Boiler Interlock And Protection

Manish DhruwAsst Manager

14843Cpp-540

Boiler Interlock - A Boiler Interlock is an arrangement of heating controls. It ensures the boiler does not fire when there is no demand for heat.

Protection of boiler – Boiler protection are provide to detect the abnormal condition by constantly measuring the various parameter under normal and faulty condition. If any abnormality happened trip the boiler to prevent from major damage.

Need of Interlocks & Protection◦ To avoid operational faults◦ To avoid equipments damage.◦ To avoid accidents to individuals.◦ To avoid system disturbances

Boiler interlock and protection

1. Both ID fan trip. 2. Both FD fans trip. 3. Emergency manual

trip. 4. Turbine tripped and

HPLP bypass not opened (RH protection act).

5. Drum level low low low (<-325mm with 5 sec delay).

6. Total air flow<30%. 7. Furnace pressure

low low low (<-254 mm of H2O).

8. Furnace pressure high high high (>+330 mm of H2O).

In case of MFT Trip

• 9. Unit flame failure.• 10. Loss of fuel.• 11. Loss of scanner

cooling air (Scanner air pressure<2 KPa with 5 min time delay).

• 12. Both APH tripped.• 13. Oil burner light off

failed. • Other than MFT-• 1. MS

temperature≥5850C (5 sec time delay).

• 2. RH temperature≥5850C (5 sec time delay).

Master Fuel Trip - it produces trip signal for fuel systems from operation , then trip the boiler out of service away from danger. this relay needs many conditions to operate , these conditions will be found at the following points.

Interlocks cum protections

1. If one ID fan trips, one FD fan will trip in the same sequence. 2. If one FD fan trips, one ID fan will trip in the same sequence. 3. If one APH trips, one ID fan, one FD fan and one PA fan will

trip in the same sequence. 4. In case of GCB opening, top elevation mill or non adjacent

mill will trip. 5. If drum level≥200 mm, EBD will open. 6. If drum level≤150 mm, EBD will close. 7. Feed water flow<50 TPH, Economiser recirculation MOV will

open. 8. Feed water flow>80 TPH, Economiser recirculation MOV will

close. 9. If superheated steam pressure is higher than 14.86 MPa ERV

will open and if pressure is lower than the value ERV will close (if kept in service).

 

Boiler

1. Boiler drum pressure- a) Higher than 17.24 MPa LHS safety valve will lift

and it will reset @ 16.35 MPa. b) Higher than 16.74 MPa RHS safety valve will lift

and it will reset @ 16.21 MPa.

2. Superheated steam pressure- a) Higher than 15.29 MPa, LHS safety valve will lift

and it will reset @ 14.765 MPa. b) Higher than 15.2 MPa, RHS safety valve will lift

and it will reset @ 14.747 MPa.

3. CRH steam pressure- a) Higher than 3.058 MPa, LHS safety valve will lift

and it will reset @ 2.947 MPa. b) Higher than 2.963 MPa, RHS safety valve will lift

and it will reset @ 2.867 MPa.

4. HRH steam pressure- a) Higher than 2.817 MPa, LHS safety valve will lift

and it will reset @ 2.726 MPa. b) Higher than 2.75 MPa, RHS safety valve will lift

and it will reset @ 2. 62 MPa.

Other Protections

Drum level 1. Level>125 mm: high

priority alarm. 2. Level>-125 mm: high

priority alarm. 3. Level>250 mm:

emergency priority alarm. 4. Level>-250 mm:

emergency priority alarm. Furnace pressure 1. Pressure>30 mm of

H2O: high priority alarm. 2. Pressure>-30 mm of

H2O: high priority alarm. 3. Pressure>50 mm of

H2O: emergency priority alarm.

4. Pressure>-50 mm of H2O: emergency priority alarm. 

MS flow 1. MS flow>200 TPH: high

priority alarm. 2. MS flow>450 TPH:

emergency priority alarm. 

Alarm

• MS & RH Temperature• 1. MS temperature>5450C:

high priority alarm.• 2. MS temperature>5500C:

emergency priority alarm.• 3. RH temperature>5450C:

high priority alarm.• 4. RH temperature>5500C:

emergency priority alarm.• Others• 1. APH flue gas inlet

temperature<3000C: high priority alarm.

• 2. O2<1: high priority alarm.

