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7SR18 Description Of Operation
Unrestricted ©2018 Siemens Protection Devices Limited
Page 45 of 78
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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