blocking Conditions
 Bypass valve priority close command
 BP position transmitter failed
 OSU-1 & 2 Oil Pressure <90 ksc
 Main steam Pressure transmitter failed

16. HP BP INTERLOCKS
BPE Valve Conditions
 Steam Bypass Valves BP1 or BP2<2 % Auto Close
Command to ensure positive shut off
 Steam Bypass Valves BP1 or BP2<2 % Spray Water
Pressure Control Valve (BD Valve) close
 Steam Bypass Valves BP1 or BP2>2 % Spray Water
System (BPE1, BPE2, BD Valve) will switch over to
Auto

17. HP BP INTERLOCKS
BPE Valve Auto Blocking Conditions
 Bypass Downstream Temp very high (>380 degC)
 BP auto command blocking
 BPE valve position transmitter failed
 BPE Temp transmitter deviation high
Therefore, it is necessary to make proper set
values for Spray Water Header Pressure &
HP BP downstream temperature before
operating the Steam Bypass Valves

18. LP BYPASS
Functions of LP Bypass System are:
 Maintaining minimum Steam Flow through Re-heater
 Maintaining desired Steam Pressure in the Re-heater
 Providing an alternative path for dumping the steam (not
accepted by the IP & LP Turbines) into the condenser
LP BP System comprises of :
 Steam Pressure Control Loop
 Valve Position Control Loop
 Automatic Control Interface (ACI)
 Condenser Temperature Protection
 Tracking Unit

19. LP BYPASS

20. LP BYPASS

21. LP BYPASS

22. LP BYPASS

23. LP BYPASS

24. LP BYPASS CONTROL LOGIC

25. SLIDING SET POINT

26. LP BYPASS SETPOINTS

27. AUTOMATIC CONTROL INTERFACE

28. LP BYPASS EHC

29. LP BYPASS PROTECTIONS
Close LP Bypass under following conditions:
 Condenser Vacuum Low (<-0.6 ksc)
 Spray Water Pressure Low (<8 ksc)
 Condenser Wall Temperature High ( > 90 DegC)
 LPBP Down Steam Pressure High (>19 ksc)
Spray Water valve open command at Steam pressure before
bypass valve >6.8 ksc

30. LP BYPASS PROTECTIONS

31. Thank You