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Dictionary of Electrical Engineering
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Commonly used terms in the Electrical industry.
MHz
egahertz, or millions of operations per second.
negative-positive-zero (NPO)
an ultra-stable temperature coefficient (@ 30 ppm/
O
C from -55
O
C to 125
O
C) temperature-compensating capacitor.
NEMA size
a standard-size device, such as a motor controller. The NEMA size establishes the rating of the device.
See
National Electrical Manufacturers Association
normal demagnetization curve
the second quadrant portion of the hysteresis loop generated when magnetic induction (B)is plotted against applied field (H ), which is mathematically related to the intrinsic curve; used to determine the performance of a magnet in a magnetic circuit.
polarization
(1) the shape traced out by the tip of the electric field vector as a function of time and the sense in which it is shaped.
(2) a description of the form of the temporal variation of the electric field vector of a light field. In general, the polarization state can be described by the ellipse that tip of the electric field vector traces each optical cycle.
Commonly encountered limiting forms are linear polarization and circular polarization.
(3) the response of material systems, an applied light field by developing a time varying dipole moment. The response is described quantitatively in terms of the dipole moment per unit volume, which is known as the polarization vector.
(4) description of the direction and motion of the electric field vector of a wave. Plane waves may be linearly or elliptically (including circularly) polarized. polarization controller a device that alters only the polarization state of the incident light.
power system stabilizer
a control device that provides an additional input signal to the AVR to damp power system oscillations.
right hand circular polarization
the state of an electromagnetic wave in which the electric field vector rotates clockwise when viewed in the direction of propagation of the wave.
saturation magnetization
the magnetic moment per unit volume of a material when the magnetization in the sample is aligned (saturated) by a large magnetic field.
saturation polarization
the value to which the externally measured electrical dipole moment of a ferroelectric body tends when subjected to an external electrical field greater than the coercive field.
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.
self-demagnetizing field
a field inside of a permanent magnet that is opposed to its own magnetization, which is due to internal coupling of its poles following the introduction of an air gap in the magnetic circuit.
synchronization
(1) a situation when two or more processes coordinate their activities based upon a condition.
(2) the process of determining (usually channel) parameters from a received signal, for example carrier frequency offset, carrier phase, or symbol timing.
synchronizing coefficient
electrical torque component in phase with the rotor angle.
synchronizing relay
a relay that monitors the voltage across an open circuit breaker to determine the frequency and phase relationship of the voltage sources on either side of the breaker. Synchronizing relays are used on generator breakers to bring the generator to the system frequency and to match the phase angle between the generator and system prior to closing the breaker.
terahertz (THz)
a frequency unit, 10
12
hertz.
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.
two-lamp synchronizing
the process to connect two three-phase power systems in parallel using the same procedure as for three-lamp synchronizing except that lamps are placed across only two phases of the switch. See also three-lamp synchronizing.
utilization factor
the ratio of the maximum demand on the system vs the rated capacity of the system.