What is a short circuit in an electrical circuit?

Anyone whose work is connected with serviceelectrical engineering, is very well aware of those troubles, which is fraught with a short circuit (AC). Sometimes it is considered that it is a damage. This is not true. A short circuit is a process, or, if you prefer, an emergency operation of any part of the electrical installation. But the consequences of it do lead to damage. The conventional definition reads: "A short circuit is the direct connection of two or more points of an electrical circuit with different potentials. It is an abnormal (unintended) mode of operation. "

To understand what is happening in the chain in thethe moment when there is a short circuit, it is necessary to remember the principles of the functioning of the contour elements. Imagine a simple circuit consisting of a power source, two conductors and a load (for example, a light bulb). Under normal conditions, there is a directed movement of charged elementary particles in the conductor, caused by the constant action of the electromotive force of the source. They travel from one pole of the source to the other through two sections of the wire and a lamp. Accordingly, the lamp emits light, since the particles perform a certain work in it.

With alternating current, the direction of travelconstantly changing, but in this case it is not important. The number of electrons passing through a certain section of the circuit per unit time is limited by the resistance of the lamp, conductors, and the source of the EMF. In other words, the current does not grow infinitely, but corresponds to the steady state.

But here for some reason is damagedisolation at the circuit section. For example, the lamp flooded with water. In this case, its electrical resistance decreases. As a result, the current flowing along the circuit is limited by the total resistance of the power source, wires and water "isthmus" on the lamp. Usually this amount is so insignificant that it is not taken into account in the calculations (special calculations are an exception).

The result is an almost infinite growthcurrent, determined by the classical Ohm law. In this case, the power of a short circuit is often mentioned. It is determined by the limiting value of the electric current, which is able to give out the power source before failure. By the way, that's why it is forbidden to connect wiring (short-circuiting) the opposite contacts of the batteries.

Although in the example we consider the elimination ofcircuit resistance of the lamp due to water on it, the causes of the short circuit a lot. For example, if we talk about the same scheme, then kz. It can also occur if the insulation of at least one wire is broken and it comes into contact with the ground. In this case, the current from the power source will follow the path of the least resistance, that is, to the ground, which has a huge capacity. Damage to the insulation of two wires at the same time and their contact will lead to the same result.

The above can be summarized: k.s can be with the earth and without it. It does not affect the processes that take place.

What kind of damage was discussed at the beginning of the article? As is known, the higher the value of the current flowing through the sections of the circuit, the greater their heating. With sufficient power of the source for short circuits. some parts of the chain simply burn out, turning into copper dust (for copper elements).

The short-circuit protection is quite simple andis effective. Reports of faults due to faults occur primarily due to improperly selected parameters of the protection devices, incorrect selectivity. If it is a household circuit 220 V, then use automatic switches. In them, with an excessive current increase, the electromagnetic release inside the circuit breaks the circuit.