ABB RELION 670 SERIES Applications Manual page 270

Section 8
Impedance protection
264
Where:
I ground current of faulty line
G
I is ground current of the parallel line
GP
Z is line positive sequence impedance
1
K is earth compensation factor for single circuit set at the relay given by
N
equation
Z is the zero sequence mutual coupling between the faulted and the
0m
parallel line
-
Z Z
K 0 1
=
N
×
3 Z
1
IECEQUATION14005 V1 EN
Z
0 m
K
=
Nm
3
Z
⋅
1
IEC13000297 V1 EN
From the above it can be deduced:
• Error is proportional to the mutual coupling factor K
• The error increases with the parallel line ground current in relation to the relay current
• The relay underreaches when I
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
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:
(Equation 167)
(Equation 168)
0m
is in phase with I + K
GP ph
Line distance protection REL670 2.2 ANSI
1MRK 506 369-UUS -
I
N . G .
when parallel line can
N
Application manual