Comprehensive Guide to Vacuum Circuit Breakers: Construction, Working & Maintenance

In modern power systems, VCBs are the unsung heroes which come to protect the system from any failure. They are capable of enhancing the reliability of a given system and are particularly useful in medium to high-voltage applications.

In this guide, we will look at vacuum circuit breakers in detail including how they work, what their construction is and their maintenance. So, keep reading to see how these magnificent tools ensure security in your electrical networks!

 

1) Introduction to Vacuum Circuit Breakers

Vacuum circuit breakers are devices used in high-voltage setups that protect machines from damage by interrupting the flow of electric current. These devices work by employing a vacuum, i.e., a gas-less space, in its chamber to prevent the occurrence of electrical arcs during circuit disruption.

These breakers can be found in the systems applying 1,000 up to 35,000 volts. The vacuum guarantees that no current passes through after the interruption of the circuit, as the absence of air or gas makes it impossible to reignite the arc. They are exceptionally quick with the ability to extinguish arcs within 0.02 seconds, thereby guarding the system from excessive harm.

2) Working Principle of Vacuum Circuit Breakers

A vacuum circuit breaker is deployed in an electrical system to stop the flow of electricity when any fault occurs. Let's discuss its working mechanism!

Step 1) Normal Functioning

• Under normal functioning scenarios, the contacts within the breaker are engaged which allows electrical flow through the contacts.

Step 2) Fault detection

• Upon occurrence of a fault event like a short circuit or an overload, the protection mechanism comes into play. It triggers the operation of the circuit breaker.

Step 3) Separation of Contacts

• You will notice that the primary contact elements which are enclosed within the circuit breaker will begin to disengage. As the contacts begin to open an electric arc is formed between the contacts.

Step 4) Formation Of Arc

• When the contacts inside a circuit breaker separate, a tiny electric spark called an arc forms. This happens because the air around the contacts turns into a gas, and electricity tries to jump across. If the arc isn’t stopped, it keeps flowing, which could burn or damage the system.

Step 5) Extinguishing Of Arc in a Vacuum

• This is where the most significant part takes place where the arc is moved to the vacuum chamber. This is because, in a vacuum, there are no particles which allow the arc to extend which in turn causes the arc to be extinguished considerably faster.

Step 6) Restoration of insulation.

• The moment the arc is turned off, the dielectric strength of the vacuum which is eight times more than that of air ensures that the circuit does not close and no current flows through it.

Step 7) Reclosing

• Once the breaker is reset, you or the system can ensure the safe closure of the breaker and the normal flow of electricity is restored.

The failure recovery time period is in milliseconds, which is why VCB breakers are exceptionally suited for all high-voltage frameworks.

3) Construction of Vacuum Circuit Breakers

Vacuum circuit breakers are aimed at enhancing reliability by having all the parts work collectively to serve their specific purposes. Let’s have a quick insight into its components and their functioning!

i) Vacuum Interrupter

This component is installed at the centre of the breaker, where the electrical arc is extinguished. It consists of the following parts:

• Contacts: These can be categorized into two classes. One set is fixed while the other set is movable and they reside on an arc fence panel which separates them to disrupt the circuit.

• Shielding (Arc Shield): This is applied to the vacuum chamber in order to prevent interference from the heat caused by the arc.

• Vacuum Envelope: It maintains a vacuum to prevent the arc from reigniting.

ii) Operating Mechanism

This mechanism is responsible for the relative movement of said contacts. There are two most standard types of operating mechanisms which are highlighted below;

• Spring Mechanism: It uses stored mechanical energy to open and close the respective contacts.

• Magnetic Mechanism: This mechanism implements electromagnetic force to ensure better contact movement.

iii) Insulation System

Encapsulating internal components prevents electrical current loss from occurring, thus providing an extra layer of safety.

iv) Conducting Parts

When the arc circuit is in a closed position, these parts are in use as they help the breaker retain minimal energy loss.

v) Arc-Extinguishing Contact System

It is aimed at withstanding the arc and putting it out efficiently within milliseconds.

vi) Housing (Enclosure)

This component is termed as a barrier protecting the internal elements from dust, precipitation and physical damage.

vii) Auxiliary Components

Auxiliary components assist in observing the state of the circuit. They are of three types, for instance:

• Mechanical Indicators: Allows you to monitor the operational state of the breaker according to its present status such as opened, closed, or tripped.

• Secondary Circuitry: Such circuits send signals and enable automatic control of functions of the breaker which promotes its use in a safe manner.

• Energy Storage Indicators: With the help of these indicators, you can gauge the stored energy in the unit which guarantees that the breaker can act when the necessity arises.

viii) Base and Connectors

The purpose of these elements is to guarantee the apparatus's support and interconnections with the primary electrical grid.

