janitza UMG 511 Manual page 9

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
A zero component can only occur if a sum current can flow back through the main conductor.
Unsymmetrical voltage
Unsymmetrical voltage (U0)
Under difference U
(EN61000-4-30)
1
U = U + U
Nullsystem L fund 1 ,
3
Unsymmetrical voltage
Unsymmetrical voltage U
+ U
L fund 2 , L fund 3 ,
U
Negative sequence
100%
U
Positive sequence
U
( 0 ) Zero sequence
U
Positive sequence
UMG 511
General
100 %
9