Chapter 5 Measurement Description
Accura 2300/2350 User Guide
Page 200
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Three-phase Total Power Measurement
Two methods are supported to calculate total reactive power[Qt] and total apparent power[St] for three-phase
sum.
1) Vector Sum: Total apparent power by vector sum of three-phase apparent powers
2) Arithmetic Sum: Total apparent power by arithmetic sum of three-phase apparent powers
Total apparent power and total reactive power can vary depending on how the total apparent power of the
three-phase sum is calculated. As total apparent power varies, the total power factor(PF) also varies.
Vector Sum Method
Total apparent power is obtained by vector-sum of 3-phase apparent powers.
The active power of each phase is summed.
𝑃
𝑡
= 𝑃
𝑎
+ 𝑃
𝑏
+ 𝑃
𝑐
The reactive power of each phase is summed.
𝑄
𝑡
= 𝑄
𝑎
+ 𝑄
𝑏
+ 𝑄
𝑐
Total apparent power magnitude is calculated by the vector sum of total active power and total reactive power.
𝑆
𝑡
= √𝑃
𝑡
2
+ 𝑄
𝑡
2
(Vector sum)
Fig 5.7 Vector Sum for Total Apparent Power
St
Qa
Qb
Qc
Pa
Pb
Pc
Qt
| St |
Pt
Qa
Sa
Sb
Pb
Qb
Pc
Qc
Sc
Arithmetic Sum Method
Total apparent power is obtained by arithmetic-sum of 3-phase apparent powers.
The active power of each phase is summed.
𝑃
𝑡
= 𝑃
𝑎
+ 𝑃
𝑏
+ 𝑃
𝑐
Calculate the total apparent power by arithmetic sum of the three-phase apparent powers.
𝑆
𝑡
= |𝑆
𝑎
| + |𝑆
𝑏
| + |𝑆
𝑐
|
(Arithmetic sum)
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