Automatic machines are intended for protection against short-circuit currents and overloads of electric lines and energy receivers, for switching on and off lines and energy receivers. The circuit breaker consists of the following parts:
- Contact system.
- The mechanism of free tripping.
- Releases (electromagnetic and thermal).
- The arcing chamber.
The contact system is designed directly for switching electrical circuits.
The mechanism of free tripping allows you to switch automatically or "manually."
The releases provide the circuit breaker tripping in case of overloads and short circuits (thermal and electromagnetic, respectively). The operation of the thermal release is based on the thermal effect of the current: when a current passes above the rated heating the bimetallic plate, due to the difference in the thermal expansion coefficient of the metals from which it consists, bends and acts on the mechanism of free tripping. Electromagnetic release acts like an anchor relay: when a short-circuit current flows. An anchor driven by an electromagnetic field acts on the same free-release mechanism.
Modern automatic circuit breakers of the BA series have two types of protection: thermal (made on a bimetallic plate), designed to protect against prolonged current overloads and dynamic (it is electromagnetic made on an electromagnetic coil), designed to protect against short-circuit currents. The contact system consists of fixed contacts fixed on the housing and movable contacts hinged on the half-axle of the control mechanism lever, and, as a rule, provides a single open circuit. The arcing device is installed in each pole of the switch and is intended for localization of the electric arc in a limited volume.
Such obsolete machines like AP50 have the same types of protection, but they are made in a much larger form factor. Modern technologies of course allow the execution of automatic switches of much smaller sizes (with the same rated current). In everyday life, the use of VA automatons in combination with modern shields is preferable. But in difficult conditions of work with frequent reconnections of cables, overloads, the use of AP50 automatic machines and others like him is still reasonable.
We are primarily interested in household electrical installations, so we’ll dwell more closely on BA automata. Combined clips of silver-plated copper and anodized steel provide reliable contact with copper and aluminum conductors with a cross section of 1 to 25 square meters. mm
Circuit breakers VA have an improved design of the control mechanism and the mechanism of free tripping to reduce the effect of a jarring contact, as a result of which, during switching on, the contact closes instantly, regardless of the speed of movement of the control handle. The installed metal plate on the side wall in the area of opening contacts protects the casing from burning out. In the manufacture of the case, high-quality non-combustible materials with high refractory, shock-proof characteristics and high mechanical strength are used. When assembling multipole switches, each pole is first spliced separately, after which the poles are connected together. The contact clips, deeply immersed inside the case, provide a high degree of safety if the person accidentally touches the device case. The bimetallic plate is connected to the free-release mechanism without backlash, which improves the sensitivity of the device to its bending. The switches are available in one-, two-, three- and four-pole versions:
One- and two-pole circuit breakers of general application serve to protect power, lighting and other electrical installations. They are designed for manual activation and automatic or manual shutdown of electrical consumers under load. Automatic switches of bipolar execution are applied, as a rule, in DC circuits up to 63 A. Fastening on a block, rail or panel. Three-pole (three-phase) circuit breakers of general application serve to protect power, lighting and other electrical installations, as well as electric motors from emergency operation, short circuits, current overloads and undervoltage. They are designed for manual activation and automatic or manual shutdown of electrical consumers under load. Three-pole circuit breakers are used in AC circuits with a three-phase load (for example, an asynchronous motor with a short-circuited rotor). The releases can be built into one, two or three poles, depending on the type of execution of the machine. Four-pole circuit breakers of general application serve to protect power, lighting and other electrical installations, as well as electric motors from emergency operation, short circuits and current overloads. They are designed for manual activation and automatic or manual shutdown of electrical consumers under load. Circuit breakers of quadripolar execution are applied in alternating current circuits with three-phase load (for example, an asynchronous motor with a squirrel-cage rotor). The releases can be built into one, two or three poles, depending on the type of execution of the machine.
Own time of operation of the switch is not more than 0.02 seconds. Operating conditions: ambient air temperature should be between -5 and +40 ° С, and its average daily value should not exceed +35 ° C. The switch is mounted on a DIN rail 35 x 7.5 mm. The working position of the switches is vertical, the symbol "OFF" down. Before installing the circuit breaker, it is necessary to check the circuit breaker for external damage, also to make several switching on and off, to make sure that the mechanism is working properly. Check the label on the machine for proper conditions. For connection it is necessary to use copper conductors (cables) or copper connecting bars. The voltage is supplied to the breaker terminals from the power source from the side of the terminals 1,3,5,7, i.e. from above. For installation in switchboards of the old model, to replace AE with VA, a plastic adapter is provided.
The circuit breakers are selected for rated current, voltage and operating conditions (based on the type of performance). If you need to choose a machine for connecting known loads, you need to calculate the current.
The magnitude of the calculated current Ip, A , is determined by the formulas:
a) for single-phase networks
Ip = Pp / (Un * cosf)
b) for three-phase networks
Ip = Pp / (1.73 * Un * cosf)
where: Рр - the estimated power determined by taking into account the coefficient of demand Кс, (from the reference literature).
Kc = PP / Rust
where: Un - rated voltage, V ; cos f - power factor. It characterizes the nature of the load (active or reactive) For incandescent lamps and heaters cos f = 1. For electric motors in the passport, the rated power on the motor shaft is indicated. The power consumed by the engine from the network will be equal to:
Rpotr = PH / n
where: PH is the rated power of the electric motor, kW; n - coefficient of performance; Rpotr - power consumption from the network, kW. Based on the obtained current value, a circuit breaker is selected. Of course, the machine still has a lot of important parameters, but in everyday life you can make your choice based on the correspondence between the rated current and voltage and the connected load.