Information
-
Patent Grant
-
6208230
-
Patent Number
6,208,230
-
Date Filed
Tuesday, October 26, 199925 years ago
-
Date Issued
Tuesday, March 27, 200123 years ago
-
Inventors
-
Original Assignees
-
Examiners
- Donovan; Lincoln
- Nguyen; Tuyen
-
CPC
-
US Classifications
Field of Search
US
- 336 5
- 336 12
- 363 2
- 363 4
- 363 5
- 363 64
-
International Classifications
-
Abstract
A transformer for a cycloconverter includes three single-phase transformers connected into a three-phase configuration. Each of the single-phase transformers includes a two-legged core, primary windings wound on at least one of legs of the two-legged core, and twelve secondary windings wound on at least one of the legs of the two-legged core. The secondary windings are connected to positive group converters and negative group converters of a three-phase output circulating current type cycloconverter composed of three single-phase output circulating current type cycloconverters connected in a three-phase configuration. Each of the single-phase output circulating current type cycloconverters includes two positive group converters and two negative group converters arranged in a twelve-pulse bridge configuration. The single-phase transformers include six sets of the secondary windings of the respective phases each of which sets is connected in a delta configuration and other six sets of the secondary windings each of which sets is connected in a wye configuration.
Description
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
31
a
″, a primary winding
30
a
″ and an outermost first negative group winding
32
a
″ in this order as viewed in FIG.
16
.
The primary windings
30
a
,
30
a
′ and
30
a
″ are connected in parallel to one another and further to primary windings
30
a
,
30
a
′ and
30
a
″ of the other two legs (not shown) each in a three-phase configuration. The secondary windings
31
a
,
31
a
′ and
31
a
″ are connected to respective secondary windings
31
a
,
31
a
′ and
31
a
″ of the other two legs each in a delta configuration and further to first positive group converters
27
a
of the respective phases. The secondary windings
32
a
,
32
a
′ and
32
a
″ are connected into a delta configuration in the same manner as described above and further to first negative group converters
28
a
of the respective phases. The transformer
36
b
has the same arrangement as described above except that the secondary windings
31
b
,
31
b
′,
31
b
″,
32
b
,
32
b
′ and
32
b
″ are connected in a wye configuration.
FIG. 17
shows an electrical arrangement of further another prior-art cycloconverter
38
. The cycloconverter
38
is constructed so that a single three-phase transformer
39
applies a predetermined AC voltage to each phase converter section
26
.
FIG. 18
shows a winding arrangement for one of legs of an iron core of the transformer
39
. More specifically, on an upper portion of one leg
40
p
of a three-legged core
40
are wound the same windings as those wound on the upper portion of the leg
37
of the above-described transformer
36
a
(see FIG.
16
). Further, on a lower portion of the leg
40
p
are wound the same windings as those wound on the lower portion of the leg of the above-described transformer
36
b.
In each of the aforesaid transformers
29
,
36
a
,
36
b
and
39
, each primary winding is interposed between the positive and negative group windings such that these windings are magnetically coupled close with one another. Accordingly, a load current flows into the primary windings during energization to either positive or negative group windings as disclosed in Japanese Patent Application Publication No. 63-186564A published on Aug. 2, 1988. Consequently, since a ratio of use of the primary windings to the secondary windings is improved, a total capacity of the primary windings can be rendered 1/{square root over (2)} times smaller than a total capacity of the secondary windings. Further, the three-legged cores
34
and
40
are excited by a twelve-pulse current through an overall period in the respective transformers
29
and
39
. Consequently, harmonics can be reduced as compared with a case where the core is excited by a six-pulse current and accordingly, a core loss can also be reduced.
Consider a case where sets of the positive group windings, primary windings and negative group windings wound on the legs
34
p
,
37
p
and
40
p
of the transformers
29
,
36
a
(
36
b
) and
39
of the respective conventional cycloconverters
33
,
35
and
38
have the same dimensions. In this case, an amount of core material used is rendered smaller as the number of transformers is decreased, and with this, no-load loss is reduced. The arrangement of the cycloconverter
38
as shown in
FIG. 17
is superior in this respect.
