by

Rudy S. Silva

Industrial circuit breakers are electrical devices used to break the electrical circuit during overload. It is used in commercial and residential purposes as part of a safety process. Electric circuit breakers are automatically-operated switches to protect the electrical circuit from damage.

Several circuit breakers are classified according to voltage class, construction type, structural features and interrupting type. Under the voltage class, three types of electric circuit breakers can be made. These are the low voltage, medium voltage and high voltage circuit breakers.

The low voltage industrial circuit breakers, containing less than 1000 VAC, are used commonly in residential, commercial and industrial application. There are two sub-types of low voltage circuit breakers, namely the miniature circuit breaker, and the molded case circuit breaker.

The miniature circuit breaker or MCB has a rated current of not more than 100A. It can be operated by thermal or thermal-magnetic operation. However, its trip characteristics are not adjustable.

The molded case circuit breaker or MCCB has a rated current of up to 1000A. Like the MCB, this too can be operated by thermal or thermal-magnetic operation. Its trip current may be adjustable in larger ratings.

Low voltage circuit breakers are made for direct current applications or DC. They have electrical motor operators, which can be opened and closed under remote control. They can be mounted in multi-tiers in low voltage switchboards.

The medium voltage industrial circuit breakers are rated between 1 and 72 kV. They may be assembled into metal-enclosed switchgear line up for indoor. They can also be installed in individual components for outdoors. The characteristics for medium voltage are defined by international standards such as International Electrotechnical Commission 62271.

There are three sub-types under medium voltage. These are vacuum circuit breakers, the air circuit breakers, and the SF6 circuit breakers. The SF6 circuit breaker extinguishes the arc in a chamber of sulfur hexafluoride gas.

The vacuum circuit breakers have a rated current of up to 3000A. They interrupt the electric current by creating and extinguishing the arc inside a vacuum chamber Vacuum industrial circuit breakers are used for voltages up to 35,000 V and tend to last longer.

The Air circuit breakers have a rated current of 10,000A. The trip characteristic is adjustable, which includes configurable trip delays and thresholds. This breaker is used for main power distribution in large industrial plant.

The high voltage circuit breakers are used to protect and control the electrical power transmission networks. Its rated current when used in power transmission is believed to be 72.5 kV, or even higher.

Typically, high voltage circuit breakers are solenoid-operated having current sensing protective relays running through current transformers. They are available with current ratings of up to 765 kV, and are used on transmission systems.

The other two types of industrial circuit breakers are magnetic and thermal-magnetic. The magnetic breakers use a solenoid electromagnet. Its inherent pulling force increases with the electric current. The thermal magnetic circuit breakers are used in distribution boards. They use electromagnet and bimetallic strip to trip the breaker.

All industrial circuit breakers share common operating features. They are set apart from each other in terms of voltage class, current rating and the type of circuit breakers. They are expected to detect faulty conditions.

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