ROOTECH ACCURA 2300S, Manual

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Accura 2300S/2350-1P3FSC User Guide Chapter 5 Measurements
ⓒ 2015 Rootech Inc. All Rights Reserved Page 159
Negative-Sequence/Zero-Sequence Unbalance
The fundamental components of three-phase voltages can be divided into zero-sequence, positive-
sequence and negative-sequence components.
Fig 5.12 Symmetrical Components
V
b1
V
a1
V
c1
V
b2
V
a2
V
c2
V
a0
V
b0
V
c0
V
a0
=V
b0
=V
c0
positive-sequence negative-sequence zero-sequence
Zero-sequence component(U0): the component with the same magnitude and phase angle
Positive-sequence component(U1): three-phase symmetrical components with the phase sequence of A-
B-C
Negative-sequence component(U2): three-phase symmetrical components with the phase sequence of
A-C-B
Zero-sequence, positive-sequence, and negative-sequence components are calculated with the
following formula.
[
𝑈
0
𝑈
1
𝑈
2
] =
1
3
∙ [
1 1 1
1 𝑎 𝑎
2
1 𝑎
2
𝑎
] ∙ [
𝑈
𝑎
𝑈
𝑏
𝑈
𝑐
] , 𝑤ℎ𝑒𝑟𝑒 𝑎 = 𝑒
𝑗∙
2𝜋
3
Negative-Sequence Unbalance
It is the ratio between the magnitudes of the negative-sequence component and the positive-sequence
component.
𝑁𝑒𝑔𝑎𝑡𝑖𝑣𝑒 − 𝑠𝑒𝑞𝑢𝑒𝑛𝑐𝑒 𝑢𝑛𝑏𝑎𝑙𝑎𝑛𝑐𝑒 𝑟𝑎𝑡𝑖𝑜 =
𝑈
2
𝑈
1
× 100 [%]
Zero-Sequence Unbalance
It is the ratio between the magnitudes of the zero-sequence component and the positive-sequence
component.
𝑍𝑒𝑟𝑜 − 𝑠𝑒𝑞𝑢𝑒𝑛𝑐𝑒 𝑢𝑛𝑏𝑎𝑙𝑎𝑛𝑐𝑒 𝑟𝑎𝑡𝑖𝑜 =
𝑈
0
𝑈
1
× 100 [%]