Further, all the secondary windings
31
a
-
32
b
″ of the transformer
39
of the cycloconverter
38
are wound on the single three-legged core
40
so as to form the same magnetic circuit with the core. Accordingly, the core
40
is excited by the twelve-pulse current through the overall period including a period in which the positive group converters
27
a
and
27
b
supply positive half-cycle voltages and a period in which the negative group converters
28
a
and
28
b
supply negative half-cycle voltages. As a result, the transformer
39
has an advantage that the core loss is reduced. This also applies to each of the transformers
29
of the cycloconverter
33
having the first and second positive group windings
31
a
and
31
b
and the first and second negative group windings
32
a
and
32
b.
However, the above-described transformer
39
has twelve secondary windings per leg. With respect to the middle leg
40
q
, a space utilized to extend lead wires is limited to two opposite directions as shown in
FIG. 19
which is a schematic plan view of the transformer
39
. As a result, it is difficult to extend the twelve lead wires regarding the middle leg
40
q
. Accordingly, the arrangement of the transformer
39
has not been employed hitherto.
On the other hand, the transformer
36
a
of the cycloconverter
35
as shown in
FIG. 15
has the secondary windings
31
a
to
32
a
″ connected to the first positive and negative group converters
27
a
and
28
a
of the respective phases. Further, three secondary windings
31
a
of the respective phases are connected in the delta configuration. All the other secondary windings
32
a
to
32
a
″ of the respective phases are also connected each in the delta configuration. Accordingly, the transformer
36
a
is excited by the six-pulse current through the overall period and accordingly has a disadvantage that the core loss is increased. This also applies to the transformer
36
b.
In view of the above-described disadvantage, the prior art has proposed a cycloconverter
41
having a modified arrangement of the secondary windings of the transformers
36
a
and
36
b
as shown in
FIG. 20. A
transformer
42
a
of the cycloconverter
41
includes parallel connected primary windings
30
a
,
30
a
′ and
30
″ of the respective phases, first positive group windings
31
a
,
31
a
′ and
31
″ of the respective phases and first negative group windings
43
a
,
43
a
′ and
43
a
″ of the respective phases. The first positive group windings
31
a
of the respective phases are connected in a delta configuration. The other first positive group windings
31
a
′ and
31
a
″ of the respective phases are each connected in a delta configuration, too. The first negative group windings
43
a
of the respective phases are connected in a wye configuration. The other first negative group windings
43
a
′ and
43
a
″ of the respective phases are each connected in a wye configuration, too. Further, a transformer
42
b
also includes second negative group windings
43
b
,
43
b
′ and
43
b
″ of the respective phases which are each connected in the delta configuration instead of the wye configuration. According to the above-described arrangement, a circulating current flowing into the cycloconverter
41
is a twelve-pulse current. However, since this circulating current component is small, each of the transformers
42
a
and
42
b
is still excited by the six-pulse current and the core loss cannot be reduced much.
To overcome the above-described drawback, the prior art has further proposed a cycloconverter
44
having a further modified arrangement of the secondary windings of the transformers
42
a
and
27
b
as shown in FIG.
21
. The transformer
45
a
includes secondary windings connected to the positive group converters
27
a
and
27
b
of the respective phases. More specifically, the transformer
45
a
includes parallel connected primary windings
30
a
,
30
a
′ and
30
a
″ of the respective phases, first positive group windings
31
a
,
31
a
′ and
31
a
″ of the respective phases which are each connected in a delta configuration, and second positive group windings
31
b
,
31
b
′ and
31
b
″ of the respective phases which are each connected in a wye configuration. Further, a transformer
48
b
also includes first negative group windings
43
a
,
43
a
′ and
43
a
″ of the respective phases which are each connected in the wye configuration and second negative group windings
43
b
,
43
b
′ and
43
b
″ of the respective phases which are each connected in the delta configuration. Consequently, each of the transformers
45
a
and
45
b
is excited by a twelve-pulse current through the overall period. However, a required total capacity of the primary windings of each transformer is equal to a total capacity of the secondary windings. This renders the size of each transformer larger than those of the above-described transformers
36
a
,
36
b
,
42
a
and
42
b
and accordingly increases the manufacturing cost of the cycloconverter.
SUMMARY OF THE INVENTION
Therefore, an object of the present invention is to provide a transformer for a cycloconverter which has such a construction that a transformer core is excited by a twelve-pulse current through the overall period and lead wires can readily be extended and which can reduce the total capacity of primary windings.
