Specifications

PowerLogic:
Glossary of terms
69
Partial interval demand
Calculation of energy thus far in a present interval. Equal
to energy accumulated this far in the interval divided by
the length of the complete interval.
Peak demand current
Highest demand current measured in amperes since the
last reset of demand. See also peak value.
Peak demand real power
Highest demand real power measured since the last rest
of demand.
Peak demand voltage
Highest demand voltage measured since the last reset of
demand voltage. See also peak value.
Peak demand
Highest demand measured since the last reset of peak
demand.
Peak value
Of voltage or current is the maximum or minimum crest
value of a waveform.
Phase notation
Symbolic representation of the phases of a three phase
supply A, B, C commonly used is USA. L1, L2, L3 used
elsewhere R,Y,B currently used in the UK.
Phase rotation
Phase rotation refers to the order in which the
instantaneous value of the voltages or currents of the
system reach their maximum positive values. Two phase
rotations are possible: A-BC or A-C-B.
Power and energy
Power is the rate at which energy is being used. The SI
units of power are watts (W) and the units of energy are
joules (J) Energy = Power x Time Power factor The
power factor is the cosine of the phase angle between
the current and the voltage.
Power Factor = Active Power
Apparent Power
Potential transformer (PT)
Also known as a voltage transformer.
Meter scaling
A meter is required to measure electricity, which is being
supplied at a wide range of voltage and current. It is
impractical to connect a meter directly to either high
voltages or high currents, so the meter must be able to
scale what it actually measures and indicate a time
reading.
Predicted demand
A circuit monitor takes into account the energy
consumption thus far in the present interval and the
present rate of consumption to predict demand power at
the end of the present interval.
Pulse input and output
A meter has the ability to produce output pulses and to
sense input pulses. Both inputs and outputs are normally
operated through relays. Outputs are often linked to one
of the metered parameters, so that a pulse is produced
for a given increase in the value in a register. Inputs are
often used to synchronise the meter to some external
timing device.
Reactive current and power
The out-of-phase component of the current supplies no
useable energy. This component is produced by the
reactance (inductance or capacitance) of the load. The
power is the product of the voltage and the out-of-phase
current Reactive power (VAr) = Voltage (V) x Out-of-
phase current (A).
Real power
Useable power (kW).
R.M.S
This is the effective value or equivalent d.c. value of the
voltage or current. Circuit monitors are true r.m.s.
sensing devices.
Synchronised demand
Demand intervals in a meter that can be synchronised
with another device using an external pulse, a command
sent over communications, or the meter’s internal real-
time clock.
STOD
Many tariffs operate using Seasonal Time of Day (STOD).
This means that they operate according to the current
time of day, which will change from one season to
another with the operation of Daylight Saving Time (DST).
In the UK this means that the time will be GMT in the
winter and BST in the summer. The alternative is that the
meter operates to a fixed time reference, such as GMT,
all the year round.
TCP/IP
Transmission control protocol/internet protocol.
Tariff
A tariff defines the way in which a customer will be
charged. Most primary meters allow a tariff to be
downloaded.
Total current and apparent power
The apparent power is the product of the voltage and the
total current and has the units of volt-amperes. As the
total current comprises an active and a reactive
component so does the apparent power. The total
current determines the size of the conductors needed to
supply the electricity.
Apparent power (VA) = Voltage (V) x Total current (A).
Total harmonic distortion (THD or thd)
This is a quick measure of the total distortion present in
a waveform. It provides a general indication of the quality
of a waveform. IEEE519 & EN 50160 use the
abbreviation THD and define the value as a function of
the fundamental. An alternative method, found in use in
Europe, uses the abbreviation thd and defines the value
as a function of the r.m.s. of the waveform.
Transient
Sudden change in the steady-state condition of voltage
or current.
UL
Underwriters Laboratories, USA approvals authority.
Undervoltage
Decrease in effective voltage to less than 90% for longer
than one minute. See also voltage sag.
Voltage interruption
Complete loss of power where no voltage remains in the
circuit.(compare with undervoltage and sag).
Voltage sag
A brief decrease in effective voltage lasting less than one
minute.
Voltage swell
Increase in effective voltage for up to one minute in
duration. See also over voltage.
Voltage transformer (VT)
A transformer used to convert voltage in a circuit to a
measureable value, usually 110V or 230V.