ABB RELION 620 Series Technical Manual page 708

Section 8
Power quality measurement functions
8.4.6
702
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
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.
Signals
Table 524: PQVUB Input signals
Name Type
V_A SIGNAL
V_B SIGNAL
V_C SIGNAL
V SIGNAL
1
V SIGNAL
2
V SIGNAL
0
BLOCK BOOLEAN
Table 525: PQVUB Output signals
Name Type
MN_UNB_AL BOOLEAN
PCT_UNB_AL BOOLEAN
OBS_PR_ACT BOOLEAN
th
percentile of the ten minutes'
Default Description
0 Phase A voltage
0 Phase B voltage
0 Phase C voltage
0 Positive phase sequence voltage
0 Negative phase sequence voltage
0 Zero sequence voltage
0=False Block all outputs except measured values
Description
Alarm active when 3 sec voltage unbalance exceeds the
limit
Alarm active when percentile unbalance exceeds the
limit
Observation period is active
1MAC504801-IB E
620 series ANSI
Technical Manual