The present invention provides a transformer for a cycloconverter comprising three single-phase transformers connected into a three-phase configuration. Each of the single-phase transformers comprises a two-legged core, primary windings wound on at least one of legs of the two-legged core and twelve secondary windings wound on at least one of the legs of the two-legged core. The secondary windings are connected to positive group converters and negative group converters of a three-phase output circulating current type cycloconverter composed of three single-phase output circulating current type cycloconverters connected in a three-phase configuration. Each of the single-phase output circulating current type cycloconverters includes two positive group converters and two negative group converters arranged in a twelve-pulse bridge configuration. The single-phase transformers include six sets of the secondary windings of the respective phases each of which sets is connected in a delta configuration and other six sets of the secondary windings each of which sets is connected in a wye configuration.
According to the above-described transformer, the two-legged core can be used in each single-phase transformer. With respect to either leg, lead wires of the primary and secondary windings can readily be extended in three directions other than a direction of the other leg. Further, all of the twelve secondary windings connected to the positive and negative group converters arranged in the twelve-pulse bridge are wound in each single-phase transformer. Consequently, since each single-phase transformer is excited by a twelve-pulse current, the core loss can be reduced.
Three transformers are required in the above-described arrangement as in the foregoing first conventional arrangement. However, the three three-phase transformers are used in the first conventional arrangement, whereas the three single-phase transformers are used in the present invention. Consequently, since an amount of core material used for each transformer can be reduced, the size of each transformer can be reduced and no-load loss can be decreased.
BRIEF DESCRIPTION OF THE DRAWINGS
Other objects, features and advantages of the present invention will become clear upon reviewing the following description of the preferred embodiments, made with reference to the accompanying drawings, in which:
FIG. 1
is a circuit diagram showing an electrical arrangement of a three-phase output circulating current type cycloconverter in which three single-phase transformers of a first embodiment in accordance with the present invention is used;
FIG. 2
is an electrical connection diagram of secondary windings of the single-phase transformers;
FIG. 3
is also an electrical connection diagram of the other secondary windings of the single-phase transformers;
FIG. 4
is a schematic plan view of one of the single-phase transformers;
FIG. 5
is a diagrammatic longitudinally sectional view of one leg of the core of one single-phase transformer, showing an arrangement of the windings in the one leg;
FIGS. 6A
,
6
B and
6
C are schematic front views of the transformers;
FIG. 7
is a schematic plan view of one of the single-phase transformers of a second embodiment in accordance with the invention;
FIG. 8
is a diagrammatic longitudinally sectional view of one leg of the core of one single-phase transformer, showing an arrangement of the windings in the one leg;
FIG. 9
is an electrical connection diagram of primary windings of the single-phase transformers of a third embodiment in accordance with the invention;
FIG. 10
is an electrical connection diagram of a conventional single-phase output circulating current type cycloconverter with six pulse bridge arrangement;
FIGS. 11A
,
11
B and
11
C are voltage waveform charts at respective portions of the cycloconverter shown in
FIG. 10
;
FIG. 12
is an electrical connection diagram of another conventional single-phase output circulating current type cycloconverter with twelve pulse bridge arrangement;
FIG. 13
is an electrical connection diagram of a prior art three-phase output cycloconverter comprising three cycloconverters shown in
FIG. 12
;
FIG. 14
is a diagrammatic longitudinally sectional view of one leg of the core of one of the transformers used in the cycloconverter shown in
FIG. 13
, showing an arrangement of the windings in the one leg;
FIG. 15
is an electrical connection diagram of another prior art three-phase output cycloconverter having a transformer arrangement differing from that shown in
FIG. 13
;
FIG. 16
is a diagrammatic longitudinally sectional view of one leg of the core of one of the transformers used in the cycloconverter shown in
FIG. 15
;
FIG. 17
is an electrical connection diagram of further another prior art three-phase output cycloconverter having a transformer arrangement differing from those shown in
FIGS. 13 and 15
;
FIG. 18
is a diagrammatic longitudinally sectional view of one leg of the core of one of the transformers used in the cycloconverter shown in
FIG. 17
;
FIG. 19
is a schematic plan view of transformers used in the cycloconverter shown in
FIG. 17
;
FIG. 20
is an electrical connection diagram of further another prior art three-phase output cycloconverter having a transformer arrangement differing from that shown in
FIG. 15
; and
FIG. 21
is also an electrical connection diagram of the three-phase output cycloconverter which is similar to that shown in
FIG. 20
but has an arrangement of secondary windings of the transformers differing from that shown in FIG.
