Functions
2.16 Underexcitation (Loss-of-Field) Protection (ANSI 40)
SIPROTEC, 7UM62, Manual
C53000-G1176-C149-7, Release date 03.2010
137
Figure 2-54 Stator circuit criterion: Pick–Up Characteristic in Admittance Diagram
A further characteristic (1/xd CHAR.3 /α
3
can be matched to the dynamic stability characteristic of the synchro-
nous machine. Since stable operation is impossible if this characteristic is exceeded, immediate tripping is then
required (time stage T CHAR 3).
Excitation voltage query
With a faulty voltage regulator or excitation voltage failure, it is possible to switch off with a short delay (time
stage T SHRT Uex<, e.g. 1.5 s). To do so, the device must either be notified of the excitation voltage failure
via binary input, or the excitation voltage must be fed in via measuring transducer TD3 and a voltage divider,
provided that at address 3012 EXCIT. VOLT. the excitation voltage query via measuring transducer has been
switched ON.
As soon as the excitation voltage undershoots a settable minimum 3013 Uexcit. <, short-time tripping is
initiated.
Instead of the excitation voltage acquisition, or also in addition to it, the signal of an external excitation voltage
monitoring can be fed in via a binary input. Here also, short-time tripping is initiated as soon as excitation
voltage failure is signalled.
Lowpass Filter
As the excitation DC voltage may contain significant AC harmonics (e.g. because of thyristor control), an analog
lowpass filter is provided on the C-I/O-6 board for connection of excitation voltage, in addition to the integrated
digital filter. This particularly attenuates multiples of the scanning frequency, which cannot be adequately sup-
pressed by the digital filter. The jumper settings for activating this filter are described in the Mounting and Com-
missioning section. On delivery from the factory, the filter is enabled. The jumper setting must match the setting
of the parameter 297 TRANSDUCER 3 (see Power System Data, Section 2.5.1). If jumper settings and param-
eters do not match, an alarm is issued and the device is reported faulty and not operative.
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