Indoor Type Substations: Descriptions & Classifications

Indoor Type Substations

Indoor Type Substations is the substations in which the apparatus is installed within the substation building. Indoor Type Substations are usually for a voltage up to 11,000 V but can be erected for 33,000 V and 66,000  volts when the surrounding atmosphere is contaminated with impurities such as metal corroding gases and fumes, conductive dust etc.


 Indoor Type Substations

The switch-gear on supply or primary side will consist of oil circuit breakers only. The high voltage supply is given to the primary of the transformer through circuit breaker. From the bus-bar various feeders emerge out. The panel for each feeder consists of an isolator switch and circuit breaker.


In  addition to isolator and circuit breaker, the panel is provided with the measuring instruments. As regards protection of feeders usually reverse power relay is employed. For the protection of oil filled transformers with conservator tanks Buchholz’s relay is most common.




The auxiliaries of the indoor type substations are

  1. Storage Batteries
  2. Firefighting equipment such as water buckets, fire extinguishers, etc.

The batteries are used for the

(i) operation of the protective gear and switch operating solenoids and

(ii) emergency lighting in substations in case of failure of supply.


The several operation compartments in which the indoor substation is divided are control compartment, indicating and metering instruments and protective device compartment, circuit breaker and operating mechanism compartment, main bus-bar compartment and current transformer and cable sealing box compartment as shown in figure below

 Indoor Type Substations


Indoor distribution and transformer substations as well as high voltage switchboards consist of a series of ope and enclosed chambers or compartments.

The main equipment of the given installation is arranged in these compartments. the chamber space within which the equipment of any one main bus-bar connection is mounted, as a whole, is called as a cell, cubicle or compartment.

According to construction indoor distribution transformer substations and high voltage switchboards are further subdivided into the following categories.

  1. Substations of the integrally Built Type
  2. Substations of the composite Built-Up Type
  3. Unit Type Factory Fabricated substations and Metal Clad Switch boards

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