U.S. patent number 3,654,543 [Application Number 05/086,028] was granted by the patent office on 1972-04-04 for pulse transformer for firing thyristors.
This patent grant is currently assigned to Hitachi, Ltd.. Invention is credited to Norio Ikemoto, Eiichi Isikawa, Tokio Isogai, Takao Miyashita, Takasi Tahara, Hisashi Yuza.
United States Patent |
3,654,543 |
Isogai , et al. |
April 4, 1972 |
PULSE TRANSFORMER FOR FIRING THYRISTORS
Abstract
An improved structure of a pulse transformer for simultaneously
firing all the gates of a multiplicity of series-connected or
series- and parallel-connected thyristors as is the case with a
converter in dc transmission equipment, having a greater insulation
strength and a good resistivity to external shocks. Specifically,
since the converter used at high tension renders the line voltage
of each thyristor higher, a molded insulating cylinder is disposed
between a primary conductor and secondary conductor units of the
transformer, whereby potential distributions between the secondary
transformer units and the insulating cylinder and between the
secondary transformer units adjacent to one another can be improved
by providing conductive layers embedded in the insulating cylinder,
and the pulse transformer can be made of a dry tape and small in
size.
Inventors: |
Isogai; Tokio (Hitachi,
JA), Isikawa; Eiichi (Hitachi, JA), Yuza;
Hisashi (Hitachi, JA), Tahara; Takasi (Hitachi,
JA), Miyashita; Takao (Hitachi, JA),
Ikemoto; Norio (Hitachi, JA) |
Assignee: |
Hitachi, Ltd. (Tokyo,
JA)
|
Family
ID: |
13933325 |
Appl.
No.: |
05/086,028 |
Filed: |
November 2, 1970 |
Foreign Application Priority Data
|
|
|
|
|
Nov 5, 1969 [JA] |
|
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44/88096 |
|
Current U.S.
Class: |
363/68; 174/143;
336/70; 336/174; 336/175; 363/35; 363/69 |
Current CPC
Class: |
H01F
30/16 (20130101); H01F 27/36 (20130101); H01F
27/324 (20130101) |
Current International
Class: |
H01F
27/34 (20060101); H01F 30/16 (20060101); H01F
27/36 (20060101); H01F 30/06 (20060101); H01F
27/32 (20060101); H02m 007/24 () |
Field of
Search: |
;321/8R,11,27R
;336/70,84,174,175,184,192,229 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Pellinen; A. D.
Claims
We claim:
1. A pulse transformer for firing thyristors comprising a primary
conductor conductively connected to a pulse generator, an
insulating cylinder through which the primary conductor extends,
and a plurality of transformer units fitted around said primary
conductor through said insulating cylinder therebetween, each of
said transformer units including a magnetic iron core, a secondary
winding wound on said iron core and connected to the gate of a
thyristor and an insulating body for insulating said secondary
winding,
a first conductive layer disposed in the inner peripheral portion
of the insulating cylinder and kept at the same potential as the
primary conductor;
second conductive layers disposed in the inner peripheral portions
of said insulating bodies of at least those transformer units which
are positioned on the higher voltage side, facing said insulating
cylinder;
third conductive layers disposed in those surface portions of said
insulating cylinder which face said second conductive layers, said
second conductive layers being electrically connected to said third
conductive layers, respectively.
2. A pulse transformer for firing thyristors as defined in claim 1,
wherein each of said second conductive layers is formed in the
inner peripheral portion and in the upper and lower surface
portions of said insulating body.
3. A pulse transformer for firing thyristors as defined in claim 1,
wherein said second conductive layers are embedded in said
insulating bodies.
4. A pulse transformer for firing thyristors as defined in claim 1,
wherein each of said third conductive layers extends beyond the
upper and lower surface of the corresponding transformer unit.
5. A pulse transformer for firing thyristors as defined in claim 1,
wherein said third conductive layers are disposed adjacent the
surface of said insulating cylinder.
6. A pulse transformer for firing thyristors as defined in claim 1,
wherein said primary conductor is formed in a hollow cylindrical
shape with a cable penetrating through said hollow portion.
