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Home / Technical Articles / AC and DC facilities in electrical station services of major power plant types

Station services switchgear in power plants

In a power plant, the electrical station services (abbreviated to SS in the following) consist of all the DC facilities from 24 to 220 V and AC facilities up to about 20 kV for controlling and supplying power to the equipment needed to keep the plant running. Hence, these auxiliary services clearly play a vital role in assuring the plant’s reliable operation.

AC and DC facilities in electrical station services of major power plant types
AC and DC facilities in electrical station services of major power plant types

Close attention must therefore be paid to requirements affecting the particular plant and the safety considerations, such as the provision of backup systems.

Table of contents:

  1. Alternating current (AC) station services
  2. Direct current (DC) station services
  3. Station services in power plants
    1. Hydro power plants
    2. Diesel power plants
    3. Gas turbine / combined-cycle power plants
    4. Conventional steam thermal power plant
    5. Combined heat and power stations
  4. Automatic station service power transfer
    1. Switchgear configuration with two circuit breakers

1. Alternating current (AC) station services

The AC services for a generating plant unit consist essentially of the station service power transformer, in most cases a medium voltage distribution network, and low voltage distribution facilities. They may include a power transformer and the necessary distribution gear fed from a separate MV network for supplying general loads, i.e. not directly related to the generating unit, and possibly for starting the units and shutting them down.

Standby power supplies are dealt with in the below technical article.

Generators applicable to high reliability requirements of healthcare and other facilities


The basic SS arrangement in a so-called unit-type system for a power plant composed of separate units is shown in Figure 1, and the corresponding layout for a bus-type system in Figure 2.

The advantages of the unit-type configuration are that the ratings for the SS distribution facilities are lower, making it easier to cope with short-circuit currents and that the units are self-contained, so enhanced availability.

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Edvard Csanyi

Electrical engineer, programmer and founder of EEP. Highly specialized for design of LV/MV switchgears and LV high power busbar trunking (<6300A) in power substations, commercial buildings and industry facilities. Professional in AutoCAD programming.

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