Siemens SIPROTEC 7SJ80 User Manual

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Figure 2-37
Logic diagram of the single-phase time overcurrent protection
High-impedance Ground Fault Unit Protection
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 protection. In
particular, they must have the same transformer ratios and approximately identical knee-point voltage.
With 7SJ80, the high-impedance principle is particularly well suited for detecting ground faults in grounded
networks at transformers, generators and shunt reactors.
Figure 2-38 shows an application example for a grounded transformer winding or a grounded motor/gener-
ator. The right-hand example depicts an ungrounded transformer winding or an ungrounded motor/generator
where the grounding of the system is assumed somewhere else.
2.5.2
Functions
2.5 Single-Phase Overcurrent Protection
SIPROTEC 4, 7SJ80, Manual 113
E50417-G1140-C343-A8, Edition 12.2017

Siemens SIPROTEC 7SJ80 Specifications

General

Rated Frequency	50/60 Hz
Rated Current	1 A / 5 A
Operating Temperature	-25°C to +55°C
Storage Temperature	-40°C to +70°C
Current Transformer Inputs	4
Application	Protection of feeders, motors, transformers, and generators
Rated Voltage	100-240 V AC/DC
Communication Protocols	IEC 61850, Modbus, DNP3, IEC 60870-5-103
Display	Graphical LCD
Mounting	Flush mounting
Protection Functions	Overcurrent, Earth fault
Communication Interfaces	Ethernet, RS485
Housing	Plastic
Weight	Approx. 1.5 kg