
Noise and Vibrations of Electrical Rotating Machines 9-21
h iN i
r r
= + = ± ± ± ±1 0( , , , , ),1 2 3 4…
(
9.45)
is the rms value of the rotor fundamental current, varying with the load and Arg(Z
_
1
) its phase angle.
Equation 9.45 shows that the number of rotor bars has an inuence on the cage rotor harmonic exis-
tence, so a good choice of the slot number is very important to avoid magnetic noise [25,26]. For exam-
ple,
i
f
t
he
n
umber
o
f
r
otor
b
ars
i
s
3
4
w
ith
p
=
2
,
t
he
r
anks
h
r
of the rst rotor harmonic are −16 and 18.
ey will interfere with the stator harmonics −17 and 19 and create force waves with a mode number 2,
as shown in (9.6).
9.5.3. ...