Hitachi Relion 670 Series Product Manual page 50

Line differential protection RED670
Version 2.2
On detection of a current reversal, the current reversal logic
provides an output to block the sending of the teleprotection
signal to the remote end, and to block the permissive
tripping at the local end. This blocking condition is
maintained long enough to ensure that no unwanted
operation will occur as a result of the current reversal.
On verification of a weak end infeed condition, the weak
end infeed logic provides an output for sending the received
teleprotection signal back to the remote sending end and
other output(s) for local tripping. For terminals equipped for
single- and two-pole tripping, outputs for the faulted
phase(s) are provided. Undervoltage detectors are used to
detect the faulted phase(s).
Current reversal and weak-end infeed logic for phase
segregated communication ZPCWPSCH
Current reversal and weak-end infeed logic for phase
segregated communication (ZPCWPSCH) function is used
to prevent unwanted operations due to current reversal
when using permissive overreach protection schemes in
application with parallel lines where the overreach from the
two ends overlaps on the parallel line.
The weak-end infeed logic is used in cases where the
apparent power behind the protection can be too low to
activate the distance protection function. When activated,
received carrier signal together with local undervoltage
criteria and no reverse zone operation gives an
instantaneous trip. The received signal is also echoed back
to accelerate the sending end.
Local acceleration logic ZCLCPSCH
To achieve fast clearing of faults on the whole line, when no
communication channel is available, local acceleration logic
(ZCLCPSCH) can be used. This logic enables fast fault
clearing and re-closing during certain conditions, but
naturally, it can not fully replace a communication channel.
The logic can be controlled either by the autorecloser (zone
extension) or by the loss-of-load current (loss-of-load
acceleration).
Scheme communication logic for residual
overcurrent protection ECPSCH
To achieve fast fault clearance of earth faults on the part of
the line not covered by the instantaneous step of the
residual overcurrent protection, the directional residual
overcurrent protection can be supported with a logic that
uses communication channels.
In the directional scheme, information of the fault current
direction must be transmitted to the other line end. With
directional comparison, a short operate time of the
protection including a channel transmission time, can be
achieved. This short operate time enables rapid
autoreclosing function after the fault clearance.
50
The communication logic module for directional residual
current protection enables blocking as well as permissive
under/overreaching, and unblocking schemes. The logic can
also be supported by additional logic for weak-end infeed
and current reversal, included in Current reversal and weak-
end infeed logic for residual overcurrent protection
(ECRWPSCH) function.
Current reversal and weak-end infeed logic for
residual overcurrent protection ECRWPSCH
The Current reversal and weak-end infeed logic for residual
overcurrent protection (ECRWPSCH) is a supplement to
Scheme communication logic for residual overcurrent
protection ECPSCH.
To achieve fast fault clearing for all earth faults on the line,
the directional earth fault protection function can be
SEMOD156473-5 v4
supported with logic that uses tele-protection channels.
This is why the IEDs have available additions to the scheme
communication logic.
If parallel lines are connected to common busbars at both
terminals, overreaching permissive communication schemes
can trip unselectively due to fault current reversal. This
unwanted tripping affects the healthy line when a fault is
cleared on the other line. This lack of security can result in
a total loss of interconnection between the two buses. To
avoid this type of disturbance, a fault current reversal logic
(transient blocking logic) can be used.
Permissive communication schemes for residual overcurrent
protection can basically operate only when the protection in
M13823-3 v7 the remote IED can detect the fault. The detection requires
a sufficient minimum residual fault current, out from this
IED. The fault current can be too low due to an opened
breaker or high-positive and/or zero-sequence source
impedance behind this IED. To overcome these conditions,
weak-end infeed (WEI) echo logic is used. The weak-end
infeed echo is limited to 200 ms to avoid channel lockup.
Direct transfer trip DTT
Low active power and power factor protection LAPPGAPC
Low active power and power factor protection (LAPPGAPC)
M13918-4 v11
function measures power flow. It can be used for protection
and monitoring of:
• phase wise low active power
• phase wise low power factor
• phase wise reactive power and apparent power as service
values
Following features are available:
• Definite time stage for low active power protection
• Definite time stage for low power factor protection
• Individual enabling of Low active power and Low power
factor functions
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