Transformer and coil bobbin therefor

Details Transformer and coil bobbin therefor Transformer and coil bobbin therefor

1999-09-16

2001-11-20

Donovan, Lincoln (Department: 2832)

Inductor devices

Wound core

C336S210000, C336S234000

Reexamination Certificate

active

06320492

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention generally relates to transformers such as a transformer for heavy current, a current transformer (CT), a potential transformer (PT) and a transformer for weak current and more particularly, to a transformer including a winding wound annularly a predetermined number of times and a pair of wound cores each obtained by winding an electromagnetic magnetic plate around the winding a predetermined number of times, and a coil bobbin for use in the transformer.
For example, Japanese Patent Laid-Open Publication No. 5-226168 (1993) filed by the assignee assigned by the present inventors discloses this kind of the transformer as shown in
FIGS. 33 and 34
. In this known transformer, an outer periphery
2
a
of a winding
2
obtained by annularly winding a conductor a predetermined number of times is coated by an insulating member (not shown) such as an insulating tape and an insulating sheet and each of a pair of wound cores
3
is obtained by winding an electromagnetic steel plate around the winding
2
. In
FIGS. 33 and 34
, reference numeral
4
denotes a spacer and reference numeral
5
denotes a magnetic shunt core. In order to produce the winding
2
, a conductor is wound around a split winding form (not shown) made of Bakelite or the like and then, the winding is coated by the insulating member by removing the winding form.
Meanwhile, the wound core
3
is formed by steps shown in
FIGS. 35A
to
35
D. Initially, after a steel plate coil
7
obtained by winding a long belt-like electromagnetic steel plate
8
so as to have inside diameter coincident with outside diameter of the winding
2
has been annealed, the electromagnetic steel plate
8
disposed at an outermost portion of the steel plate coil
7
is passed between a pair of core winding portions
2
b
as shown in FIG.
35
A. Then, as shown in
FIG. 35B
, a rear end portion
8
a
of the electromagnetic steel plate
8
is temporarily attached to an outer periphery of the steel plate coil
7
such that a large ring
9
having diameter larger than outside diameter of the steel plate coil
7
is formed by the electromagnetic steel plate
8
. Furthermore, the steel plate coil
7
is rotated by driving rollers
11
and
12
such that the electromagnetic steel plate
8
is fed to the large ring
9
as shown by the arrow A. When rotation of the steel plate coil
7
is continued, whole of the electromagnetic steel plate
8
constituting the steel plate coil
7
is fed to the large ring
9
as shown in FIG.
35
C. Since the electromagnetic steel plate
8
has elasticity, a force B for reducing diameter of the large ring
9
is applied to the large ring
9
. When not only the roller
11
is drawn from the large ring
9
but the temporary attachment referred to above is cancelled, diameter of the large ring
9
is reduced as shown in
FIG. 35D
so as to tighten one of the core winding portions
2
b
such that the wound core
3
is formed.
However, the above mentioned known transformer has the following drawbacks. Namely, for winding a conductor
10
to the winding
2
in the transformer including the wound cores
3
, if an alignment winding method of
FIG. 36
in which the neighboring conductors
10
in each layer are held in close contact with each other and the conductors
10
in the neighboring layers deviate laterally from each other through a radius r of the conductor
10
such that gaps among the conductors
10
are minimized is employed and the outer periphery
2
a
of the winding
2
is brought into close contact with the wound cores
3
, heat produced in the conductors
10
by electric current flowing therethrough, i.e., resistance loss is efficiently dissipated through the wound cores
3
. Therefore, in order to reduce rise of temperature of the winding
2
, it is preferable that the winding
2
is formed by the alignment winding method and the outer periphery
2
a
of the winding
2
is brought into close contact with the wound cores
3
.
However, in case the winding
2
is produced by using the split winding form as described above, the winding
2
is readily deformed once the winding form has been removed. As a result, it is difficult to maintain the conductors
10
in a state of
FIG. 36
in which the conductors
10
have been closely wound by the alignment winding method. Furthermore, since the winding
2
is readily deformed as described above, it is difficult to maintain a state in which cross-sectional shape of the winding
2
coincides with inside diameter of the wound cores
3
and thus, it is impossible to hold the outer periphery
2
a
of the winding
2
and inside diameter of the wound cores
3
in close contact with each other. Accordingly, in the known transformer referred to above, rise of temperature of the winding
2
caused by heat produced in the winding
2
cannot be prevented effectively and it is difficult to make the transformer compact.
Meanwhile, if insulating property of the winding
2
and the wound cores
3
deteriorates, performance of the transformer drops. In the construction in which the winding
2
is coated by the insulating member as described above, the insulating member may be damaged through contact between the outer periphery
2
a
of the winding
2
and the wound cores
3
in the step of
FIG. 35C
for feeding the electromagnetic steel plate
8
to the large ring
9
and through contact between an end of the electromagnetic steel plate
8
disposed at an innermost portion of the large ring
9
and the outer periphery
2
a
of the winding
2
, thereby resulting in deterioration of insulating property of the winding
2
and the wound cores
3
.
Furthermore, since it is difficult to make cross-sectional shape of the winding
2
coincident with inside diameter of the wound cores
3
as described above, such a case may happen in which inside diameter of the steel plate coil
7
is different from that of the wound cores
3
wound around the core winding portions
2
b
. In this case, residual strain is produced in the electromagnetic steel plate
7
constituting the wound core
3
, thus resulting in deterioration of magnetic characteristics of the electromagnetic steel plate
8
.
On the other hand, Japanese Utility Model Laid-Open Publication No. 54-177512 (1979) and Japanese Patent Laid-Open Publication No. 2-165610 (1990) disclose coil bobbins around which a conductor is wound and on which wound cores are formed. As shown in
FIGS. 37 and 38
, the former prior art document discloses a coil bobbin
19
constituted by outer and inner frames
17
and
18
formed, on the outer periphery, with grooves
17
a
and
18
a
for forming windings
16
A and
16
B by winding the conductor
10
. Meanwhile, as shown in
FIGS. 39 and 40
, a transformer disclosed in the latter prior art document includes a first bobbin
23
constituted by primary and secondary frames
21
and
22
and a second bobbin
24
surrounding the first bobbin
23
. The conductor
10
is wound a predetermined number of times around grooves
21
a
and
22
a
formed on the primary and secondary frames
21
and
22
, respectively so as to form windings
25
A and
25
B. Meanwhile, a pair of wound cores
26
are provided on an outer periphery of the second bobbin
24
.
In the above two coil bobbins, if outside diameter of the coil bobbin is made coincident with inside diameter of the wound cores when the winding is formed on the coil bobbin, the winding and the wound cores can be brought into close contact with each other. Meanwhile, if the coil bobbin is used, the wound core and the electromagnetic steel plate are held out of contact with each other when the wound core is wound around the winding, so that damage to the winding can be prevented. However, even if the coil bobbin is used, the following problem arise. Initially, in the known coil bobbins, since cross-sectional shape of the grooves
17
a
,
18
a
,
21
a
and
22
a
is semicircular, it is difficult to closely wind the conductor
10
by the alignment winding method. Hence, the windings
16
A,
16
DB,
25
A and
25
B are set to a

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