• 3. O2 zero: emergency priority alarm.

• 4. Furnace DP≥90 mm of H2O: high priority alarm.

• 5. Furnace DP≤10 mm of H2O: high priority alarm.

1. No ID fan A/B converter/ device fault. 2. No ID fan protection acted. 3. ID fan A/B inlet & outlet damper

closed. 4. ID fan IGV in minimum position. 5. APH A/B flue gas inlet & outlet damper

open. 6. APH A/B running

1. ID fan A/B breaker protection acted. Or

2. BMS trip ID fan A/B. Or 3. FD fan A/B tripped. Or 4. APH A/B tripped. Or 5. ID fan A/B temperature protection

acted. 6. ID fan A/B vibration protection acted. 7. ID fan A/B running and fan outlet

damper closed.

Start enabl

e Interlock:

TRIP enabl

e Interlock:

ID Fan interlock & protection

AND

OR

ALARM

1. Fan/ motor bearing temperature≥750C: high priority alarm.

2. Fan/ motor bearing temperature≥800C: emergency priority alarm.

3. Fan bearing vibration≥6.3 mm/sec: high priority alarm.

4. Fan bearing vibration≥11mm/sec: emergency priority alarm.

5. Motor winding temperature≥1100C: high priority alarm.

6. Motor winding temperature≥1200C: emergency priority alarm

TRIP 1. Motor winding temperature≥1300C (2 out of

6 temperatures with 60sec time delay). 2. Fan/ motor bearing temperature≥900C (with

60 sec time delay). 3. Fan bearing vibration≥11mm/sec ( with 60

sec time delay). 4. ID fan motor protection (over current, earth

fault, negative sequence, phase fault etc) acted.

5. BMS trip ID fan. 6. FD fan trip to ID fan trip. 7. ID fan running and fan discharge damper

closed. 8. APH trip to ID fan trip.

1. No FD fan A/B converter/ device fault. 2. No FD fan protection acted. 3. FD fan A/B outlet damper closed. 4. FD fan IGV in minimum position. 5. APH A/B flue gas inlet & outlet damper

open. 6. APH A/B running. 7. ID fan A/B running.

1. FD fan A/B breaker protection acted. Or

2. BMS trip FD fan A/B. Or 3. ID fan A/B tripped. Or 4. APH A/B tripped. Or 5. FD fan A/B temperature protection

acted. 6. FD fan A/B vibration protection acted. 7. FD fan A/B running and fan outlet

damper closed.

 

AND

OR

FD Fan interlock & protection

Start enable Interlock:

TRIP enable Interlock:

ALARM 1. Fan/ motor bearing temperature≥750C: high

priority alarm. 2. Fan/ motor bearing temperature≥800C: emergency

priority alarm. 3. Fan bearing vibration≥6.3 mm/sec: high priority

alarm. 4. Fan bearing vibration≥11mm/sec: emergency

priority alarm. 5. Motor winding temperature≥1100C: high priority

alarm. 6. Motor winding temperature≥1200C: emergency

priority alarm.TRIP

1. Motor winding temperature≥1300C (2 out of 6 temperatures with 60sec time delay).2. Fan/ motor bearing temperature≥900C with 60 sec time delay.3. Fan bearing vibration≥11mm/sec with 60 sec time delay.4. FD fan motor protection (over current, earth fault, negative sequence, phase fault etc) acted.5. BMS trip FD fan.6. ID fan trip to FD fan trip.7. FD fan running and fan discharge damper closed

1. No PA fan A/B converter/ device fault. 2. No PA fan protection acted. 3. PA fan A/B outlet damper closed. 4. PA fan IGV in minimum position. 5. APH A/B flue gas inlet & outlet

damper open. 6. APH A/B running. 7. ID fan A/B running. 8. FD fan A/B running. 9. No boiler trip command.

1. PA fan A/B breaker protection acted. Or

2. MFT trip PA fan A/B. Or 3. ID fan A/B tripped. Or 4. FD A/B tripped. Or 5. PA fan A/B temperature protection

acted. 6. PA fan A/B vibration protection acted. 7. PA fan A/B running and fan outlet

damper closed

Start enable Interlock

Trip enable Interlock:

PA Fan interlock & protection

AND

• OR

ALARM 1. Fan/ motor bearing temperature≥750C: high priority alarm. 2. Fan/ motor bearing temperature≥800C: emergency priority

alarm. 3. Fan bearing vibration≥6.3 mm/sec: high priority alarm. 4. Fan bearing vibration≥11mm/sec: emergency priority alarm. 5. Motor winding temperature≥1100C: high priority alarm. 6. Motor winding temperature≥1200C: emergency priority alarm.

