Medium voltage switchgear types and differences

According to the main insulation medium in the cabinet, medium-voltage switchgear is divided into: Solid insulation type(SIS), Gas Insulation Type (GIS), Air Insulation Type (AIS), Dry Air/Nitrogen Insulation Type. This article is a more detailed comparison of the different kinds of medium voltage switchgear, including their appearance and features:

1, Solid Insulation Type (SIS):

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Description: It uses solid materials like epoxy or resin to insulate the internal components.

Appearance: Typically compact with a smooth, enclosed casing.

Features: three visible windows (often transparent) to check the state of the isolation knives, allowing for visual confirmation of the switchgear’s operational status.

The control panel is usually mounted on the front, and access points for cable connections are visible at the bottom or back.

Visual Key Features:

• Compact size.
• Transparent windows for isolation knife checking.
• Enclosed, dust-tight design.

Applications: Frequently used in indoor installations where space is limited.

2, Gas Insulation Type (GIS):

Description: Uses sulfur hexafluoride (SF₆) gas for insulation.

Appearance: Sealed metal enclosure (often stainless steel or aluminum) containing all the components.

No external moving parts are visible, as everything is housed inside the enclosure.

The gas chamber might have pressure gauges or indicator panels to show the gas pressure status.

The switchgear often appears more compact due to the efficiency of gas insulation, with minimal external features visible.

Visual Key Features:

• Sealed metal enclosure.
• Compact design with minimal external windows.
• Pressure gauges or indicators.

Applications: Commonly used in urban substations and high-voltage applications where space is limited.

3, Air Insulation Type (AIS):

Description: Uses air as the insulating medium between components.

Appearance:

Bulkier and larger compared to GIS and SIS because air requires more space for effective insulation.

The components like busbars, circuit breakers, and disconnectors are often visible and not enclosed in sealed compartments.

Usually mounted on a frame with open air passages, making the switchgear easily accessible for maintenance.

Often features large, accessible compartments for inspection and operation.

Visual Key Features:

• Larger size with open design.
• Components are often visible and accessible.
• No enclosed casing, making the layout simpler and bulkier.

Applications: Typically used in outdoor substations or where space is less of a concern

4, Dry Air/Nitrogen Insulation Type:

Description: Uses dry air or nitrogen gas as an insulating medium, which is an eco-friendly alternative to SF₆.

Appearance:

Similar in appearance to GIS (gas insulation), with a sealed metal enclosure.

May have pressure indicators to monitor the nitrogen or dry air pressure, like GIS has for SF₆.

Due to the lower environmental hazard, sometimes these enclosures have visible labeling indicating the type of gas used (e.g., “Dry Air” or “Nitrogen”).

Visual Key Features:

• Sealed, enclosed structure (similar to GIS).
• Pressure indicators for the gas.

Applications: Suitable for utilities looking for greener alternatives, especially in areas with strict environmental regulations.

Slightly bulkier than SF₆ switchgear because dry air or nitrogen requires a bit more space.

These different types of switchgear have unique appearances driven by their insulation technology. Solid insulation types are typically more compact with windows for monitoring, gas insulation types have sealed metal casings with minimal windows, air-insulated types are bulkier with exposed components, and dry air/nitrogen switchgear has a sealed look similar to gas-insulated units.