ABB Relion 670 series - Page 270

Where:
I
G
ground current of faulty line
I
GP
is ground current of the parallel line
Z
1
is line positive sequence impedance
K
N
is earth compensation factor for single circuit set at the relay given by
equation
Z
0m
is the zero sequence mutual coupling between the faulted and the
parallel line
0 1
1
3
N
Z Z
K
Z
=
-
×
IECEQUATION14005 V1 EN (Equation 167)
K
Z
Z
Nm
m
=
⋅
0
1
3
IEC13000297 V1 EN (Equation 168)
From the above it can be deduced:
• Error is proportional to the mutual coupling factor K
0m
• The error increases with the parallel line ground current in relation to the relay current
• The relay underreaches when I
GP
is in phase with I
ph
+ K
N .
I
G .
For a remote end terminal fault, this underreaching effect can be as high as 25%.
The distance protection zone reaches vary with the switching state of the parallel line
configuration. We consider the three most common operation modes:
1. Case 1: Parallel line out of service and earthed at both ends
2. Case 2: Parallel line switched off and not earthed or earthed only at one line end
3. Case 3: Both lines in service.
The reach of the distance protection zone 1 will be different depending on the operation
condition of the parallel line.
Compensation of the mutual zero sequence impedance of parallel circuit can be achieved
by appropriate selection of zero-sequence compensation factor K
N
when parallel line can
be in service, out of service, or out of service and grounded at both ends.
Five zone distance protection, mho characteristic function (ZMHPDIS) can compensate
for the influence of a zero sequence mutual coupling on the measurement at single phase-
to-ground faults in the following two ways, by using:
Section 8 1MRK 506 369-UUS -
Impedance protection
264 Line distance protection REL670 2.2 ANSI
Application manual