Recommended Write Up on Boiler Aux and Interlock Protection, Rev02

VIJAYAWADA TPS EXTENSION-7, 1X500 MW, BOILER AUXILIARIES INTERLOCKS & PROTECTION

WRITE-UP ON BOILER AUXILIARIES INTERLOCKS AND PROTECTION GENERAL: The

steam generators supplied today are larger in size and sophisticated in nature.

Failure of any equipment calls for expensive replacement and results in costlier down time. This emphasises careful planning on the correct procedure for; 1. Safe sequence of start-up of equipments in the power plant. 2. Continuous trouble free & efficient operation. 3. Safe sequence of shutdown of the equipment when needed. This also leads to provision of adequate & reliable protection to safeguard the various plant equipments under abnormal and dangerous conditions. The operation of the protections shall be accompanied by visual and audible annunciation, which provide definite indication of the primary cause or causes of operation of the protection. Restarting of the equipment, which has once been tripped by protection either by remote, automatic or manual control shall be possible only after the elimination of the cause of tripping. PROTECTIONS ARE CLASSIFIED UNDER THREE GROUPS NAMELY: a) Protection causing complete shut down of the unit. b) Protection causing load reduction of the unit. c) Protection causing annunciation only. 1. PROTECTIONS CAUSING COMPLETE SHUT DOWN OF THE UNIT a) Failure of all feed pumps (i.e.) reserve feed pump if any, fails to start on tripping of running pumps even after a preset time delay. b) Boiler shutdown due to failure of both FD fans, both ID fans and other conditions. c) Reheater protection, which is to ensure continuous steam flow through reheater tubes at, specified conditions. 2. PROTECTION CAUSING LOAD REDUCTION a) ID fans: Two ID fans are required for boiler MCR. If any one of the two running ID fans trips, the boiler load shall be run down to 60% MCR. b) FD fans: Any one of the two running FD fans trip, the boiler load shall be run down to 60% MCR. c) Mills, PA fans & Coal Feeders: This reduces the boiler load correspondingly due to limitations in fuel firing capabilities. d) Boiler Circulation Water Pump : As described in clause 13.0 Page 1 of 19


3. PROTECTIONS CAUSING ANNUNCIATION: The causes that lead to visual/audible annunciation are covered under various sub systems like Furnace Safeguard Supervisory System (FSSS), Secondary Air Damper Control (SADC)

system,

Sootblower

control

system,

Auxiliary

pressure

reducing

and

Desuperheating Control System, Fuel oil system, Air & Flue gas system, Steam & water system, HP Bypass system etc. These interlocks & protection systems are divided into two portions based on the area they cover as briefly described below. a) Boiler auxiliaries interlock & protection This system takes care of sequence of starting protection and interlock of boiler Auxiliaries like FD fans, ID fans, Air-heaters, Dampers, Valves, etc. covered in this write up. b) Furnace safeguard supervisory system(FSSS) This system takes care of interlocks required for starting, supervising the operating and safe shut down of the equipments connected with fuel firing system. 1.0 ID FAN INTERLOCKS 1.1 Conditions existing when the unit is shut down and prior to starting of ID fans. a) ID fan 'A' & ID Fan 'B' off b) Regulating dampers of fans A & B fully open c) Inlet gates of fans A & B open d) Outlet gates of fans A & B open e) The regulating dampers & VFD control will be on manual control during shutdown, and impulse from furnace draft control to regulating dampers of ID fans disconnected. f)

Lube oil pumps of ID fans off

1.2 Starting ID Fan 'A' (ID fan 'B' is off) (a) ID fan 'A' shall be prohibited from starting till the following conditions are satisfied: i.

Fluegas path available.

ii. Regulating dampers of Fan-A in minimum position. iii. Outlet gate of Fan-A closed. iv. Inlet gate of Fan-A closed v. Fan/Fan motor bearing temperature not very high. vi. Motor winding temperature is not very high vii. One of the air heater is running with its inlet and outlet dampers kept open. viii. Lube oil system permissives satisfied (Refer Clause 7.0) ix. VFD system 'Auxiliary supplies healthy' permissive satisfied x. VFD system 'Channel 1 ready' or 'channel 2 ready' signal available (one contact for each channel) Page 2 of 19


xi. VFD system 'Channel 1 start permissive' or 'Channel 2 start permissive available from VFD system(one contact for each channel) (b) The starting of ID fan 'A' shall be done in following sequence i.

