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2 Functions
Figure 2-43
Consequently, the loading resistor must be situated on the other side of the measure-
ment location (current transformer, toroidal current transformer) viewed from the ma-
chine. The earthing transformer is preferably connected to the busbar. Apart from the
magnitude of the earth fault current, the direction of this current in relation to the dis-
placement voltage is needed for the secure detection of a machine earth fault with
busbar connection. The directional border between "machine direction" and "network
direction" can be altered in the 7UM61 (refer to following figure).
The protection then detects a machine earth fault if the following three criteria are ful-
filled:
• Displacement voltage larger than set value U0>,
• Earth fault current across the measurement location larger than set value 3I0>,
• Earth fault current is flowing in the direction of the protected machine.
Figure 2-44
130
Earth Fault Direction Detection with Busbar Connection
Characteristic of the Stator Earth Fault Protection for Busbar Connection
7UM61 Manual
C53000-G1176-C127-3
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