A circuit breaker is an automatically actuated electrical switch designed to protect an electrical circuit from damage caused by excessive current, usually resulting from an overload or a short circuit. Its basic function is to interrupt the current flow after a fault is detected. Unlike a fuse that operates once and then needs to be replaced, a switch can be reset (manually or automatically) to resume normal operation.
The circuit breakers are manufactured in different sizes, from small devices that protect low-current circuits or individual household appliances to large distribution devices designed to protect high-voltage circuits that supply a whole city. The generic function of a circuit breaker, an RCD, or a fuse as an automatic means of removing energy from a defective system is often abbreviated as ADS (automatic power disconnection).
Different Types Of Circuit Breakers And Discription
Low-voltage circuit breakers
Low voltage types (less than 1000 VAC) are common in domestic, commercial and industrial applications and include:
- The miniature circuit breaker (MCB) can not exceed 100 A. Shooting characteristics can not be adjusted normally. Thermal or thermo-magnetic operation. The switches illustrated above are in this category.
- Circuit breaker (MCCB) with a pressure of up to 2,500 A. Thermal or thermo-magnetic operation. The tripping current can be adjusted to higher ratings.
- Low-voltage power circuit breakers can be mounted in several levels in low-voltage distribution panels or distribution cabinets.
- The characteristics of low voltage circuit breakers are provided by international standards, such as IEC 947. These circuit breakers are often installed in discharge boxes that allow data to be removed and exchanged without removing the switch.
- The low voltage housing and the power switches can have electric motor operators so that they can be opened and closed under the remote control. These can be part of an automatic transfer switching system for the standby mode.
- Low voltage switches are also designed for DC applications, such as DC for metro lines. DC requires special switches because the arc is continuous, unlike an alternating current arc, which tends to come out every half of the cycle. A DC switch has blower coils that generate a magnetic field that rotates rapidly in the arc. Small circuit breakers are installed directly on the equipment or placed on an interrupt panel.
Magnetic circuit breakers
Magnetic circuit breakers use a solenoid (electromagnet) whose traction force increases with the current. Some models use electromagnetic forces in addition to those of the solenoid.
The contacts of the switch are held closed by a latch. As the solenoid current rises beyond the engine power, pulling the solenoid releases the locking device, which allows the contacts to be opened by the action of the spring.
Magnetic-hydraulic circuit breakers
A magnetic-hydraulic circuit breaker uses a solenoid coil to provide an operating force to open the contacts. Hydraulic hydraulic hardeners have a hydraulic delay feature using a viscous fluid. An arc stops the core until the current exceeds the breaking class. During overcharging, the velocity of the solenoid movement is limited by fluid. The delay allows for short short-circuits of current over the normal running current for starting the engine, the power supply, etc. The short-circuit currents provide a sufficient solenoid force to release the latch, regardless of the base position, thus bypassing the delay feature. Ambient temperature affects the delay but does not affect the current quality of a magnetic switch.
Medium-voltage circuit breakers
Medium voltage circuit breakers rated between 1 and 72 kV can be assembled in metal switchgear lines for indoor use, or they can be individual components installed outdoors in a substation. The air break switches replaced the oil filled units for indoor applications, but are now being replaced by vacuum circuit breakers (up to approximately 40.5 kV). Like the high-voltage circuit breakers described below, they are also operated by current sensing protection relays operated through current transformers.
The characteristics of MV switches are given by international standards such as IEC 62271. Medium voltage circuit breakers almost always use separate current sensors and protection relays, instead of relying on built-in thermal or magnetic over current sensors.