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2.25.1 Functional Description
Measuring
Principle
∆U
Z
Gen
~
Up
Generator
Figure 2-80 Voltage Vector Following a Load Shedding
Logic
7UM62 Manual
C53000-G1176-C149-3
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 is an indicator for an
abrupt change of the current flow. The basic principle is shown in Figure 2-80. The di-
agram 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.
I1
I2
U
Z
Network
U
∆U
Network/Load
φ
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
− Detection of internal sampling frequency changeover
− Minimum voltage for release
− Blocking on voltage connection or disconnection
Figure 2-81 shows the logic diagram. The phase angle comparison determines the an-
gle difference, and compares it with the set value. If this value is exceeded, the vector
jump is stored in an RS flip-flop. Tripping 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).
∆U
Z
Gen
~
Z
Up
NET
Up
Generator
± 3 Hz
N
Jump of Voltage Vector
I1'
U
Z
Network
U
U'
∆U
Network/Load
∆φ
Z
NET
173
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