Rockwell Automation 1408-EMxx PowerMonitor 1000 Unit - Manual (Page 75)

PowerMonitor 1000 Unit 75
Rockwell Automation Publication 1408-IN001E-EN-P - September 2013
KYZ pulse. Contact closure generated utility revenue meters. Each pulse indicates the
consumption of a specific number of watts. These pulses can be used to measure energy
consumption and demand.
lagging current. The current flowing in an AC circuit that is mostly inductive. If a circuit
contains only inductance, the current lags the applied voltage by 90°. Lagging current means
lagging power.
leading current. The current flowing in a circuit which is mostly capacitive. If a circuit contains
only capacitance, the current leads the applied voltage by 90°. Leading current means leading
power factor.
load. Any device or circuit consuming power in an electrical system.
load shedding. The removal of load from the line-to-limit load and control demand level.
load restoring. The energizing of loads that were previously removed from the line-to-limit load
and control demand level.
neutral. The conductor chosen as the return path for the current from the load to the source. It is
also a voltage reference point in a power system.
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). A 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.
ratchet clause. A rate schedule clause that 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 11 months, although it can be for the life of the contract.