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Figure 2-41
High-Impedance Ground Fault Unit Protection
2.5.2
Application Examples
The high impedance protection concept is based on measuring the voltage across the paralleled CT's to a
common high-resistive resistor.
The CTs must be of the same design and feature at least a separate core for high-impedance differential
protection. In particular, they must have the same transformer ratios and approximately identical knee-point
voltage
With 7SC80, the high-impedance principle is particularly suited for detecting ground faults at transformers,
generators, motors and parallel reactors in grounded systems.
Figure 2-42
on the left shows an application example for a grounded transformer winding or a grounded
generator. The example on the right shows an ungrounded transformer winding or an ungrounded generator
where the grounding of the system is assumed to be somewhere else.
SIPROTEC Compact, 7SC80, Manual
E50417-G1140-C486-A8, Edition 07.2017
Logic diagram of the single-phase time overcurrent protection
2.5 Single-Phase Overcurrent Protection
Functions
167
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