Siemens 7SJ85 - Rate of Frequency Change Protection; Overview of Functions; Structure of the Function; General Functions (Undervoltage Test, Df;Dt Calculation)

Rate of Frequency Change Protection
Overview of Functions
The function Rate of frequency change protection is used to:
•
Detect a frequency change quickly
•
Prevent the system from not secure states caused by unbalance between the generated and consumed
active power
•
Network decoupling
•
Load shedding
Structure of the Function
The function Rate of frequency change protection can be used in protection function groups containing a
3‑phase voltage measurement.
2 function block types are available:
•
df/dt rising
•
df/dt falling
The function Rate of frequency change protection is preconfigured by the manufacturer with 1 df/dt rising
stage and 1 df/dt falling stage. A maximum of 5 df/dt rising stages and 5 df/dt falling stages can operate simul-
taneously within the function. Both of the function block types are similar in structure.
Undervoltage check and df/dt calculation are general functionalities and take place on the function level. All
stages use these general functionalities.
[dwdfdt01-160113-01.tif, 1, en_US]
Figure 6-219 Structure/Embedding of the Function
General Functions (Undervoltage Test, df/dt Calculation)
Description
Logic
The following figure represents the logic of undervoltage check and df/dt calculation. It applies to all types of
stages.
6.35
6.35.1
6.35.2
6.35.3
6.35.3.1
Protection and Automation Functions
6.35 Rate of Frequency Change Protection
SIPROTEC 5, Overcurrent Protection, Manual 785
C53000-G5040-C017-8, Edition 07.2017