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Commonly used terms in the Electrical industry.
out-of-step
an abnormal condition when generators in a power system cannot operate in synchronism.
out-of-step relay
a protective relay that senses that a synchronous generator has pulled out of step, and is operating at a frequency different than the system frequency.
output impedance
the ratio of the drop in voltage to the current drawn is known as the output impedance of the electric source and is measured in units of ohms.
output power
(1) the difference in the power available under perfectly matched conditions and the reflected power taking the output return loss into account, expressed in watts.
(2) in lasers, the useful output from a laser oscillator.
over-compounded
a compound DC generator in which the terminal voltage increases as load current increases. Extra turns are added in the series winding to generate the additional voltage after compensating for the armature voltage drop and the armature resistance drop.
overcurrent protection
(1) the act of protecting electrical and electronic devices or circuits from a dangerous amount of input current.
(2) the effect of a device operative on excessive current.
overlap angle
See
commutation angle
overload protection
a protective device which opens the circuit to a piece of electrical equipment or power line in the event of current exceeding the upper design limit.
phase
(1) a notion used extensively in interpreting complex quantities such as Fourier series, Fourier transforms etc. Given a complex number
c = x+iy = r cos θ + ir sin θ
, then r represents the magnitude of c and the phase.
(2) a horizontal translation parameter of the signal. Given a sinusoidal signal
s(t) = Asin(2πft + θ)
, then
f
represents the frequency (in Hz) of
s
and
θ
the phase.
P
commonly used symbol for power in watts or milliwatts.
P
DC
common symbol for DC power in watts.
P
input
common symbol for power input to a device in watts.
P
load
common symbol for power delivered to the load.
P
ref
common symbol for power reference level in watts or milliwatts.
pad
(1) a device (network) that impedance matches and/or attenuates. Typically used to refer to a coax attenuator.
(2) a concrete foundation, usually prefabricated and used to support power transformers in underground residential distribution work.
pad-mount transformer
a heavily-enclosed distribution transformer mounted at grade level upon a concrete slab or pad.
panelboard
an assembly of one or more panel units containing power buses, automatic overcurrent protective devices, that is placed in a cabinet or cutout box located in or flush on a wall. The assembly can only be accessed from the front and may contain switches for operation of light, heat, or power circuits.
See
switchboard
parallel paths
the number of separate paths through the armature winding that exist between the brushes of a DC machine.
In a DC machine's armature, the conductors and coils are placed in their slots and connected to the commutator using either the lap winding method or the wave winding method. The number of conductors that are connected in parallel depend on the number of poles the machine has, and whether the winding connections are lap or wave. For the lap wound armature, the number of parallel paths is found by multiplying the number of poles by the number of revolutions it takes to
fill all the slots of the armature. The number of revolutions it takes to fill the slots is known as the machine's "plex" value. In a simplex wound armature, the "plex" value is 1, duplex has a "plex" value of 2, triplex has a "plex" value of 3, and so on. For the wave wound armature, the number of parallel paths is two times the "plex" value. This same concept
can also be applied to AC machinery.
parasitic capacitance
the generally undesirable and not-designed-for capacitance between two conductors in proximity of one another.
parasitic inductance
the generally undesirable and not-designed-for inductance associated with a conductor, or path of current on a conductor.