Using The 3-Watt Element (3 Ct) Method On A 3-Wire Delta Service - Dent ELITEpro XC Operator's Manual

Configure the Setup Table as follows:
U T 3-W E
SING HE ATT LEMENT
Using the two watt element method on 3-phase 3-wire Delta services is a perfectly valid measurement
technique. The 2-element method also uses less logger memory and hardware channels and allows
measuring two Delta (3-wire) loads simultaneously. However, we recommend using the 3-watt element
method because the 3-element method is more intuitive. By placing a CT on each phase wire, it is easier
to understand what is happening in each phase without referring to phasor diagrams.
In 2-element measurements, System VA is calculated from Watts and VARs using the power triangle. In
3-element measurements, System VA is calculated as the sum of the VAs from the individual phases.
Both methods are completely valid.
The major difference is how harmonics are treated. When harmonics exist, they are usually only (or
mostly) present in the current and not in the voltage. Because watts and VARs are calculated as the
instantaneous product of volts and amps and because an existing third or fifth harmonic current does
not have a corresponding voltage harmonic, then the harmonics' products are zero. Therefore, the
instantaneous product of volts and amps used to obtain watts and VARs does not include any harmonic
component. Thus, the 2-element method does not include any harmonic content in the calculation of
System VA. In 3-element systems, because System VA is calculated as the sum of the phase VAs, which
in turn are the product of the RMS volts multiplied by the RMS amps, then harmonics are included (in
the RMS amps).
There are two methods to calculate Power Factor. One is Apparent Power Factor PF=W/VA where VA=
Volts X Amps and VA would contain harmonic content. The other is Displacement Power Factor that
uses the Power triangle PF=W/SQRT (W^2 + VAR^2) which does not contain harmonic content. The
ELITEpro XC displays and records displacement Power Factor.
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ELITEpro
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