BOILER PROTECTION AND INTERLOCKS

BOILER PROTECTION AND INTERLOCKS

PROTECTION & INTERLOCKS

INTRODUCTION

In a modern power plant continuous and reliable operation of various auxiliaries of a unit becomes necessary and this calls for an elaborate system of protections. And interlocks to ensure the either defects in equipments or an operation error do not cause damage to the equipments. Extensive protections are provided to trip the boiler or turbine or any individual auxiliary in case of faults so that the faulty equipment is isolated without causing further damage. Interlocking is provided to switch on the reserve equipment in case of tripping of the running equipments to enable continuity of functions. Visual and audible signaling is provided to pin point the causes of protective action and to enable the operators to take corrective action in case of abnormal changes.

PROTECTION FOR THE STEAM GENERATOR

The steam generator will get tripped in the case of the following abnormalities.

DRUM LEVEL VERY HIGH

If the boilers drum level is more then +330 mm for 5 sec or more, the boiler will trip. Three protection contacts are provided out of which 2 contacts should be made for the protection to act. The contacts are

a) Level transmitter : LR 511012 (level recorder)

b) Level switch : LS 511435.

c) Hydra step : In the case of Hydra step

Very high tripping signals will be given only when both channel 13 (+288mm) and channel 14 (+340mm) read water (green lamp signal). This prevents tripping due to any possible spurious signals.(STAGE-II)

NOTE: In case 1/3 drum level H1/LO trip alarm is existing either in level transmitter or level switch, the hydra step test push button should not be pressed.

DRUM LEVEL VERY LOW

If the boiler drum level is very low, i.e. less then 340 mm for more then 5 seconds, then the boiler will trip if two out of the following three contacts are made.

a) Drum Level transmitter Lr.511 012.

b) Drum Level switch LS 511 425.

c) Hydra step In this case, Very low tripping signal will be given only when channel 2 (-288mm) and channel 1 (-340mm) both read steam (red lamp signal). This prevents spurious trip signals.

NOTE:

In case 1/3 drum Level H1/Lo trip alarm is existing (i.e. either transmitter or Level Switch Contact is already made), the Hydra step test push button should not be pressed.

FURNACE PRESSURE VERY LOW:

When the furnace pressure drops to 30-milli bar or more and persists for 2 seconds or more, the boiler will trip. Also it will cause tripping of both I.D. fans. The Protection will act only when 2 out of 3 contacts (PS 512 415-1A, 2A AND 3A) are made.

FURNACE PRESSURE VERY HIGH:

If the furnace pressure is very high, i.e. more than +25 mill bar for more than 2 second, boiler will trip. Furnace pressure very high Protection will also cause tripping of both FD Fans. The protection will act only when 2 out of 3 contacts are made.

BOTH AIRWAYS NOT FREE

The boiler will trip when Both Airways are not free condition exists. AIR WAY FREE condition will be satisfied only if

a) FD fan A/B is running.

b) Air Damper at FD fan discharge (AD1 A/B) is open and

c) Air Damper after RAPH (AD2 A/B) is open

Or

RAPH bypass damper (AD 3 A/B) is open.

BOTH GASWAYS NOT FREE

The boiler will trip when both Gas ways are not free condition exists. Gas Way Free condition will be satisfied only if

a) ID fans A/B is running

b) Gas Damper before RAPH (GD 1 A/B) is open

c) Gas Damper after ID fan (GD 2 A/B) is open

d) Any one of the RAPH MOTORS IS RUNNING.

e) RAPH speed is more than minimum (70 %)

BOTH SCANNER AIR FANS TRIPPING:

If both scanner air fans are in tripped condition, for more than 1 minute the boiler will get tripped. (BY PASSED)

H.P BYPASS AND TURBINE CONDITIONS NOT FULFILLED:The boiler trips on H.P. Bypass and Turbine Conditions not fulfilled Condition which arises on any one of the following causes.