VFD system channel 1 start command starts fan 'A' and runs up fan A to minimum speed.

ii. When fan 'A' reaches minimum speed, impulse for VFD channel 2 start is given by operator. When ID fan 'A' is started (ID Fan B is off), impulses shall be given for: iii. Opening the inlet gate and outlet gate of fan A iv. Connecting the regulating dampers/VFD control of Fan A to the auto control. v. Closing the inlet gate and the outlet gate dampers to minimum position.

of ID fan B and bringing the regulating

vi. Permission to start either FD Fan A or FD Fan B. 1.3 Starting ID fan B (ID Fan A is off) Interlocks similar to those at clause 1.2 shall hold good for this condition. 1.4 Tripping of ID Fan A (ID Fan B is off) ID fan 'A' trip shall mean that 'stop' impulses shall be given to VFD channel 1 and channel 2 simultaneously. a) ID fan 'A' shall trip automatically under following conditions. i.

ID fan A bearing temperature too high (prior to this, ID fan A bearing temperature high shall be annunciated in UCB) contacts shall be generated from RTD.

ii. ID fan A motor bearing/winding temperature too high (prior to this, ID fan 'A' motor bearing/winding temperature high shall be annunciated in UCB) iii. Post purge fan trip from FSSS(one contact will be provided to trip all the ID and FD fans) iv. Vibration level of fan/motor very high (high to be alarmed).

For fan, trip shall be

initiated with a delay of 10 minutes during starting and running of fan. v. ID Fan-A VFD channel 1/channel 2 input breaker (11KV) trip. Here only the respective channels shall be issued stop impulse. vi. Fault from VFD channel 1/channel 2. Here only the respective channel shall be issued stop impulse. vii. Lube oil pressure of ID fan A too low (Trip shall be initiated with a delay of 10 min.) b)

When ID fan A trips (ID fan B is off) impulses shall be given for:

i.

Opening the outlet gate of ID fan B

ii. Opening the inlet gate of ID fan B.

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iii. Disconnecting the impulse from auto control system (output from A/M station) to regulating damper and VFD control. iv. Opening the regulating damper of ID fan A to wide open position. v. Opening the regulating damper of ID fan B to wide open position. vi. Tripping the working FD fans. vii. Boiler tripping - through FSSS viii. To keep the inlet gate and outlet gate of ID fan A open 1.5 Tripping of ID fan B (ID fan A is off) Interlocks similar to those at clause 1.4 shall hold good for this condition 1.6 Starting of ID fan B (ID fan A is on) a)

ID fan B shall be prohibited from starting unless the following conditions are satisfied:

i.

Outlet gate of fan B is closed

ii. Inlet gate of fan B is closed iii. Regulating damper of fan B is in minimum position iv. Fan/Fan motor bearing temperature not very high v. Motor winding temperature not very high vi. Lube oil system permissives satisfied (Refer Clause 7.0) vii. VFD system 'auxiliary supplies healthy' permissive satisfied viii. VFD system 'channel 1 ready' or 'channel 2 ready' (one contact for each channel). ix. VFD system 'channel 1 start permissive' or 'channel 2 start permissive' available (one contact for each channel). b) The starting of ID fan 'B' shall be done in following sequence. i.

VFD system channel 1 command starts fan 'B' and runs up fan 'B' to minimum speed.

ii. When fan 'B' reaches minimum speed, impulse for VFD channel 2 start is given by operator. iii. When ID fan B is started, impulses shall be given for: iv. Opening the inlet gate and outlet gate of fan B after the motor reaches the prescribed speed. v. Connecting the regulating damper and VFD control fan 'B' to auto control (release to auto). vi. Permission to start other FD fan. 1.7 Starting of ID fan A (ID Fan B is on) Interlocks similar to those at clause 1.6 shall hold

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1.8 Tripping of ID fan B (ID fan A is on) ID fan B trip shall mean that 'stop impulses' shall be given to VFD channel 1 and channel 2 simultaneously. a)

ID fan B shall trip automatically under the following conditions:

i.

Fan bearing temperature too high (prior to this fan bearing temperature high shall be annunciated in UCB) contacts generated from RTD.

ii. Fan

motor bearing/winding temperature too high (prior to

this

fan motor

bearing/winding temperature high shall be annunciated in UCB) iii. Vibration level of Fan/motor very high (high to be alarmed).

For fan, trip shall be

initiated with a delay of 10 minutes during starting and running of fan. iv. 'Post purge Fan trip' from FSSS v. ID Fan-B motor VFD channel 1/channel 2 input breaker (11Kv) trip. Here only the respective channels shall be issued stop impulse. vi. Fault from VFD channel 1/channel 2. Here only the respective channel shall be issued stop impulse. viii. Lube oil pressure of ID fan B too low (Trip shall be initiated with a delay of 10 min.) b) When ID Fan B trips (ID fan A is on & vice versa) impulses shall be given for: i.

