Steam turbine – single-cylinder, single-flow with impulse blading.
Steam turbines are designed on the basis of advanced developments accumulated during 50-year experience in power plant industry. The process of design and production conforms to quality management standards ISO 9001:2008 in the field of power-generating equipment.
Use of proven elements, such as modules, ensures elaborate arrangement of design details and, therefore, reliability of turbine generating unit during its operation. The advantage of modular design is the possibility of structural flexibility during steam path optimization. The turbine has low steam flow and high performance.
Steam turbine has the following design features:
Full-speed back-pressure or condensing turbine depending on thermal cycle.
Steam path of the turbine consists of control stage and pressure stages with weld diaphragms.
Turbine inlet steam pressure – up to 90 ata
Turbine inlet steam temperature – up to 530ºС
Turbine output pressure – up to 1.2 ata (for back-pressure cycle) to 0.04 ata (for condensing cycle)
Power output – up to 12 MW.
Turbine cylinder is made of construction steel the quality of which meets operational requirements and specifications. Upper half of the cylinder is manufactured as part of control valve steam chest for main steam feeding. Lower half of the cylinder is manufactured integrally with supports. The cylinder casing has a horizontal joint.
For turbines of this series the exhaust is weld-fabricated and selected from modular system depending on the type of turbine cycle.
Lower and upper halves of the exhaust are connected with studs and cap nuts along the horizontal joint. The same connection is applied for junction of the cylinder and exhaust along the vertical joint.
Main steam is fed to turbine through the steam strainer installed before the stop valve. Steam strainer prevents entering of foreign objects to steam path.
The stop valve is manufactured as double-seat in order to increase steam passage. The stop valve is equipped with electric drive (SRV – safety relief valve) and extreme position sensors. All controlling electric drives of valves are equipped with electromagnetic clutches which ensure emergency closing of stop and control valves upon tripping of protection systems of the steam turbine plant.
Steam turbine plant is controlled by control valves located in the control valve steam chest behind the stop valve. Control valves are single-seat with steam relief. Steam relief is performed by relief valve manufactured integrally with valve stem and opening till separation of the valve head from the seat, thus increasing pressure under the valve head and reducing efforts necessary for head separation from the seat. Control valves are equipped with оindividual electric drives.
Picture 1. Layout of the drive of stop valve and control diaphragm
Adjustable steam extraction is performed with the help of control diaphragm (for extraction turbines)
Control diaphragm consists of the diaphragm with nozzle blades and swing ring. In “fully-open” position the ports coincide with nozzle passages of the diaphragm, and in “fully-closed” position the nozzles passages are closed by the gaps of swing ring ports. Swinging of the ring is performed with the help of special electric drive.
Profiling of the turbine steam path is performed specially for the specific project and powered by the specially designed software where the type and number of profiling stages are determined.
Rotating blades of control stage are integrally machined and manufactured as a part of wheel, and the shroud is manufactured in the form of wholly rolled ring pressed on the rotating blades.
Rotating blades of subsequent stages (pressure stages) are also machined integrally with solid forged wheel with installed shrouds in the form of rolled rings.
Due to large specific volume of steam rotating blades of low pressure stages have long lengths and are made of ganged type with integrally machined tip shrouds. Where appropriate, leading edges of the blade are strengthened peripherally in wet steam zones.
Distributors (diaphragms) are manufactured as weld-machined of solid forged material with shrouds welded peripherally. Rotor sealing is performed with the help of labyrinth gland.
Diaphragms are installed in the cylinder with the help of tested adjusting elements ensuring high thermal elasticity and easy installation. Tangential holes, intended for removal of excessive moisture, are made for low-pressure diaphragms in the event of operation in wet steam.
Rotor shaft is forged. All necessary types of control, conditioned by operational requirements, are carried out during manufacture of the shaft.
It is necessary to perform obligatory stand balancing adjustment of the bladed rotor before its installation in the turbine.
Modern mathematical computation methods are used for calculation of the rotor natural frequencies. Critical rotor speed is checked taking into account influence of hardness of the oil film and bearing assemblies. Also, strength calculation for the shaft, wheels and clutches, is performed taking into account different operation of shaft assembly.
