Rockwell Automation 1403-DM_LM_MM Powermonitor II Instruction Sheet - Manual (Page 83)

Glossary D-3
1403-IN001A-US-P
O
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.
P
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.
R
ratchet clause
A rate schedule clause which states that billing
demand may be based on current month peak
demand or on historical peak demand, depending on
relative magnitude. Usually the historical period is
the past eleven months, although it can be for the life
of the contract. Billing demand is either the current
month peak demand or some percentage (75 percent
is typical) of the highest historical peak demand.
Depending on which is largest. It is designed to
compensate the electric utility for maintaining
equipment not fully utilized.
reactance
The opposition to the flow of alternating current.
Capacitive reactance is the opposition offered by
capacitors and inductive reactance is the opposition
offered by an inductive load. Both reactances are
measured in ohms.
real power
The component of apparent power that represents
real work in an alternating current circuit. It is
expressed in watts and is equal to the apparent power
times the power factor.