7. A pulse transformer for firing thyristors as defined in claim 1,
wherein each of said transformer units includes a plurality of
electrically separated secondary windings disposed on an annular
magnetic iron core with equal spacings, and terminals corresponding
to the respective secondary windings and projected from said
insulating body.
8. A pulse transformer for firing thyristors as defined in claim 1,
further comprising a mounting base, a support seat mounted on said
mounting base, an upper and a lower vessel attached to the upper
and the lower end portion of said insulating cylinder, resilient
means for resiliently supporting said upper vessel on said support
seat, and guide means for guiding said vessel at a position in said
mounting base.
9. A pulse transformer for firing thyristors comprising a primary
conductor conductively connected to a pulse generator, an
insulating cylinder through which said primary conductor
penetrates, and plurality of transformer units fitted around said
primary conductor with said insulating cylinder disposed
therebetween, each of said transformer units including a magnetic
iron core, a secondary winding wound around said iron core and
connected to the gate of a thyristor and an insulating body for
insulating said secondary winding, a plurality of mutually
independent first conductive layers each disposed in those surface
portions of said insulating cylinder which face a respective
transformer unit, said first conductive layers being spaced with a
gap in the axial direction of said insulating cylinder; and a
plurality of second conductive layers embedded in said insulating
cylinder in groups corresponding to and electrostatically coupling
with each of said first conductive layers, said second conductive
layers being offset with respect to each other in both the radial
and axial directions, one end portion of said second conductive
layers being positioned in radial alignment with spaced points in
the gaps between said first conductive layers and being spaced and
staggered from each other with a predetermined interval in the
axial direction of said insulating cylinder.
10. A pulse transformer for firing thyristors as defined in claim
9, wherein each of said first conductive layers are kept at an
equal potential with that of the surface portion of the insulating
body of the corresponding transformer unit, and the innermost layer
of said second conductive layers being electrically connected to
the nearest first conductively layer so as to form a series of
electrostatic capacitive couplings in the axial direction of said
insulating cylinder.
11. A pulse transformer for firing thyristors as defined in claim
10, wherein said primary conductor is formed of non-magnetic
material in the form of an integral hollow cylinder through which
an energizing cable is inserted, thereby physically reinforcing
said insulating cylinder.
12. A pulse transformer for firing thyristors comprising a primary
conductor conductively connected to a pulse generator, an
insulating cylinder divided into a plurality of portions in axial
direction, said primary conductor extending through said insulating
cylinder, and a plurality of transformer units fitted around said
primary conductor through said insulating cylinder therebetween,
each of said transformer units including a magnetic iron core, a
secondary winding wound on said iron core and connected to the gate
of a thyristor and in insulating body for insulating said secondary
winding the improvement comprising:
a first conductive layer disposed in inner peripheral portion of
said insulating cylinder and kept at an equipotential to that of
said primary conductor;
second conductive layers disposed in the inner peripheral portions
of said insulating bodies of at least those transformer units which
are positioned on the higher voltage side, facing said insulating
cylinder;
third conductive layers disposed in those surface portions of said
insulating cylinder which face said second conductive layers, said
second and third conductive layers being electrically connected
respectively;
said insulating cylinder portions having a converging and a
diverging end surface;
fourth conductive layers disposed in each facing end portion of
said divided cylinder portions and electrostatically coupled to
respective one of said third conductive layers, the end lines of
said fourth conductive layers being offset in a radial direction to
form an equipotential surface substantially perpendicular to the
facing end surfaces of said insulating cylinder portion.
13. A pulse transformer for firing thyristors as defined in claim
12, further comprising gaps between said primary conductor and said
insulating cylinder, and between each pair of adjacent cylinder
portions, said gaps being continuous, and a highly insulating
medium filled in said gaps.
14. A pulse transformer for firing thyristors as defined in claim
13, further comprising an upper and a lower vessel respectively
attached at the upper and the lower end of said insulating cylinder
and an insulating medium contained in said vessel, said gaps being
continuous to said upper and lower vessel.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an improvement in pulse transformers for
firing serially connected multi-stage thyristors having a high
breakdown voltage, for example, serially connected thyristors in a
thyristor ac-dc converter for use in high voltage dc
transmission.
