YOKOGAWA WT500 User Manual page 43

2.5 Computation
Phase Difference (See section 5.5 for operating instructions)
User-Defined Functions (See section 5.13 for operating instructions)
MAX Hold (See section 5.14 for operating instructions)
Setting the Average Active Power (See section 5.15 for operating instructions)
2-20
Type 2
The apparent power of each phase is determined from equation 3, and the results are
added to derive the three-phase apparent power. The three-phase reactive power is
calculated from the three-phase apparent power and the three-phase active power using
equation 4.
Active power for a three-phase, four-wire system
Apparent power for a three-phase, four-wire system
Reactive power for a three-phase, four-wire system
Type 3 (The method used in the harmonic measurement mode of the
WT1600, the PZ4000, and the WT3000)
The reactive power of each phase is calculated directly using equation 2. The three-
phase apparent power is calculated using equation 4. This equation can be selected on
models with the harmonic measurement option.
Active power for a three-phase, four-wire system
Apparent power for a three-phase, four-wire system
Reactive power for three-phase, four-wire system
You can select the format for displaying the voltage and current phase differences
between and within each element. With the voltage of each element as a reference, one
format displays the phase difference using 360° in the clockwise direction, and the other
format displays lead up to 180° in the counterclockwise direction (D) and lag up to 180°
in the clockwise direction (G). In harmonic measurement (optional), the phase differences
between harmonics 1 to 50 of the voltage and current signals are displayed using a 360°
format or a 180° format with no sign for lead and a negative sign for lag.
Equations can be created (defined) by combining the measurement function symbols and
operators. The numeric data that corresponds to the equation can then be determined.
The combination of a measurement function and an element number, "Urms1:URMS(E1)"
for example, constitutes an operand. Eight equations (F1 through F8) can be defined.
Operators
There are 11 operators: +, –, *, /, ABS (absolute value), SQR (square), SQRT (square
root), LOG (logarithm), LOG10 (common logarithm), EXP (exponent), and NEG (negation).
Number of Operands
There can be up to 16 operands in one equation.
The maximum value of a type of numeric data can be held. The measurement functions
that the MAX hold is applied to are selected from the user-defined functions.
The average active power can be computed for devices, such as intermittent control
devices, whose power fluctuates. The equation for computing the average active power
is specified using a user-defined function.
PΣ = P1 + P2 + P3
SΣ = S1 + S2 + S3( = U1×I1 +
U2 × I2 + U3 × I3)
S 2 – P 2
Q =
PΣ = P1 + P2 + P3
P 2 + Q 2
S =
QΣ = Q1 + Q2 + Q3
IM 760201-01E