Disconnecting the regulator from acting on the regulating damper and VFD control

ii. Bringing the regulating damper of Fan B to the minimum position iii. Closing the inlet gate of Fan B iv. Closing the outlet gate of fan B v. Tripping the FD fan B, provided FD fan A is on vi. Reducing boiler load to 60% MCR. 1.9 Tripping of ID fan A (ID fan B is on) Interlocks similar to those at clause 1.8 shall hold good for this condition: 1.10 General a) Variable frequency drive i.

Individual

start/stop push buttons shall be

provided

in UCB/CRT for each VFD

channel. ii. Source breakers of VFD system have to be closed from plant I&C system only if 'Source breaker close permissive' is available from VFD system. iii. The signal interface drawing of VFD system supplier shall be referred to for preparation of interlock schemes. b)

Fan outlet gate

−

If one ID Fan is started when the other ID Fan is off, the outlet gate of starting fan shall be opened with starting of the fan to reduce the load of electrically operated gate. Page 5 of 19


−

When starting the second fan (i.e. ID Fan A started when B is On or vice versa), the respective outlet gate shall be opened after the fan reaches minimum speed.

2.0 FD FAN INTERLOCKS 2.1 Conditions prior to starting FD fans: a) FD Fan A and FD Fan B off b) Fan impellers tilted to maximum opening c) Outlet dampers are fully open d) Fan impeller regulator disconnected e) Lube oil pumps of FD fans off 2.2 Starting FD fan A (FD fan B is off): a)

FD Fan A shall be prohibited from starting until the following conditions are satisfied:

i.

ID Fan A or ID Fan B is on

ii. Fan A damper in the minimum position iii. Outlet damper of fan A in closed position iv. Fan/motor bearing temperature not very high v. Motor winding temperature not very high vi. Lube oil system permissives satisfied (Ref. Clause 6.0) b)

When FD fan A is started (FD Fan B is off) impulses shall be given for:

i.

Outlet damper of fan A to open after the motor reaches rated speed

ii.

The outlet damper of FD fan B to close & impeller blades of fan B to be driven to minimum position

iii. Connecting the impeller of Fan A control drive to auto control 2.3 Starting of FD fan B (FD fan A is off): Interlocks similar to those at clause 2.2 shall hold good for this condition. 2.4 Tripping of FD fan A (FD fan B is off) a)

FD fan A shall trip automatically under the following conditions:

i.

FD fan A bearing temperature too high (prior to this, FD fan A bearing temperature high will be annunciated in UCB)

ii. FD fan A motor bearing/winding temperature too high (prior to this, FD fan A motor bearing/ winding temperature high will be annunciated in UCB) iii. Both ID fans trip iv. Post purge fan trip

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v. Vibration level of fan or motor very high (high to be alarmed). For fan, trip shall be initiated with a delay of 10 minutes during starting and running of fan. ix. Lube oil pressure of FD fan A too low (Trip shall be initiated with a delay of 10 min.) b) When FD Fan A trips (FD fan B is off) impulses shall be given for: i.

Disconnecting the impeller control drive from auto control system (output signal from A/M station)

ii. Bringing the impeller of Fan A to the maximum position iii. Bringing the impeller of FD fan B to the maximum position iv. Opening the outlet damper of FD fan B v. To open the emergency scanner air damper vi. Boiler tripping vii. The outlet damper of FD fan A shall remain open 2.5 Tripping FD fan B (FD fan A is off): Interlocks similar to those of clause 2.4 shall hold good for this condition 2.6 Starting FD fan B (FD fan A is on): a)

FD fan B (FD fan A is on) shall be prohibited from starting until the following conditions are satisfied:

i.

Two ID fans are on

ii. Fan B impeller tilt/damper in the minimum position iii. Outlet damper of Fan B in closed position iv. Fan and fan motor bearing temperature not very high v. Motor winding temperature not very high. vi. Lube oil system permissives satisfied (Ref. Clause 6.0) b)

When FD fan B is started (FD fan A is on) impulses shall be given for:

i.

Opening the outlet damper of FD fan B after the motor reaches rated speed

ii. Connecting the impeller control drive of FD fan B to auto control 2.7 Starting FD fan A (FD fan B is on): Interlocks similar to those at clause 2.6 shall hold good for this condition. 2.8 Tripping of FD fan B (FD fan A is on): (a) FD fan B shall trip (when FD fan A is on) under the following conditions: i.

ID fan B trips

ii. FD fan B motor bearing/winding temperature too high (prior to this, FD fan B motor bearing/winding temperature high shall be annunciated in UCB) Page 7 of 19


iii. FD fan B bearing temperature too high (prior to this, FD fan B bearing temperature high shall be an annunciated in UCB) iv. Vibration level of fan or motor very high (high to be alarmed). For fan, trip shall be initiated with a delay of 10 minutes during starting and running of fan. v. Lube oil pressure of FD fan B too low (Trip shall be initiated with a delay of 10 min.) b) When FD fan B trips (FD fan A is on), impulses shall be given for: i.

