5.3.7. Neutral overvoltage (U0>; 59N)
The neutral overvoltage function is used for non-directional earth fault alarms. Each device with a
voltage protection module has four (4) stages available in the function. The function constantly
measures phase-to-ground voltage magnitudes and calculates the zero sequence component. The
neutral overvoltage protection is scaled to the level of line-to-line fundamental frequency. If the line-to-
line voltage of the system is 100 V in the secondary side, the earth fault is 100% of the
U
n
when the
calculated zero sequence voltage reaches V = 57.74 V.
The formula for symmetric component calculation (and therefore to zero sequence voltage calculation)
is presented below.
See the zero sequence calculation examples below.
Figure. 5.3.7. - 59. Normal situation.
Figure. 5.3.7. - 60. Earth fault in an isolated network.
Figure. 5.3.7. - 61. Close distance short-circuit between phases 1 and 3.
The U< function is also capable of using measured neutral voltage. If the line-to-line voltage of the
system is 100 V in the secondary side, the earth fault is 100% of the
U
n
when the measured neutral
voltage is 100 V (see picture below).
AQ-E215
Instruction manual
Version: 2.01
© Arcteq Relays Ltd
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