Technical description
4 Measurement functions
4.4 Symmetric components
VM55.EN005
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101
4.4.
Symmetric components
In a three phase system, the voltage or current phasors may be
divided in symmetric components according C. L. Fortescue
(1918). The symmetric components are:
Positive sequence 1
Negative sequence 2
Zero sequence 0
Symmetric components are calculated according the following
equations:
W
V
U
a
a
a
a
S
S
S
2
2
2
1
0
1
1
1
1
1
3
1
, where
S
0
= zero sequence component
S
1
= positive sequence component
S
2
= negative sequence component
2
3
2
1
120
1
j
a
, a phasor rotating constant
U
= phasor of phase L1 (phase current)
V
= phasor of phase L2
W
= phasor of phase L3
In case the voltage measurement mode is "2LL+Uo+LLy/LNy"
i.e. two line-to-line voltage are measured, the following
equation is used instead.
23
12
2
2
1
1
1
3
1
U
U
a
a
U
U
, where
U
12
= Voltage between phases L1 and L2.
U
23
= Voltage between phases L2 and L3.
When using line-to-line voltages, any zero sequence voltage can
not be calculated.
NOTE! The zero sequence or residual measurement signals connected to the
device are
U
0
.
