a) Wh Measurement
The active energy (Wh) measurements are carried out on 3-phase, 4-wire principle with an
accuracy as per class 0.2S of IEC-687/IEC-62053-22. The meter computes the net active energy
(Wh) in each successive 15-minutes block and stores it in its non-volatile memory along with plus/
minus sign. The 15-minute Wh shall have a +ve sign when there is a net Wh export and a –ve sign
when there is a net Wh import. Cumulative Wh reading at each midnight shall be stored in the
meters memory along with plus/ minus sign. The meter shall store all data in its memories for a
period of ten (10) days. The data older than ten (10) days shall get erased automatically.
b) VARh Measurement
The meter shall also compute the reactive power (VAR) on a 3-phase 4- wire principle with an
accuracy as per class 0.2S of IEC-687/IEC-62053-23. There shall be two reactive energy registers,
one for the period when average RMS voltage is above 103% and the other for the period the
voltage is below 97%. The registers will move forward when there is VARh export and will move
backward when there is VARh import.
c) Average Frequency
The meter shall count the number of cycles in VT output during each successive 15-minute block
and divide the same by 900 (15*60=900) to arrive at the average frequency. The average frequency
is stored in meter’s memory in 2- digit code neglecting decimals. In case the average frequency is
less than 49.0Hz, it is recorded as 00 and in case it is 51.0Hz or higher it is recorded as 99. The
actual frequency corresponding to two consecutive codes differ by 0.02Hz.
1.1.5 Operating Section of the Meter
a) Analog Section: High precision Current transformer and voltage transformer step down input
currents and voltages which are fed to an Analog to Digital converter.
b) Digital Section: A powerful microprocessor controls the Analog and Digital sections. Analog to
Digital converters are fed from high precision instrument transformers. The Digital samples from
Analog to Digital converter are used to process the metering data. The sampling rate is 3000
samples per second which gives the meter an exceptional accuracy and results.
c) Power supply Section: A switch mode power supply (SMPs) unit supplies power to the meter’s
internal circuit.
1.1.6 Display Parameters
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Special Energy Meters have the facility to display the following parameters: