Eaton Power Xpert PXR 10, Руководство пользователя

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4 Protection settings
4.6 Ground-fault settings
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PXR Electronic trip unit 01/21 MN012005EN www.eaton.com
Table 14: Settings ground-fault protection
The PXR trip unit allows for the selection of two different ground-fault
slopes:
• Flat waveform (“flat”)
• I
2
t waveform.
The slope should be chosen in accordance with the individual coordination
requirements. The I
2
t response allows for a shorter time delay than the fixed-
time response (“flat”).
The time delay t
g
and the slope should be selected together. If the selected
response time is I
2
t, this will be marked separately, while this is is not the
case for the “flat” response time. Both have a range of up to 1 second.
As soon as a ground fault causes the circuit breaker to trip, the GND
indicator will light up, provided that auxiliary power is available (on the
PXR20), or a message will appear on the display (on the PXR25).
In addition to ground-fault protection, the PXR trip unit is also equipped with
a ground-fault memory function (thermal memory for ground-fault protection)
to protect against recurrent loads if an arc to earth occurs. Without this
function, the ground-fault protection timer would be reset each time an arc is
quenched, and the arc would not necessarily cause the circuit breaker to trip.
The ground-fault memory function enables the trip unit to “remember” the
ground-fault current. The memory will be erased with time, and the time
interval corresponds to 6.25 times of the ground-fault time.
Internal current sensors are used to detect the presence of a ground fault.
If the sum of the currents of the individual phases (and, if a four-pole circuit
breaker is used, of the neutral conductor in a four-wire network) does not
equal zero, an alarm will be triggered in line with the ground-fault protection
settings. If a 3-pole circuit breaker is used in a neutral network, the neutral
current will not be detected. In this case, a ground-fault trip may occur if the
threshold values of the ground-fault release are exceeded.
Mode Description
OFF The ground-fault detection can be turned off by setting the rotary switch to “OFF”.
ALARM It is possible to set threshold values for alarm-only ground-fault detection.
When the alarm mode is selected, threshold values can be set.
This set of threshold values is marked “alarm”.
TRIP It is also possible to set threshold values for the ground-fault detection with trip.
When detection and trip mode is selected, threshold values can be set.
This set of threshold values is marked “trip”.