Maintenance step: Maintenance of turbine

Maintenance of turbine

The old saying "a stitch in time saves nine" applies to mechanical devices as well as to clothing and many other things.
It not be too strongly emphasized that a small amount of regular attention to the unit may easily avoid a large repair bill at a later date.

1. Keep the machine clean.
2. Clean the emergency stop valve stem and governor valve stem as often as necessary to prevent the accumulation of boiler compound or other foreign matters. These part must be kept working freely. All drains must be kept open whenever the unit is shut down.
3. Trip the overspeed trip occasionally to see that it is in good working order.
4. If operating for long periods without shutdown, check the emergency stop and governor valve and the governor occasionally to make sure that it is free.
5. A heavy accumulation of the scale on the turbine blades with cause a reduction in the output and increase in steam chest pressure. Therfore if the operation record is checked, and should an increase in the steam chest pressure be found, it may be attributed to the scale accumulation.
6. Check the oil temperaturs and increase in temperature, clean the oil filter and purify the oil.
7. When the turbine stopped, ensure that the steam piping is completely drained and that all valves are closed.

Operation Stopping Turbine

Stopping

1. Degrease the turbine speed gradually with the speed setting under 50% rpm of rated speed.
2. Close the emergency stop valve.
3. Make sure the auxiliary oil pump is started.
4. Close the stop valve on the main steam line.
5. Close the sealing steam valve for condensing turbine.
6. Open the drain valves, for condensing turbine, open the casing drain valve after opening the exhaust valve.
7. Close the exhaust valve.
8. Close the cooling water valve to the oil cooler.

Operation Before Starting of Turbine

Before starting turbine

1. Make sure oil reservoir is filled to teh normal level.
2. Open all drain valves of the steam inlet line, and exhaust line.
3. Supply lubricating oil into all bearings by operating a motor driven auxiliary lubrication oil pump.
4. Open the cooling water valve to the oil cooler.
5. Check the trip mechanism by pushing the trip nob and reset the trip and the emergency stop valve turning back the handle clockwise (Close).
6. Make sure the governor is minimum speed setting.
7. Open the exhaust valve after checking not to have drain on the exhaust fan. For condensing turbine, close the drain valve of the turbine casing.
8. Open the stop valve on the main stem line after checking the drain at the inlet line.
9. Open the stop valve, and adjust the pressure to 0,2 ~ 0,4kg/cm2G for condensing turbine.
10. Make sure of no drains at the steam inlet line.

Continue to Operation Starting Turbine

Lubrication And Governing System ENV-116G Turbine 3

8. Low Oil Pressure Trip

The Turbine is provided with a low oil pressure trip device, to prevent trouble due to failure of bearing oil pressure.

As with the low oil pressure trip, the pressure switch acts when the specified operation pressure is reached, and the solenoid valve is actuated to trip the turbine.

Since the overspeed trip device, excess back pressure trip device and low oil pressure trip device all tested and set in the manufacturer's shop test, never readjust them unless necessary.

9. Sentinel Valve

The sentinel valve is designed so that when exhaust pressure excessively rises, it pushes up the ball, overcoming the compression force of the spring to emit steam, thereby giving an alarm before the excess back pressure trip device to operate.

Its operating pressure can be adjusted by means of the adjust screw.

10. 3-way Solenoid Valve for Remote Trip

To remotely trip the turbine, push the remote trip push button provided in the cargo oil control room to demagnetize the solenoid valve which is provided in the hydraulic circuit let to the trip cylinder of the emergency stop valve.

In normal operation the solenoid valve is in energized state.

While it is energized, the oil circuit from the oil pump to the trip cylinder is opened and drain hole to the oil reservoir is closed. When it is deenergized, the solenoid valve inlet is closed, due to which the drain holes of solenoid valve trip and trip cylinder are opened.

