Environmental Engineering Reference
In-Depth Information
Table 8.3 Properties of lamination core coatings
Phenolic resin
Synthetic resin
Phosphate
Coating
1- or 2-sided
2-sided
2-sided
Coating thickness (
m
m)
2-8
1-2
1
cm
2
)
Resistance, 1-side (
W
50
>
90
10
180
C
180
C
850
C
Heat resistance, constant
Corrosion resistance
Very good
Good
Good
Oil resistance
Good
Good
Good
Freon resistance
Good
Very good
Good
Moisture absorption
None
None
None
Weldability
Low
Good
Good
M/G. To understand this, consider the lamination sheet of Figure 8.1 having
thickness,
d
, and infinite in extent. The skin effect depth of flux penetration into the
lamination is given by (8.5):
s
2
msw
d
¼
ð
m
Þ
ð
8
:
5
Þ
Then the distribution of flux versus position,
B
x
, in the lamination is given by
(8.6) where
x
is the distance moving from the centre of the lamination outwards to a
surface at
d
/2, and
B
0
is the flux density at the surfaces:
s
cos
h
ð
2
x
=
d
Þþ
cos
ð
2
x
=
d
Þ
cos
h
ð
d
=dÞþ
cos
ð
d
=dÞ
B
x
¼
B
0
ð
8
:
6
Þ
Figure 8.3 illustrates the penetration of flux into the bulk of lamination steel at
two base frequencies of 60 and 400 Hz. The base frequencies represent the fun-
damental frequencies in a 4-pole machine at nominal conditions. The switching
frequencies are meant to illustrate the flux penetration depth of harmonic flux due
to PWM control and slot harmonics.
High frequency flux does not penetrate the full bulk of 24 gauge lamination
steel. The higher the frequency, the less flux is present in the bulk. If the lamination
thickness is reduced to 0.2 mm, the base frequency flux of 400 Hz is shown to fully
penetrate through the lamination sheet losing only 0.05% between the surface and
the centre.
Note that in both Figures 8.3 and 8.4 the dimension
x
varies from -
d
/2 to +
d
/2
and that it is the different frequency content, hence skin depth, that determines
the extent to which flux penetrates the laminations. Comparison of Figure 8.4
to Figure 8.3 for the case of 0.2 versus 0.635 mm laminations shows clearly that
400 Hz flux in the thin lamination makes much better utilization of the bulk than it
does for the heavy gauge lamination. For the same frequency, 400 Hz, the thick
lamination loses nearly 6% of the flux density at its bulk, whereas the thin lamination
