Vacuum Circuit Breaker VS SF6 : What’s The Difference?

What is Vacuum Circuit Breakers? A vacuum circuit breaker (or a…

What is Vacuum Circuit Breakers?

vacuum circuit breaker with watch dog

A vacuum circuit breaker (or a vacuum circuit interrupter) is a type of circuit breaker where the arc termination takes place in a vacuum environment. In other words, the extinguishing of an arc occurs inside a vacuum chamber located within the breaker.

A vacuum possesses the maximum insulation potential compared to any other material, which renders it popular and accounts for its widespread application.

This type of circuit breaker is typically employed as a high voltage circuit breaker in power distribution systems and switchgear. The high voltage circuit breaker technology based on vacuum environment has been developed and extensively used.

The material and the form of contacts used in a vacuum circuit breaker determine its properties. Today, oxygen-free copper chromium alloy is said to be the best material for high voltage circuit breakers because of its excellent arc extinguishing properties and it also has a low tendency of contact welding or chopping current while switching of inductive current.

What is SF6 Gas Circuit Breaker?

As suggested by its name, a sulfur hexafluoride (SF6) circuit breaker utilizes the SF6 gas for extinguishing the arc.

This gas has an elevated dielectric strength (roughly three times more compared to air) and exceptional arc quenching properties that make it a preferable option than air or oil circuit breakers. Additionally, the SF6 gas is non-toxic and non-flammable.

The SF6 circuit breakers are most effectively used as a hv circuit breaker or for high voltage applications.

SF6 gas circuit breaker

They are also suited for medium voltages. SF6 circuit breakers have a voltage range from 33KV to 800 kV and even more.

And there are three mian types of SF6 circuit breakers. Such as Non-Puffer Piston Circuit Breaker, Single-Puffer Piston Circuit Breaker and Double-Puffer Piston Circuit Breaker.

Construction of SF6 Circuit Breaker

ZW20-12F vacuum circuit breaker

The construction of an SF6 Circuit Breaker is based on the ability of SF6 gas to extinguish an electric arc. This gas has excellent dielectric strength and arc quenching properties, making it perfect for interrupting hv circuits.

The SF6 circuit breaker is composed of two main elements: the contacts and the chamber that contains the SF6 gas. When power is applied to a circuit, an electrical arc is formed between the contacts. When this happens, the SF6 gas enters through small openings in the chamber and quickly extinguishes the arc by reducing its temperature.

This process of arc interruption helps maintain a safe level of current flow in an electrical circuit, thus protecting it from damage due to overloading or short-circuiting.

Working of SF6 Circuit Breaker

The working of SF6 circuit breaker is based on the ability of sulfur hexafluoride (SF6) gas to quench an electric arc. When an electric arc appears between the contacts in the circuit, it is quickly extinguished by the dielectric strength of SF6 gas. This process is known as arc interruption.

During this process, SF6 gas creates a barrier between the contacts and interrupts the flow of current. This barrier also prevents any further arcing until the contacts are reset or closed again.

The main advantage of using a SF6 circuit breaker is that it has high dielectric strength and can withstand high voltage and temperature fluctuations. Furthermore, due to its high thermal resistance and superior arc extinction properties, an SF6 circuit can be used for both medium-voltage and high-voltage applications.

ZW20 outdoor vacuum circuit breaker

Comparison Between Vacuum Circuit Breaker And SF6 

The function of both vacuum circuit breaker (VCB) and sulfur hexafluoride circuit breaker is the same. However, there are several differences between VCB and sulfur hexafluoride circuit breaker that are listed below

Operating energy requirements

In the case of the SF6 circuit breakers, there are both high and low operating energy requirements depending on the type of the circuit breaker. A puffer circuit breaker requires high energy from the operating mechanism so that it can compress the gas whereas a self-pressuring circuit breaker requires lower levels of energy to move small masses over short distances.

Vacuum circuit breakers require low levels of operating energy because they also have to move smaller parts at a moderate speed and that too, over short distances.

Arc extinguishing media

SF6 circuit breakers use SF6 gas which has high dielectric strength and arc quenching properties. Once the arc extinction takes place, the gas molecules recombine forming SF6 gas again which gets restored. Thus, no gas is lost during the process. SF6 circuit breakers can be supervised simply but this function becomes useless in the case of permanently sealed breakers.

In the case of a vacuum circuit breaker, there is no external medium required for the extinction of arc. The vacuum itself is a powerful extinguishing medium. The supervision of vacuum is not required and hence, the breakers could be sealed permanently.

Breaking current capacity of interrupter

An SF6 circuit breaker carries 5000-10000 times breaking current capacity whereas a vacuum circuit breaker has 10000-20000 times capacity.

Mechanical operating life

On average, both puffer and self-pressuring SF6 circuit breakers have 5000-20000 complete operations. However, for a vacuum circuit breaker, it is 10000-30000 complete operation, which is higher.

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