Introduction of Indoor Switchgear – Advantages and Limitations of Indoor Switchgear

Introduction of Indoor Switchgear

Switchgear is a generalized term given to a unit which is a combination of protective control and metering types of equipment as a whole. Switchgear can be of different forms depending on the kind of applications such as protection of feeders, protection of motors, rail traction purposes, measurements etc. For example, the switchgear installed in an electrical power substation perform various functions such as connections of incoming feeders and transformer units with the busbar, interruption of short circuit current using combinations of circuit breakers and relaying devices, switching of capacitor banks, measurement of current and voltage, monitoring and control, battery storage, etc. Depending on the voltage levels as well as economic viability, switchgear can be of indoor or outdoor types. The indoor switchgear is mostly used for medium voltages also called MV switchgear and is enclosed in a metal enclosure that is grounded. Voltage levels ranging from 3-36 kV can be termed as medium voltages. However, in recent times indoor switchgear has also been successfully employed for high voltages higher than 36 kV. In the coming sections, we will try to restrict our discussion mainly to the indoor switchgear.

Design of Indoor Switchgear

Indoor switchgear is usually gas-insulated (GIS) rather than air-insulated. GIS is used where land costs are high and air is corrosive or dusty. The switchgear is enclosed in a grounded metal case with ventilation and inspection openings. SF6 gas is preferred for insulation due to its excellent dielectric properties, which are three times better than air. This metal enclosure offers extra safety compared to outdoor systems. Indoor switchgear can be divided into two types based on metal enclosure and switching methods.

1. Metal-enclosed indoor switchgear.
2. Metal-clad indoor switchgear

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Metal Enclosed Switchgear

The switchgear arrangements are enclosed on all sides with metal sheets containing primary interrupting devices and fuses, and all the pieces of equipment are encased in a central assembly. Doors and removable coverings provide the access to the interior of the enclosure. The fig.1 shows an image of a metalenclosed type indoor switchgear system.

Metal Clad Switchgear

Metal-clad switchgear typically uses vacuum-type circuit breakers that can be withdrawn or drawn out. Relaying and metering instruments are separately isolated by grounded metal barriers. Metal-clad switchgear operates at voltage levels from 4.76 kV to 38 kV, with main bus continuous ratings of 1.2 kA, 2 kA, 3 kA, and 4 kA.

In general, all metal-clad switchgears are metal enclosed but all metal-enclosed are not metal clad switchgears. The metal-enclosed switchgear is of same voltage rating as that of metal-clad but is of simpler construction. The metal-clad switchgear is advantageous over metal-enclosed switchgear because the former is highly customizable.

Advantages of Indoor Switchgear

Compared to outdoor switchgear, the indoor switchgear system has the following advantages :
More reliable and safer.

• More reliable and safer.
• Takes lesser space than the outdoor system.
• Easier maintenance and durability.
• Lower operating costs.
• Reduced risk of electrocuting due to grounded metal enclosures.
• More security.
• Lesser prone to environment conditions.

Limitations of Indoor Switchgear

The main disadvantage of indoor switchgear is its higher installation costs compared to outdoor switchgear. For economic reasons and at high voltages, outdoor or air-insulated systems are often more viable.

Conclusion

We discussed and compared indoor and outdoor switchgear. Indoor switchgear is highly reliable, secure, and cost-effective. It is also more customizable and durable than outdoor switchgear, capable of withstanding harsh conditions. However, its economic viability and use at high voltages are limited.