KODA Turbine Type MTD30 is a modular steam turbine design which is based on the following principles:
– Turbines of various types are composed from the individual components that have been already verified in operation. The turbine is divided into the building blocks that are composed together to create a customer-requirements.
– Capacity gradation is based on the laws of similitude.
Skoda steam turbines design uses the impulse stage principle and technology with prove moving wheels and diaphragms construction.
The impulse stage design can consume higher enthalpy drop in one stage and so it requires only about half number of stages compared with reaction type turbine. The impulse turbine allows to use the ample spacing among individual stages, which enables the installation of multi teeth, spring backed labyrinth interstate glands and robust design of the components.
Greatest part of the stage pressure drop is consumed in the diaphragm nozzles and very small part of pressure drop remains for the moving blades. This produces on the rotor small axial thrust which loads the thrust bearing. The Load changes of the turbine do not result in large axial thrust changes what is important for the reliable operation of the thrust bearing.
Small diameter of solid forged monoblock rotor and notch-less design reduce the thermal stresses and makes possible the fast and big clad changes. Skoda turbines are designed to satisfy the requirement on frequent shut-downs with following quick starting and loading rates and large load variation in grid frequency control mode.
Small turbines are erected with gear box substantial part of piping and instrumentation on the common welded frame. The turbines are assembled, aligned and properly checked in the factory before the shipment.
The stator parts (casing, pedestal) are shifted by the thermal expansion from the stator’s fix point forward. The fix point is placed in the rear part of the exhaust branch. The thrust bearing, which is placed in the front bearing pedestal, is shifted with the pedestal and so the turbine rotor follows the stator displacement. The axial clearance between rotor and stator parts are due to this arrangement only slightly changed in operation and problem with insufficient clearances is avoided. Steam turbines trade mark SKODA of output category 3-30 MW can be divided in five basic groups:
– Condensing units
– Backpressure units
– Condensing units with double controlled steam extractions
– Backpressure units with controlled steam extraction.
Max, steam parameters for these turbines groups are approximately:
– Inlet steam pressure 90 ata.
– Inlet steam temperature 535 °C.
Condensing turbines are designed for the vacuum range 0.08 – 0.18 ata. They may be designed for operation out of this range. The rear exhaust part of the casing, that is bolted to the front casted part, can be exchanged if required.
Backpressure turbines are designed for exhaust pressures 2 – 20 ata. The bolted exhaust part of the casing can be exchanged also for this turbine group and extended to the range of applicable backpressures. The extraction turbines can operate in the wide range of extraction pressures and quantities. The extraction pressure is controlled by the relief valves.