Day 24: MCCB - Moulded Case Circuit Breaker

For today.. i have a task which needs me to understand the operation of the MCCB. Hurmm... What is MCCB?

MCCB stands for Moulded Case Circuit Breaker. It is commonly used in designing the Switchgear, UPS, MCC and etc.. In my understanding, the MCCB is a device which we used to protect our electrical equipment from being burn due to overload current or lightning. It works by  isolating the circuit either because we want the power off or to isolate because there is a fault. It use trip units which monitor the current flowing through the breaker and trip when it gets too high.

Hence, It is one of the obligatory device to be installed in the design for the vital protections.

                                   Example of the Breaker                Maintenance of the breaker

Previously during the FAT, i reckon that almost 70% of the manufactured design was installed with the breaker. There are many types of breaker actually..

i)   VCB    - Vacuum Circuit Breaker

ii)  Oil CB  - Oil Circuit Breaker

iii) Air CB  - Air Circuit Breaker...etc

Operation

The circuit breaker must detect a fault condition; in low-voltage circuit breakers this is usually done within the breaker enclosure. Circuit breakers for large currents or high voltages are usually arranged with pilot devices to sense a fault current and to operate the trip opening mechanism. The trip solenoid that releases the latch is usually energized by a separate battery, although some high-voltage circuit breakers are self-contained with current transformers, protection relays, and an internal control power source.

Once a fault is detected, contacts within the circuit breaker must open to interrupt the circuit; some mechanically-stored energy (using something such as springs or compressed air) contained within the breaker is used to separate the contacts, although some of the energy required may be obtained from the fault current itself. Small circuit breakers may be manually operated; larger units have solenoids to trip the mechanism, and electric motors to restore energy to the springs.

The circuit breaker contacts must carry the load current without excessive heating, and must also withstand the heat of the arc produced when interrupting the circuit. Contacts are made of copper or copper alloys, silver alloys, and other materials. Service life of the contacts is limited by the erosion due to interrupting the arc. Miniature and molded case circuit breakers are usually discarded when the contacts are worn, but power circuit breakers and high-voltage circuit breakers have replaceable contacts.

When a current is interrupted, an arc is generated. This arc must be contained, cooled, and extinguished in a controlled way, so that the gap between the contacts can again withstand the voltage in the circuit. Different circuit breakers use vacuum, air, insulating gas, or oil as the medium in which the arc forms. 

So..... How is it? get any idea bout circuit breaker? Actually we also could see MCCB in our home. The current terminal detector, which normally located high attached to our walls, was built by combining the circuit breakers. 

residential common usage

 ha...... so we always see it.. but now only i know what the device we called during this practical sessions... hahahahahahaah....