Lubrication And Governing System ENV-116G Turbine 2

6. Over Speed Trip

The turbine is aquipped with an overspeed trip which prevents overspeed of the turbine by tripping the emergency stop valve and shutting off the supply of the steam to the turbine.

If the turbine speed increases by abnormal condition as much as predetermined value (about 115% rated speed), the over-speed operates and shuts the emergency stop valve through the emergency mechanism linkage.

It is an eccentric weight type and is equipped in the main oil pump end of the gear shaft.

The center of the gravity of the weight is slightly offset from the axis of ratation and is normally held in place by the compression of the spring.

When the turbine is operating at normal speed, the lever is kept in its normal position.

But when the turbine reaches the predetermined speed (about 115% rated speed), the eccentric weight due to centrifugal force, overcomes the spring compression and moves outward, and strikes the lever. The valve moves down-ward, supply oil to trip cylinder is cut off and be drained.

Supply oil press., from overspeed trip decreases, The oil piston moves up-watd and it rotates the trip lever through the trip pin.

The latch pin and spring seat hand wheel, spindle, coupling, pilot disc and disc are moved together by the spring.

Consequently, the emergency stop valve is shut down.

The tripping speed is tested at the factory and should not be changed unless absoulutely necessary.

When needed, loose sets screw then turn the adjust screw clocwise to increase the set speed or counter clockwise to decrease the set speed.

If should be taken that to lock the set screw after adjusting of the overspeed trip.

If the overspeed trip has been operated, pull the red reset knop before the emrgency stop valve is reset.

When manual trip is needed, push the trip knob the emergency stop valve is tripped.

7. Excess Back Pressure Trip

The turbine is provided with an excess pressure trip device to prevent trouble due to excessive back pressure rise.

When the turbine back pressure rises, the steam sentinel valve begins to emit steam.

When it rises further up the operating pressure, the pressure switch acts and actuates the solenoid valve provided in the hydraulic circuit led to trip cylinder of emergency stop valve, due to which oil pressure is shut off and discharged to drain.

Therefore, in the same manner as when the overspeed trip device acts, the trip mechanism of emergency stop valve, closes the emergency stop valve to shut off steam inflow.

The operating pressure of the excess back pressure trip device can be adjusted as required by turning the adjust screw of pressure switch.

Lubrication and Governing System ENV-116G Turbine 1

1. General

• The lube oil system for turbine and reduction gear. Lube oil is sucked up from the oil reservoir by the main oil pump or aux. Oil pump and supplied to the pinion bearing, gear bearing and gear teeth surface through the stariner and oil cooler, and the it returns to the oil reservoir.
• The bearing oil pressure is regulated by oil relief valve, and excess oil returns to the oil reservoir.

2.  Speed Governor

• The rotational speed of this turbine is controlled by the Wood Ward governor.
• This governor is driven by the drive gearounted on the front end of the main oil shaft.
• It ensures an exellent speed controlling, enabling to keep always constant the rotational speed of the turbine regardless  of variation of load and steam conditions.
• The speed setting point can be significantly changed by turning the speed setting dial with hand the remote control motor.

3. Main Oil Pump and Governor Drive Gear

• The main oil pump is driven at properly reduced or increased speed by the drive gear (drive) mounted on the upper end of the gear shaft and the drive gear (follow) fitted to the gear (drive).
• A governor driving gear (drive) is mounted on one end of the pump gear.
• This gear drives the governor through the gear (follow).
• A tachometer transmitter is provided at the upper end of the pump gear (follow).

4. Auxiliary Oil Pump

• This turbine equipped with auxiliary oil to furnish bearing lubrication during starting and shut down periods.
• The until has one motor-operated pump which providess auto-start and stop by means of a pressure switch.

5. Oil Relief Valve

• The oil relief valves is mounted on the bed plate. Usually, it serves to keep constant the bearing oil pressure and gear spray oil pressure.
• The optimum oil pressure during operation is 0.7 ~ 1.5 kg/cm2 G.
• The oil pressure is regulated by the compression force of the spring.
• It is recommended to set it to obtain 1.5kg/cm2 G at the optimum oil temperature (30~50^0 C at cooler outlet) with the turbine's specified rotational speed.