From the point of view of basic distribution of the stress field and temperatures, both at rated load, and at sliding and starting operational modes, structural concepts of the rotor are based on operationally proven elements and additionally proven by modern mathematical computation methods.
Labyrinths glands are used for non-contact sealing of the shaft. Sealing is achieved due to passage of steam through labyrinth system, i.e. the chain of consecutive clearances and expanded chambers. In clearances steam flow is accelerated and then enters the chamber where kinetic energy of circulating steam is replaced with thermal energy (swirling), therefore, ensuring high resistance of labyrinths and reduction of steam leakage.
The framework serves as a support and structure of the steam turbine plant. The framework has legs upon which the turbine case and pads rest and on which longitudinal and transverse spline keys are mounted. Also, there are platforms for horizontal placement of the structure during installation. In addition, there is an oil tank on the framework below the turbine. The framework is mounted to the foundation by anchor screws.
Picture 2. Layout of the framework of steam turbine plant
Drain system ensures necessary drainage of steam turbine during starting-up, normal operation and shutdown. Drainage pipelines are equipped with manually operated shut-off valves (used during starting-up and shutdown).
Drainage pipelines are connected to the common collector. Drain well may be connected with the flash box of surface condenser or expander of the existing equipment in the power plant.
Use of gearbox enables to perform optimization of the turbine speed. Gearbox is single-stage with double helical gear. Gearbox shafts are made in parallel.
Gearbox bearings are lubricated from common lubrication system of turbine generator. High-speed shaft of the gearbox in connected with barring gear with the help of free-running clutch. Barring gear is a cylinder-conic geared motor with the possibility of manual rotor turning. Main oil pump is installed on low-speed shaft with the help of semi-permanent coupling.
Gearbox casing has rigid construction which reduces the possibility of resonance to minimum. The casing is made of gray cast iron.
High-rotating and low-rotating clutches are equipped with a guard. The shafts are sealed with the help of oil seal ring.
Journal bearings and combined journal-and-thrust bearings have a horizontal joint enabling to perform inspections and repair with no need to extract bearing pads.
The bearings are equipped with temperature gauges. Oil for lubrication of bearings and shafts is taken from the common lubrication system of the turbine. Gearbox is equipped with relative motion sensors (high-speed shaft) and absolute motion sensors (low-speed shaft).
Direction of the turbine rotor rotation and high-speed gearbox rotor is counterclockwise, and for clockwise –for low-speed gearbox rotor, as viewed from the side of turbine on generator.
Gearbox is fixed with the help of pins and studs to the foundation frame.
Lubrication system ensures lubrication of bearing of the whole plant (turbine, gearbox, generator) which is installed on the foundation frame. Foundation frame includes oil tank, startup pump, filters, coolers, connecting pipeline and fitting, as well as auxiliary equipment, including measuring sensors and gauges.
During normal operation the main oil pump feeds oil to bearings of the whole steam turbine plant. The main oil pump is installed on the gearbox and powered by low-speed shaft.
Taking into account that upon starting-up the main oil pump cannot ensure performance and head-capacity curve, this pump is deactivated and then startup oil pump is used in this mode. This pump is powered by alternating current motor. When turbine speed reaches 80% of the rated speed, the startup oil pump is deactivated and the main oil pump is activated.
Startup pump may be activated either manually, or automatically. Oil is purified by double filters with transfer valves and with possibility to replace the filters in operating mode. Double coolers (oil – water) with transfer valves are used for cooling.
The steam turbine plant is lubricated with ISO VG 32 oil which corresponds to turbine oil of type Т22 as per GOST 32-74, Тп-22 as per GOST 9972-74 or Тп-22С as per TU 38.101821-83.
U-shaped oil tank with three compartments (“clean, intermediate, dirty”) and auxiliary equipment are installed in the foundation frame
Steam turbine plant is equipped with labyrinth steam gland system which prevents leakage of steam to turbine room in all operating modes. Steam, together with induced air, is removed from labyrinth glands to the gland steam condenser and condensed there.
