Table of Contents
Advertisement
Accuracy contribution from the current 5
191ppm of 0.3 A+240 A = (0.3x0.000191)+0. 000240 = 0.000058+0.000240 = 0.000297
Modified by the sensitivity coefficient = 0. 000297x0.3 ÷ 7.041307 = 0.000013 A
Combined current uncertainty:
u
(
I
)
. 0
001388
RMS
I
RMS
2
2
S
V
Now,
RMS
Apparent Power uncertainty:
u
(
V
u
(
S
)
RMS
[
S
V
RMS
giving:
u
(
S
)
. 0
0002574
c
Apparent Power Accuracy = 774.7358 0.1994 VA
1-48. Power (P) Accuracy Calculations
Real power is the sum of the products of volt/current/phase-angle at each harmonic frequency.
∑
P
V
I
cos
n
n
where n is the harmonic order of the components.
Calculation of power accuracy uses the same techniques shown previously. The uncorrelated uncertainty
components of voltage, current and phase are combined using root sum of squares for each frequency.
2
u
(
P
)
u
(
f
[
2
V
P
f
u
(x
)
where
is the uncertainty of the component
f
at frequency
. It is easiest to express each of these contributions as ppm.
The contribution of phase angle accuracy varies with the set phase angle as shown below.
u
(
phase
)
1
where
is the set phase angle and
The power uncertainties for each frequency, modified by the appropriate sensitivity coefficient c
summed to give the combined uncertainty u
those of current and phase).
N
∑
u
(
P
)
c
c
i
i
1
th
harmonic:
. 0
000037
. 0
. 7
041307
2
.
I
110
.
02727
. 7
RMS
)
u
(
I
)
2
RMS
2
]
[
]
I
RMS
774
.
735748
. 0
Watts
n
V
)
u
(
I
)
u
f
f
2
2
]
[
]
[
I
f
f
x
and
cos(
u
(
))
cos
( u
)
is the phase accuracy.
(linearly summed because voltage components are correlated, as are
c
u
(
P
)
i
Introduction and Specifications
000013
. 0
000204
(or 204 ppm).
041307
774
.
7358
2
. 0
000157
. 0
000204
1994
VA
(
phase
)
f
2
]
phase
f
phase
is the phase angle between the current and voltage
Electrical Specifications
VA
2
. 0
0002574
, are then linearly
i
1
1-23
- Quick Links:
- Electrical Specifications
Hide quick links:
Advertisement
Table of Contents