20
.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
A first embodiment of the present invention will be described with reference to
FIGS. 1
to
6
C. Identical or similar parts in the arrangement of
FIG. 1
are labeled by the same reference symbols as in the arrangement of FIG.
12
and the description of these parts are eliminated.
Referring to
FIG. 1
, an electrical arrangement of a three-phase output circulating current type cycloconverter
61
in which the transformer of the embodiment is employed is shown. The cycloconverter
61
comprises three converter sections
26
connected in a three-phase, for example wye, configuration, a cycloconverter transformer including three single-phase transformers connected in a three-phase configuration. Each converter section
26
has a twelve-pulse bridge configuration.
Each single-phase transformer
26
comprises a two-legged core
64
, six primary windings
65
a
,
65
b
,
65
c
,
65
d
,
65
e
and
65
f
wound on legs of the core
64
, and twelve secondary windings
66
a
,
67
a
,
66
a
′,
67
a
′,
66
a
″,
67
a
″,
66
b
,
67
b
,
66
b
′,
67
b
′,
66
b
″ and
67
b
″ wound on the legs of the core
64
. The connection of the secondary windings of each single-phase transformer
62
is simplified in FIG.
1
. However, for example, concerning the phase U converter section
26
, three windings
66
a
of the respective single-phase transformers
62
are connected in a delta configuration to serve as a first positive group winding which is connected to a first positive group converter
27
a
. Further, three windings
67
a
of the respective single-phase transformers
62
are connected in a delta configuration to serve as a first negative group winding which is connected to a first negative group converter
28
a
. Three secondary windings
66
b
of the respective single-phase transformers
62
are connected in a wye configuration to serve as a second positive group winding which is connected to a second positive group converter
27
b
. Three secondary windings
67
b
of the respective single-phase transformers
62
are connected in the wye configuration to serve as a second negative group winding which is further connected to a second negative group converter
28
b
. The above-described arrangement is also applied to each of phase V and W converter sections
26
. The primary windings
65
a
to
65
f
of each single-phase transformer
62
are connected in parallel with one another so as to be extended as two lead wires, being connected to a three-phase, for example wye, configuration together with lead wires of the other two single-phase transformers
62
. The lead wires are then connected to a three-phase AC power supply
2
.
FIG. 2
shows in detail the delta connection of the secondary windings
66
a
,
67
a
,
66
a
′,
67
a
′,
66
a
″ and
67
a
″ of the respective single-phase transformers
62
.
FIG. 3
shows in detail the wye connection of the secondary windings
66
b
,
67
b
,
66
b
′,
67
b
′,
66
b
″ and
67
b
″ of each single-phase transformer
62
.
In each single-phase transformer
62
, three of the primary windings
65
a
to
65
f
are wound on one leg
64
p
of the two-legged core
64
, whereas six of the secondary windings
66
a
to
67
b
″ are wound on the other leg
64
q
of the core, as shown in FIG.
4
.
FIG. 5
shows a winding arrangement for the leg
64
p
of the two-legged core
64
. More specifically, on an upper portion of the leg
64
p
are wound an innermost first positive group winding
66
a
, a primary winding
65
a
and an outermost first negative group winding
67
a
in this order as viewed in FIG.
5
. Further, on a middle portion of the leg
64
p
are wound an innermost first positive group winding
66
a
′, a primary winding
65
b
and an outermost first negative group winding
67
a
′ in this order as viewed in FIG.
5
. Additionally, on a lower portion of the leg
64
p
are wound an innermost first positive group winding
66
a
″, a primary winding
65
c
and an outermost first negative group winding
67
a
″ in this order as viewed in FIG.
5
.
Further, the other leg
64
q
also has the same winding arrangement as described above with respect to the leg
64
p
although the winding arrangement of the leg
64
q
is not shown. More specifically, on an upper portion of the leg
64
q
are wound an innermost second positive group winding
66
b
, a primary winding
65
d
and an outermost second negative group winding
67
b
in this order. Further, on a middle portion of the leg
64
q
are wound an innermost second positive group winding
66
b
′, a primary winding
65
e
and an outermost second negative group winding
67
b
′ in this order. Additionally, on a lower portion of the leg
64
q
are wound an innermost second positive group winding
66
b
″, a primary winding
65
f
and an outermost second negative group winding
67
b
″ in this order. Alternatively, the windings may be wound on each of the legs
64
p
and
64
q
in the order of the negative group winding, the primary winding and the positive group winding from the inside.
