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Commonly used terms in the Electrical industry.
temporary fault
a fault that will not reoccur if the equipment is deenergized and then reenergized. An example of a temporary fault is when a lightning stroke causes an uninsulated overhead line to arc over an insulator, with no equipment damage.
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.
thyristor-controlled phase angle regulator
a phase shifting device used in transmission systems. The phase angle change is brought about by thyristor-based control.
torque pulsation
oscillating torque produced by the interaction between the air gap flux, consisting mainly of the fundamental component, and the fluxes produced by harmonics in the rotor. Torque pulsations can stimulate complex mechanical vibrations that can flex and damage rotor and turbine elements.
transformer vault
a fireproof enclosure in which power transformers containing oil must be mounted if used underground or indoors.
transient fault
a fault that can appear (e.g., caused by electrical noise) and disappear within some short period of time.
twelve-pulse converter
the combination of two 6-pulse converters connected through a Y-Y and a delta-Y transformer in order to cancel the characteristic 5th and 7th harmonics of the 6-pulse converters. The lowest characteristic harmonics with twelve-pulse converters under balanced conditions are the 11th and 13th harmonics. The converters are connected in parallel on the AC side and in either series or parallel on the DC side, depending on the required DC output voltage.
UL
See
Underwriters Laboratory
UL classes
a classification system established by Underwriters Laboratory (UL) for the purpose of defining certain operating characteristics of low voltage fuses. UL classes include G, J, L, CC, T, K, R, and H.
ultra-high frequency (UHF)
electromagnetic spectrum with frequencies between 300 MHz and 3000 MHz or wavelengths between 10 cm and 100 cm. Also called as decimetric waves.
ultrasound
an imaging modality that uses reflected high-frequency sound energy to image the interface between materials with different acoustic impedances.
ultraviolet
a term referring to wavelengths shorter than 400 nm, but longer than 30 nm. The region 400-300 nm is the near ultraviolet, 300-200 is the middle ultraviolet; and 200-30 nm is the far ultraviolet or vacuum.
ultraviolet laser
laser producing its output in the ultraviolet region of the spectrum.
unbalanced magnetic pull
a phenomenon in electric machines arising from the rotor not being symmetrical with respect to the stator or the axis of the rotor and stator not being coincident. Results in a higher pulling force on the side with the smaller airgap, resulting in additional bearing stresses.
unsymmetrical fault
a fault on a three-phase power line in which the fault current is not equal in all three phases, e.g., a single-line-to-ground, double-line-toground or line-to-line fault.
vacuum insulation
any insulation scheme which depends upon the dielectric capabilities of a high vacuum.
voltage regulating relay
a voltage regulating relay senses RMS voltage level and issues commands to devices such as load tap changers, which then adjust the tap position to bring the voltage back to the desired level.
voltage regulation
the change in delivered voltage from a generator or transformer from no-load to full-load. Voltage regulation is usually expressed as a percentage of the no-load voltage. For a DC generator, the voltage will always drop as the load increases and the voltage regulation will be a positive quantity. For AC generators and transformers, voltage regulation is the difference in the magnitude of the no-load and full-load voltages (ignoring phase angles). For capacitive (leading power factor) loads, the full-load voltage may have a higher magnitude than the no-load voltage, resulting in negative voltage regulation. Such a condition may lead to instability and is undesirable.
voltage regulator
similar to a voltage reference, but provides more output current at a less precisely controlled voltage. Primarily used to "clean up" (regulate) a varying input voltage to provide circuitry with a constant power supply voltage.