Electrical operating transmission systems require a method to control, protect, and isolate electrical equipment and circuits. It is designed with any combination of electrical disconnect switches, fuses, or circuit breakers. Instead of the simple “knife” switch we now have the modern computerized switchgear.
Early History of Circuit Breakers
The early electric generating stations used a simple open knife switch mounted on insulating panels of marble or asbestos. It could cut the energy to the system and allow work on a circuit without having to shut down the generator. As power generation increased, so did the need to develop safer circuit breakers to protect the worker from electrocution.
High and Medium Voltage Breaker Development
This led to oil-filled equipment to allow arc energy to be contained and safely controlled. The early 20th century switchgear was a metal enclosed container with electrically operated switching elements using oil-encased breakers. That system is obsolete and new equipment uses air-blast or a vacuum unit to protect the worker from danger.
Modern Designs for Circuit Breakers
Today, modern breakers allow large currents and power levels to be safely controlled by automatic equipment incorporating digital controls, protections, metering and communications. While we think of high voltage systems using this device, it is also located for the medium voltage side of the transformer in the substation. This development then led to industrial applications.
Modern industry power stations utilize the Unitized Substation (USS) with medium voltage switchgear incorporated within the housing. One of the basic functions is to protect the worker from electrocution. It also provides protection to the circuits (as well as the machines on that circuit) due to power surges or interruptions, while maintaining service to unaffected circuits.
While this key function is to protect and isolate circuits from power interruption, it also can enhance system availability by allowing more than one source of electric power to feed a load. Medium voltage circuit breakers require the same safety measures for workers as high voltage models.
Modern technology has improved the medium voltage switchgear to improve efficiency and functionality to prevent unwanted downtime to a production facility.