Each of the three single-phase transformers
62
constituting the cycloconverter transformer
63
includes the two-legged core
64
. The lead wires can be extended from the legs
64
p
and
64
q
in three directions as shown in FIG.
4
. In particular, one half of the primary windings
65
a
to
65
f
are wound on one leg
64
p
, whereas the other half of the primary windings are wound on the other leg
64
q
. Further, one half of the secondary windings
66
a
to
67
b
″ are wound on one leg
64
p
, whereas the other half of the secondary windings are wound on the other leg
64
q
. Consequently, the structure for extending the lead wires can be simplified and accordingly the manufacturing cost can be reduced. Further, since the cycloconverter transformer
63
comprises the three single-phase transformers
62
, an amount of core material used in the transformer
63
can be reduced as compared with the prior art cycloconverter transformer comprising the three three-phase transformers as shown in FIG.
13
.
FIG. 6A
schematically shows the two-legged cores
64
of the three single-phase transformers
62
respectively.
FIG. 6C
shows the three leg cores
34
of the prior-art three three-phase transformers
29
respectively. A set of windings wound on the leg
64
p
, for example, a set of the first positive group winding
66
a
, the primary winding
65
a
and the first negative group winding
67
a
as shown in
FIG. 5
is formed in a generally square shape. Assume that a set of windings wound on the leg
34
p
, for example, a set of the first primary winding
31
a
, the primary winding
30
a
and the first negative group winding
32
a
as shown in
FIG. 14
is formed so as to have the same shape and the same dimensions as the above-mentioned winding set wound on the leg
64
p
. In this case, when the cores
64
and
34
of the respective transformers
62
and
29
have the same thickness, the difference between the weights of the cores is proportional to the difference between areas of the cores
64
and
34
as viewed from the front.
In
FIG. 6C
, reference symbol R designates a width of each leg or the yoke of each three-legged core
34
and reference symbol W designates a width of a window portion. Reference symbol H (=W) designates a height of the window portion. Since three sets of windings are wound on each leg of the two-legged core
64
as shown in
FIG. 6A
, a width of each window portion is designated by W and a height thereof is designated by 1.5H (=1.5W). As a result, the area of the two leg core
64
as viewed from the front is smaller by 6R(R+W) than that of the three-legged core
34
, so that an amount of core material is reduced in proportion to the difference between the areas. Consequently, no-load loss is reduced in each transformer
62
as compared with the prior art transformer
29
as shown in
FIG. 13 and a
transformation efficiency can be improved.
The primary windings
65
a
to
65
f
are interposed between the positive group windings
66
a
to
66
b
″ and the negative group windings
67
a
to
67
b
″ respectively in each single-phase transformer
62
. This arrangement improves a rate of use of the primary windings
65
a
to
65
f
to the secondary windings
66
a
to
67
b
″. In this case, the primary windings
65
a
to
65
f
are magnetically coupled close to the positive group windings
66
a
to
66
b
″ and the negative group windings
67
a
to
67
b
″. Accordingly, a load current flows into the primary windings
65
a
to
65
f
during energization to either positive or negative group windings
66
a
to
66
b
″ or
67
a
to
67
b
″. Consequently, the size and the weight of each single-phase transformer
62
can be reduced since a total capacity of the primary windings
65
a
to
65
f
of each single-phase transformer
62
is rendered approximately ½ times smaller than a total capacity of the secondary windings
66
a
to
67
b″.
In each single-phase transformer
62
, the first positive group windings
66
a
,
66
a
′ and
66
a
″ and the second positive group windings
66
b
,
66
b
′ and
66
b
″ are wound on the two-legged core
64
.
Further, the first negative group windings
67
a
,
67
a
′ and
67
a
″ and the second negative group windings
67
b
,
67
b
′ and
67
b
″ are also wound on the two-legged core
64
. In other words, the windings connected to the converters
27
a
,
27
b
,
28
a
and
28
b
constituting the converter sections
26
of the respective phases are wound on a single two-legged core
64
so as to form the same magnetic circuit. Accordingly, the two-legged core
64
is excited by the twelve-pulse current through the overall period including a period in which the positive group converters
27
a
and
27
b
supply positive half-cycle voltages and a period in which the negative group converters
28
a
and
28
b
supply negative half-cycle voltages. Consequently, harmonics can be reduced as compared with the case where the core is excited by the six-pulse current and accordingly, the core loss can be reduced.