TRIP 1. Motor winding temperature≥1300C (2 out of 6 temperatures

with 60 sec time delay). 2. Fan/ motor bearing temperature≥900C with 60 sec time delay. 3. Fan bearing vibration≥11mm/sec with 60 sec time delay. 4. PA fan motor protection (over current, earth fault, negative

sequence, phase fault etc) acted. 5. MFT trip PA fan. 6. ID fan/ FD fan A/B trip to PA fan A/B trip. 7. PA fan running and fan discharge damper closed.

1. No fan converter/ device/ breaker fault.

2. Any one PA fan running. 3. Fan IGV in minimum position. 4. In case of one fan running & other

fan standby- a) If running fan getting tripped

due to any protection acting then stand by fan will start in interlock if selected.

b) If seal air pressure becomes low (<6 KPa), then standby fan will start by interlock.

4. During unit start up fan start enable will come with the start of any PA fan if selected in fan auto start interlock.

**Command will go to Seal air fan IGV for 60% opening in auto with the start of the fan.

1. Fan breaker protection acted. Or 2. Both PA fans are stopped (after

2S fan will stop).or 3. In case of both seal air fan

running and seal air header pressure>22 KPa then one seal air fan will stop in auto if selected in interlock (discharge pressure

Start enable interlock

Trip enable interlock:

Seal air fan interlock & protection

• AND

• OR

1. Seal air fan current>200 Amp: high priority alarm.

2. Seal air fan current>260 Amp: emergency priority alarm.

3. Seal air discharge pressure<800: high priority alarm.

4. Seal air discharge pressure<600: emergency priority alarm.

1. Seal air fan current≥ 284Amp.

2. Both PA fans stopped/ tripped (fan trip after 2Sec).

3. Seal air fan breaker protection acted.

4. Seal air header pressure>22 KPa (in case of both fans are running), trip one fan.

 

ALAR

M

TRIP 

1. No motor or breaker protection acted.

2. Fan is in remote. 3. In case of one fan is running

and the other is in stopped condition-

a) By interlock input if one fan is stopped/ tripped, standby fan will start in auto.

b) If scanner air header pressure<2 KPa for 5 sec, then standby fan will start in auto by interlock input.

1. Scanner air header pressure< low switch acting: emergency priority alarm.

2. Scanner air fan trip: emergency priority alarm.

1. Scanner air fan breaker protection acted.

2. Scanner air fan motor protection acted.

Start Enable Interlo

ck

Alarm

Trip

Scanner Air Fan Interlock Protection

AND

1. No breaker/ motor protection acted.

2. Lube oil pressure normal for > 5 minutes.

3. No MFT acted. 4. Boiler drum pressure>3.4

kg/cm2. 5. Secondary air

temperature>1770C. 6. Total air flow<40%

(230TPH). 7. MDVs are open. 8. Mill outlet

temperature<1150C. 9. Cold air gate is open. 10. Coal feeder is in remote. 11. PA permit satisfied. 12. Mill ignition permit

satisfied.

AND

Mill Interlock & Protection

Start Enable

Interlock

1. Feeder trip and no mill ignition permit.

2. MFT. 3. MDVs closed. 4. Lube oil pressure low (2 out of

3 lube oil pressure<low switch act).

5. Seal air differential pressure low low.

6. Loss of primary air (differential pressure between APH outlet primary air and furnace pressure less than 460mm of H2O.

Other Interlocks: 1. On tripping of mill Close

command will go to HAG. 2. In case of GCB opening and

unit coming to house load, top/ non adjacent mill will trip.

