Additional Current Protection Functions

Operating Principle

• For protection tripped by a maximum value, it is possible to set

  • A pickup threshold (1) that activates an alarm, a contact and/or tripping.

  • A pickup time delay (2) that steps in when the pickup threshold (1) is reached.

  • A dropout threshold (3) corresponding to deactivation of the alarm and/or contact.

  • A dropout time delay (4) that steps in when the dropout threshold (3) is reached.

• The dropout threshold is always less than or equal to the pickup threshold.

Ground-Fault Alarm I

• The ground-fault alarm function uses the rms value of the ground-fault current.

  NOTE: On MicroLogic 7.0 trip units, the alarm is called earth-leakage alarm, and uses the earth-leakage current.

• This alarm signals a ground-fault or earth-leakage current above the pickup value and does not trip the circuit-breaker.

Current-Unbalance Protection I unbal

This protection is activated by an adjustable level of unbalance between the rms values of the three phase currents.

This function calculates the rms value of the unbalance between the three phase currents.

I unbal = |E max|/I avg

Where:

• I avg is the average value of the rms currents of the three phases

  I avg = (I1 + I2 + I3)/3.

• E max is the maximum difference between the current of each phase and I avg.

Maximum-Current Protection Per Phase Imax

• Protection values may be set for each of the following currents:

  • I1 max: maximum current on phase 1

  • I2 max: maximum current on phase 2

  • I3 max: maximum current on phase 3

  • IN max: maximum current in the neutral

• This function calculates the rms demand value of the current for the given phase (I1, I2, I3) or the neutral (IN), over a sliding time interval.

  The time interval is the same as that for the calculation of the demand currents in the Metering menu.

  Settings are made in the Metering setup menu.