FIGS. 7 and 8
illustrate a second embodiment of the invention. The winding arrangement of each single-phase transformer
62
in the foregoing embodiment is modified in the second embodiment. The cycloconverter transformer comprises three single-phase transformers
68
connected in a three-phase arrangement as the transformer
63
in the foregoing embodiment. Each single-phase transformer
68
comprises a two-legged core
69
, six primary windings
65
a
to
65
f
wound on one leg
69
p
of the core
69
, and twelve secondary windings
66
a
to
67
b
″ wound on the leg
69
p
as shown in FIG.
7
.
FIG. 8
shows a winding arrangement for the leg
69
p
of the core
69
. On an upper portion of the leg
69
p
are wound an innermost first positive group winding
66
a
, a primary winding
65
a
and an outermost first negative group winding
67
a
in this order as viewed in
FIG. 8
so that the windings forms a set of windings. Further, five sets of windings each of which is formed by interposing the primary winding between the positive and negative windings are provided on the lower portion of the leg
69
p
. Thus, six sets of windings are formed on the leg
69
p.
The same effect can be achieved from the above-described arrangement as from the first embodiment. Since all the windings are wound on the core leg
69
p
of each single-phase transformer
68
, the number of lead wires extended from the leg
69
p
in each single-phase transformer
68
is larger than in each single-phase transformer
62
. However, the lead wires can be extended utilizing the spaces in the three directions shown by respective arrows in FIG.
7
. Further, when an amount of core material concerning the three transformers
68
is compared with an amount of core material concerning the three transformers
29
shown in
FIG. 13
on the assumption described in the foregoing embodiment, the total area of the three two-legged cores
69
as viewed from the front in the second embodiment is reduced by 2R
2
as shown in
FIGS. 6B and 6C
. Consequently, since an amount of core material is reduced in proportion to the difference between the areas, no-load loss is reduced in each transformer
68
as compared with the prior art transformer
29
as shown in
FIG. 13 and a
transformation efficiency can be improved.
FIG. 9
illustrates a third embodiment. The primary winding side of each single-phase transformer
62
in the first embodiment is modified in the third embodiment. The cycloconverter transformer comprises three single-phase transformers
70
connected in a three-phase configuration as the transformer
63
in the first embodiment. Each single-phase transformer
70
comprises a two-legged core
71
, six primary windings
72
a
to
72
f
wound on two legs of the core
71
, and twelve secondary windings
66
a
to
67
b
″ wound on the two legs of the core
71
. In this case, three of the six primary windings are wound on one leg of the core
71
, whereas the other three primary windings are wound on the other leg. Further, six of the twelve secondary windings are wound on one leg, whereas the other six secondary windings are wound on the other leg.
FIG. 9
shows an electrical arrangement of the primary winding side of each single-phase transformer
70
. In each single-phase transformer
70
, one terminals of the respective primary windings
72
a
to
72
f
are connected in common to be extended as a single lead wire
73
n
. The other terminals of the respective primary windings
72
a
to
72
f
are extended individually as six lead wires
73
a
to
73
f
respectively. These lead wires
73
a
to
73
f
are connected to current transformers
74
a
to
74
f
respectively and then connected in common, being further connected to the three-phase AC power supply
2
. The current transformers
74
a
to
74
f
constitute overcurrent detectors in the invention with overcurrent relays
75
a
to
75
f
which will be described later, respectively. The lead wires
73
n
of the respective single-phase transformers
70
are connected in common. Accordingly, the primary windings
72
a
to
72
f
of each single-phase transformer
70
constituting the cycloconverter transformer are connected in the wye configuration.
Overcurrent relays
75
a
to
75
f
constituting the overcurrent detectors are connected to the current transformers
74
a
to
74
, respectively. Each overcurrent relay opens a circuit when a current value of the corresponding lead wire detected by the respective current transformer exceeds a predetermined value.
FIG. 9
shows only one overcurrent relay
75
a
for one of the single-phase transformers
70
.
