Megger MPQSIM, User Manual

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ADDENDUM C - SAMPLE POWER QUALITY TRAINING
AVTMMPQSIM Rev 1 May 2017
45
4. Unbalance
a. View the Vectors and Unbalance on the SCOPE/UNBALANCE screen of the
MPQ analyzer.
b. Change the Phase A Current phase angle on the PQ Simulator to -30°.
c. Change the Phase A Voltage to 85% on the PQ Simulator. Note the change in the
unbalance.
NOTE: Voltage unbalance causes heating in neutral lines, motors, unbalanced
currents and uncharacteristic harmonics for electronic equipment such as
adjustable speed drives.
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High-efficiency motors can be more susceptible to negative sequence
unbalance.
Negative sequence harmonics have a magnetic field that rotate opposite of
the fundamental.
This can lead to loss of efficiency as it resists the rotation of the motor.
The negative sequence factor [(negative sequence / positive sequence) *
100] is most the key unbalance value to reference when working with
motor loads.
Negative sequence unbalance is the basis of most international standards
for unbalance.
It is recommended that the voltage unbalance be within 2% for 95% of
the time measured over a period of a week at 10 minute intervals. For
systems with large single-phase loads, the unbalance can be as high as
3%.
d. Use the UP/DOWN button on the MPQ analyzer to change from an IEC
Unbalance measurement to an ANSI unbalance measurement.
The ANSI method of measuring unbalance compares the individual line-to-line voltage to the average
of the sum of all the line to line voltages. This value can be influenced by the zero sequence voltage as
well as by the negative sequence voltage.
ANSI C84.1-2006 recommends that voltage unbalance be limited to 3%.
e. Change the Phase A Current phase angle on the PQ Simulator to 0°.
f. Change the Phase A Voltage to 100% on the PQ Simulator.