short period of time, the voltage unbalance is not a sustained one. Therefore, the voltage
unbalance may not be covered by PQVUB.
Another major application is the long-term power quality monitoring. This can be used to
confirm a compliance to the standard power supply quality norms. The function provides
a voltage unbalance level which corresponds to the 95
th
percentile of the ten minutes'
average values of voltage unbalance recorded over a period of up to one week. It means
that for 95 percent of time during the observation period the voltage unbalance was less
than or equal to the calculated percentile. An alarm can be obtained if this value exceeds
the value that can be set.
The function uses five different methods for calculating voltage unbalance.
•
Negative-sequence voltage magnitude
•
Zero-sequence voltage magnitude
•
Ratio of negative-sequence to positive-sequence voltage magnitude
•
Ratio of zero-sequence to positive-sequence voltage magnitude
•
Ratio of maximum phase voltage magnitude deviation from the mean voltage
magnitude to the mean of phase voltage magnitude.
Usually, the ratio of the negative-sequence voltage magnitude to the positive-sequence
voltage magnitude is selected for monitoring the voltage unbalance. However, other
methods may also be used if required.
8.4.6
Signals
Table 356:
PQVUB Input signals
Name
Type
Default
Description
V_A
SIGNAL
0
Phase A voltage
V_B
SIGNAL
0
Phase B voltage
V_C
SIGNAL
0
Phase C voltage
V
1
SIGNAL
0
Positive phase sequence voltage
V
2
SIGNAL
0
Negative phase sequence voltage
V
0
SIGNAL
0
Zero sequence voltage
RESET
BOOLEAN
0=False
Resets the registered values of the data banks
Section 8
1MRS240050-IB C
Power quality measurement functions
446
REF615R
Technical Manual
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