7SR18 Description Of Operation
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3.7 Current Protection: Negative Phase Sequence
Overcurrent - (46NPS)
The negative sequence phase (NPS) component of current (I2) is derived from the three phase currents. It is a
measure of the quantity of unbalanced current in the system.
Two NPS current elements are provided – 46IT and 46DT.
The 46IT element can be configured to be either definite time lag (DTL) or inverse definite minimum time (IDMT),
46IT Setting sets the pick-up current level for the element.
A number of shaped characteristics are provided. An inverse definite minimum time (IDMT) characteristic is
selected from IEC and ANSI curves using 46IT Char. A time multiplier is applied to the characteristic curves using
the 46IT Time Mult setting. Alternatively, a definite time lag delay (DTL) can be chosen using 46ITChar. When
Definite Time Lag (DTL) is selected the time multiplier is not applied and the 46IT Delay (DTL) setting is used
instead.
The 46IT Reset setting can apply a definite time delayed or ANSI (DECAYING) reset.
The 46DT element has a DTL characteristic. 46DT Setting sets the pick-up current and 46DT Delay the follower
time delay.
Operation of the negative phase sequence overcurrent elements can be inhibited from:
Inhibit 46IT A binary or virtual input.
Inhibit 46DT A binary or virtual input.
Figure 3.7-1 Logic Diagram: Negative Phase Sequence Overcurrent (46NPS)
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