Likewise, it undergoes contraction as its case cools during steam reduction. Reducing cycling damage to combined cycle steam turbines cycling a combined cycle plant places additional stresses on all equipment, but the. General rules for superheated and satured steam turbine startup and load change 88 6. Introdution during our work throughout europe we have been often confronted with steam turbines and turbomachinery suffering from asymmetric dilatation not to be confused with differential dilatation. The primary purpose of a differential expansion monitor is to guard against axial rub between rotating and stationary parts. Steam turbine casing front side is generally free and slide on the front side bearing pedestal. Steam conditions the turbine expansion line or condition curve represents steam conditions prevailing in sequential stages of the steam turbine. The blades in turn change the direction of flow of the steam however its. Impulse steam turbineimpulse steam turbine on impulse turbine a thermal expansion take place only in theon impulse turbine a thermal expansion take place only in the nozzles and static energy is converted to the kinetic energynozzles and static energy is converted to the kinetic energy there is no pressure different at inlet and outlet of. In general, a steam turbine is a rotary heat engine that converts thermal energy contained in the steam to mechanical energy or to electrical energy. In addition, other relevant thermal processes within a steam turbine are those of gland steam sealing and losses due to. The performance of the steam turbine is governed by the losses occurred in it. Steam turbines startups 1 principles of steam turbines startups. The curtis stage turbine, as it came to be called, is composed of one stage of nozzles as the singlestage.
Improvements of up to 30% were accounted to this measure. A typical large steam turbine power generation unit will have a thick case, on the order of 12 to 18. In order to improve the startup flexibility of steam turbines, it becomes relevant to analyze their dynamic thermal behavior. The steam turbine uses crossover ductingpiping to transport steam from the intermediatepressure turbine exhaust to the lowpressure turbine inlets. The differential expansion measurement is to measure this difference and ensure that the rotor does not touch the stationary parts. Warning a complete reading of this manual by personnel in contact with the steam turbine is essential to safety.
Differential expansion sensitivity studies during steam turbine startup article in journal of engineering for gas turbines and power 86 september 2015 with 385 reads how we measure reads. Request pdf differential expansion sensitivity studies during steam turbine startup in order to improve the startup flexibility of steam turbines, it becomes. Steam turbine thermal modeling for improved transient. Its modern manifestation was invented by charles parsons in 1884 the steam turbine is a form of heat engine that derives much of its improvement in thermodynamic efficiency from the use of multiple stages in the expansion of. Differential measurement for large steam turbines with long shaft systems, an additional axial position. Proceedings of the asme turbo expo, montreal, canada. Pdf power plant lecture notes chapter2 steam power. The turbine is heated up and brought to minimum speed as a reduced back pressure machine.
Sensonics technical note ds1220 differential expansion. Prior to supplying steam to the turbine, the steam supply pipelines have to be drained and heated up. Ge they require controlled thermal transients as the massive casing heats up slowly and differential expansion of the parts must be minimized. The bypass valve is also used to provide warming steam for the turbine steam chests and the high pressure turbine shell during turbine startups see chapter 11. Causes and solutions steam turbine rotors bend during operation, but the bearing and supports are designed to. A steam turbine undergoes thermal expansion as its case heats during steam admission. The studies performed serve as a base towards further understanding the differential expansion during start and establishing future clearance control strategies during turbine transient operation. When turbine is in service, superheated steam temperature above 540 degree celsius is admitted into the turbine. A steam turbine is a device that extracts thermal energy from pressurized steam and uses it to do mechanical work on a rotating output shaft. Figure 3 supersaturated expansion of steam into wet region 3. Differential expansion on a turbine is the relative measurement of the rotors axial thermal growth.
Reducing cycling damage to combined cycle steam turbines. Differentialrotor expansion sti vibration monitoring inc. What is differential casing expansion in steam turbine. The steam turbines principle is that the steam energy is converted into mechanical energy by expansion through the turbine. The principles of correct conducting startups have been developed over the longterm operation of steam turbines and contain experience of turbine designers, constructors and operators. We are commissioning this turbine for the first time.
The first steam turbine used for power generation was invented in 1884. An increase in differential expansion may be caused by too fast a change in inlet steam temperature or due to too rapid change in steam flow to the turbine. Steam turbines have a known thermal expansion, where. Flexible operations impact on steam turbine failure modes and best practices thomas r. Purpose of document and how to use it iapws has issued a series of technical guidance documents for the steam cycle chemistry control of conventional fossil and combined cycle plants. Differential expansion monitoring measures the change in axial clearances between the machine rotor and casing caused by thermal changes inherent in most machines. Request pdf differential expansion sensitivity studies during steam turbine startup in order to improve the startup flexibility of steam turbines, it becomes relevant to analyze their dynamic. Each time it starts, the turbine after rolling about 2 or 3 hours differential expansion reach to its limit 1mm, and turbine trips, we have scyncronizing and reaching to 20mw during this 3 houres. Based on saddlepoint approximation method and sensitivity analysis method, reliability sensitivity analysis for differential expansion of steam turbine with random parameters are studied. Generally in a steam turbine the rear support of the steam turbine or the rear side of the casing is fixed. A consequence of excessive thermal expansion is rotor rubbing. Flexible operations impact on steam turbine failure modes. An example is a stag 109e ms, indicating that the combinedcycle contains a single frame 9e gas turbine generator and a separate ge steam turbine generator on two different shafts.
