Environmental Engineering Reference
In-Depth Information
Table 8.1 Non-oriented steel grades M15-M47
Gauge size
Thickness (in.)
Thickness (mm)
Stacking factor
24
0.0250
0.635
0.95-0.98
26
0.0185
0.470
0.95-0.98
29
0.0140
0.356
0.95-0.98
Table 8.2 Lamination steel core coating (per ASTM standards)
ASTM type
Description
Applications
C-0
Insulation consisting of a natural
oxide film formed during the
annealing process. Insulation resistance
is low and the coating can withstand
stress-relief anneals
Small motors
C-3
Organic varnish coating sufficient for air-cooled
and oil immersed cores. Excellent interlaminar
resistance. Inadequate to withstand stress relief
annealing
Larger M/Gs and
transformers
C-4
Insulation formed by chemical treatment that is
capable of withstanding stress-relief anneal below
815
C. Adequate for 60 Hz cores
Medium size M/Gs
and transformers
C-5
High resistance chemical treatment core coating
having an inorganic filler to enhance electrical
resistance. Can withstand stress-relief anneal if
below 815
C. Insulation is suitable for large cores
and for high volts/turn designs
Large M/Gs and
transformers
Table 8.1 summarizes the available lamination thickness grades from major
steel suppliers [3,4]. Lamination steels are processed as non-oriented or grain
oriented. Laminations are core coated to insulate each from adjacent sheets to
minimize eddy current loop paths. Table 8.2 summarizes the types of core coatings
currently available.
Stacking factor, the ratio of steel equivalent length to total lamination stack
length, is dependent on burr size, surface smoothness and core coating thickness.
Table 8.3 summarizes the properties of organic and inorganic core coatings.
In Table 8.1, the production thickness of lamination grade steels is shown to
range from 0.35 to 0.63 mm. But how thin should a lamination be for a certain
electric machine application? This question is fundamental to the goal of designing
an M/G for hybrid propulsion. Clearly, the value of magnetizing intensity,
H
, and
hence induction,
B
, within the core of the lamination will be markedly lower than at
its surface, particularly if the lamination is thick. This is a skin effect phenomenon
and the basis for real concern in developing the electromagnetic design of a hybrid