Switchgear

The earliest central power stations used simple open knife switches, mounted on insulating panels of marble or asbestos.

Power levels and voltages rapidly escalated, making opening manually operated switches too dangerous for anything other than isolation of a de-energized circuit.

By the early 20th century, a switchgear line-up would be a metal-enclosed structure with electrically operated switching elements using oil circuit breakers.

High-voltage switchgear was invented at the end of the 19th century for operating motors and other electric machines.

[2] Typically, switchgear in substations is located on both the high- and low-voltage sides of large power transformers.

For industrial applications, a transformer and switchgear line-up may be combined in one housing, called a unitized substation (USS).

Growing investment in renewable energy and enhanced demand for safe and secure electrical distribution systems are expected to generate the increase.

For higher voltages (over about 66 kV), switchgear is typically mounted outdoors and insulated by air, although this requires a large amount of space.

The combination of equipment within the switchgear enclosure allows them to interrupt fault currents of thousands of amps.

This highly compressed gas bubble around the turn prevents the re-striking of the arc after the current reaches zero crossing of the cycle.

Alternatively, the contacts are rapidly swung into a small sealed chamber, the escaping of the displaced air thus blowing out the arc.

[5] Circuit breakers and fuses disconnect when current exceeds a predetermined safe level.

A protective relay detects any imbalance in currents, and trips circuit breakers to isolate the device.

Several different classifications of switchgear can be made:[7] A single line-up may incorporate several different types of devices, for example, air-insulated bus, vacuum circuit breakers, and manually operated switches may all exist in the same row of cubicles.

This test is important for user safety as modern switchgear is capable of switching large currents.

[14] Switchgear is often inspected using thermal imaging to assess the state of the system and predict failures before they occur.

Switchgear systems require continuous maintenance and servicing to remain safe to use and fully optimized to provide such high voltages.