Automatic machines are intended for protection against short circuit currents and overload of electric lines and energy receivers, for switching on and off of lines and energy receivers. The circuit breaker consists of the following parts:
- Contact system.
- Free release mechanism.
- Trip units (electromagnetic and thermal).
- 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 circuit breaker tripping during 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 exceeds the nominal heating, the bimetal plate, due to the difference in the coefficient of thermal expansion of the metals of which it consists, bends and acts on the free trip mechanism. The electromagnetic release acts like a relay with an armature: with the passage of current short circuit An anchor driven by an electromagnetic field acts on the same free trip mechanism.
Modern circuit breakers of the VA series have two types of protection: thermal (made on a bimetallic plate), designed to protect against long current overloads and dynamic (it is also electromagnetic made 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 axis of the control lever, and provides, as a rule, a single open circuit. The arcing device is installed in each pole of the circuit breaker and is designed to localize the electric arc in a limited volume.
Such obsolete machines like the AP50 have the same types of protection, but are made in a much larger form factor. Modern technologies, of course, allow circuit breakers to be made much smaller (with the same rated current). In everyday life, the use of VA automatic machines in combination with modern shields is preferable. Well, in difficult working conditions with frequent cable reconnections, overloads, the use of AP50 automatic machines and the like is still justified.
We are primarily interested in household electrical installations, so we will dwell on VA machines. Combined clamps made 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
VA switches have an improved design of the control mechanism and the free trip mechanism to reduce the effect of rattling contact, as a result of which, during switching on, the contact closure occurs instantly regardless of the speed of movement of the control handle. An installed metal plate on the side wall in the area of the opening contacts protects the housing from burning. In the manufacture of the case, high-quality non-combustible materials with high refractory, shockproof characteristics and high mechanical strength are used. When assembling multi-pole switches, each pole is first riveted separately, after which the poles are connected together. Contact clamps, deeply immersed inside the case, provide a high degree of safety in case of accidental contact of a person with the case of the device. The bimetallic plate is connected to the free trip mechanism without play, which improves the sensitivity of the device to bend it. The switches are available in one, two, three and four pole design:
Single and double pole circuit breakers of general use serve to protect power, lighting and other electrical installations. They are designed to manually turn on and automatically or manually turn off electrical consumers under load. Bipolar circuit breakers are used, as a rule, in DC circuits up to 63 A. Mounting on a block, 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 conditions, short circuits, overcurrents and undervoltage. They are designed to manually turn on and automatically or manually turn off 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 squirrel-cage rotor). The releases can be integrated in one, two or three poles depending on the type of machine design. General purpose four-pole circuit breakers are used to protect power, lighting and other electrical installations, as well as electric motors from emergency conditions, short circuits and overcurrents. They are designed to manually turn on and automatically or manually turn off electrical consumers under load. Four-pole circuit breakers are used in AC circuits with a three-phase load (for example, an asynchronous motor with a squirrel-cage rotor). The releases can be integrated in one, two or three poles depending on the type of machine design.
Own operating time of the switch no more than 0,02 sec. Operating conditions: the ambient temperature should be in the range from -5 to +40 ° C, and its average daily value should not exceed +35 ° C. The switch is mounted on a DIN rail 35 x 7.5 mm. The operating position of the switches is vertical, the designation "OFF" down. Before installing the circuit breaker, it is necessary to check the machine for external damage, also make several on and off trips, make sure that the mechanism is working properly. Check the marking on the machine for compliance with the required conditions. For connection it is necessary to use copper conductors (cables) or copper connecting busbars. The voltage is supplied to the findings of the switch from the power source from the side of 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.
Circuit breakers are selected for rated current, voltage and operating conditions (based on type of execution). If you need to choose a machine to connect known loads, you need to calculate the current.
The value of the rated 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: Rp is the estimated power determined taking into account the demand coefficient Ks, (from the reference literature).
Ks = Rr / Rust
where: Un - rated voltage, V ; cos f - power factor. It characterizes the nature of the load (active or reactive). For incandescent lamps and heating appliances, cos f = 1. For electric motors, the rated power on the motor shaft is indicated in the passport. The power consumed by the engine from the network will be equal to:
Rpotr = Rn / n
where: Rn is the rated power of the electric motor, kW; n - coefficient of performance; Rpotr - power consumption from the network, kW. Based on the current value obtained, a circuit breaker is selected. Of course, the machine has many more important parameters, but in everyday life you can make your choice based on the correspondence of the rated current and voltage and the connected load.