Indoor Substations Types: According to Constructions

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Indoor Substations Types

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


  1. Substations of the Integrally Built Type

In this indoor substations types, the apparatus is installed on site. In such substations the cell structures are constructed of concrete or bricks.


2. Substations of the Composite Built-Up Type

In this indoor substations types, the assemblies and parts are factory or workshop prefabricated, but are assembled on site with in a substation switch-gear room. The compartments of such substations take form of metal cabinets or enclosures, each of which contains the equipment of one main connection cell. Within such cabinets or enclosures an oil minimum circuit breaker, a load-interrupter switch and one or more voltage transformers may be mounted.

3. Unit Type Factory Fabricated Substations and Metal Clad Switchboards

In this indoor substations types, electrical workshops and  are shipped to the site of installations fully preassembled. After installations of substations and switchboards only connection to the incoming and outgoing power  circuits are required to be made. Cubicles for unit type switchboards or substations take the form of fully enclosed metal-clad cabinets.




Metal-clad cubicles designed with withdrawal trucks and divided into several compartments are usually employed. The several compartments in which the cubicle is divided are control compartment, indicating and metering instrument and protective device compartment, circuit breaker and operating mechanism compartment, main bus-bar compartment and current transformers and cable sealing box compartment.


By partitioning of the cubicle space into compartments safe access to the apparatus is provided. The circuit breaker and its operating mechanism are mounted on the truck, which can be withdrawn from the cubicle. In withdrawal tuck unit type cubicles the isolating device is of the plug-in-type. When the truck is rolled out from the cubicle the holes in which the isolating devices enter for making contacts are automatically closed by metal shutters serving to isolate the live parts from possible casual contact. When the truck is rolled back into the cubicle, the shutters open automatically.


To prvent any possible opening or closing of the disconnecting devices when the circuit breaker is closed,  these cubicles are designed with interlocks which prevent the truck from being rolled in or withdrawn when the circuit breaker is closed.

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