76 PowerMonitor 1000 Unit
Rockwell Automation Publication 1408-IN001E-EN-P - September 2013
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.
resistance. The property of a substance that impedes current flow and results in the dissipation
of power in the form of heat. The unit of resistance is the ohm. One ohm is the resistance
through which a difference of potential of one volt will produce a current of one ampere.
revenue meter. A meter used by a utility to generate billing information. Many types of meters
fall in this category depending on the rate structure.
root mean square (rms). The effective value of alternating current or voltage. The rms values of
voltage and current can be used for the accurate computation of power in watts. The rms value is
the same value as if continuous direct current were applied to a pure resistance.
sliding-window demand interval. A method of calculating average demand by averaging the
average demand over several successive short time intervals, advancing one short-time interval
each time. Updating average demand at short-time intervals gives the utility a much better
measure of true demand and makes it difficult for you to obscure high short-term loads.
unbalanced load. A situation existing in a three-phase alternating current system using more
than two current carrying conductors where the current is not due to uneven loading of the
phases.
volt-ampere (VA). The unit of apparent power. It equals volts times amperes regardless of power
factor.
volt-ampere demand. Where peak average demand is measured in volt-amperes rather than
watts. The average VA during a predefined interval. The highest average, that is, Peak VA
demand, is sometimes used for billing.
voltage (V). The force that causes current to flow through a conductor. One volt equals the force
required to produce a current flow of one ampere through a resistance of one ohm.
watt (W). A measure of real power. The unit of electrical power required to do work at the rate
of one joule per second. It is the power expended when one ampere of direct current flows
through a resistance of one ohm. Equal to apparent power VA times the power factor.
watt demand. Power during a predetermined interval. The highest average, that is, Peak
demand, is commonly used for billing.
watt hour (Wh). The number of watts used in one hour. Since the power usage varies, it is
necessary to integrate this parameter over time. Power flow can be either forward or reverse.
wattmeter. An instrument for measuring the real power in an electric circuit. Its scale is usually
graduated in watts, kilowatts, or megawatts.
volt-ampere reactive hours (VARh). The number of VARs used in one hour. Since the value of
this parameter varies, it is necessary to integrate it over time. VARs can be forward or reverse.
