The automatic devices are designed to protect against short-circuit currents and overload of electric lines and energy receivers, for switching on and off of power lines and receivers. The circuit breaker consists of the following parts:
- Contact system.
- The mechanism of free tripping.
- Release (electromagnetic and thermal).
- Arc interrupter.
The contact system is designed directly for switching electrical circuits.
The free release mechanism allows switching automatically or "manually".
The trip units provide disconnection of the circuit breaker under overloads and short-circuits (thermal and electromagnetic, respectively). The operation of the thermal release is based on the thermal action of the current: when the current passes through a current exceeding the nominal heating, the bimetallic plate, due to the difference in the coefficient of thermal expansion of the metals from which it is composed, bends and acts on the mechanism of free disengagement. The electromagnetic release acts like a relay with an armature: when the current is flowing, The anchor driven by the electromagnetic field acts on the same mechanism of free disengagement.
Modern automatic circuit breakers of the VA series have two types of protection: thermal (made on a bimetallic plate) designed to protect against long-time current overloads and dynamic (it is also electromagnetic on an electromagnetic coil) designed to protect against short-circuit currents. The contact system consists of fixed contacts fixed to the housing and movable contacts pivotally mounted on the semi-axis of the operating mechanism lever and provides, as a rule, a single circuit break. The arc interrupter is installed at each pole of the switch and is intended for localization of the electric arc in a limited volume.
Such obsolete machines like the AP50 have the same types of protection, but are performed in a much larger form factor. Modern technology of course allows you to perform circuit breakers of much smaller dimensions (at the same nominal current). In everyday life, the use of VA automatic machines in conjunction with modern shields is preferable. Well, in hard working conditions with frequent reconnections of cables, overloads, the use of automatic machines AP50 and similar ones is still justified.
We are primarily interested in household electrical installations, therefore, we will dwell on VA automatons in more detail. Combined clamps of silver-plated copper and anodized steel provide reliable contact with copper and aluminum conductors of cross-section from 1 to 25 square meters. Mm.
The VA switches have an improved design of the control mechanism and a free disengaging mechanism to reduce the effect of the rattling contact, so that during closing, the closing of the contacts occurs instantaneously, regardless of the speed of the handle. The installed metal plate on the side wall in the area of the opening contacts protects the case from burning out. When manufacturing the case, high-quality non-combustible materials with high refractory, shockproof characteristics and having high mechanical strength are used. When assembling multipolar circuit breakers, each pole first splits separately, after which the poles are connected together. The contact clamps, deeply immersed in the case, provide a high degree of safety when the person touches the body of the device accidentally. The bimetallic plate is connected to the mechanism of free disengagement without play, which improves the sensitivity of the device to its bending. Switches are available in single-, double-, three- and four-pole versions:
One- and two-pole circuit breakers of general use 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. Two-pole circuit breakers are used, as a rule, in direct current circuits up to 63 A. Mounting on a shoe, rail or panel. Three-pole (three-phase) circuit breakers of general use serve to protect power, lighting and other electrical installations, as well as electric motors from emergency modes, short circuits, overloads and current reduction. 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 induction motor with squirrel-cage rotor). The trip units can be installed in one, two or three poles depending on the type of the machine's execution. Four-pole circuit breakers of general use serve to protect power, lighting and other electrical installations, as well as electric motors from emergency modes, short circuits and overcurrent. They are designed for manual activation and automatic or manual shutdown of electrical consumers under load. 4-pole circuit breakers are used in AC circuits with a three-phase load (for example, an induction motor with a squirrel-cage rotor). The trip units can be installed in one, two or three poles depending on the type of the machine's execution.
The intrinsic response time of the circuit-breaker is no more than 0.02 sec. Operating conditions: the ambient air temperature should be in the range from -5 to +40 ° C, and its daily average value should not exceed +35 ° C. The switch is fixed to DIN rail 35 x 7.5 mm. The operating position of the switches is vertical, the designation "OFF" is down. Before installing the circuit-breaker, it is necessary to check the machine for no external damages, also make several start-ups and trips, make sure that the mechanism is working properly. Check the marking on the machine, if it meets the required conditions. For connection, copper conductors (cables) or copper connecting busbars must be used. Voltage supply to the terminals of the switch from the power supply is carried out from the terminals 1,3,5,7, i.е. On. On. For installation in distribution boards of the old type, for the replacement of AE with VA, a plastic adapter is provided.
Select automatic circuit breakers for rated current, voltage and operating conditions (based on the type of performance). If it is necessary to select an automaton for connecting known loads, it is necessary to calculate the current.
The value of the calculated current Ip, A , is determined by the formulas:
A) for single-phase networks
Ip = Pp / (Uh * cosf)
B) for three-phase networks
Ip = Pp / (1.73 * UH * cosf)
Where: Рр - estimated capacity determined with allowance for the demand factor Кс, (from reference literature).
Kc = Pp / Rust
Where: Uн - rated voltage, V ; Cos φ is the power factor. Characterizes the nature of the load (active or reactive) For incandescent lamps and heating appliances, cos φ = 1. For motors in the passport, the nominal power on the motor shaft is indicated. The power drawn from the mains will be:
Рпотр = Рн / n
Where: Рн - rated power of the electric motor, kW; N - coefficient of efficiency; Рпотр - power consumption from the network, kW. Based on the received current value, a circuit breaker is selected. Of course, the machine has many important parameters, but in the home you can make your choice based on the correspondence of the rated current and voltage and the connected load.