SEF protection can follow the same IDMT characteristics as described in the Overcurrent Protection Principles
section. Please r
efer to this section for details of IDMT characteristics.
8.3 EPATR B CURVE
The EPATR B curve is commonly used for time-delayed Sensitive Earth Fault protection in certain markets. This
cur
ve is only available in the Sensitive Earth Fault protection stages 1 and 2. It is based on primary current settings,
employing a SEF CT ratio of 100:1 A.
The EPATR_B curve has 3 separate segments defined in terms of the primary current. It is defined as follows:
Segment Primary Current Range Based on 100A:1A CT Ratio Current/Time Characteristic
1 ISEF = 0.5A to 6.0A t = 432 x TMS/ISEF 0.655 secs
2 ISEF = 6.0A to 200A t = 800 x TMS/ISEF secs
3 ISEF above 200A t = 4 x TMS secs
where TMS (time multiplier setting) is 0.025 - 1.2 in steps of 0.025.
EPATR Curve
1
10
100
1000
0.1 1 10 100 1000
Current in Primary A (CT Ratio 100A/1A)
T
i
m
e
i
n
S
e
c
s
V00616
Figure 57: EPATR B characteristic shown for TMS = 1.0
Not
e:
SEF CT ratios are user settable.
8.4 DIRECTIONAL ELEMENT
Where current may flow in either direction, directional control should be used.
A dir
ectional element is available for all of the SEF overcurrent stages. This is found in the ISEF>(n) Direction cell for
the relevant stage. It can be set to non-directional, directional forward, or directional reverse.
P24xM Chapter 6 - Current Protection Functions
P24xM-TM-EN-2.1 131
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