Step 4
M15282-177 v4
This step normally has non-directional function and a relatively long time delay.
The task for step 4 is to detect and initiate trip for earth faults with large fault
resistance, for example tree faults. Step 4 shall also detect series faults where one
or two poles, of a breaker or other switching device, are open while the other poles
are closed.
Both high resistance earth faults and series faults give zero-sequence current flow
in the network. Such currents give disturbances on telecommunication systems and
current to earth. It is important to clear such faults both concerning personal
security as well as risk of fire.
The current setting for step 4 is often set down to about 100 A (primary 3I
0
). In
many applications definite time delay in the range 1.2 - 2.0 s is used. In other
applications a current dependent inverse time characteristic is used. This enables a
higher degree of selectivity also for sensitive earth-fault current protection.
8.5 Thermal overload protection, one time constant,
Celsius/Fahrenheit LCPTTR/LFPTTR
IP14512-1 v7
8.5.1 Identification
M17106-1 v7
Function description
IEC 61850
identification
IEC 60617
identification
ANSI/IEEE C37.2
device number
Thermal overload protection, one time
constant, Celsius
LCPTTR 26
Thermal overload protection, one time
constant, Fahrenheit
LFPTTR 26
8.5.2 Application
M15283-3 v9
Lines and cables in the power system are designed for a certain maximum load
current level. If the current exceeds this level the losses will be higher than
expected. As a consequence the temperature of the conductors will increase. If the
temperature of the lines and cables reaches too high values the equipment might be
damaged:
Section 8 1MRK 505 393-UEN B
Current protection
180 Line differential protection RED650 2.2 IEC
Application manual
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