To be Continued: 
Lubrication and Governing System ENV-116G Turbine 12

Reduction Gear Turbine for Cargo Oil Pump ENV-116G

Type ENV-116G Turbine for Cargo Oil Pump, Reduction Gear

1. General

• This reduction gear is designed high reduction ratio and the pinion shaft end fits a turbine rotor in order to obtain high efficiency and economy of space.

2. Gear Casing

• These are made of close-grained cast iron and divided in the vertical plane through the axis of the pinion and wheel.
• The rear casing of the turbine is bolted on the rear gear casing. The rear gear casing is mounted on the bedplate and lub. Oil drains out to the bedplate.

3. Gear Wheel and Pinion

• The pinion is made from Ni-Cr-Mo steel, and the gear wheel is made from forged steel, and these are carefully heat-treated.
• The gear wheel is pressed on the gear shaft and secured with keys. The one end of the wheel shaft is connected with the load by the coupling through intermediate shaft and another end drives a oil pump and a tachometer through a drive gear.
• The gear and pinion teeth are of the involute single herical type and precisely machined.
• The pinion end thrust bearing of michell type supports against the thrust force.

4. Bearing

• The pinion and gear journal bearings is steel back lined with white metal and split in the vertical plane of the centerline to from bearing halves.
• The pinion bearings and two gear bearings is fitted gear casing rearby bearing cover with bolts firmly.
• The luch of bearing prevents to rotate and remove toward axis. Lubricating oil for bearings is supplied through the hole of the gear casing rear.
• Thrust force of pinion is supported by michell type, and the gear wheel position is by plen thrust bearing and liners.

Construction of ENV-116G Turbine 2

6. Emergency Stop and Governor Valve

The emergency stop valve is situated upper position and the governor valve is situated down position.

1. Emergency Stop Valve

• The emergency stop valve has two distinct purposes. First, to control throttling of steam when starting and bring the turbine up to speed; second, to act as quick-closing valve when tripped by hand or remote=trip, and as emergency stop valve when tripped automatically by safety device such as over speed trip, back pressure trip, low oil pressure trip.
• The spindle and the spring seat is threaded, the spring is compressed by the spring seat, and the pin on the spring seat is set by lever which is connected to the trip cylinder.
• The trip cylinder consist of the piston rod, the piston, the spring and the cylinder body. When the oil pressure in the cylinder body decrease, the piston is moved upward by the spring force together with the piston rod and the lever. At same time the pin on the spring seat is severed from the lever, so the spring seat, the spindle, the pilot disc and the disc are forced down by the spring.
• Thus, the emergency stop valve, the piston is situated at reset position by the oil pressure in thecylinder body. By hand the hand wheel is turned to the right, and by turning th hand wheel to the left is opened the emergency stop valve.
• The disc must be open after the pilot disc and being small deference pressure on the disc upper and lower face, by means of restricting the steam flow with the adjusting disc.

2. Governor Valve

• The Governor valve position is determined by movement of the governor and the governor valve controls the flow of steam to the steam chest.
• The governor valve consist of the adjusting disc, the disc guide and the stem, and is the balance type. The adjusting disc is guided by the bush and is controlled by the stem on account of the governor movement. The stem flows inter the steam chest through the port on the diec guide.

3. Governor Link

• The governing shaft of the governor and the governor valve stem are connected with the governor link. and that is consisted of ball joints, a lever, rods and fulcrum pins. The link conveys smoothly the movement of the governor to the governor valve.
• The link needs the adjustment for reassembly that the clearance between the governor valve stem and the stopper of the valve seat is about 2mm when the governor is full shutting. Changing the position of the pin needs in case the steam flow of the governor valve is reduced at full opening of the governor.