Siemens Siprotec 7UM611, Руководство пользователя

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2 Functions
124
7UM61 Manual
C53000-G1176-C127-3
Measuring Princi-
ple The vector of the positive sequence system voltage is calculated from the phase-to-
earth voltages, and the phase angle change of the voltage vector is determined over
a delta interval of 2 cycles. The presence of a phase angle jump indicates an abrupt
change of current flow. The basic principle is shown in the following figure. The
diagram on the left shows a steady state, and the diagram on the right the vector
change following a load shedding. The vector jump is clearly visible.
Figure 2-39 Voltage Vector Following Load Shedding
The function features a number of additional measures to avoid spurious tripping,
such as:
• Correction of steady-state deviations from rated frequency
• Frequency operating range limited to f
N
±
3 Hz
• Detection of internal sampling frequency changeover (Sampling frequency adjust-
ment)
• Minimum voltage for enabling
• Blocking on voltage connection or disconnection
Logic Figure 2-40 shows the logic diagram. The phase angle comparison determines the
angle difference, and compares it with the set value. If this value is exceeded, the
vector jump is stored in an RS flip-flop. Trippings can be delayed by the associated
time delay.
The stored pickup can be reset via a binary input, or automatically by a timer (address
4604 T RESET
).
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