Guide To Vacuum Circuit Breaker Advantages And Disadvantages

A breaker which used vacuum as an arc extinction medium is…

A breaker which used vacuum as an arc extinction medium is called a vacuum circuit breaker. This article discusses an overview of what is a vacuum circuit breaker, vacuum circuit breaker advantages and disadvantages.

What is Vacuum Circuit Breakers?

AB-3S vacuum circuit breaker

A Vacuum Circuit Breaker is a type of circuit breaker that uses a vacuum as the superior dielectric medium for interrupting electric circuits. The Vacuum Circuit Breaker uses two contacts, which are connected to an arc-quenching chamber and housed in a hermetically sealed environment.

This allows it to work with higher voltages than other types of circuit breakers. The vacuum provides excellent insulation properties, helping to ensure the service life of the breaker exceeds that of other types.

It also produces minimal contact erosion and low noise levels, making it ideal for use in many applications. In addition, its high speed operation and low maintenance requirements make it an attractive choice for many industrial applications.

Vacuum Circuit Breaker Features

Vacuum circuit breakers have mainly two remarkable properties:

In comparison to various other insulating media used in the circuit breaker, It is a superior dielectric medium. It is better than all other media except air and SF6, which apply at high pressure.

When an arc is opened by moving apart from the contacts in a vacuum, an interruption occurs at the first current zero. With the arc interruption, their dielectric strength increases up to a rate of thousands of times as compared to other breakers.

Advantages of Vacuum Circuit Breaker

  • It has a small operating mechanism, small size, and lightweight.
  • The inertia of the movable guide rod is small and can be used frequently.
  • The control power is small, and the action noise is low during switch operation.
  • With multiple reclosing functions, it is suitable for the application requirements of the distribution network.
  • The contact gap is little, generally about 10mm, the closing power is low, the mechanism is simple, and the service life is long.
  • The arc extinguishing time is short, the arc voltage is low, the arc energy is small, the contact loss is small, and the number of breaking times is numerous.
  • The contact head classifies into a completely sealed structure, and its performance is not going to decline by the influence of moisture, dust, harmful gases, etc. Reliable work, stable on-off performance.
  • The ring will not age or need to be replaced. Within the service life, the contact part does not need to be repaired or inspected. Generally, it can be up to about 20 years without inspection. The maintenance workload is small, and the maintenance cost is low, only about 1/20 of the oil-less circuit breaker.

Disadvantages of Vacuum Circuit Breakers

The main disadvantage is that it is uneconomical at voltages exceeding 38 KVolt. The cost of the breaker becomes excessive at higher voltages. Besides, production in small quantities is uneconomical.

The one-time investment price of the product is relatively high, which is mainly determined by the professional production of the vacuum interrupter and the requirements of institutional reliability. If you consider the operation and maintenance costs comprehensively, the price is not high.

When the inductive load or capacitive load is disconnected, it is easy to cause over-voltage due to current interception, justification, reignition, etc., and don’t forget to adopt corresponding over-voltage protection. 

ZW8 vacuum circuit breaker

Since the contact structure of vacuum circuit breakers adopts the butt connection type. And the operating mechanism uses a spring, it is easy to produce closing bounce and opening rebound.

Closing bounce will not only end to high over voltages that affect the stable operation of the power grid but also cause contact burn-out or even welding when the capacitor bank generates inrush current and short-circuit closing.

Opening bounce will reduce the distance between the contacts after the arc, leading to a breakdown, and the consequences are so significant.

Vacuum Circuit Breaker Applications

ZW10 vacuum circuit breaker

Vacuum circuit breakers are employed in both metal-clad switchgear and porcelain housed circuit breakers, predominantly for medium voltage uses. In India where distances are vast and access to remote locations is troublesome, the installation of these outdoor, hassle-free circuit breakers should prove to be of great benefit.

Vacuum circuit breakers are beneficial for outdoor applications in the range of 22 kilovolts to 66 kilovolts. Despite the confined capacity of 60 to 100 megavolt-amperes, they are suitable for most uses in rural areas.

Because of the short gap and excellent recovery of a vacuum circuit breaker, they are beneficial as very high speed making switches in many industrial applications.

  • When the voltage is high and the current to be interrupted is little, these breakers have definite superiority over the other breakers.
  • For small fault interrupting capacities, the cost is low in comparison to other interrupting devices.
  • Because of the least requirements of maintenance, these breakers are very suitable for the system that requires voltage from 11 to 33 kV.

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