Steam Turbine

What is Steam Turbine Generator?

The steam turbine generator is the main power conversion element of the power plant. The steam turbine generator's function is to transform the steam generator's thermal energy from the steam generator to electrical energy. It generally consists of two distinct components: the steam turbine to transform the thermal energy to rotating mechanical energy, and the generator to transform the mechanical energy to electrical energy. Typically, the turbine is directly joined to the generator.

Steam turbine-driven generators are commonly high-speed machines. Most of the electric power worldwide is generated by steam turbine-driven power plants. In the United States alone, about 85.0% of the electricity is generated using steam turbine generators.

Steam Turbine Generator Parts and Diagram

Typically, a steam turbine consists of the following parts:

• Rotor - The rotor is rotated by steam hitting against attached blades or vanes on which it exerts a force.
• Stator / Diaphragm - Stators are packed with curved nozzles to transform the enthalpy of the low-velocity steam coming off the blade back into kinetic energy before impelling on the next blade.
• Blades - Steam turbine blades are crucial components in power plants that transform the linear motion of high temperature and pressure steam flowing down a pressure gradient into the turbine shaft's rotary motion.
• Bearings - Holds the rotor and join casing and steam chest.
• Valves - Steam turbine valves are the essential elements of modern steam turbines from the aspects of operation, performance, reliability, and safety.
• Seals - Seal the shaft and the casing.
• Casing - Holds the whole system.
• The principal components of an electric generator can be broadly grouped as follows:
• Fuel System - usually used to keep the generator operational for 6 to 8 hours on average.
• Engine - the origin of the input mechanical energy to the generator.
• Voltage Regulator - as the name suggests, this component adjusts the output voltage of the generator.
• Alternator - the section of the generator that generates the electrical output from the mechanical input provided by the engine.
• Lubrication System - Because the generator includes moving parts, it needs lubrication to ensure stability and continuous operations for an extended period.
• Cooling and Exhaust Systems - Continuous usage of the generator makes its different components to get heated up. It is necessary to have a cooling system to withdraw the heat generated in the process.
• Battery Charger - The start function of a generator is battery-operated. The battery charger maintains the generator battery charged by providing it with a definite ‘float’ voltage.
• Control Panel - This is the user interface of the generator and includes provisions for electrical outlets and controls.
• Main Assembly / Frame - All generators have customized housings that give structural base support.

Types of Steam Turbine Generator

There are two fundamental types of steam turbines: impulse turbines and reaction turbines. I a steam turbine, the blades are intended to control the speed, pressure, and direction of the steam as it progresses through the turbine. The generator is connected to the turbine, and when the turbine blades rotate, the generator starts working on the principle of magnetic induction and produces electricity. The method of recovering electrical energy depends on how it is used. The steam is usually condensed into a condenser. Hence, a boiler, steam turbine, generator, and condenser are the principal components in a steam-powered generator plant. Steam Turbines can also be performed to operate without a condenser as well but present a significantly lower power capacity for the same size of turbine.

• In Impulse Turbines, the rotor rotates because of great force or the direct steam pushing on the blades.
• In Reaction Turbines, the rotor rotates from a reaction force rather than an impulse or impact force.

Turbines also differ in their cooling method of steam. Condensing turbines, regularly used in large power plants to produce electricity, transform the steam to water utilizing condensers, allowing the steam to expand more and facilitate the turbine in obtaining maximum energy from it. This causes the electricity generating process much more effective. Non-Condensing turbines don’t have this feature and therefore are infrequently used except for small, auxiliary systems where only low power is required.

1.1. Working Principle of a Steam Turbine Generator

Heat is produced from a process like combustion in a boiler in a steam turbine driven generator. The heat in the boiler is applied to transform it into steam, which is of high temperature and pressure. Steam production depends on the heat transfer flow rate and surface area, and the combustion heat applied. This steam from the boiler is forced into the turbine within nozzles, which turns the blades installed on a shaft. The steam turbine includes a casing to which fixed blades are set inside and a rotor that drives blades on the periphery.

The working of a giant steam turbine may be complicated and challenging to comprehend since it employs a set of blades on the rotor. Each set of blades is designated as a stage that operates by either reaction or impulse. A mixture of reaction and impulse stage complicates its operation since these sets of blades are all installed on the same rotor axle and all turning the generator at the same time.

Steam turbines adjust their speed using a control governor and automated valves, producing optimum power as required at any particular time.