V Measured voltage (maximum phase-to-phase voltage)
V
rated, obj.
Adjusted rated voltage of the protected object
f Measured frequency
f
rated
Adjusted rated frequency
Based on the definition above, the protection function refers exclusively to primary values of the protected
object. A deviation between the primary rated voltage of the voltage transformer and the protected object is
corrected automatically.
NOTE
This fact must be considered during a secondary test.
More information can be found in chapter 11.16 Functional Test for Overexcitation Protection .
The function compares the calculated value of the measured V/f ratio with the threshold value and the user-
defined thermal characteristic curve.
Depending on the characteristic curve, a thermal trip signal is triggered after a pre-determined duration.
Characteristic Curve
You can freely configure the thermal characteristic curve with the user-defined values. This provides a flexible
adjustment to the specified characteristics of the protected object. If the set threshold value (parameter (_:
13591:3) Threshold) is exceeded, the evaluation of the characteristic curve is initiated. Exceeding the
threshold value triggers an indication (
(_:13591:55) Pickup
). In addition, a definite-time stage may be
used to generate a delayed indication output as (
(_:13591:301) Warning
).
The pickup is used to start the integration process (weighted counting) of the thermal characteristic curve. If
the time as a factor of V/f is reached, the pickup is triggered. Based on the replica of the thermal behavior, the
trigger value is always 100 % (see Thermal Behavior, Page 820).
If the value drops below the pickup threshold, the trip command is rescinded and the internal counter of the
parameterized cooling time (parameter (_:13591:102) Cooling time therm.replica) is reduced.
The dropout threshold of the pickup threshold is fixed to 0.98 * Threshold.
A maximum of 30 overexcitation value pairs V/f (referring to the rated values) and operate time t can be set.
The default characteristic curve refers to a standard transformer.
[scaulskn-200214-01, 1, en_US]
Figure 6-240 Data Sheet for Adjustment of Thermal Characteristic Curve
The parameter Threshold (pickup threshold) affects the evaluation of the characteristic curve as follows:
If the Threshold is smaller than the first characteristic pair, the set time will be extended (see Figure 6-241).
Protection and Automation Functions
6.39 Overexcitation Protection
SIPROTEC 5, Overcurrent Protection, Manual 819
C53000-G5040-C017-8, Edition 07.2017
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