Disconnecting regulating impulse from acting on impeller control drive of fan B

ii. Bringing impeller of fan B to the minimum position iii. Closing the outlet damper of fan B iv. Reducing boiler load to 60% MCR. v. Tripping coal elevation in service more than three through FSSS 2.9 Tripping of FD fan A (FD fan B is on): Interlocks similar to those at clause 2.8 shall hold good for this condition. 3.0 PA FAN INTERLOCKS : 3.1 Conditions prior to start up a) PA fan A and PA fan B off b) Outlet dampers of fan A and fan B closed c) Regulating vanes of fan A and fan B in closed position. d) Regulating vane regulator disconnected e) Lube oil pumps of PA Fan off 3.2 Starting PA fan A (PA fan B off) a) PA fan A shall be prohibited from starting until the following conditions are satisfied: i.

Regulating vanes of PA Fan A in the minimum position

ii. Outlet damper of PA fan A in closed position iii. Anyone FD fan is on iv. Purge complete v. PA fan and fan motor bearing temperature not very high vi. Motor winding temperature is not very high vii. Lube oil system permissives satisfied (Ref. Clause 8.0) b) i.

When PA fan A is started (PA fan B is off), impulses shall be given for: Opening the outlet damper of PA Fan A

ii. Connecting the regulating vanes of PA fan A to auto control iii. Bringing the regulating vanes of PA fan B to the minimum position iv. Closing the outlet damper of PA fan B Page 8 of 19


v. Permission to start any three coal elevation through FSSS. 3.3 Starting PA fan B (PA fan A is off) Interlocks similar to those at clause 3.2 shall hold good for this condition. 3.4 Tripping of PA fan A (PA fan B is off) a) PA fan A shall trip (PA fan B is off) under the following conditions: i.

PA fan A bearing temperature too high (prior to this bearing temperature high shall be annunciated in UCB)

ii. PA fan A motor bearing/winding temperature too high

(prior to

this,

motor

bearing/winding temperature high shall be annunciated in UCB) iii. Boiler trips iv. Vibration level of fan or motor very high(high to be alarmed). For fan, trip shall be initiated with a delay of 10 minutes during starting and running of fan. v. Lube oil pressure of PA fan A too low (Trip shall be initiated with a delay of 10 min.) b)

When PA fan A trips, (PA fan B is off)impulses shall be given for:

i.

Disconnecting the regulating vanes of PA fan A from auto control

ii. Bringing the regulating vanes of PA fan A to minimum position iii. Closing the outlet damper of PA fan A iv. Tripping all the operating mills (done through FSSS) 3.5 Tripping of PA fan B (PA fan A is off) Interlocks similar to those at clause 3.4 shall hold good for this condition 3.6 Starting PA fan B (PA fan A is on) a) i.

PA fan B shall be prohibited from starting unless satisfied: Any one FD fan on

the

following conditions are

ii. Regulating vanes of PA fan B in the minimum position iii. Outlet damper of PA fan B in closed position iv. PA fan B and fan motor bearing temperature not very high v. Motor winding temperature is not very high vi. Lube oil system permissives satisfied (Ref. Clause 8.0) b)

When PA fan B is started (PA fan A is on) impulses shall be given for:

i.

Opening the outlet damper of PA fan B after the motor reaches rated speed

ii. Connecting the regulating vanes of PA fan B to auto control iii. Permission to put in service remaining coal elevation through FSSS Page 9 of 19


3.7 Starting PA fan A (PA fan B is on) Interlocks similar to those at clause 3.6 shall hold good for this condition 3.8 Tripping of PA fan B (PA fan A is on) a) PA fan B shall trip (PA fan A is on) under the following conditions: i.

PA fan B bearing temperature too high (prior to this, fan bearing temperature high shall be annunciated in UCB)

ii. PA fan B motor bearing/winding temperature too high (prior to this, fan motor bearing/winding temperature high shall be annunciated in UCB) iii. Boiler trips iv. Vibration level of fan or motor very high (high to be alarmed). For fan, trip shall be initiated with a delay of 10 minutes during starting and running of fan. v. Lube oil pressure of PA fan B too low (Trip shall be initiated with a delay of 10 min.) b)

When PA fan B trips (PA fan A is on), impulses shall be given for:

i.

