Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

star network
a network topology where a central node broadcasts radially to all subscribers. The central node is a vulnerable element on which the whole network depends.
star-star transformer

See wye-wye transformer
starting torque
the torque at zero speed obtained at the very beginning of the starting process of an electrical machine. The condition to obtain the rotation of the rotor is that the starting torque has to be greater than the load torque at zero speed.
static excitation system
an excitation system derived from solid state devices such as thyristors that convert the AC terminal voltage to DC before application to the rotor.
static var compensator
a device for fast reactive compensation, either inductive or capacitive, brought about by thyristor-based control of an effective shunt susceptance. It is typically used to regulate voltage at a bus on the high voltage transmission system.
static VAR regulator
also called a static VAR compensator. A nonrotating electrical device designed to adjust the reactive power flow of an AC power system. It typically consists of a reactive load (either inductive or capacitive) and a series electronic switch (thyristor) that controls the reactive power.
station battery
a battery used to provide operating energy for the protective relay operations and to initiate circuit breaker operations in a generating station. The battery is necessary, as the equipment must work reliably during severe voltage sags and outages on the AC system.
station control error
in economic dispatch studies, the difference between the desired generation of all plants in a control area and the actual generation of those plants.
station insulator
refers to a large-sized insulator used in substations.
steady-state control
operation and mechanisms of the control system in which the main objective is to keep the controlled process in the condition where the state variables relevant to the controlled process performance are constant i.e., to keep the process in a required operating point. Steady-state control structure may be composed of several control layers, including direct regulatory layer, optimization layer and, eventually, other layers; steady-state control is widely used in chemical and power industries.
steady-state gain
the gain that a system applies to DC (constant) input signals.
step voltage
in power system safety studies, the voltage measured across two points on the ground which are separated by a distance equal to an average person's step while walking over the area in question.
step-down converter

See buck converter
step-up converter

See boost converter
strain insulator
an insulator which forms an insulated tensile link between two conductors in overhead line work.
submersible transformer
a transformer, used in underground distribution work, which is capable of operation while submerged in water.
substation
a junction point in the electric network. The incoming and outgoing lines are connected to a busbar through circuit breakers.
substation battery
a battery used to provide operating energy for the protective relay operations and to initiate circuit breaker operations in a generating substation. The battery is necessary, as the equipment must work reliably during severe voltage sags and outages on the AC system.
subsynchronous resonance
an electric power system condition where the electric network exchanges energy with a turbine generator at one or more of the natural frequencies of the combined system below the synchronous frequency of the system.
subtractive polarity
polarity designation of a transformer in which terminals of the same polarity on the low-and high-voltage coils are physically opposite each other on the transformer casing. With subtractive polarity, a short between two adjacent terminals results in the difference of the two coil voltages appearing between the remaining terminals.
Subtractive polarity is generally used on transformers larger than 500 kVA and higher than 34.5 kV. Smaller units use additive polarity.
See additive polarity
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