Electrical Engineers and Master Electricians (EEAME) Portal

Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

a field inside of a permanent magnet that is opposed to its own magnetization, which is due to internal coupling of its poles following the introduction of an air gap in the magnetic circuit.

selsyn

See synchro

semi-rigid cable

a coaxial cable with a solid metal outer-conductor. Typically used where the cable is bent to fit the application only once.

semiconductor

a material in which electrons in the outermost shell are able to migrate from atom to atom when a modest amount of energy is applied. Such a material is partially conducting (can support electrical current flow), but also has properties of an insulator. The amount of current conduction that can be supported can be varied by "doping" the material with appropriate materials, which results in the increased presence of free electrons for current flow. Common
examples are silicon and GaAs.
See semi-insulator

set point

(1) a specified constant value of the controlled variable of a dynamical process that a controller is required to maintain. The controller must generate a control signal that drives the controlled variable to the set point and keeps it there, once it is reached. The set point is often referred to as reference point or operating point. In aircraft flight control, the set point is also called the trim condition.

(2) the intersection of the load line and the normal B-H curve, indicating the flux density and energy a permanent magnet is delivering to a given magnetic circuit geometry.

SF6

See sulfur hexaflouride

SF6 circuit breaker

a power circuit breaker where sulfur hexaflouride (SF6)gas is used as an insulating and arc clearing agent.

shaded-pole motor

a single-phase induction type motor that uses shaded poles on the stator to create a weak quasi-rotating magnetic field. Shaded-pole motors are only built in small fractional horsepower sizes and produce a very low starting torque that is suitable only for fan-type loads. See also shaded pole.

shell-type transformer

a power transformer in which the magnetic circuit surrounds and normally encloses a greater portion of the electrical winding.

shield wire

(1) a ground wire placed above an electric transmission line to shield the conductors from lightning strokes.

(2) a ground wire buried directly above a buried communications cable for lightning protection.

short circuit

a condition on the power system where energized conductors come in contact (or generate an arc by coming in close proximity) with each other or with ground, allowing (typically large) fault currents to flow.

short circuit admittance

the admittance into an N-port device when the remaining ports are terminated in short circuits. For port 1 of a 2-port device, it is the input admittance into port 1 when port 2 is shorted.

short circuit gain-bandwidth product

a measure of the frequency response capability of an electronic circuit. When applied to bipolar circuits, it is nominally the signal frequency at which the magnitude of the current
gain degrades to one.

short-circuit protection

the beneficial effect provided by an overcurrent device when it acts to interrupt short-circuit current.

short-circuit test

a transformer test conducted by placing a few percent of rated voltage on the voltage side while the low voltage winding is shorted. By measuring the voltage, current, and input power, it is possible to calculate the equivalent winding impedance for the transformer equivalent circuit.

shunt

(1) a device having appreciable impedance connected in parallel across other devices or apparatus and diverting some of the current from it. Appreciable voltage exists across the shunted device or apparatus, and an appreciable current may exist in it.

(2) an inductive element connected across a power line or bus. Those connected to buses are known as bus-connected reactors, while those connected across a power line are called line-connected reactors.

shunt capacitor

a capacitor or group of capacitors which are placed across an electric power line to provide a voltage increase or to improve the power factor of the circuit. A switchable shunt may be disconnected from the circuit when conditions warrant, while a fixed shunt is permanently connected to the power line.

shunt DC machine

a DC machine with the field winding connected in shunt with the armature. In shunt generators, residual magnetism must be present in the machine iron in order to initiate the generation process. These machines are also known as self-excited, since they supply their own excitation.

shunt field

a field winding of a DC machine consisting of many turns of fine wire, connected in parallel with the armature circuit. It may be connected to the same source as the armature or a separate source.