Positive sequence-negative sequence-zero sequence
• The extent of a voltage or current imbalance in a three-phase system is identified using the positive sequence, negative
sequence and zero sequence components.
• The balance of the rotation current system strived for in normal operation is disturbed by the unsymmetrical loads, errors
and equipment.
• A three-phase system is called symmetric, when the three phase conductor voltages and currents are the same size and
are displaced against each other by 120°. If one or both conditions are not fulfilled, the system is described as unsym-
metrical. By calculating the symmetrical components consisting of the positive sequence, negative sequence and zero
sequence, the simplified analysis of an imbalanced error is possible in a rotary current system..
• Imbalance is a feature of the network quality for the limits specified in international norms (EN 50160 for example).
Positive sequence
Negative sequence
Zero sequence
UU
A zero component can only occur if a sum current can flow back through the main conductor.
Under difference U
(EN61000-4-30)
Unsymmetrical voltage (U0)
Unsymmetrical voltageU
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