21
E
N
G
L
IS
H
P
N
becomes: 3 x U
N
x I x cos
ϕ
=
3 x 6000 / š 3 x 265 x 0.85 = 2.33MW
P
I
becomes: 3 x U
I
x I
I
x VT (ratio) x CT (ratio) =
3 x 100 / š 3 x 5 x 60 x
60 = 3.12MW, the ratio P
N
is: 0.75
P
I
In both examples the accuracy of the measurement is 0.5% F.S. when
considering the amplitude range of the measured voltage from 0.9U
n
to
1.1U
n
and the amplitude range of the measured current from 0.6I
n
to 1I
n
with a PF (cos
ϕ)
of 0.85 (according to the graph on page 19).
The accuracy of the output is connected to the accuracy of the measure-
ment plus the scale ratio of both inputs (Hi.E - Lo.E) and outputs (Hi.A -
Lo.A) as shown in the graph on page 19.
When: S
R
= AFS x (Hi.A - Lo.A) - 1.25
100 x (Hi.E - Lo.E)
where
AFS = automatically calculated electrical full scale value
S
R
= scale ratio.
There isn't any additional accuracy error on the output signal if S
R
- 1.25.
Example 7:
AFS = 3.30MW; Lo.E = 0; Hi.E = 3.30MW; Lo.A = 20%; Hi.A = 99.9%
S
R
becomes: 3.30 x (99.9-20) = 0.8
100 x (3.30-0)
0.8 - 1.25 no additional error.
Example 8:
AFS = 3.30MW; Lo.E = 1.00MW; Hi.E = 3.00MW; Lo.A = 20%
Hi.A = 99.9%
S
R
becomes: 3.30 x (99.9-20) = 1.32
100 x (3-1)
1.32 > 1.25, according to the graph on page 19 there is an additional error
of 0.2% F.S.