Areva MiCOM P441, Техническое руководство

Страница: 275 / 636

Application Notes P44x/EN AP/E33
MiCOM P441/P442 & P444 Page 101/220
3.1.10 Residual Compensation for Earth Fault Elements
The residual compensation factor can be applied independently to certain zones if required.
This feature is useful where line impedance characteristics change between sections or
where hybrid circuits are used. In this example, the line impedance characteristics do not
change and as such a common KZ0 factor can be applied to each zone. This is set as a
ratio “kZ0 Res. Comp”, and an angle “kZ0 Angle”:
kZ0 Res. Comp,

kZ0

= (Z
0
- Z
1
) / 3.Z
1
Ie: As a ratio.
kZ0 Angle,
∠
kZ0 =
∠
(Z
0
- Z
1
) / 3.Z
1
Set in degrees.
Z
L0
- Z
L1
= (0.426 + j1.576) - (0.089 + j0.476)
= 0.337 + j1.1
= 1.15 / 72.9
°
kZ0 =
1.15 / 72.9°
3 × 0.484 / 79.4°
= 0.79 / –6.5°
Therefore, select:
kZ0 Res. Comp = 0.79 (Set for kZ1, kZ2, kZp, kZ4).
kZ0 Angle = –6.5° (Set for kZ1, kZ2, kZp, kZ4).
3.1.11 Resistive Reach Calculations
All distance elements must avoid the heaviest system loading. Taking the 5A CT secondary
rating as a guide to the maximum load current, the minimum load impedance presented to
the relay would be:
Vn
(phase-neutral)
/ In = (115 /
√
3) / 5 = 13.3
Ω
(secondary)
Typically, phase fault distance zones would avoid the minimum load impedance by a margin
of
≥
40% if possible (bearing in mind that the power swing characteristic surrounds the
tripping zones), earth fault zones would use a
≥
20% margin. This allows maximum resistive
reaches of 7.9
Ω
, and 10.6
Ω
, respectively.
From Table 1 (see §2.4.4), taking a required primary resistive coverage of 14.5
Ω
for phase
faults, and assuming a typical earth fault coverage of 40
Ω
, the minimum secondary reaches
become:
RPh (min) = 14.5 x 0.12 = 1.74
Ω
(secondary);
RG (min) = 40 x 0.12 = 4.8
Ω
(secondary).
Resistive reaches could be chosen between the calculated values as shown in Table 10.
The zone 2 elements satisfy R2Ph
≤
(R3Ph x 80%), and R2G
≤
(R3G x 80%).
Minimum Maximum Zone 1 Zone 2 Zones 3 & 4
Phase (RPh)
Ω
1.74
7.9 R1Ph = 3 R1Ph = 4 R3Ph-4Ph = 8
Earth (RG)
Ω
4.8 10.6 R1G = 5 R1G = 6 R3G-4G = 10
TABLE 10 - SELECTION OF RESISTIVE REACHES
R3Ph-R4Ph should be set
≤
80% Z minimum load –
∆
R.