Starting Means (Diesel Engine) - Ms5001

System Description

STARTING MEANS (DIESEL ENGINE) – MS5001

Starting Means (Diesel Engine) GENERAL Before the gas turbine can be fired and started it must be rotated or cranked by accessory equipment. This is accomplished by a diesel engine, operating through a torque converter to provide the power required by the turbine for startup. Starting system components include: the diesel engine, torque converter with ratchet mechanism, starting jaw clutch and a hydraulic ratchet self-sequencing control valve assembly. Also, there are several supplementary components required for sequencing and operation of turbine starting system.

FUNCTIONAL DESCRIPTION The starting system provides power for both cranking and turning during gas turbine startup and shutdown cycles. In the starting cycle there are three primary functions provided by the starting system: start the gas turbine rolling (breakaway from standstill); accelerate the gas turbine to a speed where it can be fired; and after the turbine has fired, further-accelerate it to a self sustaining speed (a speed at which gas turbine develops net positive power output). During the starting sequence, the gas turbine is driven through the accessory gear by the diesel engine, torque converter, output gear and the starting clutch. The starting clutch assembly and the engagement cylinders are mounted on the accessory gear assembly. The accessory gear is permanently coupled to the turbine compressor shaft by a flexible coupling.

Diesel engine When operating, the diesel engine draws combustion air from the accessory compartment through a filter into the turbocharger inlets. Air dampers, located downstream of the turbochargers are equipped with a manual emergency shutdown latch. Engine coolant is drawn from the gas turbine cooling water system tank located on the accessory compartment roof. The flow rate is controlled by thermostats on the engine.

Bharat Heavy Electricals Limited, Hyderabad

Page 1 of 6

System Description

STARTING MEANS (DIESEL ENGINE) – MS5001

The engine operates on a completely self-contained lube oil system. Lube oil pressure can be read on a panel mounted pressure gauge and is monitored by pressure switch 63QD-1. A fuel tank has been fabricated in the turbine base. Refilling of this tank is a manual operation. An engine driven, high lift pump draws fuel from the tank and pumps it through a filter to the canister mounted on the side of the engine. The main fuel pump draws fuel from canister and pumps it through a filter and into the injector’s headers. Each fuel injector draws the required amount of fuel from the headers, while the excess fuel (used to cool the injectors) is returned to the canister and through the overflow drain back to the tank. There is a manual “priming” pump installed in parallel with the high lift pump.

CAUTION Attempting to “prime” the engine fuel system by cranking the engine can seriously affect the life of the engine starter.

Diesel Engine Controls The basic control elements include a starter, speed control system, stop mechanism and electronic logic in the gas turbine control panel for unattended automatic protection and control. Engine starter 88DS-1 is a direct current motor that engages with the engine through a Benedix clutch. Engine speed is controlled by the positioning of a lever on the variable speed governor. The positioner is a hydraulic cylinder controlled by solenoid valves 20DA-1 and 20DA-2. A small engine driven pump, pressure limited by relief valve VR13-1, supplies a controlled flow rate of engine oil for cylinder operation. When 20DA-2 is energized, the governor lever is driven to and held at the maximum speed position. When 20DA-2 is de-energized, the lever is returned to the idle position. Energizing 20DA- 1 when the lever is anywhere between the end positions, stops the positioner travel and holds the lever at the existing position (governing at an intermediate speed). This system allows control of the gas turbine cranking speed.

Bharat Heavy Electricals Limited, Hyderabad

Page 2 of 6

System Description

STARTING MEANS (DIESEL ENGINE) – MS5001

NOTE Except under certain emergency conditions, the engine is only stopped with the governor lever in the idle position. Following an emergency shutdown, the engine can be safely restarted regardless of governor lever position; but the operator has the option of manually resetting the lever before attempting a restart. (Manually shift the 20DA- 1 valve and pull the cylinder to the idle position.)

The engine stop device is an "energize-to-stop" solenoid (20DV-1) connected to the governor that when energized activates the shutdown mechanism and stops the engine. Electronic, logic in the control panel provides automatic sequencing of 88DS-1, 20DA-1, 20DA-2 and 20DV-1 for normal unit startup, for normal and emergency engine shutdown and for exercising and/or test of the engine. To protect the system hardware, the logic also monitors the starting clutch position (33CS-1), the engine lube oil pressure (63QD-1) and the engine speed. Necessary and ALARMS and / or TRIPS are built into the control system. NOTE A tachometer on the diesel engine local gauge panel allows reading engine speed. Pressure switch 63DM-1 senses that the diesel engine is at minimum operating speed. The engine will operate at constant speed when the unit is between 2300 and 2700 rpm during the startup sequence. Routinely checking the engine speed in the unit speed range will provide a good check on engine performance level in that a persistent speed decrease of more than about 35 rpm from the "normal" indicates a need to have the engine serviced by a qualified mechanic.

