Unearthed network
Figure. 5.3.5 - 41. Angle tracking of I0dir> function (unearthed network model) (32N)
When the unearthed (capacitive) network mode is chosen, the device expects the fault current to be
lagging zero sequence voltage by 90 degrees. Healthy phases of healthy feeders produce capacitive
current during earth fault just like a faulty feeder but the current is floating towards the busbar and
through an incoming transformer or a earthing transformer and into a faulty feeder. Healthy feeders do
not trip since capacitive current is floating to the opposite direction and selective tripping can be
ensured.
The amplitude of the fault current depends on the capacitance of the network. The outgoing feeders
are the sources for capacitive currents. The bigger the network the greater the capacitive current
during a fault. Each outgoing feeder produces capacitance according to the zero sequence capacitive
reactance of the line (ohms per kilometer). It is normal that in cable networks fault currents are higher
than in overhead lines.
A
AQ
Q-M255
-M255
Instruction manual
Version: 2.06
84
© Arcteq Relays Ltd
IM00020
Summary of Contents for AQ-M255
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