Disconnecting the regulating vanes of PA fan B from auto control

ii. Bringing the regulating vanes of PA fan B to minimum position iii. Closing the outlet damper of PA fan B iv. Reducing boiler load to 60%. v. Tripping any three coal elevation through FSSS. 3.9 Tripping of PA fan A (PA fan B is on) Interlocks similar to those at clause 3.8 shall hold good for this condition.

3.10 Both the PA fans shall trip simultaneously when any boiler trip condition is present (impulses from FSSS). 3.11 GENERAL i.

If one PA Fan is started when the other PA Fan is off, the outlet gate of starting fan shall be opened with starting of the fan to reduce the load of electrically operated gate.

ii. When starting the second fan (i.e. PA Fan A started when B is on or viceversa), the respective outlet gate shall be opened after the fan reaches full speed. 4.0 AIRHEATER INTERLOCKS: 4.1 Conditions before start up of AHs: -

Both AHs are OFF (both electric motors and air motors are OFF) Page 10 of 19


-

The inlet dampers and the outlet dampers in the primary air path, the inlet dampers in the gas path and out let damper in the sec. air path are in full open condition.

4.2 Starting AH A (AH B is OFF): a) AH A electric motor is started if the sump oil temperature of the bearings measured through RTD is less than 70 deg c. b) Whenever AH-A electric motor trips, impulse shall be given for starting the AH air motor by de-energising the solenoid provided the pump oil temperature of support / guide bearing of AH a is less than 70 deg c. c) Impulse shall be given for closing of the inlet and outlet dampers of AH B which is OFF 4.3 Tripping of AH A (AH B is OFF) (a) Whenever the sump oil temperature of support/guide bearing is greater than 70 deg c an alarm shall be initiated through RTD to alert the operator. The operator shall check the circulation pump operation and the coolant flow at local to bring down the sump oil temperature. In case if the temperature of sump oil is unable to be brought down AH electric motor/air motor shall be tripped manually. (b) Air motor shall trip automatically when AH-A electric motor starts. Note: Trip signal of AH is to be taken from proximity switch (Sensing stoppage of AH motor) or both electric motor trip and air pressure for air motor low. 4.4. Starting of AH B (AH A is OFF): The interlocks are said above(clause no. 4.2) for AH A starting (AH B OFF) are applicable here. 4.5 Tripping of AH B (AH A is OFF): The interlocks are said above (clause no. 4.3) for AH A tripping (AH B OFF) are applicable here. 4.6 Both AHs are working . when AH A trips & AH B continues to run: The gas inlet damper, the secondary air outlet damper and primary air outlet damper of the tripped AH shall be automatically closed. The primary air inlet damper, the gas inlet damper of the tripped AH need not be closed. However if the operator wants to manually close these dampers they can be closed. 4.7 Both AHs are working .when AH B trips & AH A continues to run: The interlocking conditions are said above under 4.6 are applicable here. 4.8 Both AHs working and the one AH trips: (a) The operator shall try for restarting the AH by either air motor or electric motor. If the restarting is not possible the boiler load shall be brought down to 60 % 4.9 Both AHs are tripped: Page 11 of 19


If both AHs A & B trip the operator may try for restarting the AHs. If anyone of the AH is not started within 5 minutes the operator shall manually trip the boiler. 4.10 Interlocks for oil Circulation Pumps of support bearing: (Applicable for Air heater A and Air heater B) 2 x 100% oil circulation pump have been provided for the support bearing. Anyone of the two oil circulation pumps can be pre-selected as main pump and the other as standby. Following interlocks shall be provided for oil circulation pumps. -

Whenever the sump oil temperature of support bearing of air heater A is high (40 deg.C) impulse shall be given to start the main oil circulation

-

The standby oil circulation pump shall start when the main oil circulation pump fails to start or trip.

-

The main oil circulation pump/stand-by oil circulation pump shall trip when the temperature of the support bearing falls below a preset value (40 deg.C).

-

Manual operation of the lube oil pumps shall be prohibited when the ambient temperature is too low. Since viscosity of the oil will be high so that the pump couldn't be started.

4.11 Interlocks for oil circulation pumps of guide bearing: 2 x 100% oil circulation pumps have been provided for guide bearing. Anyone of the two oil circulation pumps can be pre-selected as main pump and the other as standby. The interlocks for these pumps shall be similar to those for support bearing as envisaged in clause 4.10.