Diesel Engine Operation After the starting clutch is engaged, 88DS-1 is energized to start the engine. The engine idles through the warm-up cycle and then 20DA-2 is energized to accelerate the engine to maximum speed for unit breakaway (requires assistance of the hydraulic ratchet). Following breakaway, 20DA-2 is de-energized to decelerate the engine to approximately 1900 rpm at which point 20DA-1 is energized to hold constant engine speed until the gas turbine is sequenced through the end of warm-up. Then 20DA-1 is de-energized and 20DA-2 energized to accelerate the engine Bharat Heavy Electricals Limited, Hyderabad

Page 3 of 6

System Description

STARTING MEANS (DIESEL ENGINE) – MS5001

back to maximum speed (and power) for acceleration of the unit to self-sustaining speed. At a unit speed of about 3100 to 3200 rpm, the clutch automatically disengages and 20DA-2 is deenergized. The engine returns to idle speed, idles through a cool-down period, and stops when 20DV-1 is energized for several seconds. NOTE Solenoid valves 20DA-1 and 20DA-2 are equipped with manual operators (pushbuttons in the ends of the solenoids). Torque Converter Assembly This assembly includes the torque converter, the hydraulic ratchet mechanism and an output gear unit. It is mounted on the diesel engine flywheel housing. During the operation of the diesel engine a small engine-driven pump supplies turbine lube oil to the torque converter loop. The loop is pressurized by an orifice in the discharge port. The gear unit and the clutch in the ratchet mechanism are lubricated by pressurized oil from the converter loop. Drain oil from the assembly returns to the turbine sump by gravity. The torque converter consists of an engine driven pump rotor that supplies oil to a hydraulic turbine connected to the Input shaft of the output gear. The pump rotor requires rated engine horsepower at rated speed, independent of the output load. Power absorption of, the pump rotor varies as the cube of the input speed. The hydraulic ratchet mechanism is a rack-and-pinion type rotary actuator connected through a roller-ramp type one-way clutch to the input shaft of the output gear. The output gear unit connects the ratchet mechanism and the output side of the torque converter to the starting clutch. Hydraulic Ratchet System Components of the ratchet system include: the rotary actuator/one-way clutch mechanism in the torque converter assembly, control valve module, pump assembly, and a relief valve. The rotary actuator develops 563 lb/ft of torque per hundred psi supply pressure. The one-way clutch is rated 7600 lb/ft @ 1350 psig to the actuator. In the system, the valve module controls the starting clutch engagement and the hydraulic selfsequencing operation of the rotary actuator. The module includes the ON/OFF solenoid valve Bharat Heavy Electricals Limited, Hyderabad

Page 4 of 6

System Description

STARTING MEANS (DIESEL ENGINE) – MS5001

20CS-1, the modulating backpressure valve that maintains adequate pressure to the clutch engagement cylinders, two pilot operated valves to control flow to the rotary actuator, and the 33HR-1 limit switch. Assembly of the pump is made up of a 125v dc motor, driving a 1.5 gpm pump at 1725 rpm. The assembly pumps lube oil from the unit-bearing header to the inlets of the VR5-1 relief valve and the control valve module. CAUTION Setting relief valve VR5-1 at a "cracking" pressure above 1350 psig can damage the one-way clutch in the ratchet mechanism.

Ratchet System Operation With the pump in operation and solenoid valve 20CS-1 energized, oil from the lubrication system is ported to the starting clutch and the ratchet system. This causes the ratchet mechanism to operate continuously as the hydraulic self-sequencing control automatically shifts the oil flow between the forward and reset strokes of the ratchet mechanism. A forward stroke advances the starting clutch about 47 degrees during the 10 second duration. The reset stroke is of about 4.5 second duration. Operation for unit cool down is automatically sequenced by the control panel. Once every three minutes, the mechanism is operated, through one complete cycle. The cycle is terminated in the forward stroke position to lock the clutch in the engaged position. Ratchet operation is normally required to achieve breakaway of the unit rotor system during the unit startup sequence. With the starting system at maximum power, 88HR-1 and 20CS-1 are energized for continuous operation until breakaway is achieved. If breakaway is not achieved within three minutes, the ratchet system is de-energized. The ratchet system can also be manually operated by use of "Jog" switch 43HR-1 located in the accessory compartment. Actuation of the "Jog" switch interrupts and terminates operation in any automatic sequence. Switch actuation energizes 88HR-1 and 20CS-1 and maintains both in an energized state as long as switch contact is maintained. Release of the switch immediately deenergizes both 88HR-1 and 20CS-1 independent of the ratchet stroke position. Bharat Heavy Electricals Limited, Hyderabad

Page 5 of 6

System Description

STARTING MEANS (DIESEL ENGINE) – MS5001

CAUTION Operation of the ratchet system without oil pressure in the gas turbine bearing header may damage the ratchet pump and/or the gas turbine bearings.

Excessive continuous ratchet operation and/or jogging ("inching the rotor") by use of the "jog" switch can seriously affect the life of 88HR-1 and/or 20CS-1.

Starting Jaw Clutch A starting clutch connects the output shaft of the torque converter assembly to the main shaft of the accessory gear. The clutch is engaged by hydraulic cylinders (oil supplied from the ratchet control valve module) and disengaged by return springs in the cylinders. Engagement is maintained by transmitted torque generated in the torque converter and/or ratchet mechanism. Because of the one-way clutch in the ratchet mechanism, the sliding-clutch hub cannot be turned backwards except during a reset stroke of the ratchet mechanism. The system is designed to maintain the clutch in the engaged position at all times except when the gas turbine is running. To allow inspection and maintenance of the clutch mechanism, manual valve VM2-1 has been installed in the hydraulic lines between the ratchet control module and the clutch cylinders. To disengage the clutch, shift the valve and operate the ratchet with the "Jog' switch: the clutch will disengage during the ratchet reset stroke. Starting clutch operation is automatically controlled through the ratchet control valve module by the control panel. The panel also includes adequate protection against any component malfunction or failure. CAUTION The jaw clutch will be severely damaged by any attempted engagement with the sliding hub turning. Before any control device in the starting system, ratchet system and/or clutch system is disarmed and/or electrically bypassed, the clutch mechanism should be disengaged and locked out of engagement by clutch disengagement valve VM2-1.

Bharat Heavy Electricals Limited, Hyderabad

Page 6 of 6