3. In case of one ID fan tripping, one top elevation mill will trip.

 

TRIP Enabl

e Interlock

AND

1. Mill lube/ hydraulic oil tank temperature>750C: high priority alarm.

2. Mill lube oil thrust pad oil temperature>600C: high priority alarm.

3. Mill lube oil thrust pad oil temperature>700C: emergency priority alarm.

4. Mill motor front/ rear bearing temperature>750C: high priority alarm.

4. Mill motor winding temperature>1000C: high priority alarm.

5. Mill outlet, roller bearing temperature>900C: high priority alarm.

6. Mill current>60 amp: high priority alarm.

7. Mill inlet PA flow< 50 TPH: high priority alarm.

8. Mill hydraulic pressure>150 kg/cm2: high priority alarm.

9. Mill hydraulic pressure<70 kg/cm2: high priority alarm.

10. Seal air header pressure<800 mm of H2O: high priority alarm.

11. Seal air header pressure<600 mm of H2O: emergency priority alarm.

 

Alarm

1. Mill motor protection (over current, earth fault, negative sequence, phase fault etc) acted.

2. MFT trip mills. 3. MDVs closed trip mill (2 out of 4

MDVs). 4. Mill lube oil pressure low (2 out of

lube oil pressure<low switch acting) trip mill.

5. Loss of primary air (differential pressure between APH outlet primary air and furnace pressure less than 460mm of H2O).

6. Feeder trip and no mill ignition permit.

7. Seal air differential pressure low low.

8. Mill lube oil pump in local. OTHERS 1. In case of GCB opening and unit

coming to house load, top/ non adjacent mill will trip.

2. In case of one ID fan tripping, one top elevation mill will trip.

Trip

 Start enable Interlock: 1. No breaker or motor

protection acted. 2. Respective mill ignition

permit. 3. Feeder speed (VFD

command) minimum. 4. No mill trip command. 5. Feeder is in remote.

  1. Mill trip/ emergency stop. 2. MFT. 3. Feeder running and no coal. 4. Mill outlet

temperature<540C and HAG closed and feeder VFD command<2%.

AND

OR

Coal Feeder Interlock & Protection

 Start Enable

Interlo

ck

Stop/Trip Enable Interlo

ck:

1. Belt deviation of feeder switch act: high priority alarm.

2. No coal switch act: high priority alarm.

3. Coal jam switch act: low priority alarm.

4. Feeder cleaner motor fault: low priority alarm.

5. Coal flow zero: low priority alarm.

1. Mill trip to feeder trip. 2. MFT to feeder trip. 3. Feeder motor/ breaker protection

acted. 4. Feeder running and no coal. 5. Mill outlet temperature<540C and

HAG closed and feeder VFD command<2%.

 

Alarm

Trip

1. No breaker or motor protection acted.

2. LOP is in remote. 3. Oil pool temperature of lube

oil>600C.

1. Oil pool temperature of lube oil<450C.

2. After LOP starting if oil pool temperature of lube oil<450C and mill not running (30 mins time delay).

3. After mill stopping after 4 hrs time delay stop command will go for LOP.

AND

OR

Start enable Interlock

Stop/trip enable Interlock

Mill Lub Oil Pump Interlock & Protection

1. Lube oil pump stopped: emergency priority alarm.

2. Lube oil pressure<low switch act: emergency priority alarm.

3. Oil pool temperature>: 750C high priority alarm.

4. Lube oil thrust liner sump temperature>: 600C high priority alarm.

5. Lube oil thrust liner sump temperature>: 700C emergency priority alarm.

1. LOP motor/ breaker protection acted.

2. Oil pool temperature of lube oil<450C.

3. After LOP starting if oil pool temperature of lube oil<450C and mill not running (30 mins time delay).

4. After mill stopping after 4 hrs time delay stop command will go to LOP.

Alarm

Trip

1. No breaker or motor protection acted. 2. APH is in remote. 3. Guide and support bearing oil pump

running for minimum of 300 sec (for U#2 APH).

  1. APH flue gas inlet temperature<800C

and fans (ID, FD & PA) are running. 2. For APH auxiliary motor, with the start

of APH main motor trip command will go.

Start enabl

e Interlock

Stop/trip

enable

Interlock:

APH Interlock & Protection

AND

OR

• Other Interlocks:• 1. Start command will go for APH auxiliary motor (DC) with

the tripping of APH main motor.• 2. In case of APH main motor VFD getting bypassed due to

any fault, APH main motor DOL supply will pick up.• 3. For U#2 APH-• a) If APH support/guide bearing temperature> 540C, lube oil

pump will start.• b) If APH support/guide bearing temperature< 500C, lube oil

pump will stop

Thanks