Turbine gland from low-pressure side, where negative pressure is produced by admission of steam to the gland with pressure 1.2 bar, thus preventing from air penetration to the turbine during its operation. Pressure control valve maintains pressure of the gland steam.
Steam-air mixture is removed from the glands to the gland steam condenser and condensed there.
Depending on the operational feature, the fan evacuates such amount of steam-air mixture which is necessary to achieve the pressure approximately 0.95 bar in the turbine glands.
|В||Steam-air mixture from the glands|
|Г||Air extraction by fan|
|Е||Unloading of water chamber|
|Ж||Unloading of steam chamber|
Steam turbine plant is equipped with complete condensing equipment which provides condensation of exhaust steam of the turbine. Condensing plant consists of the following modules: shell-and-tube condenser, main steam-jet ejector, starting ejector, condensate pumps, condensate level controller in the condenser.
The main purpose of the condensing system is condensation of steam escaping from the turbine, removal of gases contained in steam and which cannot condense, as well as return of condensate to feedwater system of the boiler.
Condenser consists of welded shell, water chambers and tube bundles. The construction of water chambers is split-type, thus enabling to perform cleaning of one half of the condenser at low capacity of steam turbine plant.
Cooling tubes are flanged to the tube sheets. The condenser is designed for cooling with non-aggressive cooling water which does not contain mechanical impurities. Lower shell is equipped with a condenser tank for collection of condensate, which is then pulled out by condensate pump. The condenser is joined with the turbine exhaust with the help of transition piece. The connection is flanged or welded. Special coil springs are installed for compensation of vertical temperature expansions of the turbine and condenser exhaust.
Condensate pumps are used to extract condensate from the condenser to low-pressure regeneration system. The pumps may be of different versions – vertical or horizontal driven by electric motors. The control system (or higher-level control system) must provide automatic activation of pumps.
Condensate level controller provides the required level of condensate in the condenser in all operating modes and minimum condensate flow for condensate pumps. Condensate level controller is managed by servo motor.
AUTONIT is a standard system designed for monitoring and protection of turbines produced by ENERGOTECH LLC. AUTONIT is a digital multi-channel microprocessor-based monitoring and protection system. This modern sophisticated monitoring and protection system with simultaneous data processing was developed specially for modern steam turbines. Also this system may be used for renovation and retrofitting of old steam turbines.
AUTONIT combines efficiency of the modern software with reliable, time-proven and tested hardware, as well as experience of our specialists who gained their skills and knowledge on the basis of long-term trouble-free operation of electronic-electric turbine control system. Such combination enables to create new and developed digital monitoring and protection system.
AUTONIT monitoring system is supplied in different hardware versions – single-channel (basic), dual or triplex (optionally).
Architecture of this monitoring system is based on decentralization principle. This means that the signals from measuring instruments are collected in one cabinet, located in the plant, processed in this cabinet and then the necessary output actions are produced, and the data displayed are transferred via communications to the operator. This solution significantly reduces the amount of necessary cable wiring and significantly increases reliability of the entire system.
AUTONIT software is optimally consistent with hardware. Applied software is recorded in RAM or EPROM memory. All necessary changes and corrections may be made with the help of portable computer (not included in the scope of supply) at the moment of turbine generating unit commissioning.
The proposed monitoring system is manufactured in compliance with high industrial requirements, and quality is assured according to ISO 9001 regulations.
Monitoring and control system of the turbine generating unit is designed for remote control. To start up the turbine generating unit it is necessary to perform manual preparation of equipment in the turbine room. First of all, this is applied to manually controlled valves, in particular, in drain system of the turbine.
Upon completion of these works the turbine can be controlled remotely from the turbine control board, in particular: automatic testing and startup of lubrication system, barring gear of the valves, etc. Once all tests are completed, the turbine speed is increased automatically – up to rated speed of the turbine and, if necessary automatic synchronization and loading of the turbine.
Advanced concept of AUTONIT is adjusted to the specific operational requirements:
Where necessary it is possible to expand the proposed monitoring and control system with the help of other programs and software modules and other hardware.
Turbine governor is based on the independent central processing unit (CPU). The signals intended for quick control loop (for example, speed control) are introduced to specialized rotary speed processing modules. Control valves and diaphragms of the turbine are controlled via digital bus.
