[logik-umz-1ph-strom-me-121102-wlk, 1, en_GB]
Figure 2-87
Logic diagram of the single-phase overcurrent protection — example for detection of the
current at input
Ι
8
High-impedance Differential Protection
Application Example
With the high-impedance scheme all current transformers at the limits of the protection zone operate parallel
to a common relatively high-ohmic resistance R whose voltage is measured. With 7UT6x the voltage is regis-
tered by measuring the current through the external resistor R at the high-sensitivity single-phase current
measuring input.
The current transformers have to be of equal design and provide at least a separate core for high-impedance
differential protection. They also must have the same transformation ratio and approximately the same knee-
point voltage.
With 7UT6x, the high-impedance principle is very well suited for detection of earth faults in transformers,
generators, motors and shunt reactors in earthed systems. High-impedance differential protection can be used
instead of or in addition to the restricted earth fault protection (refer also to Section
).
shows an application example for an earthed transformer winding or an earthed motor/generator.
The example on the right side shows a non-earthed transformer winding or an non-earthed motor/generator
where the earthing of the system is assumed to be somewhere else.
2.7.2
Functions
2.7 Single-Phase Time Overcurrent Protection
178
SIPROTEC 4, 7UT6x, Manual
C53000-G1176-C230-5, Edition 09.2016
Summary of Contents for SIPROTEC 4 7UT6 Series
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