short circuit

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short circuit,

abnormal connection of low resistance between two points of a circuit that usually causes a high, potentially damaging current to flow. To protect against damage, devices such as a fusefuse, electric,
safety device used to protect an electric circuit against an excessive current. A fuse consists essentially of a strip of low-melting alloy enclosed in a suitable housing. It is connected in series with the circuit it is to protect.
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 or a circuit breakercircuit breaker,
electric device that, like a fuse, interrupts an electric current in a circuit when the current becomes too high. The advantage of a circuit breaker is that it can be reset after it has been tripped; a fuse must be replaced after it has been used once.
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 are used. They sense the excess current and break the circuit so that no current can flow. They must be replaced or reset manually once the cause of the short circuit is removed.

Short circuit

An abnormal condition (including an arc) of relatively low impedance, whether made accidentally or intentionally, between two points of different potential in an electric network or system. See Electrical impedance

Common usage of the term implies an undesirable condition arising from failure of electrical insulation, from natural causes (lightning, wind, and so forth), or from human causes (accidents, intrusion, and so forth). From an analytical viewpoint, however, short circuits represent a severe condition that the circuit designer must consider in designing an electric system that must withstand all possible operating conditions.

In circuit theory the short-circuit condition represents a basic condition that is used analytically to derive important information concerning the network behavior and operating capability. Thus, along with the open-circuit voltage, the short-circuit current provides important basic information about the network at a given point.

The short-circuit condition is also used in network theory to describe a general condition of zero voltage. Thus the term short-circuit admittance (or impedance) is used to describe a network condition in which certain terminals have had their voltage reduced to zero for the purpose of analysis. This leads to the terms short-circuit driving point admittance, short-circuit transfer admittance, and similar references to the zero voltage condition. See Admittance

Short-circuit protection is a separate discipline dedicated to the study, analysis, application, and design of protective apparatus that are intended to minimize the effect of unintentional short circuits in power supply systems. For these analyses the short circuit is an important limiting (worst) case, and is used to compute the coordination of fuses, circuit reclosers, circuit breakers, and other devices designed to recognize and isolate short circuits. The short circuit is also an important parameter in the specification of these protective devices, which must have adequate capability for interrupting the high short-circuit current.

Short circuits are also important on high-frequency transmission lines where shorted stub lines, one-quarter wavelength long and shorted at the remote end, are used to design matching sections of the transmission lines which also act as tuning elements.

Short Circuit

 

a low-resistance connection between points in an electric circuit having different potentials that is not contemplated under normal operating conditions.

A short circuit occurs as a consequence of insulation failure and the connection of current-carrying parts of electrical equipment to one another or to grounded surfaces (directly or through a conductive material). In three-phase systems, short circuits may be single-phase (phase-to-ground), two-phase (two phases together), two-phase-to-ground (two phases together and simultaneously from the same point to ground), and three-phase (three phases together). In electrical machines and apparatus, short circuits may occur between turns of windings, between windings and a metal chassis, and so on.

A short circuit is an extremely hazardous phenomenon; the current in the circuit usually increases abruptly. As a result, strong mechanical forces are created in electrical apparatus, and the temperature of the conductors is increased substantially, which may cause damage. An electric arc frequently develops at the point of the short circuit, causing a breakdown. In an electrical system the voltage to consumers is decreased during a short circuit; for single-phase, two-phase, and two-phase-to-ground short circuits the voltages become asymmetric, thus partially or completely disrupting the normal power supply. A short circuit can disturb the dynamic stability of an electrical system and, as a result, cause serious system damage.

When the conductors of power lines are short-circuited to ground, a strong electromagnetic field is produced in the surrounding space, inducing electromotive forces in nearby communications lines that are hazardous for both service personnel and apparatus. When current is flowing from the point of a short circuit along the surface of the earth, a potential difference (a voltage hazardous to a walking person across the distance of one pace) that is dangerous to life may occur. To provide protection from the effects of short-circuit currents and to ease the requirements for mechanical and thermal stability of electrical equipment, measures are taken to reduce the magnitude of the currents (current-limiting reactors, sectionalization of electric networks, and so on) and to automatically and rapidly disconnect the faulty parts of the network (fuses and automatic circuit breakers, as well as relaying devices and automatic apparatus).

REFERENCES

Ul’ianov, S. A. Elektromagnitnye perekhodnye protsessy ν elektricheskikh sistemakh. Moscow, 1970.
Venikov, V. A. Perekhodnye elektromekhanicheskie protsessy ν elektricheskikh sistemakh, 2nd ed. Moscow, 1970.

V. P. VASIN and V. A. SROEV

short circuit

[′shȯrt ′sər·kət]
(electricity)
A low-resistance connection across a voltage source or between both sides of a circuit or line, usually accidental and usually resulting in excessive current flow that may cause damage. Also known as short.

short circuit

In an electric circuit, an abnormal connection, having relatively low resistance, between two points of different potential; causes an abnormally high current flow through the connection.

short circuit

a faulty or accidental connection between two points of different potential in an electric circuit, bypassing the load and establishing a path of low resistance through which an excessive current can flow. It can cause damage to the components if the circuit is not protected by a fuse