Control functions of the governor are following:
Turbine governor with adjusted preset value is automatically activated by the signal from generator circuit breaker in the event of power tripping from the exterior electrical network. The transition to island operation mode is also possible by operator command. The turbine cannot be operated in the island mode with simultaneous control of live steam pressure or control of back pressure.
Turbine power controller influences the setting of speed governor and enables to maintain preset generated power to the network.
Regulation limiters are intended to prevent exceedance of unacceptable parameters of live steam pressure, turbine output pressure, steam power and pressure in adjustable extraction (if available). The function of regulation limiters prevents shutdown of the turbine.
The EET converts output digital signal from the governor to proportional position of the shaft of servo drive which establishes the position of the turbine control valves.
Due to the fact that turbine protection is the most important function, this function is tested during operation either, starting from rotary speed metering channel to stop valves (including control valves). There are two independent overspeed protection systems set for exceedance by 7% and 8%, respectively, in excess of rated speed.
All parameters required for shutdown of the turbine (except overspeed protection) are developed based on selection logic 1 of 1, 1 of 2 or 2 of 3. The control system operates on “fail-safe” principle, i.e. turbine shutdown before potential accident. If turbine shutdown criteria are met, the electromagnetic clutch of stop valve, which is closed immediately, is deactivated through independent output circuit. Electromagnetic clutches of stop valves, which are closed immediately, are also deactivated at the same time. All shutdown signals of the turbine are always identified and sequentially recorded for storage (in the system memory).
The turbine is shutdown if the system achieves one of shutdown safety levels specified below:
overspeed 2х(2 of 3)
axial thrust of the turbine rotor 2 of 3
low lube-oil pressure 2 of 3
increase of steam absolute pressure in the condenser 2 of 3
increase of vibration speed of the turbine and generator bearings 1 of 1
increase/decrease of live steam temperature 1 of 1
“STOP” button actuation 3х(1 of 2)
signal of higher-level control system 1 of 1
Electromagnetic clutches control quick-closing stop and control valves of the turbine. These clutches represent electrically operated kinematic connection of the drives and valves. In the event of EMC deactivation, kinematic connection is broken and the valve is closed instantly under the influence of strong spring.
All input and output signals of the turbine generating unit are connected to I/O modules (input-output). These modules, as well as module of the main processor unit, are placed in Rittal cabinet which is located near the turbine and connected to automated workstation of process operator and automatic control engineer via dual communication channel.
Control of auxiliary equipment of the turbine is also performed in AUTONIT system. The system controls separate electric drives, for instance, oil pumps, barring gears, etc.
Signals exchange between the turbine control system and generator control board is performed via communications interface, therefore, ensuring control of generator with the help of operator station of the turbine.
AUTONIT does not include protection logic or generator control.
Signals exchange between the turbine control system and gener
ator synchronization panel is performed via communications interface, therefore, ensuring generator synchronization to the network with the help of operator station of the turbine.
Signals exchange between the turbine control system and service switchgear is performed via additional I/O modules and communications interface.
Personal computer with color LCD monitor and UPS (uninterruptible power supply system) are used as operator AWS. AUTONIT software used for display of OPERATOR AWS provides comfortable control of the turbine.
Simultaneously operator AWS displays measured values, produces warning and alarm signals, and displays plotted values.
Operator AWS is connected to AUTONIT low-level monitoring system via the system unit.
The turbine can also be controlled by higher-level control system.
Personal computer with color LCD monitor, color printer and complete uninterruptible power supply system are used as engineering work station.
AUTONIT ENGINEERING CONSOLE software provides adjusting of the turbine control system, creation of daily time-sheets, viewing of the past events in the form of printable diagrams.
Operator AWS software is also installed at the engineering work station and it can be used as operator AWS.
Engineering work station is connected to operator AWS via Ethernet communication channel.
AUTONIT archive system has broad options for storage, display and analysis of the condition of turbine generating unit. This archive system is very efficient during commissioning operations and during operation, especially upon occurrence of emergency situations at operator interventions) are registered by two archive systems.
