Power Calculation Algorithm

Presentation

The algorithms are given for both calculation methods (2 wattmeters and 3 wattmeters). The power definitions and calculation are given for a network with harmonics.

The MicroLogic E trip unit displays all the calculated quantities as follows:

On the MicroLogic trip unit display screen
Using the communication network
On the FDM121 display

With the 2-wattmeter calculation method, it is not possible to deliver power metering for each phase.

Input Data

The input data are the voltages and currents for each phase. For more information about calculating harmonics, see harmonic currents.

Using this data, the MicroLogic E trip unit calculates the various power ratings according to the sequence described below.

Active Powers

Metering on a 3-pole or 4-pole circuit breaker with ENVT option	Metering on a 3-pole circuit breaker without ENVT option
The active power for each phase and total active power is calculated.	Only the total active power can be calculated.
	–

P_W1 and P_W2 are the fictional powers calculated by the 2-wattmeter method.

Apparent Powers for Each Phase

Metering on a 3-pole or 4-pole circuit breaker with ENVT option	Metering on a 3-pole circuit breaker without ENVT option
The apparent power is calculated for each phase.	–
	–

Reactive Powers With Harmonics for Each Phase

Reactive power with harmonics is not physically significant.

Metering on a 3-pole or 4-pole circuit breaker with ENVT option	Metering on a 3-pole circuit breaker without ENVT option
The reactive power with harmonics is calculated for each phase.	–
	–

Reactive Powers

The reactive power of the fundamental corresponds to the physical reactive power.

Metering on a 3-pole or 4-pole circuit breaker with ENVT option	Metering on a 3-pole circuit breaker without ENVT option
The reactive power for each phase and total reactive power is calculated.	Only the total reactive power can be calculated.
	–

QfundW1 and QfundW2 are the fictional reactive powers calculated by the 2-wattmeter method.

Distortion Power

Distortion power is the quadratic difference between the reactive power with harmonics and the reactive power (fundamental).

Metering on a 3-pole or 4-pole circuit breaker with ENVT option	Metering on a 3-pole circuit breaker without ENVT option
The distortion power for each phase and the total distortion power is calculated.	Only the total distortion power can be calculated.
	–

Dw1 and Dw2 are the fictional powers calculated by the 2-wattmeter method.

Total Reactive Power (With Harmonics)

The total reactive power (with harmonics) is not physically significant.

Metering on a 3-pole or 4-pole circuit breaker with ENVT option	Metering on a 3-pole circuit breaker without ENVT option
The total reactive power is calculated.	The total reactive power is calculated.

Total Apparent Power

Metering on a 3-pole or 4-pole circuit breaker with ENVT option	Metering on a 3-pole circuit breaker without ENVT option
The total apparent power is calculated.	The total apparent power is calculated.