starting means write up

5/28/2018 Starting means write up

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STARTING MEANS (DIESEL ENGINE) MS5001

Bharat Heavy Electricals Limited, Hyderabad Page 1 of 6

System Description

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 startingsystem: 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.


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System Description

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 injectors 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.


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System Description

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 governorthat 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


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System Description

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 de-

energized. 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 self-

sequencing operation of the rotary actuator. The module includes the ON/OFF solenoid valve


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System Description

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 areenergized 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 de-

energizes both 88HR-1 and 20CS-1 independent of the ratchet stroke position.


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System Description

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.

starting means write up

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