Fluke 434-II/435-II/437-II
Users Manual
14-4
Tips and Hints
The voltages and currents in the Meter screen can e.g. be used to check if power applied
to a 3-phase induction motor is in balance. Voltage unbalance causes high unbalanced
currents in stator windings resulting in overheating and reduced motor life. The Negative
Voltage component Vneg. should not exceed 2 %. Current unbalance should not exceed
10 %. In case of too high unbalance, use other measuring modes to further analyze the
power system.
Each three phase voltage or current can be split-up into three components: positive
sequence, negative sequence, and zero sequence.
The positive sequence component is the normal component such as present in balanced
3-phase systems. The negative sequence component results from unbalanced phase-to-
phase currents and voltages. This component for instance causes a ‘braking’ effect in
3-phase motors: this will result in overheating and life reduction.
Zero sequence components may appear in an unbalanced load in 4 wire power systems
and represent the current in the N (Neutral) wire. Unbalance exceeding 2 % is considered
as too high.
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