Long-term archive is maintained automatically accurate to 1 second. All records in long-term archive are stored for 30 days. Upon expiration of 30 days the oldest records are replaced with the new ones. Any part of long-term archive may be converted to the file for longer storage.
Short-tern archive is maintained automatically accurate to 200 milliseconds five minutes before and five minutes after the initiated event (accident, operator command, etc.). Short-tern archives are automatically converted to the files for longer storage.
Software module of short-term archive with response time of 20 milliseconds (not included in the standard scope of supply) may be installed additionally. This software module provides the broadest options for hardware debugging and analysis of time-response characteristics and emergency situation at the station.
AUTONIT communications interface with higher-level control system is usually performed with the help of Ethernet serial connection with communications protocol of OPC DA2 server. Software of OPC DA2 server is not included in the standard scope of supply.
The signals connected directly to higher-level control system:
1х DO – Emergency turbine shutdown (signal from AUTONIT system)
1х DI – Emergency turbine shutdown (command to AUTONIT system)
The number of the above specified signals may be expanded in accordance with the Customer’s requirements.
All electronic modules, except operator AWS and AWS of automatic control engineer, are located in the cabinet of turbine control system (cabinet of local hardware and software package (LHSP)):
LHSP cabinet is made of steel coated with primer and treated with RAL 7035 (Rittal) paint. Standard cabinet has the following dimensions: approximately 800 mm wide, 2,200 mm high and 600 mm deep. The cabinet must be accessed from the front and back. Standard version of the cabinet has IP54 protection class and bottom conduit of cables.
Permissible ambient temperature range for LHSP is from 0°С to 50°С with relative humidity of 80% at 35°С and lower temperatures, without condensation of moisture.
Permissible ambient temperature range for AWS is from 5°С to 35°С with relative humidity of 80% at 30°С and lower temperatures, without condensation of moisture.
The scope of supply includes the sensors and gauges for remote measurement, regulation, protection and control (except flow meters, power sensors and power frequency sensors) which are necessary for operation of the turbine unit. Analog sensors are widely used both for control and regulation of the turbine, and protection of the turbine unit.
Initial configuration provides monitoring of vibration speed of bearings of the turbine, generator and gearbox.
Standard offer includes the following configuration of sensors:
Cabling routing is performed on the foundation frame or on the turbine generating unit
On the foundation frame (or near the turbine if there is no foundation frame) there are a strong steel cable channels which contain cables between the sensors of the turbine generating unit and terminal boxes.
Cables are made of copper in accordance with IEC 228 regulations, class 5, with enhanced mechanical resistance, with flame-retardant insulation, electrically stable to 300/500 V where it is necessary.
Power cabling is mounted on the foundation frame, except for special electric cables for servo drives of the control system included in the scope of supply of ENERGOTECH LLC.
Remote monitoring system (RMS) for industrial use represents a system of remote monitoring which enables the supplier to provide the customer with enhanced maintenance. Information received with the help of this system may in future help the customer to get maximum performance of its plant.
The system is supplied complete with all necessary communications means.
The standard scope of supply includes the following auxiliary equipment necessary for routine repairs and maintenance of MST steam turbine plant (STP).
Lifting equipment provides removal and installation of STP.
Device for lifting the turbine cylinder head allows to
In addition, for maintenance purposes the scope of supply includes a lifting beam for extraction of the turbine rotor, i.e. complete kit of spare parts and tools necessary for starting-up and adjustment.
Standard kit of supplied tools enables to perform repair of STP. Repair is performed when STP disassembling with turbine cylinder disassembling is required.
In order to use the equipment for extraction of the rotor, all pipelines laid on above ground level and near the foundation MUST be located not closer than 500 mm from the framework edge.
The requirements to standard inspection procedures for all equipment are specified below:
|8,000 operating hours||Type “А” inspection|
|16,000 operating hours||Type “А” inspection|
|24,000 operating hours||Type “B” inspection|
|32,000 operating hours||Type “А” inspection|
|40,000 operating hours||Type “А” inspection|
|48,000 operating hours||Type “C” inspection|
Operating hours are determined as the number of operating hours + 10 х number of registered start-ups.
