Series compensation additionally exaggerates the effect of zero sequence mutual
impedance between two circuits, see figure 103. 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 103: 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
104, 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.
en06000629_ansi.vsd
RAA RBAI
FC1
I
FC1
X
F
RAB RBBI
FC2
CSAB CRBB
RAA RBAI
FC1
X
F
RAB RBBI
FC2
CSAB CRBB
ANSI06000629 V1 EN
Figure 104: Current reversal phenomenon on parallel operating circuits
It is possible to expect faster IED operation and breaker opening at the bus closer to
fault, which will reverse the current direction in healthy circuit. Distance IED RBB
will suddenly detect fault in forward direction and, if CRBB signal is still present due
to long reset time of IED RAB and especially telecommunication equipment, trip its
related circuit breaker, since all conditions for POTT have been fulfilled. Zero
sequence mutual impedance will additionally influence this process, since it increases
the magnitude of fault current in healthy circuit after the opening of first circuit
breaker. The so called current reversal phenomenon may cause unwanted operation of
Section 3 1MRK504116-UUS C
IED application
234
Application manual
To Next Page
Loading...
Need help?
General
