In this post, we will discuss the description of steam turbine components. This post will be helpful to understand the Steam Turbine Components
DESCRIPTION OF STEAM TURBINE COMPONENTS
Inlet Stop and Emergency Trip Valve
The valves are the flanged type and bolted to the nozzle chest from both end and spring supported from the turbine base.
The unit combines two functions:
- That of isolating the turbine from the steam main when stationary
- To provide immediate steam cut-off should any security trip operate
The complete assemblies are cantilevered from the nozzle chest at both ends in a vertical position, requiring the spring supports to relieve, dead weight, steam forces and pipe loads from the flange mounting. The correct setting for the supports is extremely important to avoid misalignment of the casing to the rotor.
This single beat valve is designed with steam-on-top so that when shut, the inherent steam out of balance across the valve maintains a tight seal against steam leakage and provides, in addition, a tamper-proof stop valve.
For both valves, the lower end of the combined stop valve body houses a hydraulic servo, which provides the Operator with ‘muscle’ to open the valve against full steam pressure. When the turbine oil system is functioning correctly is only control oil available to operate both the stop and emergency valves.
Control oil is supplied via the Low-Pressure Trip unit which cuts off the high-pressure Control oil supply should a running fault occur thus initiating instant closure of the stop valve.
Throttle Valve Chest
The throttle valve chest is mounted on top of the steam end casing. This chest houses three control valves each of which feeds an arc of the nozzle belts integral with the valve chest. The chest passes through an aperture in the top of the steam casing and is secured by a bolted joint.
The throttle valves are of the single beat type, with spindle and valve head guides. The valve and guide assemblies are housed in separate columns, bolted on the top face of the valve chest.
The cylinder or casing is divided at the horizontal joint and is arranged with centerline support, ie the support points are on the same horizontal plane as the center line of the turbine.
At each end – two right-angled palm pieces are keyed and bolted to the casing on vertical facings. The horizontal faces of the palms rest on pads equi-spaced about the pedestal center lines. A transverse key though each palm piece and its mating pad – serves to locate axially to each pedestal.
The exhaust end pedestal is anchored rigidly to the baseplate, whereas the steam end pedestal sits upon a flexible ‘panting plate’. The latter provides rigidity in the vertical and lateral planes but allows flexibility in the axial (horizontal) plate of casing thermal expansion.
A key located vertically underneath the cylinder at each end, mates with a matching keyway on each pedestal, allowing free radial expansion of the casing whilst at the same time restraining any transverse movement.
The cylinder supported thus, moves axially away from the fixed exhaust end, the rotor thrust bearing housed in the steam end pedestal, therefore, experiences this movement. The rotor located by the thrust bearing expands towards the exhaust end pedestal so that axial expansion of the cylinder and rotor ensures controlled relative movement between moving blades an stationary nozzles.
The clearance between stationary and moving parts allows for abnormal operating conditions.
The exhaust opening of the cylinder passes down through the baseplate and is connected to the exhaust main through a suitable bellows system.
The turbine rotor designed to run at speeds above the first transverse critical speed and is machined from a solid alloy steel forging. A number of integral straight sided discs (corresponding to the number of stages) are formed with inverted ‘T’ root grooves to accept the blading.
Blade gates are slotted radially into the discs and are arranged diametrically to minimize the out-of-balance effects.
After blading, special closing blades are pinned in position. These close the blading gates giving a uniform arc of blades with no gaps or caulking pieces. Such gaps give rise to increased and non- uniform bending stresses and could cause vibrations.
Balancing strips are formed integrally on all stage discs. These strips permit metal to be removed for dynamic balancing purposes without encroachment on to the stressed disc profile.
Steam balance holes are drilled axially through the discs. These holes are carefully finished to avoid any local stress concentrations.
The shaft end and interstage gland seals have common stepped diameters on the rotor and match the high-low tooth, stepped, spring-loaded labyrinth packings.
The rotor journals and the thrust bearing collar, which is integral with the rotor shaft, are all precision ground. The rotor shaft has a flange as part of the forging at the driving end to accept the high-speed coupling.
another steam turbine components will be discussed in the next post.
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