a) CRH Temperature downstream of H.P.by pass valve on any one side exceeds 370 ( C for more than 5 seconds.

b) When Turbine has tripped but fuel flow in the boiler is more than 60 % for more than 15 seconds (Load and combustion control should reduce fuel flow to well below 60 % in 12 seconds in the event of turbine trip via run back system.

c) When turbine has tripped and even if one of the two H.P. bypass valves remains closed.

d) When turbine has tripped and one or both Super heater 50 % Safety valves have opened.

e) If even one out of the two super heater outlet stop valves closes, with boiler at high firing rate (i.e. oil Burners in service with an oil flow > 20 % i.e.3.2 T/hr (or) any one of the end conveyors is in operation for more than 30 seconds).

BOILER INTERLOCKING FULFILLED:

Boiler Interlocking Fulfilled annunciation normally persists in the control desk indicating that none of the above protection has acted and the boiler can operate/ continue to operate. When any one of the above protections acts, Boiler interlocking fulfilled lamp will go off.

NOTE:

The boiler will also trip when the boiler emergency key switch on the control desk is pressed. The switch should be normally in released condition for Boiler Interlock Fulfillment

EFFECTS OF BOILER TRIPPING :

Whenever any one of the above causes actuates Boiler Tripping the following effects take place

1. Boiler Interlocking Fulfilled Lamp Vanishes.

2. Oil Main Valve closes (TRIP VALVE) cutting off oil supply to the burners.

3. Ignition Release for oil Fire Existing lamp vanishes no oil burner can be started.

4. All the running pulverizing mills will trip.

5. All the running end conveyors will trip.

6. Ignition Release for Lignite Firing goes off-no feeder/ mill group can be switched on.

7. Turbine tripping is also actuated.

PROTECTIONS AND INTERLOCKS OF BOILER AUXILIARY EQUIPMENT:

REGENERATIVE AIR PRE-HEATER:

LUBRICATING OIL SYSTEM:

There are two lubricating oil pumps for each RAPH, out of which one is in normal service for supplying lubricating oil to RAPH bearings. Illuminated push button (ILPB) switches are provided for starting and stopping of the lubricating oil pumps and manual starting and stopping are done by pressing the respective switches. There is also a standby selector switch in the control desk for lubricating oil pump with two positions 1 & 2 .If this switch is put in 1 or 2 position, the corresponding lubricating oil pump becomes a standby.

MANUAL STARTING

The RAPH lub oil pump can be started on manual mode when the ILPB is pressed provided the pre selection switch is selected for the respective pump starting. It can be stopped from the control desk by pressing the stop ILPB,

AUTO STARTING OF LUBRICATION OIL PUMP

The reserve pump will start on auto when running lubrication oil pump trips provided the stand selector switch in the control desk is in corresponding pump stand-by position

PROTECTION FOR LUBRICATION OIL PUMP

1.The running lubrication oil pump will trip if the lubrication oil level in the tank is less than a minimum oil level specified.

2.Both (LOP) motors of RAPH remain in tripped condition for one hour.

RAPH A/B MOTOR

Each RAPH has two motors out of which one will be in service and the other will be stand b

MANUAL STARTING

The RAPH motor can be started or stopped from the control desk by pressing the corresponding ILPB switch. The motor will start only if the following conditions are satisfied.

1. The other RAPH motor is in stopped condition.

2. Selector switch of the motor is put in main position.

3. Any one of the two lubricating oil pumps is running for more then 30 seconds.

MAGNETIC COUPLING

Whenever the RAPH motor is started its magnetic coupling engages after 9 seconds of motor starting. The coupling can also be engaged by pressing the push button switch at the desk. (Removed)

NOTE

The RAPH motor has a selection switch with two positions M1 and M2 .if the switch is put in M1 position the motor becomes main and M2 motor becomes stand by and vice versa.

