2.9 Zero sequence voltage
protection U0> (59N)
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Recorded values of the undirectional earth fault stages (8
latest faults) I
0
>, I
0
>>, I
0
>>>, I
0
>>>> (50N/51N)
Time stamp of the recording, date
Maximum earth fault current
Elapsed time of the operating time
setting. 100% = trip
Active setting group during fault
2.9. Zero sequence voltage protection U
0
>
(59N)
The zero sequence voltage protection is used as unselective
backup for earth faults and also for selective earth fault
protections for motors having a unit transformer between the
motor and the busbar.
This function is sensitive to the fundamental frequency
component of the zero sequence voltage. The attenuation of the
third harmonic is more than 60 dB. This is essential, because
3n harmonics exist between the neutral point and earth also
when there is no earth fault.
Whenever the measured value exceeds the user's pick-up
setting of a particular stage, this stage picks up and a start
signal is issued. If the fault situation remains on longer than
the user's operation time delay setting, a trip signal is issued.
Measuring the zero sequence voltage
The zero sequence voltage is measured with three voltage
transformers, e.g. broken delta connection (see chapter 4.7):
U
0
: The zero sequence voltage is measured with voltage
transformers for example using a broken delta connection.
The setting values are relative to the VT
0
secondary voltage
defined in configuration.
NOTE! The U
0
signal must be connected according the connection diagram
(Figure 8.8.1-1) in order to get a correct polarization
Two independent stages
There are two separately adjustable stages: U
0
> and U
0
>>.
Both stages can be configured for definite time (DT) operation
characteristic.
The zero sequence voltage function comprises two separately
adjust-table zero sequence voltage stages (stage U
0
> and U
0
>>).
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