BOILER PROTECTION AND INTERLOCKS

PROTECTION AND INTERLOCKS INTRODUCTION: In modern power plant continuous and reliable operation of various auxiliaries if a unit becomes necessary. Extensive protection 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 equipment to enable continuity of functions.

PROTECTION FOR THE STEAM GENERATOR Drum level is very high. Drum level is very low. Furnace pressure is very high. Furnace pressure is very low. Both airway not free. Both flue gasway not free. Scanner air fan in trip condition. H. p bypass and turbine condition is not fulfilled.

BOILER INTERLOCKING FULLFILLED “BOILER INTERLOCKING FULLFILLED” 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 protection acts, “BOILER INTERLOCKING FULFILLED “ lamp will go off. 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 INTERLOCKING FULFILLMENT”.

EFFECTS OF BOILER TRIPPING Boiler interlocking fulfilled lamp vanishes. Oil main valve closes (TRIP VALVE) cutting off oil supply to the burner. Ignition release for oil fire existing lamp vanishes no oil burner can be started. All the running pulverizing mill will trip. All the running end conveyors will trip. Ignition release lignite firing goes off no feeder/ mill group can be switched on. Turbine tripping is also actuated.

BOILER AUXILIARY EQUIPMENT A) REGENRATIVE AIR PREHEATER 1.LUBRICATING OIL SYSTEM: There are two lubricating oil pump for each RAPH, out which one is in normal service for supplying lubricating oil to RAPH bearing. Illuminated push button switch are provided for starting and stopping of the lubricating oil pump and manual starting and stopping are done by pressing the respective switches. PROTECTION FOR LUBRICATING 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. 2. Both LOP motors of RAPH remain in tripped condition for the one hour.

2) RAPH MOTOR: MAGNETIC COUPLING : Each RAPH has two motors of which one will be in service and the other will be in stand by . MAGNETIC COUPLING : whenever the RAPH motor is started its magnetic coupling engages after 9 seconds of motor starting.

B.INDUCED DRAUGHT FAN 1.COOLING AIR FAN: Two 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 the normal service and the other will be a stand by. By pressing the switch on the control desk we can manually start the fan. AUTO STARTING : 1. The running cooling air trips. 2. When the I.D. fan in stopped condition and its bearing pressure is greater than 80.

2.ID FAN LUBRICATION OIL PUNP There are two lubricating oil pump for each I.D. fan. One will be in the service and the other is kept as a stand by. The lub oil pump is provided with an ILPB in control desk and also a stand by selection switch.

I.D FAN START UP LOGICS Any one of the corresponding RAPH motors (1 or 2) is in service Any one of the two cooling air fans of the respective I D fans is in service. Any one of the two lubricating oil pumps is in service. Control oil pressure is more than 6 bar. Impeller blades in closed position. Hand brake of the respective fan should be in released condition

ID FAN TRIPPING LOGICS When both motors of the corresponding RAPH trip and the tripped‘ condition exists for more than 5 seconds Speed of RAPH is less than minimum (70 %) for more than 60 seconds I D fan stator winding temperature is more than 140 c Oil level in the lubricating and control oil tank is less than preset minimum Vibration is greater than 11 mm / sec . Motor bearing temperature is more than 100 c

FORCED DRAUGHT FAN LUBRICATING OIL PUMP TRIPPING OF LOP 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 . TRIPPING OF LOP When oil level in the tank is less than preset minimum. When FD fan (A or B) is not running for more than 60 minutes.

FD FANS START UP LOGICS Any one lubricating oil pump is in service. The control oil pressure is more than 6 bar. Hand brake of the fan is in released condition. Impeller blades are in closed position. STOPPING OF FD FAN

DAMPERS GAS SIDE DAMPERS DAMPER IN THE AIR PATH GAS DAMPER AFTER ID FAN DAMPER AFTER FD FAN A/B

FLUE GAS WAY FREE LOGIC AIR WAY FREE LOGIC FD fan A/B is running. Damper after FD fan A/B ( is opened. Damper after RAPH A/B (A or RAPH bypass damper is opened. Any one of the RAPH motors (A1/A2 OR B1/B2) is in running condition. Speed of RAPH A/B is greater than minimum (70%) ID fan A/B is in service. Damper before RAPH A/B (GD 1A/1B) is in open condition. Damper after ID fan A/B (GD 2A/2B) is in Open condition

SCANNER AIR FAN There are two scanner air fan our boiler. One in running condition and other one is in stand by condition. The scanner air fan can be started by manual and auto. If the two scanner air fan in tripped condition for more than 2 minutes than the boiler will be trip.

FUEL OIL PUMP THE PUMP WILL TRIP: Each boiler is provided with two fuel oil pump at fuel oil pump house. The pump will start by manual and auto. THE PUMP WILL TRIP: If the suction pressure is low There is switching gear trouble.

P&I CHECKS RAPH : After completion of all the work confirm that the concerned LCs is in returned condition. Start any one LOP of concerned RAPH Reserve LOP starting from the UCB may be checked for the both LOPs by stopping running pump from UCB. Reserve LOP starting from the local may be checked for the both LOPs by applying the local latch on the running pump. Oil level is very low may checked by lifting the level switch. Reserve motor starting from UCB may checked for the both RAPH motors by stopping the running motor from UCB.

I.D.FAN INTERLOCKING : If the control oil pressure is less than 6 bar then fan will not start. Fan will not start without PCD minimum. Reserve oil pump will start at control oil pressure is less than 8 bar. Closing of the discharge damper if the only one I.D. fan is on.

PROTECTION : Fan trip will check by DE, thrust bearing by making the high, very high contacts respectively. Fan motor bearing temperature is check by making the high, very high contacts respectively. By applying the local latch , check the fan stop will confirm for local latch. Lub oil tank level is very low check by lifting the level switch. ID trip will be check for the RAPH trip.

FD FAN INTERLOCKING : Fan will be not start if the control oil pressure is less than 6 bar. Fan will not start without minimum PCD. Reserve lub oil pump start at oil pressure is less than 8 bar. Close the discharge damper, if the only other fan in running condition.

PROTECTION: Fan trip will be check for DE, thrust bearing by making the very high contacts. Fan motor will be check for DE, by making the very high contacts. Lub oil tank level is very low check for FD fan by lifting the level switch. FD fan trip will checked for “FLUE GASWAY NOT FREE CONDITION”. By applying the local latch, fan stop will be confirm for the local latch.

BOILER MAIN PROTECETON AND INTERLOCKING By making 2/3 contact at very high and very low furnace pressure, trip signal will be confirmed. Furnace pressure very low and high will be checked by making the respective switch contact. Drum level very low/high will checked during boiler filling before lighting up or hydro test. Boiler trip for CRH L/R is greater than 370 will be checked by making respective switch contact.