Power Metering (MicroLogic E)

Presentation

The MicroLogic E trip unit calculates the electrical quantities required for power management:

The instantaneous values of the:
- Active powers (total Ptot and per phase) in kW
- Reactive powers (total Qtot and per phase) in kVAR
- Apparent powers (total Stot and per phase) in kVA
- Fundamental reactive powers (total Qfundtot and per phase) in kVAR
- Distortion powers (total Dtot and per phase) in kVAR
The maximum and minimum values for each of these powers
The demand values and the peaks for the total Ptot, Qtot, and Stot powers
The cos ϕ and power factor (PF) indicators
The operating quadrant and type of load (leading or lagging)

All these electrical quantities are calculated in real time and their value updated once a second.

Principle of Power Metering

The MicroLogic E trip unit calculates the power values from the rms values of the currents and voltages.

The calculation principle is based on:

Definition of the powers
Algorithms depending on the type of trip unit (4-pole or 3-pole)
Definition of the power sign (circuit breaker powered from the top or bottom side)

Calculation Algorithm

The calculation algorithm, based on the definition of the powers, is explained in the specific topic.

Calculations use harmonics up to the fifteenth.

3-Pole Circuit Breaker, 4-Pole Circuit Breaker

The calculation algorithm depends on the presence or absence of voltage metering on the neutral conductor.

4-Pole or 3-pole with ENVT: 3-wattmeter method	3-Pole without ENVT: 2-wattmeter method

When there is voltage metering on the neutral (4-pole or 3-pole circuit breaker with ENVT option), the MicroLogic E trip unit measures the power by using three single-phase loads downstream.	When there is no voltage metering on the neutral (3-pole circuit breaker), the MicroLogic E trip unit measures the power: Using the current from two phases (I1 and I3) and composite voltages from each of these two phases in relation to the third (V12 and V23) Supposing (by definition) that the current in the neutral conductor is zero:
The calculated power Ptot equals:	To calculate power Ptot equals PW1 + PW2:

4-Pole or 3-pole with ENVT: 3-wattmeter method

3-Pole without ENVT: 2-wattmeter method

When there is voltage metering on the neutral (4-pole or 3-pole circuit breaker with ENVT option), the MicroLogic E trip unit measures the power by using three single-phase loads downstream.

When there is no voltage metering on the neutral (3-pole circuit breaker), the MicroLogic E trip unit measures the power:

Using the current from two phases (I1 and I3) and composite voltages from each of these two phases in relation to the third (V12 and V23)
Supposing (by definition) that the current in the neutral conductor is zero:

The calculated power Ptot equals:

To calculate power Ptot equals PW1 + PW2:

The following table lists the metering options:

Method	3-Pole circuit breaker, non-distributed neutral	3-Pole circuit breaker, distributed neutral	3-Pole circuit breaker, distributed neutral with ENVT option	4-Pole circuit breaker
2 wattmeters	✓	✓ ⁽¹⁾	–	–
3 wattmeters	–	–	✓	✓
(1) The measurement is incorrect once there is current circulating in the neutral.

3-Pole Circuit Breaker, Distributed Neutral

To activate the ENVT option on a 3-pole circuit breaker with distributed neutral, it is necessary to:

Connect the wire from the ENVT option to the neutral conductor.
Declare the ENVT option with EcoStruxure Power Commission software (password-protected) or by sending a setting command using the communication network (password-protected).

NOTE: Declaration of the ENCT option alone does not result in correct calculation of the powers. It is essential to connect the wire from the ENVT to the neutral conductor.

Power Sign and Operating Quadrant

By definition, the active powers are:

Signed + when they are consumed by the user, that is, when the device is acting as a receiver.
Signed - when they are supplied by the user, that is, when the device is acting as a generator.

By definition, the reactive powers are:

Have the same sign as the active energies and powers when the current lags behind the voltage, that is, when the device is inductive (lagging).
Have the opposite sign to the active energies and powers when the current is ahead of the voltage, that is, when the device is capacitive (leading).

These definitions therefore determine four operating quadrants (Q1, Q2, Q3, and Q4):

NOTE: The power values are:

Signed on the communication (for example, when reading the FDM121 display).
Not signed when reading the MicroLogic LCD display.

Top or Bottom-Side Connection to the Power Supply

ComPact NSX circuit breakers can be connected to the power supply from the top (standard, considered to be the default position) or from the bottom side: the sign for the power running through the circuit breaker depends on the type of connection.

NOTE: By default, the MicroLogic E trip unit signs as positive the powers running through the circuit breaker supplied from the top with loads connected from the bottom side.

Circuit breakers powered from the bottom side must have the powers signed as negative.

Modify the Power sign parameter:

With EcoStruxure Power Commission software (password-protected)
By sending a setting command using the communication network (password-protected)