88
ML0047 December 1, 2017 Copyright 2017 Bitronics, LLC
5.5 Power Factor
The per-phase Power Factor measurement is calculated using the "Power Triangle",
or the per-phase WATTS divided by the per-phase VAs. The Total PF is similar, but
uses the Total WATTS and Total VAs instead. The sign convention for Power Factor
is shown in Figure 12.
5.6 Watts / Volt-Amperes (VAs) / VARs (Uncompensated)
On any power connection type (2, 2½, and 3 element), the PPX II calculates per-element
Watts by multiplying the voltage and current samples of that element together. This
represents the dot product of the voltage and current vectors, or the true Watts. The
per-element VAs are calculated from the product of the per-element Volts and Amps.
The per-element VARs are calculated from fundamental VARs.
In any connection type, the Total Watts and Total VARs is the arithmetic sum of the
per-element Watts and VARs. The sign conventions are shown in Figure 12.
When used on 2-element systems, the reference phase voltage (typically phase B)
input, is connected to the Neutral voltage input, and effectively causes one of the
elements to be zero. It is not required to use any particular voltage phase as the
reference on 2-element systems. When used on 2-element systems the per-
element Watts, VARs, and VAs have no direct physical meaning, as they would
on 2½ and 3 element systems where they represent the per-phase Watts, VARs, and
VAs.
When used on 2½ element systems, one of the phase-to-neutral voltages is
fabricated, as described in Section 5.3. In all other respects, the 2½ element
connection is identical to the 3 element connection.
5.6.1 Geometric VA Calculations
22
TOTAL TOTAL TOTAL
GEOMETRIC VA Watts VARs
This is the traditional definition of Total VAs for WYE or DELTA systems, and is the
default method for Total VAs calculation. The value of Total VAs calculated using this
method does not change on systems with amplitude imbalance, relative to a balanced
system.
There is also a relationship to the Total Power Factor, which is described in Section
5.4. Total Power Factor calculations using the Geometric VA method will still indicate
a "1" on a system with phase amplitude imbalance, or canceling leading and lagging
loads.
To Next Page
Loading...