7.5mw condensing steam turbine type: c7.5-35/53115177.5mw_condensing_steam_turbine.pdf · at the...

CONDENSING STEAM TURBINE TYPE: C7.5-35/5

7.5MW CONDENSING STEAM TURBINE

Type: C7.5-35/51. Scope of Application

This steam turbine is applicable to the electric utility as well as the self-sustained hpower stations owned by enterprises

2. Specification

- Model: N7-3.43-1- Rated power: 7.5

MW- Rated speed: 3000 rpm- Hand of rotation: ckw, seeing in the direction of steam flow- Rated inlet pres. And variation range: 3.43 +0.2, - 0.3 (ab.) Mpa- Rated inlet tempt. And variation range: 435 +10, -15 (degree C)- Tempt. Of cooling water (normal/max.): 27 / 33 degree C- Temperature of feed water: 150 degree C

3. Construction of Steam Turbine Proper

3.1Rotor

A built-up rotor is used, consisting of a steel shaft on which all wheels and gland sleeves are shrunk. The rotor is linked with the rotor of a generator by a butt-muff coupling.

3.2Nozzle block, diaphragm and guide blade carrier

3.2.1 Nozzle block is of assembled welding construction or shroud band welding construction, which is fixed to the nozzle box of the casing with studs.

3.2.2 The HP section diaphragms are of shroud band wilding construction, and the LP section diaphragms are of cast iron type. The lower half of a diaphragm is suspended by means of two suspension tacks at the horizontal split of the casing and positioned by a flat key between the bottom of the diaphragm and the casing. There are sealing keys and dowels at the splitting surface between the upper and lower halves of the diaphragm.

3.2.3 The upper and lower halves of the guide blade carrier are fixed in the

Shandong Machinery I&E Group Corporation


grooves to casing. There are positioning keys between the top and bottom of the guide blade carriers and the casing, and shields over the arc area of non-admission passage.

3.3Casing

With a perpendicular and a horizontal splits, the turbine casing is composed of front and rear parts, namely, inlet casing and exhaust casing, which can not be separated again once they are linked with one another along their perpendicular splitting surfaces. The nozzle chamber and the inlet casing are cast separately.

The live steam enters the casing via the admission pipes at the two sides, left and right, of the inlet casing. The extraction points for regenerative purpose are provided at the lower half casing. The exhaust of the exhaust casing is linked with the condenser in a flexible or solid manner. The inlet casing is linked with the front bearing pedestal by semicircular flanges or a lower lugs, while the exhaust casing is seated on the rear pedestal with its support feet at the two sides. There are transverse sliding pints between the support feet and the rear pedestal support. The inter sectoon point formed by the centerline of the said transverse sliding pins and that of the longitudinal sliding pins on the front bearing pedestal and support serve as the fixed point for thermal.

3.4Front bearing pedestal

Equipped with a thrust-journal bearing, main oil pump, speed governor, safety devices, tachometer and thermometer, the pedestal is mounted on the support, at the joint of which is a longitudinal sliding key, allowing of an axial slide of the pedestal. In the case that a lug construction is applied, cooling water orifices will be provided for the sliding keys that match the lugs of the casing.

3.5Rear bearing pedestal

The lower part of the rear bearing pedestal is cast integrally with the exhaust casing. In the pedestal are mounted the rear bearing of turbine, front bearing of



generator, turning gear device and thermometer, At eigher of the two sides, left and right, of the lower part of the rear bearing pedestal is provided an inlet and an outlet of lube oil, allowing of a leftward or rightward layout of the unit.

3.6Bearing

A spherical combined bearing, i.e. a thrust-journal bearing, formed with a journal bearing and a thrust bearing, has been chosen for the turbine. The thrust bearing is of tilting pad type. For the front bearing with diameter >=Dia. 180mm or more, a needle valve is used to regulate the returning oil flow in the thrust bearing in response to the returning oil temperature.

Both the front and rear radial bearings are elliptical ones.Copper thermistors are provided for the main thrust pads and the lower half bush of the radial bearings.

3.7Main stop valve and manipulation seat

The main stop valve has a single seat. The valve disc is of profile one with a pre-inlet valve, above which a steam filter gauze is fit.A hydraulic manipulation seat is used for the main stop valve, in which the pressurized oil is controlled by any one of the safety devices. After the safety devices switch in and as a result the oil pressure rises up to about 0.4 Mpag (4 atg) inside the oil reservoir of the manipulation seat, turn the handwheel counter-clockwise slowly to open the main stop valve. A switch-off action of a safety device will sluice off the pressure oil flow leading to the oil reservoir with the result that the main stop valve shuts rapidly due to the action of a spring inside the manipulation seat.Both a travel indicator and a travel switch are mounted at the lower part of the manipulation seat.

