Overexcitation Protection
Overview of Functions
The Overexcitation protection (ANSI 24) is used for detecting high induction values in generators and trans-
formers. It protects the equipment from excessive thermal loads.
The induction is recorded indirectly by analyzing the V/f ratio (also referred to as Volt per Hertz protection).
Overvoltage leads to excessive magnetizing currents, while underfrequency leads to higher losses when reset-
ting the magnetization.
If the power system is disconnected and the voltage and frequency control function in the remaining system
does not react quickly or the power imbalance is excessive, there is a risk of overexcitation.
Structure of the Function
The Overexcitation protection function is used within protection function groups that have a 3-phase
voltage input. The function comes with the following factory-set stages:
•
Thermal stage adjustable with a user-defined characteristic curve
•
Definite-time stage which can be delayed using a time component
Within this function, the following maximum number of stages can be operated simultaneously: one stage
with a user-defined characteristic curve and 2 definite-time stages.
The group-indication output logic (see following figure) uses the logical OR function from the stage-selective
indications to generate the following group indications of the entire Overexcitation protection function:
•
Pickup
•
Operate Indication
[dwovexuf-080513-01.tif, 3, en_US]
Figure 6-238 Structure/Embedding of the Function
Function Measured Value
Measured Value
Description
(_:2311:322) V/f
Value calculated by the voltage and the frequency
6.39
6.39.1
6.39.2
Protection and Automation Functions
6.39 Overexcitation Protection
SIPROTEC 5, Overcurrent Protection, Manual 817
C53000-G5040-C017-8, Edition 07.2017
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