Hitachi Relion REL670 Product Manual page 49

Line distance protection REL670
Version 2.2
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.
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
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
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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
the remote IED can detect the fault. The detection requires
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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)
function measures power flow. It can be used for protection
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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
• Low active power trip with 2 selection modes '1 out of 3'
and '2 out of 3'
• Phase wise calculated values of apparent power, reactive
power, active power and power factor are available as
service values
• Insensitive to small variations in voltage and current
Compensated over and undervoltage protection
COUVGAPC
Compensated over and undervoltage protection
(COUVGAPC) function calculates the remote end voltage of
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the transmission line utilizing local measured voltage,
current and with the help of transmission line parameters,
that is, line resistance, reactance, capacitance and local
shunt reactor. For protection of long transmission line for in
zone faults, COUVGAPC can be incorporated with local
criteria within direct transfer trip logic to ensure tripping of
the line only under abnormal conditions.
Sudden change in current variation SCCVPTOC
Sudden change in current variation (SCCVPTOC) function
is a fast way of finding any abnormality in line currents.
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When there is a fault in the system, the current changes
faster than the voltage. SCCVPTOC finds abnormal
condition based on phase-to-phase current variation. The
main application is as a local criterion to increase security
when transfer trips are used.
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