Inductor devices – Polyphase
Reexamination Certificate
1999-10-26
2001-03-27
Donovan, Lincoln (Department: 2832)
Inductor devices
Polyphase
C336S012000
Reexamination Certificate
active
06208230
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a transformer suitable for use in a power supply for a three-phase output circulating current type cycloconverter having a twelve-pulse bridge arrangement.
2. Description of the Prior Art
FIGS. 10
,
11
A,
11
B and
11
C, and
12
illustrate a basic arrangement of a conventional single-phase output circulating current type cycloconverter
1
. Referring to
FIG. 10
, an electrical arrangement of the cycloconverter
1
is shown. The cycloconverter
1
comprises a three-phase transformer
3
connected to a three-phase alternating current (AC) power supply
2
and a converter section
8
including a positive group converter
4
and a negative group converter
5
both of which are connected via circulating current limiting reactors
6
and
7
in reverse parallel to each other. The positive group converter
4
comprises six thyristors
9
to
14
connected into a three-phase bridge configuration, whereas the negative group converter
5
comprises six thyristors
15
to
20
connected into a three-phase bridge configuration. The transformer
3
includes a primary winding
21
connected in a three-phase configuration and two secondary windings
22
and
23
each of which is connected in a delta configuration, for example. One secondary winding
22
is connected to input terminals of the positive group converter
4
, whereas the other secondary winding
23
is connected to input terminals of the negative group converter
5
. A load
24
is connected between neutral points of the reactors
6
and
7
.
In the above-described cycloconverter
1
, gate signals having predetermined patterns are supplied to the thyristors
9
to
14
of the positive group converter
4
and the thyristors
15
to
20
of the negative group converter
5
, respectively. As a result, substantially sinusoidal voltages e
op
and eon as shown by bold solid lines in
FIGS. 11A and 11B
are generated between output terminals Tp
1
and Tp
2
of the positive group converter
4
and between output terminals Tn
1
and Tn
2
of the negative group converter
5
, respectively. A substantially sinusoidal voltage e
o
, which is equal to a mean value of the voltages e
op
and e
on
as shown by bold solid line in
FIG. 11C
, is obtained between both terminals of the load
24
. Each of thin solid lines in
FIGS. 11A
to
11
C shows a voltage of the three-phase AC power supply
2
. Broken lines in
FIGS. 11A
to
11
C show fundamental wave components of the voltages e
op
, e
on
and e
o
respectively.
The input voltage is thus supplied into the cycloconverter
1
from the three-phase AC power supply
2
when the gate signals are supplied to the thyristors
9
to
20
respectively. A power supply frequency of the input voltage is directly converted to a lower frequency in a predetermined range such that a single-phase AC voltage is delivered. Accordingly, the cycloconverter
1
serves as a frequency converting circuit.
FIG. 12
shows another conventional cycloconverter
25
including a converter section
26
. The converter section
26
comprises a positive group converter including a first positive group converter
27
a
and a second positive group converter
27
b
both of which are connected to each other so as to form a cascade. The converter section
26
further comprises a negative group converter including a first negative group converter
28
a
and a second negative group converter
28
b
both of which are connected to each other so as to form a cascade. Each of the positive group converters
27
a
and
27
b
has the same arrangement as the above-described positive group converter
4
, and each of the negative group converters
28
a
and
28
b
has the same arrangement as the above-described negative group converter
5
.
A three-phase transformer
29
includes primary windings
30
a
and
30
b
, a first positive group winding
31
a
and a first negative group winding
32
a
both of which serve as secondary windings corresponding to the primary winding
30
a
as shown in FIG.
14
. The transformer
29
further includes a second positive group winding
31
b
and a second negative group winding
32
b
both of which serves as secondary windings corresponding to the primary winding
30
b
, as shown in FIG.
14
. The first positive and negative group windings
31
a
and
32
a
are connected to the first positive and negative group converters
27
a
and
28
a
respectively. The second positive and negative group windings
31
b
and
32
b
are connected to the second positive and negative group converters
27
b
and
28
b
respectively.
For example, each of the first positive and negative group windings
31
a
and
32
a
is connected in a delta configuration, and each of the second positive and negative group windings
31
b
and
32
b
is connected in a wye configuration. This arrangement results in a phase difference of 30 degrees between the first and second converters of the positive and negative groups respectively. Accordingly, the cycloconverter
25
reduces harmonic components of the output voltage e
o
more than the cycloconverter
1
. The converter section
8
of the cycloconverter
1
has a six-pulse bridge arrangement, whereas the converter section
26
of the cycloconverter
25
has a twelve-pulse bridge arrangement. The above-described cycloconverter
25
is connected in a three-phase configuration such that a three-phase output cycloconverter
33
having the twelve-pulse bridge arrangement as shown in
FIG. 13
is composed.
Various transformer arrangements have conventionally been used for the above-described cycloconverter
33
in the prior art.
FIG. 13
shows one of the prior-art transformer arrangements. The above-described three transformers
29
are provided in the respective phase converter sections
26
.
FIG. 14
shows a winding arrangement for one of legs of an iron core of each transformer
29
. More specifically, on an upper portion of one leg
34
p
of a three-legged core
34
are wound an innermost first positive group winding
31
a
, a primary winding
30
a
and an outermost first negative group winding
32
a
in this order as viewed in FIG.
14
. Further, on a lower portion of the leg
34
p
are wound an innermost second positive group winding
31
b
, a primary winding
30
b
and an outermost second negative group winding
32
b
in this order as viewed in FIG.
14
.
The primary windings
30
a
and
30
b
are connected in parallel to each other and further connected to the respective primary windings
30
a
and
30
b
wound on the other two legs (not shown) each in a three-phase configuration, further connected to the three-phase AC power supply
2
. Furthermore, the first positive and negative group windings
31
a
and
32
a
are connected to the respective first positive and negative group windings
31
a
and
32
a
of the other two legs each in a delta configuration. The second positive and negative group windings
31
b
and
32
b
are connected to the respective second positive and negative group windings
31
b
and
32
b
of the other two legs each in a wye configuration.
FIG. 15
shows an electrical arrangement of another prior-art cycloconverter
35
. The cycloconverter
35
is constructed so that two three-phase transformers
36
a
and
36
b
apply predetermined AC voltages to the respective phase converter sections
26
.
FIG. 16
shows a winding arrangement for one of legs of an iron core of the transformer
36
a
. More specifically, on an upper portion of one leg
37
p
of a three-legged core
34
are wound an innermost first positive group winding
31
a
, a primary winding
30
a
and an outermost first negative group winding
32
a
in this order as viewed in FIG.
16
. Further, on a middle portion of the leg
37
p
are wound an innermost first positive group winding
31
a
′, a primary winding
30
a
′ and an outermost first negative group winding
32
a
′ in this order as viewed in FIG.
16
. Additionally, on a lower portion of the leg
37
p
are wound an innermost first positive group winding
3
Donovan Lincoln
Kabushiki Kaisha Toshiba
Nguyen Tuyen
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