What is the difference between a Air circuit breaker and a molded case circuit breaker?

Can the Moulded case replace the frame when the rated current, breaking capacity and protection are satisfied? For example, can the T7 molded case circuit breaker of ABB1600 be used in the main inlet line? If so, why is it common practice to use frames instead of Moulded cases, which are much cheaper?

Molded case circuit breaker with Air circuit breaker is the circuit breaker product has been widely used in the product, but a lot of people are not quite understand the existence difference, in the choose and buy when also often appear indecisive, I faced some customers often have such problems, here first understand the concept of the two, second to understand the difference between the two, Finally understand the choice of the two.

One the concept of frame and Moulded case circuit breaker

1. Air circuit breaker:

Air circuit breaker is also known as air circuit breaker or universal circuit breaker, mainly used for low-voltage distribution system into the line, busbar and other large current circuit close. It is composed of contact, arc extinguishing device, operating mechanism and tripping system, housing and control unit. According to the way of installation can be divided into fixed type and drawer type two, fixed shell with metal materials, the size of the larger, lower protection level. Drawer TYPE adopts engineering Moulded shell, more compact structure, high protection level, convenient maintenance. According to the protection characteristics, Air circuit breakers can be divided into non-selective (class A) and selective (class B), class B circuit breakers mostly use electronic over-current tripping, with long delay, short delay and instantaneous action protection of three protection characteristics. Intelligent Air circuit breaker built-in microcontroller, with display, alarm, self-check and communication functions, and industrial computer can be composed of monitoring system. Air circuit breaker is the biggest characteristic of large capacity, high breaking capacity limit current and short enough tolerance, such as delixi CDW3 type circuit breaker rated current up to 6300 a, current up to 85 ka rated short-time tolerance, which makes the Air circuit breaker has good selectivity and stability, it is because of these characteristics, make the price of Air circuit breaker is higher.

2, Moulded case circuit breaker

Moulded case circuit breaker is also known as device circuit breaker, which is mainly used to protect the incoming and outgoing lines and motors of low-voltage distribution system. All the parts are sealed in the shell. Auxiliary contacts, undervoltage tripping and shunt tripping are mostly modular. Because the structure is very compact, the Moulded case circuit breaker can not be repaired, most of the manual operation, large capacity can choose electric splitting and closing. Due to the application of electronic overcurrent trip, Moulded case circuit breaker can also be divided into two categories: A and B. Moulded case circuit breaker is usually used in A class. In the case of short circuit, selective protection without artificial short delay, so there is no short-term tolerance current (Icw) value; Moulded case circuit breaker is characterized by small size, good contact protection, easy installation and cheap price.

Two, the difference between the frame and the Moulded case circuit breaker

1. The appearance and installation size of the two are different:

First of all, from the appearance, the size of the two different, Air circuit breaker size, larger volume, Moulded case circuit breaker size and volume is relatively small.

CDW6i Air circuit breaker CDM6i Moulded case circuit breaker

2. The protective functions of the two trip devices are different:

Framework of circuit breaker intelligent tripping devices have the functions of protection, measurement, auxiliary functions, special function and communication function, the protection function with long time delay protection, short time delay protection, transient protection, MCR protection, earthing protection, low voltage protection/alarm, overvoltage protection/alarm, voltage unbalanced phase protection/alarm, Phase sequence protection, low frequency protection, high frequency protection, reverse power protection, voltage harmonic alarm, current harmonic alarm;

Measurement function: current measurement, voltage measurement, power measurement, frequency measurement, electric energy measurement, harmonic measurement;

Auxiliary functions: alarm warning, self-diagnosis function, fault history recording function, function;

Special functions: load monitoring, regional joint control, high and low temperature range;

Communication function: communication protocol function, etc.

The MCCB mainly provides long delay protection, short delay protection (overload protection), and instantaneous protection (short circuit protection).

It can be seen that the protective function of Air circuit breaker is more powerful than the protective function of Moulded case.

3. The scope of application is different

The limit current of the Air circuit breaker from 400A to 6300A, mainly used in the distribution network, used to distribute electric energy, protect the line and power equipment, so as to avoid the overload, undervoltage, short circuit, single-phase ground fault hazard;

The MCCB has a current limit of 10 to 800A. It is used to protect the lines and equipment in distribution lines when they are overloaded, short-circuited, or undervoltage. It can also provide overload, short circuit, or undervoltage protection when the motor is infrequently started.

As shown in the picture:

Primary distribution units, collectively known as power distribution centers, are centrally installed in a company's substations and distribute power to lower-level distribution units in different locations. This level of equipment is close to the transformer side, so the electrical parameters are required to be high, the output circuit capacity is also large, generally in the main power distribution cabinet, the main component Air circuit breaker.

Secondary distribution equipment, power distribution cabinet and motor control center is collectively. Power distribution cabinet used in the load is more dispersed, less circuit occasions; Motor control center for load concentration, circuit more occasions. They distribute electrical energy from a circuit of the upper distribution equipment to a nearby load. This type of equipment should provide load protection, monitoring and control, generally choose to use circuit breakers: Moulded case circuit breakers, micro break switches, etc.

4. Different types of use

The use of Moulded case circuit breaker is usually A class, in the case of short circuit, selective protection without artificial short delay, so there is no short-term tolerance current (Icw) value;

The Air circuit breaker is usually used in class B, in the case of short circuit, selective protection for short delay (adjustable), so there is a short time tolerance current (Icw) value;

For specific use, select different circuit breakers according to the load.

Three, the selection of frame and Moulded shell

Compared with Air circuit breaker, Moulded case circuit breaker has lower parameters and simpler structure. Normally its rated current does not exceed 1600A. Because the Moulded case circuit breaker is in the next level of the Air circuit breaker, after a section of the line, the short-circuit current will be reduced, the parameters and performance of the Moulded case circuit breaker can meet the requirements of operation and use, and the size is small, flexible installation, the price is lower than the Air circuit breaker, suitable for large number and wide range of installation and use.

Generally, due to the high parameters of Air circuit breakers (rated voltage, rated current, and corresponding breaking capacity are higher than those of Moulded cases and micro-break products), they are usually installed in places where the load current and fault current are high and high safety and reliability are required. Air circuit breaker is mainly used for incoming line, contact and high current load feeder. The next stage uses a molded case circuit breaker. As shown in the figure above, the low-voltage switches in the line should be determined in the following order: low-voltage power supply -- Air circuit breaker -- molded case circuit breaker -- micro circuit breaker. In some special environments, the products that meet the requirements can also be selected according to the requirements. If the parameters meet the requirements of the application, the molded case circuit breaker can also be used as the incoming switch of the low-voltage side connected to the transformer.