4) Types of Vacuum Circuit Breakers

Within the realm of vacuum circuit breakers, several distinctive types exist to cater to varying levels of voltage and electrical applications. So, let's have look at its types!

i) By Voltage Rating

• Low Voltage Vacuum Circuit Breakers: They are designed to handle voltage up to 1000 V. A typical setting where these breakers would be used is within residential houses or light industrial settings.

• Medium Voltage Vacuum Circuit Breakers: These can handle voltage ranges between 11- 33KV. The common usage of mv vacuum circuit breakers involves operation in industrial plants, factories and urban power distribution systems.

• High Voltage Vacuum Circuit Breakers: While being electrically superior like holding voltage above 3500 V. These types of breakers are able to operate smoothly with large current loads. Some use cases include electrical power grids and power transmission systems.

ii) By Application

• Indoor Vacuum Circuit Breakers: Indoor types of these breakers can be utilized in a factory, substation, or any other building or structure which has a controlled environment. Such indoor electrical breakers protect electrical equipment and are typically of compact dimensions.

• Outdoor Vacuum Circuit Breakers: They can be deployed at open-air substations, or on pole installations where they are constantly exposed to wind and rain and low or high temperatures.  

5) Advantages of Vacuum Circuit Breakers

+ Great reliability: Vacuum circuit breakers can be relied upon for their dependability and performance in different settings. They ensure a high and steady performance which minimizes errors in any electric circuits.

+ Long-service life: Such breakers can last for anywhere between twenty to thirty years with little to no wear and tear. This is because they operate in a vacuum which prevents most of the damages usually caused by arc formation.

+ Compact design: Their size makes it much easier to both install and construct. Additionally, when placed in electrical substations they occupy a significantly smaller region than traditional types which allows for easier construction.

+ Eco-friendly: They are SF6, Sulfur HexafluorideOne which make vacuum circuit breakers so much more environmentally sustainable than the traditional type. SF6 is a very hazardous chemical used to assist with the breaking process.

6) Disadvantages of Vacuum Circuit Breakers

While vacuum circuit breakers (VCBs) are widely known for their advantages, they do come with some limitations:

- Higher Initial Costs: Although vacuum circuit breakers are superior in terms of technology and have long-term benefits. But their cost is significantly higher than that of oil or air circuit breakers. Such a high cost will mainly inhibit small-sized applications.

- Limited Current Interruption Capability: The best application for vacuum circuit breakers is in medium voltage applications, (11-33 kV) which cannot be used on very high voltage levels. Thus, it restricts their use in some industrial or power grid applications.

- Sensitivity to Temperature Variations: Vacuum circuit breakers can at times be too sensitive under extreme hot and cold temperatures which may cause them to malfunction.

7) Applications of Vacuum Circuit Breakers

? Substations: These breakers are valuable in substations where medium voltage levels have to be controlled.

? Solar and Wind Power: Vacuum circuit breakers are effective in the field of renewable energies because of their miniature size.

? Industrial Machinery: While operating with large machinery in the industrial sectors, vacuum circuit breakers act as a safeguard against power overloads and faults ensuring that the machines are operational at all times.

 

8) Vacuum Circuit Breaker Maintenance Precautions

• Regular Inspection: Although they require minimal maintenance, a regular inspection for damage or loss of vacuum in the interrupter should be done as it affects its operation.

• Cleaning: It is necessary to clean the vacuum interrupters so that accumulated dust or dirt is removed. Thus, internal components continue to work at their best.

• Sealing Check: You also have to look for a properly leak-tight vacuum seal. Even a partial break of the seal may affect the efficiency of the breaker.

• Mechanical Operation Test: Inspect the mechanical operating mechanism for any signs of defects. This test includes checking the spring or other magnetic mechanism drive applied to operate the breaker. Lubrication of moving and some other components may help avoid failures which result from friction.

• Arc Extinguishing Test: Carry out tests on the arc extinguishing ability of the vacuum interrupter from time to time to check that the circuit breaker works during an overcurrent condition as it should.

 

9) FAQs

i) What is the difference between ACB and VCB?

ACB means air-circuit breaker whereas VCB stands for vacuum-circuit breaker, both differ on the basis of the arc quenching medium they use.

Air breaker uses air as a medium whereas VCB utilizes a vacuum which makes VCB faster, more reliable and used on a majority of medium voltage circuits whereas ACB is ideal for lower voltages.

ii) Where can I buy vacuum circuit breakers?

You can buy 11-33Kv vacuum circuit breakers from Delixi, their models are durable and offer various voltage and current ratings. They are ideal for various outdoor applications such as rural areas and high-altitude regions. They are also resistant to extreme temperatures and corrosion. For further details about these high-end goods check out the official Delixi website.