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1MRK 506 369-UEN B
16.4.3
Line distance protection REL670 2.2 IEC
Application manual
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.
Setting guidelines
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.
Section 16
Scheme communication
SEMOD156555-1 v2
SEMOD156562-5 v4
719
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