In the above-described arrangement, the six primary windings
72
a
to
72
f
are connected in parallel with one another in each single-phase transformer
70
, and the primary windings
72
a
to
72
f
are interposed between the positive group windings
66
a
to
66
b
″ such that these windings are magnetically coupled close to one another. Accordingly, when an overcurrent due to a short circuit etc. at the side of the secondary windings
66
a
to
67
b
″ flows into the secondary windings
66
a
to
67
b
″, a primary current according to the overcurrent flows concentrically into the primary windings magnetically coupled close to the secondary windings. Consequently, a detecting sensitivity for a fault current can be increased.
Although each single-phase transformer
62
comprises the parallel connected six primary windings
65
a
to
65
f
in the foregoing first embodiment, two or three primary windings may be provided for each single-phase transformer, instead. Further, each single-phase transformer
68
may comprise two primary windings in the foregoing second embodiment.
In the third embodiment, the six lead wires
73
a
to
73
f
may be connected so as to be formed into three or more wires according to a required current detecting sensitivity, and a single current transformer common to the lead wires constituting each connected wire may be connected to each wire. For example, when the lead wires
73
a
to
73
f
connected so as to be formed into three wires each composed of two lead wires, only three current transformers are required for each one of the single-phase transformers
70
. Further, when the required current detecting sensitivity is low, a single current transformer may be provided so as to be common to the six lead wires
73
a
to
73
f
. In this case, only one current transformer is required for each one of the single-phase transformers
70
. Thus, by connecting the lead wires into a suitable number of wires, the number of current transformers can be rendered the smallest while a desired current detecting sensitivity can be obtained.
The foregoing description and drawings are merely illustrative of the principles of the present invention and are not to be construed in a limiting sense. Various changes and modifications will become apparent to those of ordinary skill in the art. All such changes and modifications are seen to fall within the scope of the invention as defined by the appended claims.
Claims
- 1. A transformer for a cycloconverter comprising:three single-phase transformers connected into a three-phase configuration, each of the single-phase transformers comprising: a two-legged core; primary windings wound on at least one of legs of the two-legged core; and twelve secondary windings wound on at least one of the legs of the two-legged core, the secondary windings being connected to positive group converters and negative group converters of a three-phase output circulating current type cycloconverter composed of three single-phase output circulating current type cycloconverters connected in a three-phase configuration, each of the single-phase output circulating current type cycloconverters including two positive group converters and two negative group converters arranged in a twelve-pulse bridge configuration; wherein the single-phase transformers include six sets of the secondary windings of the respective phases each of which sets is connected in a delta configuration and other six sets of the secondary windings each of which sets is connected in a wye configuration.
- 2. The transformer according to claim 1, wherein six secondary windings of each single-phase transformer are wound on a first leg of the core and the other six secondary windings of each single-phase transformer are wound on a second leg of the core.
- 3. The transformer according to claim 1, wherein the primary windings of each single-phase transformer are wound on the legs of the core so as to be interposed between the secondary windings connected to the positive group converters and the secondary windings connected to the negative group converters.
- 4. The transformer according to claim 2, wherein the primary windings of each single-phase transformer are wound on the legs of the core so as to be interposed between the secondary windings connected to the positive group converters and the secondary windings connected to the negative group converters.
- 5. The transformer according to claim 1, wherein the primary windings of each single-phase transformer include a plurality of parallel connected primary windings, and the primary windings are provided with overcurrent detectors which detect overcurrents flowing into the primary windings respectively.
- 6. The transformer according to claim 2, wherein the primary windings of each single-phase transformer include a plurality of parallel connected primary windings, and the primary windings are provided with overcurrent detectors which detect overcurrents flowing into the primary windings respectively.
- 7. The transformer according to claim 3, wherein the primary windings of each single-phase transformer include a plurality of parallel connected primary windings, and the primary windings are provided with overcurrent detectors which detect overcurrents flowing into the primary windings respectively.
- 8. The transformer according to claim 4, wherein the primary windings of each single-phase transformer include a plurality of parallel connected primary windings, and the primary windings are provided with overcurrent detectors which detect overcurrents flowing into the primary windings respectively.
Priority Claims (1)
| Number |
Date |
Country |
Kind |
| 10-307012 |
Oct 1998 |
JP |
|
US Referenced Citations (4)
