# S

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## SI unit

SI units are most widely used units of measurement belong to an international system of units which is also known as SI or Metric System.

## Shunt

A precision resistor connected in parallel with a current indicating meter for the purpose of bypassing a specific fraction of current around the meter.

## Static Electricity

Opposite static charges that occur when friction between two bodies causes electrons to transfer from one body to the other.

## Scalable digital multimeter

A scalable digital multimeter is a device used to measure multiple electrical quantities knowing their initial values of voltage, current, and resistance.

## Series Circuit

In series circuits, components are connected in such a way that same current flows through each component. However, the voltage drop across each element is different.

## Self-Inductance

The phenomenon is which a changing current in a coil induces an emf in itself is called self-induction.

## Susceptance

The reciprocal of circuit’s reactance, measured in Siemens; BL designates inductive reactance and BC capacitive susceptance.

## Semiconductor

Material that lies midway between conductor and insulator in its ability to pass an electric current.

## Short Circuit

An abnormal connection of very low resistance between two points of a circuit, resulting in a flow of excess current.

## Superposition Theorem

Superposition Theorem states that in any linear network having more than one voltage source, the current and voltage in any one component of the network can be determined by algebraically adding the effect of each voltage source separately while all other sources are temporarily shorted.

## Specific Resistance

The resistance of a conductor expressed in ohms per unit length per unit area, that is, per circular mil foot.

## Salient, or projecting, pole

A ﬁeld pole that juts out from the yoke towards the primary winding core.

## Saturation curve

A device characteristic curve that shows the magnetic saturation degree as a function of a certain property of the magnetic excitation.

## Short-circuit characteristic (SCC)

The relationship between the current in the short-circuited armature winding and the ﬁeld current.

## Short-circuit test

A test applied to a transformer with one winding short-circuited and reduced voltage applied to the other winding such that rated current ﬂows in the windings.

## Single-phase transformer

A device consisting of two or more windings coupled by a magnetic core that is used to transform a single-phase voltage.

## Skin effect

The phenomenon in which an alternating current starts to flow on the conductor surface (low impedance area).

## Slip RPM

The difference between the synchronous speed and the actual speed of the rotor expressed in revolutions per minute (rpm).

## Slip s

The quotient of the difference between the synchronous speed and the actual speed of a rotor, to the synchronous speed, expressed as a ratio or percentage.

## Speed regulation

The relationship between the speed and a load of a motor under specified conditions.

## Square matrix

A matrix in which the number of rows is equal to the number of columns.

## Squirrel-cage rotor

A rotor core assembly consisting of a number of conducting bars having their extremities connected by metal rings or plates at each end, like a squirrel’s cage.

## Stator

The portion of the rotating machine that includes and supports the stationary active parts.

## Stranded conductor

A conductor made by a group of wires is called stranded conductor.

## Swing equation

The differential equation used to describe the dynamic motion of a synchronous machine.

## Synchronization

The process whereby a synchronous machine, with its voltage and phase suitably adjusted, is paralleled with another synchronous machine or system.

## Synchronous machine

It is a type of machine in which the normal operating speed is precisely proportionate to the system frequency to which it is linked.

## Synchronous speed

It is the speed of rotation of the magnetic ﬂux in a synchronous machine, generated by or associating the primary winding.

## Scientific notation

A classification for representing a large or small number as a number between 1 and 10 times a power of ten.

## Strain gauge

Transducer that changes its value based on an external force stretching or compressing it

## Sensor

A device that converts a physical condition into an electrical signal for use by a controller, such as a PLC.

## Servo Motor

It is a linear or rotary actuator that provides accurate control of linear or angular position, speed as well as acceleration. It comprises of an appropriate motor which is linked to a sensor in order to get position feedback.

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