Micom P721, Technical Manual

Page: 186 / 334

P72x/EN AP/C21 Application Guide
Page 50/52 MiCOM P721/P723
13.1 Restricted earth fault/Balanced earth fault (REF/BEF) applications
The operating characteristics shown in FIGURE 35, FIGURE 36 and FIGURE 37 are valid
when
5
≤
X/R
≤
120, 0.5
≤
I f
≤
20, [87N] Threshold I Diff = 0.1In and [87] Fault timer tDiff = 0 s.
FIGURE 35 shows the CT requirements when the P72x is used in a REF/BEF application
and the Measurement Mode is set to Fourier. When V
K
/V
S
is 4, the average operating time
is 40 ms and K is approximately 0.8. The user should consider these characteristics when
selecting Vk/Vs, K factor and average operating time as has been explained in the previous
setting examples.
NOTE: For the P721 and the P723 (current inputs 55-56 and 47-48), the maximum internal
fault level threshold (for the 0.004 to 2In range) must not exceed 20In.
FIGURE 35 shows the CT requirements when the P72x is used in a REF/BEF application
and the Measurement Mode is set to Fourier. The maximum K factor is approximately 0.98.
The operating time when V
K
/V
S
= 4 is 41 ms and K is approximately 0.76.
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1.00
1.10
0 2 4 6 8 10 12 14 16
Vk/Vs
K
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
av
er
ag
e
o
p
.
ti
m
e
(
s)
K average op. time
stable
unstable
FIGURE 35: CT REQUIREMENTS- REF/BEF- FOURIER MODE
FIGURE 36 shows the CT requirements when the P72x is used in a REF/BEF application
and the Measurement Mode is set to Fast Sample. The maximum K factor is approximately
0.91. The operating time when V
K
/V
S
= 4 is 41 ms and K is approximately 0.76.
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1.00
0 2 4 6 8 10 12 14 16
Vk/Vs
K
0
0.01
0.02
0.03
0.04
0.05
0.06
aver
ag
e
o
p
. t
im
e
(
s
)
K average op. time
stable
unstable
FIGURE 36: CT REQUIREMENTS- REF/BEF- FAST SAMPLE MODE