ABB Relion 670 series - Page 425

en06000627.vsd
-jX
C
-jX
C
Z
AC
Z
CB
ZAC ZCB
A B
Z
m0AC
Z
m0CB
IEC06000627 V1 EN
Figure 217: Double circuit, parallel operating line
Zero sequence mutual impedance Z
m0
cannot significantly influence the operation of
distance protection as long as both circuits are operating in parallel and all precautions
related to settings of distance protection on series compensated line have been considered.
Influence of disconnected parallel circuit, which is grounded at both ends, on operation of
distance protection on operating circuit is known.
Series compensation additionally exaggerates the effect of zero sequence mutual
impedance between two circuits, see figure
100. It presents a zero sequence equivalent
circuit for a fault at B bus of a double circuit line with one circuit disconnected and
grounded at both IEDs. The effect of zero sequence mutual impedance on possible
overreaching of distance IEDs at A bus is increased compared to non compensated
operation, because series capacitor does not compensate for this reactance. The reach of
underreaching distance protection zone 1 for phase-to-ground measuring loops must
further be decreased for such operating conditions.
en06000628.vsd
jX
m0
j(X
0L
-X
m0
)
j(X
0L
-X
m0
)
-jX
C
-jX
C
A B
IEC06000628 V1 EN
Figure 218: Zero sequence equivalent circuit of a series compensated double circuit
line with one circuit disconnected and grounded at both IEDs
Zero sequence mutual impedance may disturb also correct operation of distance
protection for external evolving faults, when one circuit has already been disconnected in
one phase and runs non-symmetrical during dead time of single pole autoreclosing cycle.
All such operating conditions must carefully be studied in advance and simulated by
dynamic simulations in order to fine tune settings of distance IEDs.
If the fault occurs in point F of the parallel operating circuits, as presented in figure
101,
than also one distance IED (operating in POTT teleprotection scheme) on parallel, healthy
circuit will send a carrier signal CSAB to the remote line end, where this signal will be
received as a carrier receive signal CRBB.
1MRK 506 369-UUS - Section 8
Impedance protection
Line distance protection REL670 2.2 ANSI 419
Application manual