An adjustable speed drive (ASD) is instrumented to find the harmonic content of the load current. Only fifth and seventh harmonic currents exist, and these harmonic currents are in phase with the fundamental. State estimation is used to find the seventh harmonic current. The peak value of the current is measured to be
(1.00+0.39)(1.414)
per unit from which one deduces
I 5
​
+I 7
​
=0.39( ∗
)
(
I 5
​
+I 7
​
in rms, per unit).
Also ​
​
it is assumed that the harmonic
1/h
rule applies
5I 5
​
=7I 7
​
(∗∗)
And for this
ASD
, the manufacturer states that
(I 5
​
/0.15)=(I 7
​
/0.1)(∗∗∗)
Unbiased state estimation applied to equations
( ∗
),(( ∗∗
)
, and
( ∗∗∗
)
gives an estimate of the seventh harmonic current as (in per unit, rms, approximately) (A)
0.2000
(B)
0.1609
(C)
0.1542
(D)
0.1149
(E)
0.0715