Both methods of measurement are characterized by a high measuring accuracy combined with a short
response time. Disturbance values such as harmonics, high frequency disturbances, phase-angle jumps during
switching operations and compensation processes due to power swings are effectively suppressed.
Behavior on Leaving the Operating Range
The sampling-frequency tracking makes a wide frequency operating range possible. If the stage has picked up
before leaving the frequency operating range and the measuring voltage is higher than the set minimum
voltage, the pickup is maintained. A dropout of the pickup is only possible by means of a blocking.
Blocking the Stage
In the event of blocking, a picked-up stage will be reset. The following blocking options are available for the
stage:
•
Via the binary input signal
>Block stage
from an external or internal source
•
Internally when the voltage drops below the Minimum voltage
Application and Setting Notes
Routing: Frequency-Measurement Method
The frequency measurement method is selected with the functional configuration from the DIGSI functions
library. Redundant solutions can be implemented by combining 2 different frequency measurement methods.
You can implement a 2-out-of-2 decision by linking the operate indications of both functions in CFC with a
logical AND gate. This increases the reliability of protection.
Method of Measurement
Description
Angle difference method (func-
tional configuration A)
Select this method of measurement if the frequency protection stage is
used for the protection of machines.
Filtering method (functional
configuration B)
Select this method of measurement if the frequency protection stage is
used in an electrical power system.
Parameter: Threshold
•
Recommended setting value (_:61:3) Threshold = 49,80 Hz for f
rated
= 50 Hz
The Threshold parameter is used to define the pickup threshold of the underfrequency protection stage in
dependence of the application. 49,8 Hz is a typical warning threshold in 50 Hz systems.
Parameter: Operate delay
•
Recommended setting value (_:61:6) Operate delay = 10 s
The Operate delay parameter is used to set the stage so that overfunctions due to disturbing influences
(for example, switching operations) are avoided. Fairly high time delays are sufficient for warning indications.
Parameter: Minimum voltage
•
Recommended setting value (_:2311:101) Minimum voltage = 37.5 V
For the Undervoltage blocking, 65 % of the protected object's rated voltage is recommended.
When determining the setting value, please keep in mind the measurement method and the measuring
connection that you have selected. If you work with the positive-sequence voltage, remember that the
maximum voltage is equal to the phase-to-ground voltage. The default setting is referred to this value.
Parameter: Dropout differential
•
Recommended setting value (_:2311:109) Dropout differential = 20 mHz
For a precise frequency measurement, the default setting value for the Dropout differential can be left
at 20 mHz. For a later dropout of the stage, increase the setting value of the dropout differential. For instance,
7.19.4
Protection and Automation Functions
7.19 Underfrequency Protection
SIPROTEC 5, High-Voltage Bay Controller, Manual 831
C53000-G5040-C015-9, Edition 11.2017
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