Power-Apparent: Apparent power is the product of voltage and current in
a circuit in which voltage and current reach their peaks at different times.
In other words, there is a phase angle between the voltage and current.
Apparent power is measured in volt-amperes.
Power-Reactive: Reactive power, also called wattless power, is q easured
in terms of voltampere-reactive (VAR). Reactive power increases as power
factor decreases and is the component of apparent power that does no real work
in the system.
Power-Real: Real power is the component of apparent power that
represents true work in an alternating current circuit. It is expressed in
watts and is equal to apparent power times power factor.
Signal-Analog: An analog signal is a voltage or current signal that is a
continuous function of the measured parameter. Analog signals provide direct,
instantaneous information. It is most often used for onsite monitoring with
meters and pen chart recorders. If analog signals are to be transmitted over
long distances, the signal is generally converted into a numerical value
Signal-Digital: A digital signal (numerical display) is pulse generated
and discrete. Systems used for transmission are RS-232, 4-20 ma, and 1-10
Time-of-Use Charges: Many utilities adjust energy charges for the
time-of-day or time-of-year that energy is used. For time-of-day billing,
onpeak energy costs will be higher than midpeak and offpeak costs. Other
utilities have established winter and summer rates.
Volt (E or V):
Unit of electromotive force.
Unit of apparent power; EI (single phase); E x I x
Volt Amperes (VA):
1.73 (3 phase).
Watt (W): Unit of true or real power; VA x p-f.
3. ELECTRIC METERS AND BILLING . In charging for electric energy, utility
companies use three types of meters. These are demand, power factor, and
watthour meters. Total energy charges are obtained from a watthour meter,
power factor from a power factor meter, and demand values from a demand
meter. Typically, watthour and demand meters are combined.
3.1 Total Energy Charges. The total energy used on an installation is
recorded on watthour meters and is billed in kilowatthours. The greater the
wattage of electrical devices, the higher the charges for total energy. Any
method that reduces the time of operation or the power used by an electrical
device will result in decreased energy charges. Many manufacturers now
produce products that use significantly less energy, but perform essentially
the same tasks as higher powered equipment.