RESERVE STARTING

The reserve RAPH motor M1/M2 will start automatically when the other running motor trips provided,

1. Any lub oil pump is in service for more then 30 seconds.

2. Selector switch for the reserve motor is in corresponding stand by position

AUTO STOPPING

The RAPH motor trips on protection if,

a) Lubricating oil pressure is less then 1.5 Ksc for more then 5 seconds (contact is to be made in two out of the three oil pressure switches at the local)

b) Support bearing temperature is >110(c

c) Guide bearing temperature is >110(c

INDUCED DRAUGHT FAN

COOLING AIR FANTwo cooling air fans are provided for each I.D fan for cooling purpose of I D fan bearing etc. One of the two fans will be in normal service and the other will be a standby. There is a selection switch with two positions 1 & 2.

MANUAL STARTING

The cooling air fan can be started from the control desk by pressing the corresponding ILPB if the selection switch is selected for the corresponding fan.

AUTO STARTING

The reserve cooling air fan will start provided the pre selection switch is in standby position and

When

1. The running cooling air fan trips.

2. When the ID fan A/B is in stopped condition, and its bearing temperature is greater than 80(c contact in (any one out of the three bearing temp.switches), its cooling air fan will start automatically.

AUTO STOPPING

Cooling air fan will stop automatically when

1. I D fan is switched off and the condition exists for 5 minutes and

2. All the bearing temperatures are less than 50(c

ID FAN LUBRICATION OIL PUMP

There are two lubricating oil pumps for each ID fan, one will be in service and the other is kept as stand by .The lub oil pump is provided with an ILPB in the control desk and also a stand by selection switch.

MANUAL STARTING

Any of the lubricating oil pump can be started from the control desk by pressing the start ILPB provided the selector for the pump is pre selected

AUTO STARTING

The lubricating oil pump will start automatically provided the selection switch is in stand by position in the following cases

When the running lub oil pump trips and tripped condition exists for 5 seconds.

a) If the other lubricating oil pump is running for more then 5 seconds, but the control oil pressure is less than 8 bar

b) When bearing temperature of I D fan is more then 80(c even when I D fan is in stopped condition (One out of three bearing temperature switches).

AUTO STOPPING

The lub oil pump will trip

a) If the oil level in the lubricating oil tank is less then the preset minimum level.

b) 5 minutes after stopping of the corresponding ID fan provided all the three bearing temperatures are less than 50(c

INDUCED DRAUGHT FAN ( A or B )

START UP LOGICS

ID fan A or B will start when the start push button is pressed only if the following conditions are fulfilled

1. Any one of the corresponding RAPH motors (M1 or M2) is in service

2. Any one of the two cooling air fans of the respective I D fans is in service.

3. Any one of the two lubricating oil pumps (of fan A or B) is in service.

4. Control oil pressure is more than 6 bar.

5. Impeller blades in closed position ( 0 indication)

6. Hand brake of the respective fan should be in released condition (originally existing and now it is removed).

ID FAN TRIPPING LOGICS

I D fan A or B will trip on auto due to any one of the following causes

1. When both motors of the corresponding RAPH trip and the tripped condition exists for more than 5 seconds

2. Speed of RAPH (A or B) is less than minimum (70 %) for more than 60 seconds

3. I D fan stator winding temperature is more than 140 (c

4. Oil level in the lubricating and control oil tank is less than preset minimum

5. Vibration is greater than 11 mm / sec

6. Motor bearing temperature is more than 100 (c (one out of two contacts)

7. Fan bearing temperature is more than 110 (c (two out of three contacts)

8. Lubricating oil flow is less than minimum for more than 5 seconds

9. Furnace pressure is less than 30 mill bar (for this protection two out of three contacts)

10. When ID fan is running more than 120 seconds with any one of the corresponding dampers before RAPH -GD1or after GD2, is in closed condition

FORCED DRAUGHT FAN

LUBRICATING OIL PUMP

Each FD fan is provided with two lubricating and control oil pumps out of which one will be in service and the other will be kept as stand by. There is also pre-selection switch at control desk

