Characteristic of the operation of the circuit-breaker - the principle of operation in various situations

marverick984 (61)in #steemstem • 8 years ago

In the electrical wiring of an apartment or house there must necessarily be an element called an automatic switch, or, more often, an automatic device. Such a device is designed to automatically protect the electrical network from troubles that may occur during overload or short circuit. In addition, it can be used to manually turn on and off the electrical circuit.

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Features of the internal circuit-breaker device

There are many different designs of machines that are designed to protect electrical networks as individual apartments or houses, as well as industrial enterprises or trading halls.

The circuit breakers are determined by the rated current and the group. Depending on these characteristics, the protection automatons are divided into 3 groups - B, C and D. In household circuits, devices of type C are usually used, in which the instantaneous turn-off current lies in the range of 5 to 10 values of the nominal current. Next we consider automata of type C of modular form.

The short-circuit protection circuit includes the following mains and network overloads:

the body;
control mechanism;
switching device;
releases;
arc interrogation chamber.

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The body of the device is a plastic box, the dimensions of which are standardized. On the front side there is a lever for switching on and off the machine, there is a latch for fastening on the DIN-strip at the rear, and terminals for connecting the wires from above and below.

One of the distinguishing characteristics of the electric machine is the control mechanism, which is designed for manual switching on and off. It consists of a handle or buttons.

The switching device is a set of power and auxiliary contacts. These contacts can be moving or stationary.

Trip units are devices designed to open the electrical circuit in the event that the current in the circuit exceeds the set values. The machine has electromagnetic and thermal releases. Electromagnetic is an inductor with a metal core connected by a system of levers with a movable power contact of the machine. In the thermal one, a bimetallic plate is used which, under the action of the current flowing through it, bends and through the levers affects the movable contact of the machine.

Before operating the device, it is necessary to check the operation of the trip units of the circuit breakers.

To reduce the effect of the arc, which arises when the power contacts are opened, a special chamber consisting of metal plates is provided in the machine. The electric arc falling into this chamber is divided into several parts by plates and is extinguished.

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The principle of operation of the machine during overloading

If a too large number of consumers are included in the power circuit, a current may appear in the circuit, the value of which may exceed the maximum value for a given power grid. In practice, this can arise, for example, when a washing machine, an iron, a kettle, a boiler, a microwave oven and other powerful electricity consumers are turned on in the apartment.

In the case when the actual current of the circuit exceeds the rated current of the machine, the thermal trip is triggered in the latter.

The bimetallic plate, consisting of two metal layers, heats up when a current passes through it. Under the influence of heat, this plate bends, acts on the movable contact of the machine and opens the circuit.

The value of the thermal trip triggering current is usually larger than the rated current of the circuit breaker by 13-45%. This value can be changed with the help of an adjusting screw at the factory setting in a fairly wide range. The time delay for switching off the machine when overloading is necessary so that there are no unnecessary outages with a short increase in current, which, for example, happens when the motor is started.

Action of the device in case of a short circuit

When a short circuit appears in the circuit, a rapid and sharp increase in the current occurs throughout the network, including the coil of the electromagnetic release. Under the influence of a sharply increased electromagnetic field, the core is drawn into the coil. The lever located on the core acts on the movable power contact, disconnects it from the stationary contact and opens the electric circuit.

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The impact of short-circuit currents can adversely affect the condition of the connected devices, wiring and even cause a fire. To reduce the impact of such currents, the tripping time of the release must be kept to a minimum. Modern machines with the action of short-circuit currents operate within a time not more than 0.02 seconds.

Re-engaging the machine - what needs to be done?

When the machine is activated due to overload, it is possible to re-engage the circuit only after the bimetallic plate has cooled. In this case, before turning on the circuit breaker, it is necessary to analyze the load of the circuit and try to reduce it by switching off excess devices.

Before reconnecting the circuit after the short-circuit tripping of the machine, it is necessary to try to find the cause of this phenomenon and eliminate it.

For example, by turning off all consumers of electricity, you can check for a short circuit of the electrical wiring itself. Then check the electricity consumers and find the culprit for a short circuit.

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Conclusions:

A circuit-breaker is used to protect the electrical circuit from overload and short-circuit.
In the circuit breaker, when the thermal overload is overloaded, the circuit is opened with a time delay, and in case of a short circuit, an electromagnetic release is instantaneous.
Before switching on again after triggering an overload controller, it is necessary to reduce the number of consumers.
Before switching on again after the short-circuit breaker has tripped, the cause of the short circuit must first be eliminated.