Application - ABB 615 series Technical Manual

Section 10
Power quality measurement functions
10.4.5
1068
The recorded data can be reset with the RESET binary input signal by navigating to the
HMI reset (Main menu/Clear/Reset recorded data/PQVUBx) or through tools via
communications.
When voltage unbalance is detected in the system, PQVUB responds with the
MN_UNB_AL alarm signal. During the alarm situation, PQVUB stores the maximum
magnitude and the time of occurrence and the duration of alarm MN_UNB_AL. The
recorded data is stored when MN_UNB_AL is deactivated.
Table 937: Recorded data
Parameter
Alarm high mean Dur
Max unbalance Volt
Time Max Unb Volt

Application

Voltage unbalance is one of the basic power quality parameters.
Ideally, in a three-phase or multiphase power system, the frequency and voltage
magnitude of all the phases are equal and the phase displacement between any two
consecutive phases is also equal. This is called a balanced source. Apart from the balanced
source, usually the power system network and loads are also balanced, implying that
network impedance and load impedance in each phase are equal. In some cases, the
condition of a balance network and load is not met completely, which leads to a current
and voltage unbalance in the system. Providing unbalanced supply voltage has a
detrimental effect on load operation. For example, a small magnitude of a negative-
sequence voltage applied to an induction motor results in a significant heating of the
motor.
A balanced supply, balanced network and balanced load lead to a better power quality.
When one of these conditions is disturbed, the power quality is deteriorated. PQVUB
monitors such voltage unbalance conditions in power transmission and distribution
networks. PQVUB calculates two sets of measured values, a three-second and a ten-
minute non-sliding average value. The three-second average value is used for continuous
monitoring while the ten-minute average value is used for percentile calculation for a
longer period of time. It can be applied to identify the network and load unbalance that
may cause sustained voltage unbalance. A single-phase or phase-to-phase fault in the
network or load side can create voltage unbalance but, as faults are usually isolated in a
short period of time, the voltage unbalance is not a sustained one. Therefore, the voltage
unbalance may not be covered by PQVUB.
Description
Time duration for alarm high mean unbalance
Maximum three-second voltage
Time stamp of voltage unbalance
1MAC059074-MB A
615 series ANSI
Technical Manual