5.0 BLOW DOWN VALVE: a) When drum water level rises to 125mm above normal water level an annunciation 'Drum level high shall be given in UCB. b) When drum level rises to 125mm above normal water level, blow down valves shall open and this condition shall be annunciated. c) Blow down valves shall close automatically when the water level falls down to NWL. One interlock switch shall be provided for both the valves for manual operation. d) The signals for the above interlocks shall be derived from level transmitters. 6.0 INTERLOCKS FOR FD FAN LUBRICATING OIL SYSTEM: 6.1 FD fan A lube oil system: a) Pump A will start automatically if pump B trips provided A/M switch is in auto position b) Pump A will start automatically with a time delay of 0-60 seconds if lube oil pressure falls below a set value and the pump B is working provided A/M switch is in auto position. Page 12 of 19


c)

Pump B will start automatically if pump A trips/has not started provided A/M switch is in auto position.

d) Pump B will start automatically with a time delay of 0-60 seconds if lube oil pressure falls below a set value and the pump A is working provided A/M switch is in auto position. e) Pump A or pump B can be started/tripped by pressing the respective push button provided on local pushbutton box when A/M switch is in manual position. f)

FD fan A shall be prohibited from starting until the lube oil pressure is adequate.

6.2 FD fan B lubricating oil system: Interlocks similar to those at 6.1 (a), (b), (c) and (d) above shall hold good for FD fan B lubricating oil system. 7.0 INTERLOCKS FOR ID FAN LUBRICATION OIL SYSTEM 7.1 ID fan A lube oil system: a) Pump A will start automatically if pump B trips provided A/M switch is in auto position b) Pump A will start automatically with a time delay of 0-60 seconds if oil pressure falls below a set value and the pump B is working provided A/M switch is in auto position. c) Pump B will start automatically if pump A trips/has not started provided A/M switch is in auto position. d) Pump B will start automatically with a time delay of 0-60 seconds if lube oil pressure falls below a set value and the pump A is working provided A/M switch in auto position. e) Pump A or pump B can be started/tripped by pressing the respective push button provided on local pushbutton box when A/M switch is in manual position. f)

ID fan A shall be prohibited from starting until the lube oil pressure is adequate.

7.2 ID fan B Lube oil system: Interlocks similar to those at 7.1(a), (b), (c) & (d) above shall hold good for ID fan B lubricating oil system also. 8.0 INTERLOCKS FOR PA FAN LUBE OIL SYSTEM 8.1 PA fan A lube oil system: a) Pump A will start automatically if pump B trips provided A/M switch is in auto position b) Pump A will start automatically with a time delay of 0-60 seconds if oil pressure falls below a set value and the pump B is working provided A/M switch is in auto position. c) Pump B will start automatically if pump A trips/has not started provided A/M switch is in auto position. d) Pump B will start automatically with a time delay of 0-60 seconds if lube oil pressure falls below a set value and the pump A is working provided A/M switch in auto position. Page 13 of 19


e) Pump A or pump B can be started/tripped by pressing the respective push button provided on local pushbutton box when A/M switch is in manual position. f)

PA fan A shall be prohibited from starting until the lube oil pressure is adequate.

8.2 PA fan B Lube oil system: Interlocks similar to those at 8.1(a), (b), (c) & (d) above shall hold good for PA fan B lubricating oil system also. 9.0 FURNACE TEMPERATURE PROBE a) Furnace temperature probe can be advanced/retracted using the provided in UCB as well as from local starter box.

pushbuttons

b) Furnace temperature probe shall be prohibited from being advanced further into the furnace if furnace temperature sensed by it is more than 540 deg. C c) If furnace temperature probe is inside the furnace and the temperature exceeds 540 deg. C it will be retracted back automatically. d) If furnace temperature probe is inside the furnace and the Cooling air pressure not O.K., it will be retracted back automatically. 10.0 MISCELLANEOUS INTERLOCKS: 10.1 Interlock and protection write-up for DDI gate/Biplane dampers with motor operated blowers/manually operated seal air isolation valve: 10.1.1 Guillotine Gate (ID Fan outlet) with motor operated blower and manually operated isolation valve. a) Gate will close and open according to BHA interlock and protection. b) Blower shall be continuously working irrespective of whether the gate is in close or open position, when boiler is working. The manual operated valve shall remain open so long as the blower is working. c) Blower motor for ID fan outlet gate shall be started simultaneously with ID fan. 10.1.2 Interlocks for Guillotine Gate without blowers but with manual isolation ( EP inlet/outlet, ID Fan inlet & AH flue gas inlet): Valve has to be kept open irrespective of the position of the gate. 10.1.3 Interlock for Biplane damper blower with pneumatically operated isolation valve: (AH flue gas outlet): a) Biplane damper will open/close according to BHA interlock & protection. b) The pneumatically operated valve shall be commanded to open and shall remain open so long as the biplane damper is in closed position. c) The pneumatically operated valve shall close once Biplane damper is fully open. Page 14 of 19


11.0 MOTOR OPERATED VALVE INTERLOCK REQUIREMENTS 11.1

Gate valves 100mm and above in 1500 CL and above ratings: Valve closing: Actuator motor tripping shall be done by limit switch. Torque switch shall be used in the control circuit as a back up. Valve opening: Actuator motor tripping shall be done by limit switch. Torque switch shall be used in the control circuit as a back up.

