Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

magnetic monopole
a magnet system that produces a magnetic field of a single polarity. Although nonexistent, may be approximated by one pole of a very long magnet.
magnetic permeability tensor
relationship between the magnetic field vector and the magnetic flux density vector in a medium with no hysteresis; flux density divided by the magnetic field in scalar media.
magnetic polarization vector
an auxiliary vector in electromagnetics that accounts for the presence of atomic circulating currents in a material. Macroscopically, the magnetic polarization vector is equal to the average number of magnetic dipole moments per unit volume.
magnetic separator
a device employing magnetic fields to separate magnetic materials from nonmagnetic ones.
magnetic susceptibility
the ratio of the magnetization to the applied external field.

Tensor relationship between the magnetic field vector and the magnetization vector in a medium with no hysteresis; magnetization divided by the permeability of free space and the magnetic field in scalar media. It is an indicator of how easily a material is magnetized and has no units in the SI system of units (pure number).
magnetic suspension

See magnetic levitation
magnetic torque coupling
any device utilizing a magnetic field to transmit torque.
magnetic vector potential
an auxiliary field used to simplify electromagnetic computations. This field satisfies a wave equation, the curl of this field is related to the magnetic field intensity vector field, and the divergence of this field is specified by some gage which is to be specified in each problem.
magneto plasma
a plasma medium that in the presence of a static magnetic field behaves like an anisotropic dielectric medium whose dielectric function is a tensor.
magnetotransport
motion of electrons or holes in a conducting material in the presence of an applied magnetic field.
major hysteresis loop
for a magnetic material, the loop generated as intrinsic or magnetic induction (Bi or B) is plotted with respect to applied field (H) when the material is driven from positive saturation to negative saturation and back, showing the lag of induction with respect to applied field.
manually-controlled shunt capacitors
a bank of shunt capacitors that are controlled via SCADA signals from an operating center as opposed to local automatic control by voltage sensing.
maximum transducer power gain
maximum value of transducer power gain a circuit or device exhibits; occurs when the input and output ports of the circuit are terminated with simultaneous conjugate match conditions. The transducer power gain is defined as the ratio of power delivered to a load to the power available from the source.
momentary interruption
a loss of voltage of less than 0.1 pu for a time period of 0.5 cycles to 3 seconds.
momentary monitoring the duration at supply frequency from 30 cycles to 3 seconds.
motor circuit protector (MCP)
a listed combination motor controller containing an adjustable instantaneous-trip circuit breaker and coordinated motor overload protection. MCPs can provide short-circuit and bolted ground-fault protection via the circuit breaker magnetic element, overload protection via the overload device, motor control, and disconnecting means all in one assembly.
motor operated switch
a switch operated by a motor that is capable of being controlled from a remote location.
multiplex
(1) to use a single unit for multiple purposes, usually by time sharing or frequency sharing. multiplexer

(2) the armature winding of a commutated electrical machine in which multiple, identical coil windings are placed on the rotor. In general, the number of the "plex" describes the total number of parallel windings between brush positions and, thus, also the multiplier on the number of parallel paths between brushes that would be provided by a simplex winding. For example, a duplex winding will have twice as many parallel electrical paths between brushes as a simplex winding, a triplex winding will have three times the number of paths, etc. See simplex, duplex, reentrancy.
multiplexer
a combinational logic device with many input channels and usually one output, connecting one and only one input channel at a time to the output.
multiplexing
(1) the process of transmitting a large number of information units over a smaller number of channels or lines. For example, if we have N independent signals that we want to transmit, then without using a multiplexer we need N independent channels to do so. Using a multiplexer to control the flow of these signals in only one channel reduces the number of wires, thus decreasing cost and increasing efficiency. Multiplexing is the superimposition of multiple signals to make up one signal. This is done to make the transmission of the signals efficient. Signals are multiplexed at the sending end of communication systems, and demultiplexed at the receiving end, in order to obtain the original signals.

(2) of or being a communication system that can simultaneously transmit two or more messages on the same circuit or radio channel.
multispeed motor
a motor that can be operated at any one of two or more definite speeds. For DC and induction motors, the speed settings are practically independent of the load, although the speed may vary with load for certain types of motors. Multispeed induction motors typically have two or more sets of windings on the stator with a different number of poles, one of which is excited at any given time.
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