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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



(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.


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A pulse, damped oscillation, or other temporary phenomenon occurring in a system prior to reaching a steady-state condition.


1. <electronics> A sudden, brief increase in current or voltage in a circuit that can damage sensitive components and instruments.


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.
References in periodicals archive ?
The elusiveness of the sources of transients means many trips to the field by the engineers.
Looking into a 1991 gamma-ray burst found by the WATCH detector on the Soviet space observatory Granat, the researchers discovered that an optical transient -- a short, bright visual flare that quickly faded to obscurity -- had popped off in 1905 very close to the area where the burst was detected 86 years later.
There are three different methods for specifying transients (video leakage): peak voltage broadband, peak voltage in-band and power in the frequency domain (dBm).
External generated transients are caused by lightning, normal utility operations, unusual power line conditions, and noisy electrical surroundings.
Villaraigosa himself says the 3,600 transients packed into the few square blocks east of downtown that compose Skid Row make it the ``highest concentration of homelessness anywhere in America.
The damage caused by transients carried down cables and wires ranges from the minor to the devastating.
Computer-controlled systems, for example, are much more sensitive to surges as the increased integration of electronic circuits into smaller packages has increased their sensitivity to transients.
But the program -- in which the Los Angeles Police Department deployed 50 additional officers to Skid Row -- has resulted in complaints from some transients who say they are being kept from the missions, the shelters and the streets they call home.
This project investigates whether low and negative pressure transients actually occur in real distribution systems--not just within large transmission mains--and if they cause contaminants external to the pipe to be intruded into a drinking water main through a leaking pipe barrel, pipe joint, or other orifice.
Pulse's video-grade splitters, which do not saturate during ring trip, eliminate video errors by suppressing high-frequency voltage transients from entering the VDSL2 spectrum.
Circuit Court of Appeals decision, officers will allow transients to camp overnight on sidewalks within a 50-square block area downtown, except in front of doorways and loading docks.
provides the knowledge base for addressing the problems of electromagnetic transients in power systems caused by lightning strikes and switching surges.