1MAC309294-MB F Section 4
Protection functions
RER620 171
Technical Manual
4.1.5.2 Function block
Figure 75: Function block
4.1.5.3 Functionality
A small percentage of the ground faults have very large impedance. It is possible to detect
these faults by using a very sensitive earth-fault protection. It is applicable for networks
where normal unbalance current level is low enough to allow for sensitive setting of
50SEF.
The function also contains a blocking functionality. It is possible to block function outputs.
4.1.5.4 Principle of operation
Same as 51N as described in 4.1.3.4 above.
4.1.5.5 Measurement modes
Same as 51N as described in 4.1.3.5 above.
4.1.5.6 Timer characteristics
Same as 51N as described in 4.1.3.6 above.
4.1.5.7 Application
Electric power lines experience faults for many reasons. In most cases, electrical faults
manifest in mechanical damage, which must be repaired before returning the line to
service.
Most of these faults are ground faults. A small percentage of the ground faults have a very
large impedance. They are comparable to load impedance and consequently have very
little fault current. These high impedance faults do not pose imminent danger to power
system equipment. However, they are a considerable threat to people and property. If the
natural unbalance in the system is low, the sensitive earth-fault protection can be used to
detect the ground fault.
4.1.5.8 Signals
Same as 51N as described in 4.1.3.8 above.
4.1.5.9 Settings
Same as 51N as described in 4.1.3.9 above.
4.1.5.10 Monitored data
Same as 51N as described in 4.1.3.10 above.
4.1.5.11 Technical data
Same as 50N as described in 4.1.3.11 above.
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