11.2 Other gate and globe valves: Valve closing: Actuator motor tripping shall be done by torque switch. Limit switch shall not be used in the control circuit for tripping. Valve Opening: Actuator motor tripping shall be done by limit switch. Torque switch shall be used as a backup in the control circuit. 11.3 Thermostat shall be connected without fail in the starter circuit. 11.4 Motorised actuators of valve & dampers are provided with integral starters. 12.0 REHEATER PROTECTION LOGIC: Reheater protection shall be provided as part of Boiler House Auxiliaries Interlock and protection system. This protection is provided to protect the Reheater against starvation of steam flow during abnormal conditions. To take care of Reheater protection, the Boiler shall be tripped after 10 seconds, when any of the following conditions occur: a) When Boiler is working to provide sufficient heat energy to overheat RH coilsand if i) Generator circuit breakers open and ii) HP Bypass or LP Bypass valves remain closed less than 2% When Boiler is working to provide sufficient heat energy to overheat RH coilsand if i) Turbine trips and ii) HP Bypass or LP Bypass valves remain closed less than 2% Copy of Recommended Reheater Protection Logic is enclosed. 13. INSTRUMENTATION AND CONTROLS FOR REMOTE MANUAL OPERATION OF BOILER CIRCULATION PUMPS ON CONTROLLED CIRCULATION UNITS 13.1 Unit operation

Page 15 of 19


The boiler circulation system of a Controlled Circulation Unit is designed for the following unit operating modes. −

Two or three pumps in service - no restriction in unit operation at design maximum continuous rating.

−

One pump in service - unit load is limited to not more than 60% MCR.

−

No pumps in service - unit must be tripped.

It is BHEL’s strong recommendation that two (2) pumps be in operation prior to purging the furnace and during initial firing. One (1) pump is sufficient, however. If two (2) pumps are in operation at a boiler load greater than 60% MCR, and one (1) of the pumps trips, an alarm and load limit signal must be generated. A manual or automatic load run back at the maximum controlled rate must be commenced after a time delay of "5" sec. and continued to 60% load or until the other pump has been started and proven in service. If only one (1) pump is in service, and this pump is tripped, an automatic master fuel trip (MFT) must be generated if another pump is not started with in five seconds. Please refer table below for more details regarding the operation of boiler circulating water pumps:

No. of pumps in operation

3 pumps

2 pumps

1 pump

Unit Load allowed for different DP(psi)across circulating water pump MCR 60% MCR MFT a. Each>10psi and < 18psi b. Two>10psi and and < 18 psi and One <10psi a. Each>18psi a. Each<10psi c. One > 18 psi and b. Two>18psi and two < 18 psi and One <18psi > 10 psi d. One >10psi and < 18 psi and Two <10psi a. *Each>10psi and < 18 psi b. *One >10psi and a. *Each <18psi and one a. Each>18psi <10psi < 10 psi c. * One< 18 psi and >10 psi and one > 18 psi a. *>10psi a. *<10psi

NB: * 5 secs delay for starting the standby pump before resorting to automatic action for rundown or MFT as applicable. The above table is based on the following concept: Page 16 of 19


• • •

Unit load of 100 % MCR shall be allowed only if two BCWPs generate DP > 18 psi When at least one BCWP pump generates DP > 10 psi, unit load of 60 % MCR shall be permitted. When all pumps generate DP < 10 psi, boiler shall be tripped.

Vent valves HAN 10 AA201, HAN 10 AA 202 , HAN 10 AA 203 and HAN 10 AA 204 shall be closed before starting the boiler circulating water pump. 13.2 Unit protection To prove a pump is in service, BHEL is furnishing two (2) differential pressure transmitters for each pump to monitor the differential pressure across the pump. When only one pump is in service, the differential pressure across that pump will be lower than the differential pressure across the pump if more than one pump is in service. The differential pressure transmitters will be installed so that they sense the pressure at the pump suction nozzle and the pressure at the pump discharge nozzles. A monitoring system that will monitor the output of the differential pressure transmitters for all three pumps shall be provided. The monitoring system shall develop contact outputs for each pump which, in conjunction with a control signal that the respective pump motor breaker is closed, will give a positive indication that the pump is running and pumping effectively. Required motor control interlock for starting a boiler circulation pump: −

Stems in both discharge valves must be proven open by position switches.

−

The interlock must prevent starting a pump with either one of the discharge valve stems not open and trip the pump if either one leaves the open position.