MANUAL STARTING

Pressing the ILPB in the desk after pre selecting the pump can start the lub oil pump

AUTO STARTING

The reserve lub oil pump of FD fan starts automatically provided the selection switch is kept in the corresponding pump position and

1. When the running lubricating oil pump trips (with in 5 second of tripping) and

2. When the control oil pressure drops below 8 bar provided the other lubricating circulating oil pump is running for more than 5 seconds

STOPPING OF LOP

Pressing the ILPB switch in the control desk can stop the lubricating and control oil pump of FD fan

TRIPPING OF LOP

The running lubricating oil pump (of FD fan A or B) will trip automatically.

a) When oil level in the tank is less than preset minimum.

b) When FD fan (A or B) is not running for more than 60 minutes.

FD FANS START UP LOGICS.

FD fan A/B will get started when the Start ILPB is pressed provided the following conditions are fulfilled.

1. Any one lubricating oil pump is in service.

2. The control oil pressure is more than 6 bar.

3. Hand brake of the fan is in released condition.

4. Impeller blades are in closed position.

STOPPING OF FD FAN:

MANUAL STOPPING:

The FD fan can be stopped by pressing

a) FD fan A/B validation push button

b) Stop push button in the control desk

AUTO STOPPING:

The FD fan (A or B) will trip if

1. Flue gas way is not free

2. FD fan is running for more than 120 seconds with its discharge damper (AD 1A/1B) in Closed position.

3. When damper after RAPH (AD 2A/2B) and RAPH bypass damper (AD 3A/3B) are in closed condition and FD fan (A/B) is running for more 120 seconds.

4. Furnace pressure is more than +25 mill bar (2 out of 3 contacts)

5. FD fan motor bearing temperature exceeds 100 (c (1 out of 2 contacts.)

6. FD fan bearing temperature exceeds 110 (c (2 out of 3 contacts).

7. Stator winding temperature exceeds 140(c.

8. Vibration is more than 11 mm/sec.

9. Oil level in the tank is less than preset minimum level.

10. The lub. Oil flow is less than 6 lit/ Minute for more than 5 seconds

INTER LOCKING OF AIR AND GAS DAMPERS

GAS SIDE DAMPERS

MANUAL OPERATION

To open the gas damper 1A /1B, the open ILPB. switch in the control desk should be pressed. The damper will open only after one second after the fan is started. It is possible to close the damper manually by pressing close ILPB only when the fan is not running.

AUTO OPENING

When ID fan A/ B is started, the corresponding gas damper 1A/ 1B opens automatically

AUTO CLOSING

1. When one of the two ID fans trip or is stopped and the other is running, the corresponding gas damper (1A /1B) will close automatically.

2. When both ID fan s trip both gas dampers 1A & 1B remain open.

GAS DAMPER AFTER ID FAN A/B/ (GD 2A/2B)

Manual operation:

1.Gas Damper 2A/2B can be opened manually by pressing ILPB switch in any of the following conditions.

i. When the corresponding fan is started and the other fan is in stopped condition.

ii. When both fans are running

iii. When both fans are in stopped condition.

2.The gas Damper 2A/2B can be closed with Close ILPB if no open command is persisting.

AUTO OPENING:

1. The gas damper 2A/2B will open automatically when ID fan A/B is started.

2. When ID fans are stopped, then both the dampers GD 2A and 2B will open automatically and control vanes of the fan open fully.

AUTO CLOSING

Whenever ID fan A/B trips, the corresponding discharge damper 2A/2B will close automatically, if the other fan is running.

DAMPER IN THE AIR PATH

Damper after FD fan A/B (AD 1A/1B)

MANUAL OPERATION:

1. FD fan discharge damper 1A/1B can be opened manually by pressing ILPB switch in any of the following conditions.

a) When the corresponding fan is started and the other fan is in stopped condition.

b) When both fans are running.

c) When both fans are stopped or tripped condition.

