The logic can be controlled either by the autorecloser (zone extension) or by the
loss-of-load current (loss-of-load acceleration).
The loss-of-load acceleration gives selected overreach zone permission to operate
instantaneously after checking the loss-of-load condition. It can not operate for
three-phase faults.
16.5.3 Setting guidelines
M13854-4 v4
The parameters for the local acceleration logic functions are set via the local HMI
or PCM600.
Set ZoneExtension to On when the first trip from selected overreaching zone shall
be instantaneous and the definitive trip after autoreclosure a normal time-delayed
trip.
Set LossOfLoad to On when the acceleration shall be controlled by loss-of-load in
healthy phase(s).
LoadCurr must be set below the current that will flow on the healthy phase when
one or two of the other phases are faulty and the breaker has opened at remote end.
Calculate the setting according to equation
534.
min0.5 Load
Base
I
LoadCurr
I
×
=
EQUATION1320 V1 EN-US (Equation 534)
where:
ILoadmin is the minimum load current on the line during normal operation conditions.
The timer tLoadOn is used to increase the security of the loss-of-load function for
example to avoid unwanted release due to transient inrush current when energizing
the line power transformer. The loss-of-load function will be released after the
timer tLoadOn has elapsed at the same time as the load current in all three phases
are above the setting LoadCurr. In normal acceleration applications there is no
need for delaying the release, so set the tLoadOn to zero.
The drop-out timer tLoadOff is used to determine the window for the current
release conditions for Loss-of-load. The timer is by default set to 300ms, which is
judged to be enough to secure the current release.
The setting of the minimum current detector, MinCurr, should be set higher than
the unsymmetrical current that might flow on the non faulty line, when the breaker
at remote end has opened. At the same time it should be set below the minimum
load current transfer during normal operations that the line can be subjected to. By
default, MinCurr is set to 5% of IBase.
1MRK 506 369-UEN B Section 16
Scheme communication
Line distance protection REL670 2.2 IEC 721
Application manual
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