Circuit breakers are a form of electrical switching device that is implemented to regulate and protect electrical systems that are operated manually or automatically. These devices can be used to interrupt the current flow of electricity and prevent damage brought about by a short circuit or overcurrent.
There are a few different types of circuit breakers that are used at variable voltages – either medium or high – and they can be implemented into a number of electrical systems. In this article, we’re going to look at the different types of high voltage circuit breakers that you might find in a substation.
What Are the Types of High Voltage Circuit Breakers in a Substation?
Vacuum Circuit Breakers (VCB)
A vacuum circuit breaker is used when working with voltage ranges between 3 kV and 38 kV. Their construction comprises a vacuum container known as a bottle. Inside the bottle, there are moving and fixed contacts that open and close inside the vacuum chamber. This is the area of the circuit breaker where the arc quenching occurs.
A VCB can function well in indoor or outdoor environments. For indoor usage, these types of circuit breakers are made of VCB trucks which are installed in a control and relay panel. This panel can then be racked in a variety of ways to suit the system. For outdoor usage, the units are normally affixed to a permanent structure.
SF6 Circuit Breakers
An SF6 circuit breaker contains an inert gas, Sulfur HexaFluoride (SF6) which acts as the medium for arc quenching in the unit. It’s an excellent medium to use because it provides much better recombination and insulation for electrical systems.
These circuit breakers work by releasing highly pressurized SF6 gas into the gap between the contacts of the housing where an arc forms. The gas has strong electronegative properties which allow it to absorb free electrons. Any conducting free electrons from the arc are absorbed in this way. As this occurs, the dielectric medium is created which works to put out the arc.
Oil Circuit Breaker
Oil circuit breakers use, as the name suggests, oil as their medium when quenching an arc. The contacts are totally immersed in the oil, which provides insulation and dielectric properties.
When in use, there is a significant amount of heat that is built up as the arcing creates oil vapors which break down into hydrogen gas. This creates a large hydrogen bubble around the arc by moving the oil. This bubble begins to shrink, which moves the oil towards the arc, where the hydrogen gas cools it. There are two different types of oil circuit breakers: bulk oil circuit breakers and minimum oil circuit breakers.
Airblast Circuit Breaker
An airblast circuit breaker uses compressed gas or air to break the arc. This gas is stored in a tank that releases gas through a high-velocity nozzle. While in use, an air valve that connects the tank and arcing chamber opens, allowing pressurized air to make its way to the arcing chamber.
The blast of gas or air pushes the two moving contacts and cools the arc down. It also moves any ionized particles away from the contacts, increasing the dielectric strength of the gas. This is what causes the arc to be extinguished when using an airblast circuit breaker.