Application And Setting Notes - Siemens 6MD85 Manual

Measuring-Element Release
When the controlling voltage drops below the setting Undervoltage threshold, the respective measuring
element is released.
The release of the measuring elements is carried out phase-selectively. The assignment of voltages to current-
carrying phases is shown in
Blocking of the Stage with Measuring-Voltage Failure
The stage can be blocked if a measuring-voltage failure occurs. In case of a blocking, the picked up stage is
reset. The following blocking options are available for the stage:
•
From an internal source upon pickup of the Measuring-voltage failure detection function
•
From an external source via the binary input signal
b., which links in the tripping of the voltage-transformer circuit breaker
The Blk. by meas.-volt. failure parameter can be set so that measuring-voltage failure detection
blocks the stage or does not block it.
7.12.4.2

Application and Setting Notes

This stage is structured in the same way as the Inverse-time overcurrent, voltage-dependent stage. The
only differences are the conditions for the pickup and the influence on the operate curve. This chapter only
provides the application and setting notes for the setting Blk. by meas.-volt. failure and Under-
voltage threshold. For guidance on the other parameters of this stage, refer to chapter
tion and Setting
Parameter: Blk. by meas.-volt. failure
•
Recommended setting value (_:10) Blk. by meas.-volt. failure = yes
You can use the Blk. by meas.-volt. failure parameter to control the response of the stage when a
measuring-voltage failure is detected.
A measuring-voltage failure can only be detected if one of the following 2 conditions is met:
•
The device-internal Measuring-voltage failure detection function is configured and switched on.
•
The binary input signal
the voltage-transformer circuit breaker.
Parameter Value
no
yes
Parameter: Undervoltage threshold
•
Default setting (_:104) Undervoltage threshold = 75.0 V
When the controlling voltage is below the set value, the Inverse-time overcurrent protection stage is
released.
The parameter is set to a value just below the lowest phase-to-phase voltage admissible during operation, for
example, from 75 % to 80 % of V
SIPROTEC 5, High-Voltage Bay Controller, Manual
C53000-G5040-C015-9, Edition 11.2017
Figure 7-138.
Notes.
>Open of the function block Voltage-transformer circuit breaker is connected to
Description
The overcurrent-protection stage is not blocked when a measuring-voltage
failure is detected.
The overcurrent-protection stage is blocked when a measuring-voltage
failure is detected. Siemens recommends using the default setting, as
correct operation of the stage cannot be guaranteed if a measuring-voltage
failure occurs.
.
rated
Protection and Automation Functions
7.12 Voltage-Dependent Overcurrent Protection
>Open of the function block Volt.-transf. c.
7.12.3.2 Applica-
781