Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

scrubber
a means of removing sulfur dioxide from coal-burning power plant exhaust gas by forcing it through a chemical solution.
seal-in relay
an auxiliary relay that remains energized through one of its own contacts, which bypasses the initiating circuit until deenergized by some other device.
sealing current
the current necessary to complete the movement of the armature of a magnetic circuit closing device from the position at which the contacts first touch each other.
sealing voltage
the voltage necessary to complete the movement of the armature of a magnetic circuit closing device from the position at which the contacts first touch each other.
search coil
a solenoid that is wound with an air core or around a magnet or permeable component of a magnetic circuit to measure the change of flux within the coil; used with a fluxmeter.
second harmonic component
the signal component of a periodic signal whose frequency is twice the fundamental frequency.
secondary
(1) the load-side winding.

(2) refers to the portion of a nuclear power plant containing non-radioactive components such as turbines and generators.
secondary
winding the transformer winding to which the loads are connected.
See primary winding
secondary distribution system
a distribution system in which a significant the subdivision of power to customers is done on the secondary, or low-voltage side of the distribution transformer, as opposed to the practice of assigning a small distribution transformer to each customer or small group of customers.
secondary resistor
a resistor connected to the rotor of a wound-rotor induction machine to permit variation of the effective rotor resistance. By varying the resistance, machine characteristics may be optimized for starting or varying load conditions.
secondary selective service
a redundant electric service in a critical load is supplied by two distribution transformers, each of which is served by a separate, independent distribution primary circuit.
secondary system of equations
a system of algebraic and differential equations obtained from the primary system of equations by transformation of network variables.
secondary voltage
in power distribution work the voltage at the secondary of the distribution transformer.
secondary voltage control
an automatic voltage control scheme that is similar in function to the automatic voltage regulator, but its purpose is to control a bus voltage which need not have a synchronous generator connected at the bus.
sectionalizer
a switch placed in distribution lines and programmed to open during a line dead time. The sectionalizer will sense the presence of current surges due to faults, and is programmed to open after a set number of faults occur during a short period of time. When the fault is cleared by the protecting recloser or circuit breaker, the sectionalizer will open, allowing the recloser or breaker to successfully reenergize the portion of the line upstream from the sectionalizer.
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.
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