1
1
1
3
3
Ph-Ph
145 kV
22 kV
ANSI11000124-1-en.vsd
REC650
Y
Y
Y
51_67
ANSI11000124 V1 EN
Figure 8:
Fault calculation for phase overcurrent protection
A phase-phase-ground short circuit is applied. In this calculation the short circuit power
of the feeder shall be minimized (the source impedance maximized).
1.
Set
Pickup2
to
140 %
of
IBase
2205 A primary current.
The longest 22 kV feeder has an impedance of Z = 3 + j10 Ω. The external network
has a maximum source impedance of Zsc = j10 Ω (145 kV level). This impedance is
transformed to the 22 kV level:
2
,22
22
10
0.23
145
sc
Z
j
j
æ
ö
=
×
=
W
ç
÷
è
ø
GUID-BA67F1FC-2DCE-4E04-BBB3-FABB86FDEA3A V1 EN
(Equation 11)
The transformer impedance, referred to 22 kV level is:
The phase-to-phase fault current can be calculated as follows:
2
3
22000 / 3
949
2
0.23
0.97 3
10
sc ph
I
A
j
j
j
=
×
=
+
+ +
GUID-BAA8989B-EF8F-4277-9B2B-EBBCA35ED7C2 V1 EN
(Equation 12)
This current is smaller than the required minimum setting to avoid unwanted trip at
large load current. This means that the 22 kV phase overcurrent protection cannot
serve as complete back-up protection for the outgoing 22 kV feeders.
2.
Set
TD4
to
0.15
The feeder short circuit protections has the following setting:
I>: 300 A.
I>>: 6 000 A.
Characteristic: IEC Normal Inverse with k-factor = 0.25
The setting of the k-factor for the 22 kV phase overcurrent protection is derived from
graphical study of the inverse time curves. It is required that the smallest time
1MRK 511 286-UUS A
Section 3
REC650 setting examples
49
Application manual
Summary of Contents for REC650 ANSI
Page 1: ...Relion 650 series Bay control REC650 ANSI Application manual...
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Page 66: ...Section 3 1MRK 511 286 UUS A REC650 setting examples 60 Application manual...
Page 71: ...IED IED ANSI05000460 V2 EN 1MRK 511 286 UUS A Section 4 Analog inputs 65 Application manual...
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