Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

tesla
a unit of magnetic flux density equal to one weber per square meter, i.e., one volt-second per square meter. Denoted by T. The unit is named in honor of Nikola Tesla, an early pioneer in the electric industry, who is most commonly credited with building the first practical induction motor.
Tesla
Tesla, Nikola (1856-1943) Born: Smiljan, Croatia

is best known as the electrical pioneer who championed the use of alternating current. When Tesla first came to the
United States he worked for Edison. He soon split with Edison, because Tesla approached invention from a theoretical standpoint, whereas Edison was a "trial and error" type experimentalist. Together with his financial backer, George Westinghouse, they battled with Edison, who championed the use of direct current for electrifying the world. Tesla is also known for his many inventions including the Tesla coil and the AC induction motor. It was Westinghouse who made a fortune from Tesla's inventions. Tesla was known for his eccentricities and died a recluse in New York City.
THD

See total harmonic distortion
thermal control

See thermal management
thermal expansion mismatch
the absolute difference in thermal expansion of two components.
thermal fin
an extension of the surface are in contact with a heat transfer fluid, usually in the form of a cylinder or rectangular prism protruding from the base surface.
thermal light
light generated by spontaneous emission, such as when a group of excited atoms or molecules drops to a lower energy state in a random and independent manner emitting photons in the process; contrasted with laser light.
thermal management
the process or processes by which the temperature of a specified component or system is maintained at the desired level. Also called thermal control.
thermal reactor
a reactor which maintains a critical reaction with thermal neutrons.
thermal resistance
a thermal characteristic of a heat flow path, establishing the temperature drop required to transport heat across the specified segment or surface; analogous to electrical resistance.
thermionics
direct conversion of thermal energy into electrical energy by using the Edison effect (thermionic emission).
thermit welding
a welding process that produces coalescence of metals by heating them with superheated liquid metal from a chemical reaction between a metal oxide and aluminum with or without the application of pressure.
third rail
a method of transmitting power to an electric locomotive. An insulated steel rail is laid along the railbed just outside the traction rails. This third rail is maintained at (typically) 600 volts DC by the railroad power supply, and contact is made to the locomotive by a shoe which slides atop the rail. Ground return is through the traction rails.
Thomson
Thomson, William (Lord Kelvin) (1824-1907) Born: Belfast, Ireland

is best known as a physicist who championed the absolute temperature system that now bears his name (Kelvin). Thomson did significant work to expand Faraday's ideas. It was Thomson's work that Maxwell would extend into his seminal publications on electromagnetics. Thomson received a knighthood for his theoretical suggestions for the use of low-voltage signals in
the trans-Atlantic telegraph cable. Thomson was proved correct when on a third attempt, a cable was laid and worked. An earlier high-voltage cable had failed.
three-lamp synchronizing
a method used to connect a three-phase power system in parallel to another one. In order to connect two systems, they must have the same voltage magnitude, frequency, and phase-shift. To determine that is the case, an open switch is connected between the phases of the two systems and a lamp is connected across the open switch pole in each phase.

If the criteria previously listed are met, the lamps will all be dark. If there is a difference in voltage, the lamps will glow. If there is a difference in frequency, the lamps will alternately glow and go dark in unison. Finally, if the two sides have different phase rotations, the lamps will blink sequentially as only one phase can be aligned at a time. In order to synchronize the two systems, it is necessary to close the contactor when the phase-shift is minimum, which means that the three lights are dark.
three phase fault
a fault on a three phase power line in which all three conductors have become connected to each other and possibly the ground as well.
three-phase inverter
an inverter with a three-phase AC voltage output.
three-phase rectifier
a rectifier with a three-phase AC voltage input.
three-point starter
a manual DC motor starter in which a handle is pulled to start the motor. The motion of the handle causes a contact to move across a variable resistance in the armature circuit to limit the starting current. When the handle is moved to its fullest extent, the resistance is out of the armature circuit and an electromagnet holds the handle in place. With a three-point starter, the electromagnet is in series with the shunt field and loss of the field will shut down the motor. The disadvantage is that if it is desired to weaken the field for speed control, the motor starter may drop out. Also, the three-point starter cannot be used on a series DC motor.
three-winding transformer
a transformer with three windings, typically primary, secondary, and tertiary. Common three phase, three winding transformers employ wye connected primary and secondary windings and a delta connected tertiary winding.

In some cases, an autotransformer is used to form the primary-secondary combination.
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