Description of the Prior Art
When serially-connected thyristors are used in an ac-dc converter
for high voltage dc transmission use, they may be operated either
as a forward converter (rectifier) or as a reverse converter
(inverter) by controlling the firing phase of the thyristors in
respective stages.
When such a converter is to be operated at high voltage e.g., a
hundred thousand to several hundred thousand volts, a single
thyristors cannot bear a reverse voltage or forward voltage during
the nonconductive period at such magnitude and so an appropriate
number of thyristors must be used in series in such a
converter.
One important problem when using serially connected thyristors is
how to fire all the thyristors at the same instant in response to a
fire signal. The prior art includes as firing systems for providing
multiple fire signals such systems wherein fire signals are
produced from a light pulse using phototubes, and a system wherein
fire signals are produced through secondary windings wound on an
iron core provided with a common primary winding, as is disclosed
in British Pat. No. 1,130,925.
Compared with the former firing system utilizing a light pulse, the
latter system of a pulse transformer has an advantage of using an
electric pulse in that the manufacture of the firing circuit is
easier. Theoretically, a desired number of firing circuits can be
made simply by winding the desired number of secondary windings on
a continuous iron core and all the thyristors can be fired at the
same instant by supplying a pulse current to a primary winding on
the core. However, in such a pulse transformer, there is the need
for strengthening the insulation against ground potential in the
respective transformer units, each being formed for one thyristor,
as going from the lower to the higher voltage side of the
thyristors. Due to this consideration, an oil-immersed type is
usually employed in which respective transformer units and the
primary winding, etc. are immersed in an oil vessel.
However, pulse transformers of the oil-immersed type are relatively
large in size and need, monitoring of insulating oil, therefore the
maintenance and inspection is troublesome.
Based on these facts, there has been proposed a dry type insulation
in such a pulse transformer in which insulation is provided by an
insulating cylinder disposed between transformer units and a
primary conductor. But, in such a system, corona discharges often
occur between the insulating cylinder and the primary conductor,
between the insulating cylinder and the respective transformer
units, and between adjacent transformer units, and at the end
portions of the insulating cylinder, etc. Thus, the dry type
insulation is considered very difficult to achieve.
Further, in a pulse transformer of the dry type insulation, the
insulating distance between each pair of adjacent transformer units
should be selected large enough to prevent any occurrence of corona
discharge thereat, and thereby the total height of the pulse
transformer becomes larger than that of piled thyristors,
contradictory to the requirement for compactness.
Yet further, for higher voltages, the number of transformer units
inevitably increases, resulting in an increase in the total height
which affects the structural strength against external mechanical
shocks, such as earthquakes.
SUMMARY OF THE INVENTION
An object of this invention is to provide a pulse transformer of a
dry insulation type in which the occurrence of a corona discharge
can be effectively prevented.
Another object of this invention is to provide a pulse transformer
in which the insulating distance between each pair of adjacent
transformer units is decreased and the surface potential gradient
in an insulating cylinder is uniformalized by uniformly sharing the
absolute potential, thereby decreasing the total height of the
structure.
A further object of this invention is to provide a pulse
transformer having a large number of transformer units in which the
manufacture of a long insulating cylinder is easy.
Another object of this invention is to provide a pulse transformer
which is hard to get damaged by external mechanical shocks.
According to a feature of this invention, a conductive layer is
formed on the inner peripheral portion of an insulating cylinder
and kept at an equal potential with a primary conductor extending
through the cylinder, other conductive layers are formed at least
in the surface portions of transformer units on the high voltage
side facing said insulating cylinder and in the corresponding
surface portions of said insulating cylinder with respective
conductive connections therebetween, and further, the conductive
layers in the insulating cylinder are coupled electrostatically to
one another.
According to another feature of the invention, an insulating
cylinder in a pulse transformer is divided into plural portions
which are piled one on another. The end portions of the divided
cylinder portions facing each other have diverging and converging
surfaces to fit one another. In these end portions of the
insulating cylinder, conductive layers electrostatically coupled in
a radial direction are provided with their ends offset so as to
form an equipotential surface perpendicular to said facing
surfaces.
