Siemens 6MD85, Manual

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Expanded Checks (df/dt and Smoothing of Oscillations)
When configuring the Expanded delta-f options function block, you can expand the synchronization checks
to include the following aspects:
•
Limitation of the frequency change rate
With this option, you can define additional upper limits for the rate of permissible requency difference
change. The release checks for both stage types take these additional upper limits into consideration.
Both activation (parameters
(_:140) Limit dfdiff/dt for sync. op
and
(_:142) Limit
dfdiff/dt for asyn. op
) and the upper limits (parameters
(_:141) Max. value dfdiff/dt
syn
and
(_:143) Max. value dfdiff/dt asyn
) for the frequency change rate are adjustable
selectively for synchronous and asynchronous conditions. Both stage types consider the frequency
change rate when issuing the release for switching and indicate when the rate is exceeded.
If you also activate the option to compensate for low-frequency oscillations (parameter
(_:150)
Suppr. frequ. oscillations
), the frequency change rate is stabilized in the presence of such oscil-
lations. Stabilization is in effect for asynchronous as well as synchronous operating modes.
•
Compensation for low-frequency oscillations
If you activate this option (parameter
(_:150) Suppr. frequ. oscillations
), low-frequency
oscillations, for example, as a consequence of power swings in the range of 0.8 Hz to 1.6 Hz are detected
and smoothed. This stabilizes the release checks in the presence of frequently changing violations of
upper and lower limits for the specified frequency threshold values. The option affects the frequency
check of the Synchrocheck stage types and the synchronous operating mode of the Synchronous/Asyn-
chronous stage type. It does not affect the asynchronous operating mode.
In the example of the following figure, the synchrocheck function would initiate energization, if the
allowed frequency difference was set to 10 mHz without the parameter
Suppr. frequ. oscilla-
tions
as soon as the frequency f2 enters the 10-mHz band. If the parameter
Suppr. frequ. oscil-
lations
is activated, energization is not initiated, since the average value of f2 is outside the band.
[dwsynfre-101013-01.vsd, 1, en_US]
Figure 6-90 Example: Frequency Difference between the Constant Frequency f1 and the Sinusoidal
Oscillating Frequency f2
With this option active, the range of function measured values is expanded by the smoothed frequency.
Release of switching in synchronous networks occurs after one second at the earliest. This time is needed
to smooth the frequency measured values.
The actual frequency can be larger or smaller than the smoothed value at any instant. The
Max. diff.
"f threshold"
parameter makes it possible to limit the increase in instantaneous frequency value in
relation to the respective frequency threshold value.
6.4.10
Control Functions
6.4 Synchronization Function
408 SIPROTEC 5, High-Voltage Bay Controller, Manual
C53000-G5040-C015-9, Edition 11.2017