protection shall be connected to input IRVLx and the output IRVOPLx shall be connected to
input BLKCS on the communication function block ZCPSCH.
Weak-end infeed logic
Permissive communication schemes can basically operate only when the protection in the
remote IED can detect the fault. The detection requires a sufficient minimum fault current,
normally >20% of Ir. The fault current can be too low due to an open breaker or low short-
circuit power of the source. To overcome these conditions, weak-end infeed (WEI) echo logic is
used. The fault current can also be initially too low due to the fault current distribution. Here,
the fault current increases when the breaker opens in the strong terminal, and a sequential
tripping is achieved. This requires a detection of the fault by an independent tripping zone 1.
To avoid sequential tripping as described, and when zone 1 is not available, weak-end infeed
tripping logic is used.
The WEI function sends back (echoes) the received signal under the condition that no fault has
been detected on the weak-end by different fault detection elements (distance protection in
forward and reverse direction).
The WEI function can be extended to trip also the breaker in the weak side. The trip is achieved
when one or more phase voltages are low during an echo function.
Together with the blocking teleprotection scheme some limitations apply:
•
Only the trip part of the function can be used together with the blocking scheme. It is not
possible to use the echo function to send the echo signal to the remote line IED. The echo
signal would block the operation of the distance protection at the remote line end and in
this way prevents the correct operation of a complete protection scheme.
•
A separate direct intertrip channel must be arranged from remote end when a trip or
accelerated trip is given there. The intertrip receive signal is connected to input CRL.
•
The WEI function shall be set to
OperationWEI=Echo&Trip. The WEI function block will then
give phase selection and trip the local breaker.
15.4.3
Setting guidelines
SEMOD156555-1 v2
SEMOD156562-5 v3
The parameters for the current reversal and weak-end infeed logic for phase segregated
communication function (ZC1WPSCH) are set via the local HMI or PCM600.
Common base IED values for primary current (
IBase), primary voltage (UBase) and primary
power (
SBase) are set in Global base values for settings function GBASVAL.
GlobalBaseSel: It is used to select a GBASVAL function for reference of base values.
Current reversal logic
Set
OperCurrRev to On to activate the function.
Set
tDelayRev timer at the maximum reset time for the communication equipment that gives
the carrier receive (CRLx) signal plus 30ms. A minimum setting of
40ms is recommended,
typical
60ms.
A long
tDelayRev setting increases security against unwanted tripping, but delay the fault
clearing in case of a fault developing from one line to involve the other one. The probability of
this type of fault is small. Therefore set
tDelayRev with a good margin.
Set the pickup delay
tPickUpRev to <80% of the breaker operate time, but with a minimum of
20ms.
Section 15
1MRK 505 343-UEN B
Scheme communication
614
Application manual
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