When a transformer is of higher voltage, the number of transformer
units increases, hence the height of the insulating cylinder
becomes higher, and accordingly the structure becomes weaker
against external shocks.
To solve this problem, it may be considered to independently
support portions of the insulating cylinder. However, the surface
potential of the insulating cylinder becomes higher going further
away from its base which is kept at ground potential, therefore
this support system is undesirable from the insulation
viewpoint.
A larger insulating support is necessary to support an object body
with enough insulation strength, contradictory to the requirement
for reduction in size. Further, to solidly fix an insulating
cylinder on a mount invites direct affects from external
forces.
According to an embodiment of this invention, an insulating
cylinder is supported by a frame through an upper vessel connected
at the top portion of the cylinder and resilient means for
receiving said vessel. Thus, external forces are absorbed by said
resilient means.
Other features of this invention will be readily apparent from the
following detailed description on certain preferred embodiments
taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic electrical connection diagram of an example
of a circuit for firing thyristors in a high voltage thyristor
converter using a pulse transformer;
FIG. 2 is a partially cross-sectional front view of an embodiment
of a pulse transformer for firing thyristors according to the
invention;
FIG. 3 is an elevated partial cross-section of an insulating
cylinder and transformer units of the pulse transformer shown in
FIG. 2;
FIG. 4 is an explanatory front view of the insulating cylinder for
showing the surface potential distribution of the cylinder;
FIG. 5 is a cross-sectional view of an alternative embodiment of
the transformer unit; and
FIG. 6 is a cross-section along line VI -- VI of FIG. 3.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 shows a circuit for firing a thyristor converter in which
thyristors SR.sub.1, .... SR.sub.n.sub.-1 and SR.sub.n are serially
connected to have two lead-out terminals L.sub.1 and L.sub.2 and
are fired by pulse signals applied to respective gates G.sub.1,
G.sub.n.sub.-1 and G.sub.n. Voltage dividing circuitry B.sub.1,
...., B.sub.n.sub.-1 and B.sub.n is usually formed of resistors R
and capacitors C for uniformalizing the applied voltages on
respective thyristors. Zener diodes Z.sub.1, ...., Z.sub.n.sub.-1
are connected between the gate and the cathode of the respective
thyristors through rectifiers D.sub.1, ...., D.sub.n.sub.-1 and
D.sub.n. An input pulse current is generated in a pulse current
generator PG and is allowed to flow through a primary conductor
W.sub.1 conductively connected to this pulse generator PG. At
positions of this primary conductor W.sub.1, a multiplicity of
superposed annular iron cores RC.sub.1, ...., RC.sub.n.sub.-1 and
RC.sub.n are disposed, which are wound with respective secondary
windings W.sub.21, ...., W.sub.2n.sub.-1 and W.sub.2n. The outputs
of the secondary windings are rectified by the respective
corresponding rectifiers and supplied to the respective thyristor
at a predetermined voltage through the respective Zener diode, to
fire the respective thyristors simultaneously.
FIG. 2 shows an overall structure of a pulse transformer according
to the invention in which an insulating support frame 2 is fixed on
a base 1 with bolts 2a. The insulating support frame 2 is formed of
a plurality of insulating stays 3 standing vertically on the base
1, insulating transverse bars 4 connecting and reinforcing the
insulating stays 3, and insulating cross bars 5 connecting and
reinforcing the transverse bars 4 and the insulating stays 3. A
receiving seat 7 for a pulse transformer 6 is provided on the
insulating support frame 2. The pulse transformer comprises a
primary conductor 8, an insulating cylinder 10 around the primary
conductor 8, and a plurality of transformer units 11 fitted around
the insulating cylinder 10. The insulating cylinder 10 is formed by
wrapping a sheet of insulating cloth, such as glass cloth or a
tetron (polyethylene terephthalate) cloth, around a central tube 9
through which the primary conductor 8 penetrates, adding epoxy
resin thereon, and thermally setting the structure.