2. The damper can be closed manually by pressing CLOSE ILPB switch only if the fan is stopped and open command is persisting.

AUTO OPENING:

1. When FD fan A/B is started, the damper will open automatically.

2. When both FD fans trip both the dampers will open automatically.

AUTO CLOSING:

When FD fan A/B trips or is stopped and the other fan is running, the respective discharge damper. (AD 1A/1B) will close.

AIR WAY FREE LOGIC:

Air way free condition is satisfied only if,

a) FD fan A/B is running.

b) Damper after FD fan A/B (AD 1A /1B) is opened.

c) Damper after RAPH A/B (AD 2A/2B) or RAPH bypass damper (AD 3A/3B) is opened.

NOTE:Boiler will trip when BOTH AIR WAYS ARE NOT FREE condition appears.

FLUE GAS WAY FREE LOGIC :

Flue gas way free logic is satisfied only when following conditions are fulfilled.

a) Any one of the RAPH motors (A1/A2 OR B1/B2) is in running conditions.

b) Speed of RAPH A/B/ is greater than minimum (70%)

c) ID fan A/B is in service.

d) Damper before RAPH A/B (GD 1A/1B) is in open condition.

e) Damper after ID fan A/B (GD 2A/2B) is in Open condition.

Note: Boiler will trip when both gas ways are not free.

SCANNER AIR FAN:

There are two Scanner air fans in our boilers, out of which one will be in service and the other is a stand by.

1. The scanner air fan can be started or stopped on manual command from control desk.

2. When the running scanner air fan trips, the reserve starts provided the selection switch is in standby position.

3. If both Scanner air fans are in tripped condition for more than two minutes the boiler will trip.

FUEL OIL PUMP:

Each boiler is provided with two numbers of fuel oil pumps at the fuel oil pump house. One of these two will be in continuous service and the other is kept as standby. The fuel oil pump-starting/stopping switch is also provided in the boiler control desk.

MANUAL STARTING:

The fuel oil pump will start on manual command (by pressing the ILPB switch) provided the suction header pressure is not low.

AUTO STARTING:

The reserve fuel oil pump starts when running pump trips or fuel oil discharge pressure is low provided,

1. Suction pressure is not low.

2. Operation selection switch is in auto position.

TRIPPING:

The fuel oil pump trips when

1. Suction pressure is low

2. There is switchgear trouble.

SLAG REMOVER MANUAL OPERATION:

Pressing the push button at local after selecting the desk system selection switch is manual position can start the slag remover.

AFTER BURNING GRATES:

1. The After Burning grates can be started manually from local only if slag remover, is running.

2. The After Burning grates will trip, if the slag remover trips or is stopped.

EMERGENCY DRUM DRAIN VALVES:

1. The Emergency Drum drain Valve will open when boiler drum level is more than +300mm and will close when the level drops down to +250 mm. provided the selection switch is in auto position.

2. The valve can be, opened or closed on manual command if the selection switch is in manual position.

P&I CHECKS (Stage I):

I.RAPH:

1.After completion of mechanical, Electrical and Instrumentation works in RAPH, Air dampers, Gas dampers and confirm that concerned LCs are in deposited /returned condition.

2.Start any one of LOP of concerned RAPH

3.Reserve LOP starting from UCB may be checked for both LOPs by keeping selector switch in appropriate position and stopping running pump from UCB.

4.Reserve LOP starting from local may be checked for both LOPs by keeping selector switch in appropriate position and applying local latch for running pump.

5.Lub oil tank level very low contact for lifting the level switch may check both LOPs tripping.

6.By keeping any one of LOP in service, start any one motor of RAPH by selecting other motor in stand by condition.

7.Reserve motor starting from UCB may be checked for both RAPH motors by keeping selector switch in appropriate position and stopping running motor from UCB.

8.By making RAPH support bearing/Guide bearing temperature High contact for annunciation and V.High for RAPH trip will be checked.

9.By keeping RAPH in service, Lub oil pressure