10-17
IM 253710-01E
Numerical Computations
10
Explanation
Selecting the equation for apparent power
The apparent power, in the normal measurement mode, can be determined by the
product of the voltage and current. There are three types of voltages and currents
when measuring in the normal measurement mode. Select which voltage and current
to use to determine the apparent power from the following list of choices.
• Urms
∗
Irms
Determines the apparent power from the true rms values of voltage and current.
• Umean
∗
Imean
Determines the apparent power from the rectified mean value calibrated to the rms
value of the voltage and current.
• Udc
∗
Idc
Determines the apparent power from the simple average of the voltage and
current.
Setting the equation for corrected power
Depending on the applicable standard, when the load that is connected to the
potential transformer is extremely small, the active power of the potential transformer
that is measured needs to be compensated. In such case, set the compensating
equation and the coefficient. Corrected power (Pc) is a measurement function in the
normal measurement mode.
• Selecting the applicable standard
Select the standard from the following choices. The equation varies depending on
the selected standard.
• IEC76-1(1976), IEEE C57.12.90-1993
Equation
P
P
1
+ P
2
Urms
Umn
2
Pc =
Pc : Corrected Power
P : Active power
Urms : True rms voltage
Umn : Voltage (rectified mean value calibrated to the rms value)
P
1
, P
2
: Coefficient as defined in the applicable standard (see “Setting the
coefficient.”)
• IEC76-1(1993)
Equation
Umn – Urms
Umn
1 +
Pc = P
Pc : Corrected Power
P : Active power
Urms : True rms voltage
Umn : Voltage (rectified mean value calibrated to the rms value)
• Setting the coefficient
Set coefficients P1 and P2.
Set the coefficients in the range from 0.0001 to 9.9999.
Note
The equations of apparent power and corrected power are applied to measurement functions
in the normal measurement mode.
10.4 Setting the Equations for Apparent Power and Corrected Power