What is Moulded Case Circuit Breakers (MCCB)?
An electrical MCCB is a moulded case circuit breaker in its entire form. MCCBs are automatic electrical devices that guard against overload, short circuit, sudden overcurrent, and earth faults in electrical equipment. It is an improved MCB version (Miniature circuit breaker). With a voltage range of 230V to 11kV, it comes in capacities ranging from 32 Amps to 1600 Amps.
The main benefit of an MCCB is that it can be customised to meet our needs by being installed with new features like remote closure, UV trip, etc. It is the most cost-effective and functionally superior alternative to an air circuit breaker. Additionally, you can change the time setting and the current setting in moulded case circuit breaker. Moulded case circuit breakers are electromechanical tools that can be used to manually or automatically open a circuit and protect it from overcurrent and short circuit. There are several different types of tripping mechanisms for MCCBs.
Tripping Mechanism of MCCB:
MCCBs use a variety of operating mechanisms.
- Thermal Trip
- Magnetic Trip
- Thermal- Magnetic Trip
- Electronic Trip
- Microprocessor Trip
Thermal Trip Mechanism:
- An MCCB’s thermal trip mechanism serves as a delay fuse.
- A circuit will be protected from a brief but persistent minor overload.
- A bimetal strip is linked in series with the circuit load in a thermal trip MCCB.
- When a typical current flows through a bimetallic strip, the temperature rises and the strip’s length increases, but the expansion rate is insufficient to allow the strip to bend, so the contacts stay closed.
- As the MCCB’s current rises above the load current. It sufficiently warms the bimetal, causing the bimetallic strip to bend according to the current level and open the close contact.
- The size of the bimetallic strip affects how much current is required to trip the MCCB.
- The current has an inverse relationship with the amount of time the bi-metal takes to bend and trip the circuit.
- It features properties of inverse time, which allow for a long delay under light overloads and a quick response under heavy overloads.
- The circuit will be protected from temperature increases by the thermal element as well.
- It is sensitive to the temperature outside.
- At 40 degrees Celsius, the MCCB must continually deliver its full rated current.
- Tripping Time will be influenced by the current. The faster the circuit breaker trips, the greater the overload
- To protect against overload, this tripping mechanism is used.
Magnetic Trip Mechanism:
- In a magnetic trip MCCB, the circuit load is connected in series with an electromagnet – an iron core with a wire coil surrounding it.
- The connections will remain closed because the electromagnet won’t have enough electromagnetic field to attract the trip bar to move.
- The strength of the electromagnet’s magnetic field grows as high current or short circuit current flows through the coil. When the circuit’s current reaches a certain level, the contacts open, the trip bar is dragged toward the electromagnet, and the current stops.
- The space between the trip bar and the magnetic element determines how much current is required to trip the MCCB.
- This gap (trip current) is fixed on some MCCB and changeable on others.
- When the predetermined current is present, a magnetic circuit breaker will trip immediately.
- used to protect against short circuits magnetic tripping mechanism is used.
Thermal – Magnetic Tripping Mechanism:
- The most popular type of circuit protection for over current and short circuits is the thermal-magnetic circuit breaker.
- It combines a magnetic circuit breaker and a thermal circuit breaker.
- It has two separate switching mechanisms: an electromagnet and a bimetal switch.
- Both the overload and the short circuit are detected using magnetic properties: magnetic flux and induction are utilised to detect the thermal property (Bimetal Strip lengthens when heated).
- Both the thermal element (a bimetallic strip) and the magnetic element (an electromagnet) are linked in series with the load in a thermal-magnetic circuit breaker.
- The normal load current heats a bimetallic element, which does not bend and does not attract the trip bar when placed under normal load.
- The bimetallic element will flex, push the trip bar, and release the latch if the temperature or current rises steadily. It will trip the circuit breaker.
- The magnetic element will draw the trip bar, release the latch, and trip the circuit breaker if the current rises abruptly or quickly enough.
- Both Thermal Trip and Magnetic Circuit Breaker (instantaneous-trip circuit breakers) provide an inverse time characteristic.
- 10 A to 1600 A for MCCB rating range and operating Time is 4 microseconds.
Electronic Trip Mechanism:
- Each conductor has a coil attached to it that measures the current flowing through it continually.
- When the settings’ values are exceeded, the circuit breaker is controlled to trip by an electronic module that processes this information.
- The overload trip action and short-circuit trip actions of breakers with electronic trip units are accomplished using current transformers and solid-state circuitry that monitors the current and starts tripping through a flux shunt trip when an overload or short circuit is present.
- MCCB Rating for the aforementioned mechanism: 20 A to 2500 A
- Running Time: 4 milliseconds
- Protection Scope: From 60% to 100% of the nominal current, the adjustable overload protection is available.
- It is possible to set a short circuit between 2 and 10 times the rated current.
Microprocessor Trip Mechanism:
- When a microprocessor-type tripping mechanism is released, the microprocessor executes sensing and tripping using a CT or current sensing resistor.
- Compared to TMD Release, it provides a much faster response.
- MCCB Rating applicable for the above tripping mechanism 20 A to 2500 A
- Operating Time for MCCB: 4 milliseconds.
- Protection Range is The adjustable overload protection ranges from 60% to 100% of the nominal current (0.6 to 1xIn)
- Short circuit settings ranging from 2 to 10 times the rated current are achievable.
- An advantage of the aforementioned trip mechanism As the trip history is stored in the internal memory, system diagnosis is possible.
- Additionally, trip current indication is available to help with site setup and fault type analysis.
- High repeatability and reliability.
- Provide other MCCB coordination and interlocking and high flexibility.