Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

sectionalizing fuse
a sectionalizing fuse is a fuse employed on the primary distribution system to isolate laterals from the main feeder in the event of a fault on that lateral.
sectionalizing switch
a switch on primary distribution systems used to isolate laterals and segments of main feeder lines. On radial distribution systems, sectionalizing switches are placed to allow rerouting of power to minimize extended outages following a line segment failure.
security
the ability of the power systems to sustain and survive planned and unplanned events without violating operational constraints.
selective fuse coordination

See fuse coordination
selectivity
the ability of a receiver to receive only its desired band of frequencies and reject those on either side. This not only improves the signal properties but also the noise characteristics of the receiver.
self-commutated

See natural commutation
self-demagnetizing field
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.
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