User manual

UMG 96RM
9
General
Positive sequence-negative sequence-zero sequence
• Theextentofavoltageorcurrentimbalanceinathree-phasesystemisidentied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speciedininternationalnorms(EN50160forexample).
Positive sequence
UUUe
Ue
MitLfund Lfund
j
Lfund
j
=+⋅+ ⋅
1
3
12
2
3
3
4
3
,, ,
ππ
Negative sequence
UU
Ue
Ue
GegLfund Lfund
j
Lfund
j
=+⋅+ ⋅
−−
1
3
12
2
3
3
4
3
,, ,
ππ
Zero sequence
UU
UU
Nullsystem Lfund Lfund Lfund
=++
1
3
123
,,,
A zero component can only occur if a sum current can flow back through the main conductor.
Voltage imbalance
Unsymmetrie
U
U
Geg
Mit
=
Under difference U (EN61000-4-30)
U
U
U
n
U
unter
din
rms unter i
i
n
din
=
−
[]
−
=
∑
,
%
2
1
Under difference I
I
I
I
n
I
unter
Nennstrom
rms unter i
i
n
Nennstrom
=
−
[]
−
=
∑
,
%
2
1