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Functions
2.7 Monitoring Function
Figure 2-46
Broken Conductor
A broken wire of the protected line or in the current transformer secondary circuit can be detected if a minimum
current PoleOpenCurrent flows via the line. If the minimum phase current is below this limit while the other
phase currents are above this limit, an interruption of this conductor may be assumed. If current asymmetry
occurs (see margin heading „Current symmetry"), the device issues the indication „Fail Conductor"
(No. 195).
Voltage Symmetry
In healthy network operation it can be expected that the voltages are nearly balanced. The monitoring of the
measured values in the device checks this balance. The smallest phase voltage is compared to the largest.
Non-symmetry is detected when
|U
| / | U
min
max
U
is the largest of the three phase-to-phase voltages and U
max
FACTOR U (address 2903) represents the allowable asymmetry of the voltages while the limit value BALANCE
U-LIMIT (address 2902) is the lower limit of the operating range of this monitoring (see Figure 2-47). The
dropout ratio is about 97%.
After a settable time, this malfunction is signaled as „Fail U balance" (no. 167).
134
Current symmetry monitoring
| < BAL. FACTOR U as long as | U
| > BALANCE U-LIMIT
max
the smallest. The symmetry factor BAL.
min
C53000-G1176-C159-3, Release date 05.2009
SIPROTEC, 7VK61, Manual
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