In the embodiment shown in FIG. 2, two pulse transformer elements
6A and 6B are disposed in side-by-side relationship (but series in
connection) and are fitted in metal supports 13 through flanges 12
provided on the upper ends of the insulating cylinders 10. The
metal supports 13 are fixed to an upper vessel 14, for example
through bolts 15.
The upper vessel is filled with an insulating medium 16, e.g.
insulating oil. The upper ends of the respective insulating tube
10, the central tube 9 and the primary conductor 8 are disposed in
this insulating oil 16 and both the primary conductors 8 are
connected together by a conductor 17. For facilitating the
connection of the primary conductor 8 with the connection conductor
17, a cover 18 is provided in the upper vessel 14.
For absorbing thermal expansion or contraction of the insulating
oil 16 in the upper vessel 14, an inert gas 19 may be sealed in the
upper portion of the vessel 14 and a well-known pressure absorbing
means which can absorb the pressure variation of the inert gas 19
may be provided according to need. The pulse transformers 6A and 6B
received in the upper vessel 14 are resiliently supported on said
receiving seat 7. As this resilient support means, combinations of
a spring 20 and a guide 21 may be disposed between the upper vessel
14 or the metal supports 13 and the receiving seat 7.
At the lower end portions of the insulating cylinders 10, a lower
vessel 23 is attached through flanges 22. This lower vessel is
filled with insulating oil 16 and is continuously supplied with
insulating oil 16 in the upper vessel 14 through the inner space of
the central tube 9. Bolts 24 fix the flanges 22 to the cover 25 of
the lower vessel 23 and bolts 26 fix the cover 25 to the lower
vessel 23. The lower ends of the pulse transformers 6A and 6B are
introduced into this lower vessel 23 in a manner similar to the
upper vessel and the ends of the primary conductor 8 disposed in
the lower vessel are conductively connected to a pair of terminals
27a and 27b by way of lead-out conductors 28a and 28b. A pulse
current generator is conductively connected to these terminals 27a
and 27b.
On the bottom of the lower vessel 23, a projection comprising a rod
29 and a flange 30 is fixed to rest on a lower guide means 33
including a spring 32 in a cylinder 31 mounted on the base 1. Thus
the pulse transformer 6 is elastically supported by said upper
elastic support means and said lower guide means 33 to protect it
from external shocks.
The primary conductor 8 may be dispensed with by forming the
central tube 9 from a good conductor to work also as a primary
conductor. The structures of said insulating cylinder 10 and said
transformer units 11 will be described in detail hereinafter
referring to FIGS. 3 to 6. In case of using a central tube 9 also
as a primary conductor, hollow insulating cylinders 10a and 10b,
vertically divided, surround the central tube 9. Conductive layers
34 and 35 are disposed on the inner periphery of the insulating
cylinder 10a and 10b along an imaginary longitudinal axis and are
conductively connected to said central tube 9, respectively, so as
to keep the oil gap between the central tube 9 and the insulating
cylinders 10a, 10b at the same potential. A transformer unit is
fitted around an insulating cylinder, 10a or 10b, and comprises a
magnetic iron core 37 made of molybdenum permalloy, etc., a
secondary winding 38 wound on the magnetic iron core 37, a
conductive layer 39 formed at least on such surface portion of the
secondary winding 38 which faces the insulating cylinder 10a or
10b, and an insulating body 40 for insulating and molding the
secondary winding 38 and the conductive layer 39. Said conductive
layer 39 may be either embedded in the insulating body 40 as is
shown in FIGS. 3 and 4, or adhered to the surface of the insulating
body 40 as is shown in FIG. 5. A conductive layer 41 is formed in
the surface portion of the insulating cylinder 10a or 10b
corresponding to and facing each transformer unit 11 and is
conductively connected to the conductive layer 39 of the
corresponding transformer unit 11 by a conductor 42 to keep the gap
between the insulating cylinder 10a or 10b and the transformer unit
11 at a uniform potential. In the upper and lower end portions of
each insulating cylinder, a plurality of conductive layers 43a and
44a are disposed to form a voltage dividing capacitor to
uniformalize the electric field in the end portions of the
insulating cylinder. Conductive layers 45 electrostatically couple
respective pairs of adjacent conductive layers 41 in a longitudinal
direction, the detailed structure of which will be described with
reference to FIG. 4.