Form this we can observe that, to get more power output the steam. Common techniques for measuring large differential expansion ranges include extended range. The velocitycompounded impulse turbine was first proposed by c. Differential expansion sensitivity studies during steam. Expansion occurs through a series of fixed blades nozzles and also moving blades. What is steam turbine description and characteristics. Instruction manual for single stage 350, 500, and 700. Length of turbine expansion between the turbine shell in the axial direction. Both the ends are supported on independent pedestals. Chaplin encyclopedia of life support systems eolss both of these have double casings with the exhaust steam circulating in the annular space between the casings as in the case of the high pressure turbine. Steam flow to the condenser is minimal during an uncoupled slow speed run. Plotted on a mollier diagram it provides a useful visual image of these conditions. Differential expansion sensitivity studies during steam turbine.
Hence, it is necessary to maintain the highpressure turbine hpt, intermediatepressure turbine ipt, and lowpressure turbine lpt differential expansions within the predetermined limits. Oneonone configurations are further qualified as being multishaft ms, or single shaft ss. Curtis to solve the problems of a singlestage impulse turbine for use with high pressure and temperature steam. Steam turbine performance 3 4 2 1 46 45 44 43 42 41 43 42 41 40 39 % % 1. Hga excess air discharge flue gas temperature main steam condition reheat back pressure lhv. In case of turbines with cooling water preheating and lowpressure lp bypass, prior to supplying steam the regeneration and dumping systems have to be. Sensitivity studies during steam turbine start up, gt201542214. For that reason, startup times must be extended under.
Turbine differential expansion increased vibration levels turbine water induction boiler issues. The extremely large casing sizes and extremely high steam temperatures of turbines used in electric power generation service can easily result in up to two inches 50 mm of axial growth. Turbine supervisory instrument tsi instrumentation and. The steam jets are directed at the turbines bucket shaped rotor blades where the pressure exerted by the jets causes the rotor to rotate and the velocity of the steam to reduce as it imparts its kinetic energy to the blades. This measurement is typically performed on larger steam. On the premise of the probability distribution of random parameters, using saddlepoint approximation method, probability density function of limit state function of differential expansion of steam. Steam turbine crossover expansion joint for a new gtcc. Steam turbines are one of the most versatile and oldest prime mover technologies still in general production used to drive a generator or mechanical machinery. While there are multiple connotations for the term differential expansion in the context of a steam turbine, it is predominantly a reference to the thermally.
Steam does not condense at the saturation temperature. The interaction between mechanical and electrical system and the fact that the structural damping of the torsional modes is low are the main reasons for most of the root causes leading to torsional vibration problems. With todays steam turbine arrangements exceeding the 900mw barrier this measurement is as relevant as ever and a continuing challenge. In a steam turbine, highpressure steam from the boiler expands in a set of stationary blades or vanes or nozzles. Caution must be exercised to avoid overpressurizing the surface condenser expansion joint and the steam turbine exhaust casing.
Three basic phases can be distinguished in the process of steam turbine unit start. Alstoms ultrasupercritical steam turbine at the boxberg power plant in germany can produce 600 mw. Unesco eolss sample chapters thermal power plants steam turbine components and systems r. Axial differential expansion between the rotor and the casing is a major. Keywords asymmetric dilatation, thermal expansion, misalignment, turbomachinery i. Boiler, turbine, condenser, pump, carnot cycle for steam, disadvantages of carnot cycle application. Turbine loading leads to positive expansion, while unloading results in negative differential. In its simplest form, a steam turbine consist of a boiler steam generator, turbine, condenser, feed pump and a variety of auxiliary devices. The crossover allows differential thermal expansion between the crossover and the connecting stationary equipment without im posing large axial forces due to steam pressure. Turbine lifting oil and jacking oil pumps in service tg engaging sequence. Schofield ge company schenectady, ny introduction the need to provide stateoftheart products for a diverse and everchanging market is the chal lenge facing steam turbinegenerator manufactur ers in the 90s.
1286 1001 41 925 1139 998 1316 824 454 1301 1029 24 1144 383 1028 409 1199 881 1073 104 1330 1252 1330 826 1438 114 270 1264 499 978 566 66 901 486 538 738 361 1255 173 117 1460 1470 665 1277 1044 1277 1259 679 770