Real-Time Measurements

Instantaneous Values

MicroLogic trip units:

• Measure the following in real time and as an rms value:

  • Instantaneous current for each phase and the neutral (if present)

  • Ground-fault current (MicroLogic 6 trip unit)

  • Earth-leakage (residual) current (MicroLogic 7 trip unit)

• Calculate the average phase current in real time

• Determine the maximum and minimum values for these electrical quantities (phase, neutral, ground, and residual currents)

• Measure the instantaneous phase-to-phase and phase-to-neutral voltage (if present), in real time and as an rms value

• Calculate the associated electrical quantities from the rms values of the currents and voltages:

  • Average phase-to-phase voltage and phase-to-neutral voltage (if present)

  • Current unbalances

  • Phase-to-phase voltage unbalances and phase-to-neutral voltage unbalances (if present)

  • Powers

  • Quality indicators: frequency, THD(I) and THD(V), and power factor PF and cos ϕ measurement

• Display operating indicators: quadrants, phase rotation, and type of load

• Determine the maximum and minimum values for these electrical quantities

• Increment in real time, three energy meters (active, reactive, apparent) using the total power real-time values

The sampling method utilizes the values of the harmonic currents and voltages up to the fifteenth order. The sampling period is 512 microseconds.

The values of the electrical quantities, whether measured or calculated in real time, update once a second.

Setting of the Phase Rotation (MicroLogic 5 and 6 Trip Units)

Phase currents are assigned by default to the poles as follows:

• I1: left pole

• I2: middle pole

• I3: right pole

If the phases connected to the poles do not correspond to the default assignment, you can modify the phase rotation setting in MicroLogic 5 and 6 trip units as follows:

• I3: left pole

• I2: middle pole

• I1: right pole

• With EcoStruxure Power Commission software (password-protected).

• By sending a setting command using the communication network (password-protected).

Measuring the Neutral Current

MicroLogic 4-pole or 3-pole trip units with the ENCT option measure the neutral current:

• For a 3-pole trip unit, the neutral current is measured by adding a special current transformer on the neutral conductor for the transformer information, refer to LVPED221001EN ComPacT NSX & NSXm Catalogue.

• For a 4-pole trip unit, the neutral current is measured systematically.

The neutral current is measured in the same way as the phase currents.

Measuring the Ground-Fault Current

The ground-fault current is calculated using the phase currents, according to the circuit breaker configuration, as shown in the following table.

Measuring the Earth-Leakage Current (MicroLogic 7 Trip Unit)

The earth-leakage current is measured by an embedded sensor encompassing the three phases or the three phases and neutral.

Measuring the Phase-to-Neutral Voltages

MicroLogic 4-pole trip units or 3-pole trip units with the ENVT option (MicroLogic 5 and 6 trip units) measure the phase-to-neutral (or line-to-neutral) voltages V1N, V2N, and V3N:

• For a 3-pole trip unit, 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: The ENVT option cannot be configured on a MicroLogic 7 trip unit.

• For 4-pole trip units, the phase-to-neutral voltages are measured systematically.

The phase-to-neutral voltages are measured in the same way as the phase-to-phase voltages.

Calculating the Average Current and Average Voltage

MicroLogic trip units calculate the:

• Average current Iavg, the arithmetic mean of the 3 phase currents:

  

• Average voltages:

  • Phase-to-phase Vavg, the arithmetic mean of the 3 phase-to-phase voltages:

    

  • Phase-to-neutral Vavg, the arithmetic mean of the 3 phase-to-neutral voltages (4-pole trip unit or 3-pole trip unit with the ENVT option (MicroLogic 5 or 6 trip unit)):

    

Measuring the Current and Voltage Phase Unbalances

MicroLogic trip units calculate the current unbalance for each phase (3 values).

The current unbalance is a percentage of the average current:

MicroLogic trip units calculate the:

• Phase-to-phase voltage unbalance for each phase (3 values)

• Phase-to-neutral (if present) voltage unbalance for each phase (3 values)

The voltage unbalance is expressed as a percentage compared to the average value of the electrical quantity (Vavg):

Maximum/Minimum Values

The MicroLogic trip unit determines in real time the maximum (MAX) and minimum (MIN) value reached by the following electrical quantities organized in groups for the current period:

• Current: Phase, neutral and residual currents, average currents and current unbalances

• Voltage: Phase-to-phase and phase-to-neutral voltages, average voltages, and voltage unbalances

• Power: Total power and power for each phase (active, reactive, apparent, and distortion)

• Total harmonic distortion: the total harmonic distortion THD for both current and voltage

• Frequency

• The maximum values (MAXMAX) of all phase currents and the minimum values (MINMIN) of all phase currents.

The current period for a group starts at the last reset of one of the maximum values in the group (see the following information).

Resetting Maximum/Minimum Values

Reset the maximum and minimum values for a group:

• By sending a reset command using the communication network (password-protected)

• On the FDM121 display (password-protected)

Reset the maximum and minimum values in a group on the keypad using the menu for the following groups:

• Currents

• Voltages

• Powers

Only the maximum values are displayed, but both the maximum and minimum values are reset.