Normal AC Electrical Systems in Nuclear Power Plants

Electrical Systems

Function

There are two (2) main function of electrical systems in a power plant:

distribute the electrical power from the power supply to the components
provide electrical protection for the power source and also for the components supplied.

Major Components

In nuclear plants there are several levels of electrical power distribution (other than from the generator to the generator transformer):

High Voltage (e.g. 4160, 6900, or 13,800 Volts AC, may also be abbreviated VAC)
Medium Voltage (e.g. 480 VAC)
Low Voltage (e.g. 120, 240 VAC, 260 VAC)

High voltage systems are used to supply equipment that have motors with high horsepower ratings. Examples of these are:

Feedwater pumps
Recirculating or Reactor Coolant Pumps
Circulating Water Pumps
Condensate Pumps
Cooling Tower Pumps and Fans
High Pressure Emergency Makeup Pumps
Containment Spray Pumps

Medium voltage systems are used to supply equipment that have motors with moderate horsepower ratings. Examples of these are:

Auxiliary or Emergency Feedwater pumps
Heating Ventilating Air Conditioning (HVAC) Fans and Chiller Units
Control Rod Drive Motor-Generator Sets
Motor operated valves

Low voltage systems are used to supply equipment that have motors with low horsepower ratings. Examples of these are:

Lights
Small pumps

Electrical Switchgear

This photo shows electrical switchgear (distribution panels) as may be found in a nuclear plant.

Detailed description.

Diesel Generator

Photo shows a diesel generator used for emergency power generator as may be found in a nuclear plant.

Detailed description.

Cable Trays

A cable tray that holds electrical cables as may be found in a plant located in an area with high sensitivity to earthquakes. Note the structural supports.

Example System Diagram

Below is an example of an overall electrical distribution system for a nuclear plant:

Graphic courtesy USNRC