FIG. 4 shows a structure of a voltage dividing capacitor 46 formed
in the surface portion of the insulating cylinder 10a at a position
intermediate a pair of adjacent transformer units 11a and 11b. Said
voltage dividing capacitor 46 comprises conductive layers 47a, 47b
and 47c disposed offset to each other between the conductive layers
41 corresponding to a pair of adjacent transformer units 11a and
11b.
The number of the conductive layers forming said voltage dividing
capacitor 46 may be arbitrarily selected. And the innermost
conductive layer 47c of the capacitor 46 is conductively connected
to the conductive layer 41.
By the above structure, the potential at the surface portion of
each insulating cylinder can be determined and lines of electric
force l between each pair of adjacent transformer units are
distributed perpendicularly from the respective conductive layers
of the capacitor 46 to the surface of the insulating cylinder 10a.
Thus, the potential distribution in the spacing between said
transformer units can be uniformalized, rationally enabling a
reduction in the size of this spacing.
The insulating cylinder on which respective transformer units are
to be fitted may be composed of a single continuum. However, when
the voltage in the thyristor circuit is relatively high, the
insulating cylinder may be divided into two or more portions to
facilitate the manufacture thereof, as is the case with the
embodiment of FIG. 3.
In the case of a divided insulating cylinder, consideration should
be given not to allow the occurrence of a corona discharge at the
jointed portions of the divided cylinder. In FIG. 3, for example,
the upper end of an insulating cylinder 10b has a tapered
projection and the lower end of another insulating cylinder 10a has
a cone-shaped dent to fit on the above projection. Further, the
ends of respective conductive layers of the voltage dividing
capacitor 43a at the end of the insulating cylinder 10a and those
of the capacitor 44a at the end of the insulating cylinder 10b are
correspondingly offset to arrange for an equipotential surface
between said ends of the two capacitors to perpendicularly cross
the facing end surfaces of the two cylinders, thereby setting the
electric lines of force so that they extend along and within the
gap g between the two cylinders. Thus, the insulation in the
junction portion is strengthened. Here, the innermost electrodes of
the voltage dividing capacitors 43a and 44a are maintained at an
equal potential through the conductive layers 34, 35 and the
central tube 9, and the outermost electrodes are conductively
connected to each other by a connection wire 48. The gap g between
said insulating cylinders 10a and 10b is continuously open at the
inner periphery to the oil gap 36 to introduce insulating oil and
is hermetically sealed at the outer periphery with a packing
49.
In the above embodiments, one secondary winding is wound in each
transformer unit. However, a plurality of secondary windings may be
wound on each unit as is shown in FIG. 6. In the figure, secondary
windings 38a, 38b, 38c and 38d are separately disposed on a
magnetic iron core 37 and respectively connected to lead-out
terminals 50. The transformer unit 11 is coupled to an insulating
cylinder 10b through coupling means 51a to 51d. It will be apparent
that the above structure enables a reduction in the number of
transformer units and hence the overall size of the pulse
transformer is also reduced.
Further, as is shown in FIG. 2, the primary conductor may be folded
to reduce the height. In this structure, connection to the serial
thyristors is alternately made from the right half portion and the
left half portion to uniformalize the electric field in the
transformer.
As is described above, in a pulse transformer for firing high
voltage thyristors, the threshold voltage for allowing corona
discharge between the primary conductor and the insulating
cylinder, between the insulating cylinder and the transformer
units, between the transformer units, etc. can be increased
according to this invention, thereby enabling a reduction in the
thickness of the insulating cylinder and/or the size of the
transformer unit. Further, the surface potential distribution in
the insulating cylinder can be arranged in preferable form to
improve the voltage resistant property of the surface. Thus, the
height of the pulse transformer can be reduced.
Therefore, according to this invention, a smaller pulse transformer
of the dry type having a larger insulation strength can be provided
for use in firing high voltage thyristors.
* * * * *