3.8Steam governing valve and link rod

The steam governing valves are of poppet type, with profile valve discs. In response to any load variation, the valve discs will open or close in a predetermined sequence. The travel lift of the valve discs have been set before the delivery of the steam turbine.

4. Governing and safety systems

4.1Governing system

A two-stage amplification pure hydraulic governing system is chosen for this unit, which is composed of the main oil pump, pressure transducer, pilot valve,



(starting valve), servo-motor and synchronizer.

Turbine speed serves as the variable for governing the unit. Any speed variation will result in an outlet pressure variation of the main oil pump, so this pressure variation is a pulse signal for speed governing.

4.2Operation principle of the governing system

A pulse signal from the speed governing system, after being amplified in two stages, will bring the servo motor into function to control the steam flow getting into the turbine.

The loading reduction can be taken as an example to illustrate the operation princile of the governing system, as following:

4.3Operating sequence of the governing system

Before the starting of the steam turbine, no pressure has been built up inside the pulsating oil piping. So, the plungers of the pressure transducer and pilot valve ( and starting valve) all stay at their lowest position due to the action of springs, while the synchronizer has to be set at its lower limit position.

After the starting of the motor-driven high pressure oil pump or turbo-oil pump, the pressurized oil flow will pass through a check valve and then is divided into two sub-flows. The first sub-flow will pass through the starting valve to enter a chamber below the plunger of the pilot valve to make the plunger move upward. After passing through the pilot valve, the said sub-flow will go into a chamber below the piston of the servo motor with the result that the steam governing valve is closed.

In the case that no starting valve is provided for the steam turbine, the pressure



oil will, after passing through the pilot valve, enter a chamber above the servo piston with the steam governing valve being opened as a result.

The second sub-flow of pressure oil will pass through the axial displacement limiting device, emergency governor pilot valve and solenoid cutout valve to enter an oil reservoir inside the manipulation seat of main stop valve and that inside the extraction check valve (No-return cut-off valve).

Open the main stop valve to start the turbine. When the turbine speeds up so that the outlet pressure of the main oil pump reaches a stipulated valve, the motor-driven or turbo-oil pump will stop working. The accleration will go on till the governor begins its function.

4.4Safety Devices

4.4.1 Emergency governor

This device is of fly-weight structure. In case of an overspeed ranging from 9 to 11% of the rated speed, i.e. a speed ranging from 3270 to 3330 rpm, the fly-weight will fly outward to strike off the pull hook of the emergency governor pilot valve, causing a trip-off action.The return speed is 3000 r.p.m.

4.4.2 Emergency governor pilot valve

Together with the emergency governor, this device protects the unit form overspeed. In case that the fly-weight of the emergency governor fly outward to strike off the pull-hook at the end of this device, the plunger of this device will, due to the action of a spring, move rapidly to cut off the high pressure oil flow leading to the oil reservoirs inside both the manipulation seat of main stop valve and the extraction check valve (no-return cut-off valve), thus causing both the main stop valve and the extraction valve close rapidly. At the same time, the high pressure oil flow will enter a chamber below the plunger of the pilot valve, effectuating a speedy closedown of the steam governing valve.

This device can also be operated manually. If necessary, strike the small spring cover at the upper part of this device with hand to detach off the pull hook, as a result, the above –said action will be repeated and the turbine unit will thus be shut down.

When a reseat of this device is wanted, it is necessary to wait till the turbine speed drops to 3000 rpm or less, push down the big spring cover at the upper part of the device to hitch up the pull-hook once again.



This device is forbidden to be reset while the speed is higher than 3000 rpm in order to protect both the fly-weight and pull-hook from being damaged.

4.4.3 Axial displacement limiting device

This device functions to sent out an alarm signal and cause a stoppage of the steam turbine in case that the axial displacement of the turbine rotor exceeds a permissible valve. In assembling, a clearance of 0.5mm should be kept between the oil nozzle and oil baffle while the clearance between the thrust collar and main thrust pad is zero.

In case that the axial displacement of the rotor reaches 0.7mm, i.e. the clearance between the oil nozzle and the oil baffle reaches 1.2mm, the spring force applied on the plunger will overbalance the oil pressure and the plunger will move to cut off the high pressure oil flow leading to the reservoir inside the manipulation seat of main stop valve and that of the extraction check valve, causing both the main stop valve and extraction check valve close instantly. Meanwhile, the high pressure oil flow will enter a chamber below the plunger of the pilot valve, causing the steam governing valve close rapidly.