13.3 Boiler Circulation Pump protection The following conditions must be verified prior to local or remote manual starting of a circulation pump. (Start permissive interlocks) −

Low pressure cooling water flow established.

−

Differential temperature between pumps casing and suction manifold less than 28°C.

−

Motor cavity temperature more than 2°C (cold boiler start up), but less than 54°C (abnormal hot standby condition). (Manual check only)

After the pump starts, it must be tripped if the motor cavity temperature is greater than 65 °C. If an automatic trip function is adopted, a five (5) second time delay is allowable to permit remote manual starting of the other pump. Starting a hot standby pump should reduce the motor cavity temperature immediately. An instantaneous alarm signal must be activated if the motor cavity temperature exceeds 60°C. 13.4 Pump Instrumentation and unit operation control functions

Page 17 of 19


In addition to the normal motor overload protection devices, the recommended instruments and major control circuitry items for the boiler circulation pump system are listed below. In the following tabulation, the A series covers items for the boiler circulation pumps. Item B applies to the discharge valves. The items in the C series apply to the circulation pump differential pressure transmitter. The initiating differential pressure contacts for the load limit alarm and fuel trip under series - C shall be part of DDCMIS. These contacts, used in conjunction with the contact proving that the respective pump motor breaker is closed, determine whether each pump is running and delivering the expected capacity.

This

indication is used within the pump control system, which counts the number of operating pumps and develops the load limit alarm signal and fuel trip. Item No.

Quantity

Description

A1

3

A2

3

Start-run-stop switch for pump motor and associated lights (on-off) from motor breaker Ammeter for pump motor current

A3

3

Motor cavity temp. high alarm

A4

3

Motor cavity temp. high trip

A5

3

A6

3

A7

3

A8

3

A9

3

Pump casing & suction manifold temp. differential indication(thermocouples by BHEL) Pump motor breaker closed signal to C1 and C2 Motor cavity temperature trend recorder Low flow alarm for cooling water to pump motor cooler Motor overload/ground fault trip

A10

3

Purge filter DP high alarm

B

3 pairs

C1

1

C2

1

C3

1

C4

3

C5

3

14.5

Discharge valve stem position pairs lights (open contact by BHEL) Low differential alarm and load limit signal for less than two pumps operating Fuel trip signal for less than one pump operating (5sec. time delay) Differential pressure 3-pen Local or strip chart recorder or computer trend recorder Differential pressure indicator(not required if differential recorder is at UCB) Differential pressure adequate or circulation correct

Location

UCB UCB / DDCMIS Annunciator / DDCMIS Motor control cabinet / DDCMIS UCB / DDCMIS Motor control cabinet / DDCMIS Console / DDCMIS Annunciator / DDCMIS Motor control cabinet Annunciator / DDCMIS UCB / DDCMIS Annunciator / DDCMIS FSSS UCB / DDCMIS UCB / DDCMIS FSSS

Alarm and trip settings for Boiler Circulation Pump Instrumentation

Page 18 of 19


Item No.

Pump Operation Control Instruments

A3

Motor cavity temperature high alarm Y = 60°C*

A4

Motor cavity temperature high pump trip X = 65°C after 5 sec. time delay

A5

Pump casing/suction manifold temperature differential: +/- 28°C max.

A7

Motor cavity minimum starting temperature Z = 2.0°C

A8

Low pressure cooling water low flow alarm 8.0 m³/hr.*

A10

Purge filter pressure drop alarm = 25 psi Unit Operational Controls

Pump differential pressure alarm and load limit signal with any two pumps less than H = 18 psi* or any two motor breakers open. Pump differential pressure fuel trip with all three pumps less than L = 10 psi or C2 all three motor breakers open (5sec. time delay for transient pressure fluctuations and emergency bus transfer). * These alarm circuits must always be active on idle pumps. C1

13.6 The pneumatic valves in emergency cooling water line The pneumatic valves (HAG10 AA201& HAG10 AA202) in emergency cooling water line shall open automatically during boiler black out condition. 14.0 Drain oil pump at boiler front Start/Stop command and status indication for Drain oil pump at boiler front shall be issued/indicated from DDCMIS. 15.0 Pulverised fuel (PF) pipe choking monitoring The surface temperature of PF pipes shall be recorded. When this temperature falls below the associated mill outlet temperature by more than 10 deg C in any of these pipes, then alarm shall be generated. If further fall in temperature is noticed in the pipe, then this indicates that there is choking in the pipe and necessary action shall be taken.

The settings for

temperature difference shall be fine adjusted at site seeing actual operating conditions. **********************

Page 19 of 19

Recommended Write Up on Boiler Aux and Interlock Protection, Rev02

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