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Figure 3.4.14 Pressurizer relief valve specifications (example)

  1. Turbine System

  1. Outline

The key component of a turbine system is a turbine-generator unit. The turbine of this unit, called the main turbine, is composed of a high pressure turbine and a set of low pressure turbines. The turbine converts the thermal energy of steam into rotational energy and the generator, which

is directly coupled with the turbine, converts the mechanical energy into electrical energy. The turbine system includes several subsystems other than the turbine-generator unit such as the main steam system, condensate and feed water system, and circulating water system. The components of the turbine system are briefly described in the following sections and their functions are summarized in Table 3.5.1,

  1. Main Turbine and Its Appurtenances

  1. Characteristics of Nuclear Power Plant Turbines

© Steam generated in the steam generators of PWR NPPs is saturated steam at a pressure of 4.9 to 6.9 MPa (gage].

(2) Heat drops at NPP turbines are relatively small and steam flow rates are about 1.6 to 1.8 times those for fossil fueled power plant turbines of similar capacities.

@ Due to the larger flow rates and the lower steam pressures compared to fossil fueled plant turbines of similar capacities, the volumetric flow rates for PWR NPP turbines are approximately 4 to 5 times larger than those for fossil fueled plant turbines.

© Consequently, the sizes of PWR NPP turbines are larger than those of fossil fueled power plant turbines of similar capacities. This requires that the design speeds of the former are lower than those of the latter to keep the stresses of the rotating components below their allowable limits and they are 1500 rpm (50 Hz) or 1800 rpm(60Hz).

® The moisture contents of the steam increase as the initially dry and saturated steam expands as it flows through the turbine. Since these water droplets will erode the turbine rotating blades and reduce the turbine internal efficiency, the turbine is designed with mechanisms and equipment to remove water droplets from the steam flow.

  1. Turbine types, blade designs and steam cycles

i) Turbine types and blade designs

The last stage blade designs of PWR NPP

NSRA, Japan

3~48

Chapter 3 Systems of PWR Nuclear Power Plants

Table 3.5.1 Function of main components of turbine system

Component

Function

Turbine

To convert steam energy into rotating energy

Generator

To take out electrical energy from rotating energy

Main Steam Valve

To isolate steam and regulate velocity and load

Condenser

To condenser turbine exhaust steam to reduce exhaust pressure and to recycle condensate

Air Ejector (Vacuum Pump)

To eject non-condensable gases from steam

Gland Steam Condenser

To cundensate and recycle leaked steam from turbine gland seal

Feedwater Heater

To heat feedwater by turbine extraction steam in order to improve thermal efficiency

Deaerator

To separate and remove dissolved oxygen in feed water and to heat feed water by turbine extraction steam

Moisture Separator and Reheater

To separate moisture from steam and reheat steam

Feedwater Pump

To pressurize feedwater and feed it to steam generator

Condensate Pump

To draw condensate water from condenser and feed to feedwater pump

Cundensale Denineralizcr

To purify condensate water

Chemical Injection Device

To control feed and condensate water quality with chemical injection pump and tank

Make-up Water Facility

To supply feedwater with pump, tank, and filtering demineralizer

Circulating Water Pump

To circulate cooling water into condenser

Component Cooling Water Cooler

To coot component coot tog water

Compunent Coot log Water Pump

To circulate component cooling water

Turbine By-pass Device

To discharge steam from steam generator to condenser in order to improve operating performance during start-up and rapid boad reduction

Electrical Facility

To transmit electrical power and supply power to each component