Allen-Bradley 1404-M4, User Manual

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Publication 1404-UM001D-EN-E - October 2004
Glossary 21
ohm
The unit of electrical resistance. One ohm is the value of resistance
through which a potential difference of one volt will maintain a
current flow of one ampere.
peak demand
The highest average load over a utility specified time interval during a
billing period. If there is no ratchet clause in the rate schedule, then
the peak demand is also the billing demand.
polyphase
Having or utilizing several phases. A polyphase power circuit has
several (typically three) phases of alternating current with a fixed
phase angle between phases.
potential transformer (PT)
An transformer with the primary winding connected in parallel with
the circuit whose voltage is to be measured or controlled. PT’s are
normally used to step down high-voltage potentials to lower levels
acceptable to measuring instruments. Also known as voltage
transformer (VT).
potential transformer ratio
The ratio of primary voltage divided by secondary voltage.
power factor
The ratio of real power in watts of an alternating current circuit to the
apparent power in volt-amperes. Also expressed as the cosine of the
phase angle between the fundamental voltage applied to a load and
the current passing through it.
power factor correction
Steps taken to raise the power factor by closely aligning the current to
be in phase with the applied voltage. Most frequently this consists of
added capacitance to increase the lagging power factor of inductive
circuits.
power factor penalty
The charge utilities impose for operating at power factor below some
rate schedule-specified level. This level ranges from a lagging power
factor of 0.80 to unity. There are innumerable ways by which utilities
calculate power factor penalties.
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