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Physics a brief change in the state of a system, such as a sudden short-lived oscillation in the current flowing through a circuit
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.



(or transient phenomenon). A transient in an electric circuit is a phenomenon that occurs during a transition from one circuit condition to another that differs from the initial condition in the amplitude, phase, shape, or frequency of the voltage acting in the circuit, the values of the parameters, or the configuration of the circuit. Transients occur chiefly when circuit elements are switched into or out of the circuit. The transients arise because the current flowing through an inductance and the voltage across a capacitance cannot be altered abruptly—that is, the energy of the electric and magnetic fields in the circuit’s capacitive and inductive elements cannot be changed instantaneously.

Theoretically speaking, a transient continues for an indefinite period because the voltage and current in an electric circuit after the closing or opening of a switch approach their final (steady-state) values asymptotically. In electrical engineering, however, a transient is considered to be ended when the voltage and current reach values differing from the steady-state values by 5 to 10 percent, a condition that occurs within a comparatively short finite interval of time. An electric circuit that is characterized by constant or periodically varying currents and voltages is said to be in a steady-state condition.

A simple example of a transient is the charging of a capacitor C (Figure 1) from a DC source (a storage battery) having an electromotive force (emf) E and an internal resistance r through a resistor R, which limits the current in the circuit. If the switch is closed at the time t = 0, the current in the circuit decreases according to an exponential law and approaches zero. Simultaneously, the voltage increases and approaches asymptotically the value of the source emf. The rate of change of the voltage and the current depend on the capacitance of the capacitor and the resistance in the circuit: the larger the capacitance and resistance, the longer the duration of the charging process. After a time interval τ = (R + r)C, called the time constant for the charging of the capacitor, the voltage across the capacitor’s plates attains the value uc = 0.6327, and the current i reaches 0.37I0, where I0 is the initial current. I0 is equal to the ratio of the emf and the resistance in the circuit. After a time interval of 5τ;, UC > 0.99E and i < 0.01I0; with an error of less than 1 percent, the transient can be regarded as having ended. During the transient, the energy of the capacitor’s electric field is increased from zero to Wc = CE2/2.

During a transient, in individual parts of a circuit there may occur voltage surges and overcurrents—that is, voltages and currents substantially greater than the steady-state voltages and currents. When equipment is not selected properly, the voltage surges can result in the breakdown of insulation in, for example, capacitors, transformers, and electrical machines. Overcurrents can cause the actuation of protective devices and the disconnection of equipment; they can burn out instruments, burn contacts, and cause mechanical damage to windings as a result of electro-dynamic stresses. Transients play an exceptionally important role in automatic control systems, pulse engineering, computer technology, measurement technology, electronics, radio engineering, and power engineering.


Osnovy teorii tsepei. Moscow-Leningrad, 1965.
Neiman, L. R., and K. S. Demirchian. Teoreticheskie osnovy elektrotekhniki, vol. 1. Leningrad, 1967.
Ginzburg, S. G. Metody resheniia zadach po perekhodnym protsessam ν elektricheskikh tsepiakh, 3rd ed. Moscow, 1967.
Venikov, V. A. Perekhodnye elektromekhanicheskie protsessy ν elektricheskikh sistemakh. Moscow, 1970.
Teoreticheskie osnovy elektrotekhniki, part 1. Moscow, 1972.
Bessonov, L. A. Teoreticheskie osnovy elektrotekhniki. Moscow, 1973.


The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.


A pulse, damped oscillation, or other temporary phenomenon occurring in a system prior to reaching a steady-state condition.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.


1. <electronics> A sudden, brief increase in current or voltage in a circuit that can damage sensitive components and instruments.
This article is provided by FOLDOC - Free Online Dictionary of Computing (


A malfunction that occurs at random intervals and lasts for a short duration such as a spike or surge in a power line or a memory cell that intermittently fails. See spike and power surge.
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References in periodicals archive ?
In order to prove the viability of the RSTFT technique, for broken rotor bar detection, the algorithm is applied to both stator current, and synthetic signals, this last have the typical waveform of startup transient of a VSD fed IM.
(8) The statute upon which it is based provides a host of reasons that a hotel can cite as grounds for removing transient occupants: the illegal possession of controlled substances; being intoxicated, profane, lewd; brawling; indulging in language or conduct that disturbs the peace and comfort of other guests; failing to pay rent; failing to check out timely; or being considered a person the continued entertainment of whom would be detrimental to such hotel.
In contrast, standard transients arising from normal supernovae take at least a few weeks to reach their peak level of brightness.
In the analysis of transient processes we have assumed that the thyristors VT and [VT.sub.1] are ideal switches (without energy losses and with instantaneous commutation), and the inductance value L is less by two orders of the inductance [L.sub.1], therefore, value L can be ignored in the analysis of the first transient process.
The reason we choose these specific values is the fact that each value corresponds to a different propagation regime of SRS, [[GAMMA].sub.c] = 0.4 corresponds to [[GAMMA].sub.c] [much less than] 1 1 or steady-state regime, [[GAMMA].sub.c] = 2 corresponds to [[GAMMA].sub.c] = 1 which is the fairly transient regime, and [[GAMMA].sub.c] = 60 corresponds to [[GAMMA].sub.c] [much greater than] 1 or highly transient regime.
Therefore, we focus on the influence on the system transient voltage stability when different short circuit faults occur at Line 1.
When primary congenital hypothyroidism is evaluated in terms of the underlying cause and the disease period, it is divided into two subgroups as permanent and transient PCH.
The main contributions of the paper are the following: i) The effect of both wind generators and PhotoVoltaic (PV) units along with the displacement of synchronous generators and network topology changes, on transient stability of the overall system, is investigated.
Two testing processes were used to map each engine while it was on an engine dynamometer and tethered to its respective vehicle, intending to cover both steady-state and transient operation.
To assess the contribution of different ion channels to the development of the biphasic action potential [Ca.sup.2+] transient, 5-day-old cultured fibers were exposed to either gadolinium (Axxora, San Diego, CA, catalog number 400-023-M500), apamin (Sigma-Aldrich, St.
Exposure of the differentiating cells to 2 [micro]M thapsigargin induced a transient increase of cytosolic calcium in all the cells assessed in the five independent experiments (Figure 3(a)).