Siemens 7SJ85 - Overvoltage Protection with Negative-Sequence Voltage; Overview of Functions; Structure of the Function; General Functionality

Overvoltage Protection with Negative-Sequence Voltage
Overview of Functions
The function Overvoltage protection with negative-sequence voltage (ANSI 47) is used to:
•
Monitor the power system and electric machines for voltage unbalances
•
Establish a release criterion of overcurrent protection for unbalanced faults
Voltage unbalances can be caused by various factors:
•
The most common cause is unbalanced load, caused by different consumers in the individual phases, for
example.
•
Voltage unbalance can also be caused by phase failure, for example due to a tripped 1-phase fuse, a
broken conductor, etc.
•
Other causes can include faults in the primary system, for example, at the transformer or in installations
for reactive-power compensation.
Structure of the Function
The Overvoltage protection with negative-sequence voltage function is used in protection function groups,
which are based on voltage measurement.
The Overvoltage protection with negative-sequence voltage function comes factory-set with 2 stages.
A maximum of 3 stages can be operated simultaneously in the function.
The stages have an identical structure.
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Figure 6-187 Structure/Embedding of the Function
General Functionality
Description
Logic
The following figure represents the logic of the average-value calculation of the negative-sequence voltage.
The average value is forwarded to all subordinate stages.
6.26
6.26.1
6.26.2
6.26.3
6.26.3.1
Protection and Automation Functions
6.26 Overvoltage Protection with Negative-Sequence Voltage
714 SIPROTEC 5, Overcurrent Protection, Manual
C53000-G5040-C017-8, Edition 07.2017