If diagnostic system is used, the maintenance interval may be increased depending on operating conditions of the plant.
The cycle specified above is equal to six-year overhaul cycle.
The following Table provides routine tasks and performed works (aggregate description is given) and recommended intervals. These data may be corrected in accordance with the specific conditions of application based on operating modes and operating experience
|1||Checks before shutdown:-|
|Recording of all operating parameters in Shutdown Log (i.e. temperature, pressure, etc.)||Yes||Yes||Yes|
|Recording of all alarm messages of unit control panel||Yes||Yes||Yes|
|Measurement of vibration level by portable instrument||Yes||Yes||Yes|
|Recording of vibration level by contact hardware tools||Yes||Yes||Yes|
|Recording of parameters of control valves settings||Yes||Yes||Yes|
|Visual inspection of liquid systems||Yes||Yes||Yes|
|Control/recording of all pressure drops during operation||Yes||Yes||Yes|
|Check of all auxiliary electric driven equipment||Yes||Yes||Yes|
|Control/recording of temperature values of the collector||Yes||Yes||Yes|
|2||Check of complete unit, control system and drive unit (continuation):-|
|Check of water/steam supply system||Yes||Yes||Yes|
|Copying of the documents, check of tracer mechanism function and testing of battery charger||Yes||Yes||Yes|
|Function test and calibration of instruments included in the kit (analog and/or digital) and check of accuracy||Yes||Yes||Yes|
|Check of connections of unit control panel (STP control panel), removal of accumulated dust, cleaning of filters, check of lamps and terminal boxes||Yes||Yes||Yes|
|Function test and calibration of control valve system, check of functioning of all emergency shutdown buttons||No||Yes||Yes|
|Check of all auxiliary gearboxes and clutches in the assembled condition – actuators of control and stop valves||No||Yes||Yes|
|Check of settings of tightening torque of anchor screws||No||No||Yes|
|Check of high-speed clutch and coaxial alignment||No||No||Yes|
|3||Check of MST unit|
|Actuators of control and stop valves||Yes||Yes||Yes|
|Check of thermocouples and terminals/wires||Yes||Yes||Yes|
|Check of resistance and wiring of rotary speed sensor||No||No||Yes|
|Opening and inspection of the turbine||No||No||Yes|
|4||Check of start-up and operation|
|Acceleration and shutdown, recording of rotor run-down time, etc.||Yes||Yes||Yes|
|Check of functioning of stop and control valves||Yes||Yes||Yes|
|Leakage test of all liquid systems||Yes||Yes||Yes|
|Check of cold and hot start-up||Yes||Yes||Yes|
|Recording of all data about the turbine in Inspection Log||Yes||Yes||Yes|
|Check of vibrations by portable instrument at peak load conditions||Yes||Yes||Yes|
|Final copy of the documents on completion of inspections||Yes||Yes||Yes|
Category “A” inspections
Routine annual inspections of STP (every 8,000 hours)
Category “B” inspections
As a rule, category “B” inspections are performed when STP reaches 24,000 operating hours (or approximately every 3 years). The scope of inspection corresponds to the scope of category “A” inspection, but with more thorough inspection of the condenser and components of auxiliary systems, and with filed replacement depending on the condition. Through inspections of regulating systems are also included.
Category “C” inspections – major repairs
As a rule, category “C” inspections are performed when STP reaches 48,000 operating hours (or approximately every 6 years). The scope of inspection corresponds to the scope of category “B” inspection, but with more thorough internal inspection of the gearbox assembly and steam path of STP.
Engineers must perform works in compliance with the detailed and pre-developed inspection schedule. In accordance with the instructions maintenance group must record all meter readings, mark all works performed in inspection Log, register observations, make changes to the documents and, if necessary agree such changes with the Customer, if appropriate, prior to proceeding to the following stage or continuation of works.
Standard plant downtime in days and for each inspection schedule is specified in the Table below. Specified downtime provides for work of two persons per shift. The necessity to inspect the generator is not included in the data below.
|Plant type||Scheduled downtime|
|“A” type||“B” type||“C” type|
Warranty service life is 24 months from the date of putting into operation, but no more than 30 months from the date of plant delivery to the customer.