A pressure gauge with an electric contact can also be used for this device to indicate the pilot oil pressure. In case that the axial displacement of the rotor exceeds 0.4mm, this gauge will sound an alarm; and, in case that the said valve exceeds 0.7mm, the solenoid cut-out valve will take action, resulting a shutoff of all the main stop valve, extraction check valve and steam governing valve. The setting data for this pressure gauge are shown in the test record for the axial displacement limiting device.

This device can also be operated manually to shut down the turbine unit. For this purpose, the only thing for the operator to do is to pull out the red knob of this device. When a start-up of the turbine unit is wanted, the operator should, after the high pressure oil pressure is built up, push in the knob to engage closely the sealing surface at the end of the plunger with that at the end of the extension arm to put through the high pressure oil path.

4.4.4 Solenoid cut-out valve

This is an electric-operated safety device for turbine stoppage in case of an accident. When the electric magnet is energized, this device will act to cut off the high pressure oil flow, with the result that the main stop valve, extraction check valve and steam governing valve all close rapidly, After this device trips off, pull out the safety bolt to reset the plunger to its original position in order



to put through the high pressure oil path.

5. Turbine Auxiliary System

5.1Lube Oil System

Lube oil system is designed to provide oil to lubricate all bearings; to provide pressure oil for operation of the governing protection system and for turning gear and rotor jacking device. The lube oil system mainly consists of: oil reservoir, oil ejectors, AC oil pump, DC motor-drive emergency oil pump, oil relief valve, oil vapor extracting device, main oil pump, rotor jacking oil piping, oil cooler and etc.

Two oil ejectors (one for oil supply to main oil pump and the other for lube oil supply) are mounted in the oil reservoir, Oil relief valve, DC motor – driven emergency oil pump, oil vapor extracting device and etc. are located on the cover plate of the oil reservoir.

The lube oil system is supplied with oil via the main oil pump-ejector device driven by the turbine shaft directly. The function of main oil pump is to provide pressure oil to the governing & protection system, and to oil ejectors as working oil. The No.1 oil ejector is to supply oil to main oil pump inlet. The No.2 oil ejector is to provide lube oil to all bearings of turbine-generator unit, to supply oil to turning gear and jacking device.

The system is equipped with two oil coolers. During normal operation, one cooler is in service, and the other is kept in stand-by condition.

The lube oil system is equipped with oil relief valve so as to keep lube oil pressure in a constant valve. In addition, there is also low oil pressure trip mechanism in the system.

The system is installed with an oil vapor extracting device and its blower.

AC motor driven lube oil pump and DC motor driven lube oil pump of vertical arrangement with its motor mounted on the cover plate of oil reservoir and its imeller is submerged in the reservoir, the AC motor driven auxiliary oil pump is provided as automatic back up to main oil pump and also for use during start – up and shutdown, in addition that, the DC motor driven emergency oil will supply bearings oils in the even of loss of AC suppliers.

5.2Gland Sealing System

Gland sealing system acts as a precaution against steam leaking to atmosphere and into the bearing pedestal, and to prevent air from leaking into the vacuum



space.

There are two sets of the glands at the inlet end and exhaust end of the turbine casing, either has its own number of gland sections, depending upon leadoff steam pressure.

The system is composed of piping for steam supply, steam leaking off (from the turbine shaft end gland and the steams of the main stop valve and governing valves), and the equipment concerned.

The first leak-off steam from the gland at the inlet end is led to the deaerator when this is taken out of service, the second leak-off steam is led to the LP heater.

Steam from the deaerator or the steam balance pipe is supplied to the glands at the inlet end and the exhaust end through the valve for gland steam pressure control, before which a steam strainer is equipped in the main pipe.

Both streams of the leaking off steam ( a mixture of steam and air) from the glands at the inlet and exhaust ends are collected together into one pipe and led to the air ejector for gland seal and condensed.

Finally the remaining mixture, consisting of air and a small amount of uncondensed steam, is exhausted after being led to the water jet air ejector.

In addition, the first leak-off steam pipe for the gland at the inlet end is connected to a steam pipe, led from the steam-mixing header for supplying high temperature steam to meet the requirements of hot stating of the unit.

5.3Drain System of Turbine & Piping

The major function of the drain system is to drain condensate forming in the turbine proper and the steam piping during start up and shutdown to prevent possible severe incidents such as a bowed rotor due to collection of water in the casing.

The system consists mainly of all kinds of drain piping, valves and the drain flash tank.

The system serves to drain the casings, the steam chambers, the main steam inlet pipes, and the drainage from all the steam extraction



piping and valves.

The drain piping is connected to the main drain inlet pipes of the drain flash tank sequentially in pressure order shown in the drain system.


7.5mw condensing steam turbine type: c7.5-35/53115177.5mw_condensing_steam_turbine.pdf · at the...

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