DESCRIPTION TRANSFORMER AND ARC-DISCHARGE PROCESSING MACHINE

TECHNICAL FIELD

The present invention mainly relates to a transformer having a circular core and also relates to an arc-discharge processing machine containing the transformer.

BACKGROUND ART

A core of a transformer disposed in a conventional inverter circuit is generally made of a silicon steel sheet, a magnetic steel sheet, and ferrite. The aforementioned materials have advantages of being processed easily and being changed freely into a desirable shape. With the materials above, the core is partly cut and a gap is formed into a desired size between the cut-off surfaces facing each other in such a way that the facing surfaces have no contact with each other.

Fig. 8 schematically shows the structure of a core forming a conventional transformer used for a welding machine. As is shown in Fig. 8, the circular core of the transformer has a structure where some gap materials are inserted in the gap in the circular core. In such a conventionally known structure, characteristics of the transformer are determined by changing the combination of the gap materials and the thickness of the materials (see patent literature 1, for example).

However, the circular toroidal core forming a conventional transformer of
Fig. 8 has a problem. To insert gap 106 into core 105, core 105 is cut at a part and insulation member 101, magnetic member 102, and spacer 103 are sandwiched and fixed between the both cut-off surfaces. In such a fixing method above—core 105 is partly cut and gap 106 and other members are inserted between the cut surfaces, the strength of the structure may be lowered in some fixing methods. In addition to decrease in strength, variations in cutting accuracy affect gap thickness, causing inconsistency in an intended effect by changing characteristics. This causes difficulty in producing transformers having same characteristics.

Besides, in a transformer with core 105 on which a winding has been wound, when the transformer needs changing or adjusting the characteristics, the already wound winding needs rewinding prior to inserting gap 106. That is, after rewinding and changing the fixed thickness of the gap, the winding has to be wound again. As described above, the conventional structure has difficulty in changing the characteristics of the transformer. [Citation List] [Patent Literature] [PTL1] Japanese Unexamined Patent Application Publication No. 2002-075747

SUMMARY OF THE INVENTION

The present invention provides a transformer capable of changing the characteristics and offering easy production without using a complicated structure and a method, and also provides an arc-discharge processing machine containing the transformer.

To address the problem earlier, the transformer of the present invention has a first core, a primary winding wound around the first core, a secondary winding wound around the first core, a tertiary winding wound around the first core, and a second core. A portion of the tertiary winding on the side in which the tertiary winding is not wound around the first core is wound around the second core, and the tertiary winding forms a closed loop structure.

The structure above allows the transformer to change the characteristics and to be easily produced without employing a complicated structure and a method.

The arc-discharge processing machine of the present invention has a first rectifier to rectify AC power fed from outside, an inverter to convert the output from the first rectifier into AC, the aforementioned transformer to transform the output from the inverter, and. a second rectifier to rectify the output from the transformer into DC.

The structure above allows the arc-discharge processing machine to change the characteristics and to be easily produced without employing a complicated structure and a method.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a plan view showing a general structure of the transformer in accordance with a first exemplary embodiment of the present invention.

Fig. 2 is a schematic view showing general circuitry of the transformer in accordance with the first exemplary embodiment of the present invention.

Fig. 3 shows an amount of heat generated in the second core for a turn ratio of the number of turns of the tertiary winding wound on the second core to the number of turns of the tertiary winding wound on the first core of the transformer in accordance with a third exemplary embodiment of the present invention.

Fig. 4 is a circuit diagram showing a general structure of the arc-discharge processing machine in accordance with a sixth exemplary embodiment of the present invention.

Fig. 5 is a waveform chart of driving signals that have temporal change with variations in load in accordance with the sixth exemplary embodiment of the present invention.

Fig. 6 is a waveform chart showing temporal change in the electric current that flows through the primary winding in the structure where the tertiary winding is not disposed and a gap material is not inserted in the core in accordance with the sixth exemplary embodiment of the present invention.

Fig. 7 is a waveform chart showing temporal change in the electric current that flows through the primary winding and the tertiary winding in the structure where the tertiary winding is added in accordance with the sixth exemplary embodiment of the present invention.

Fig. 8 is a plan view showing a general structure of a core that forms a conventional transformer used for a welding machine.

DESCRIPTION OF EMBODIMENTS

Hereinafter, exemplary embodiments of the present invention will be described with reference to accompanying drawings. In the drawings below, like components have the same reference marks and the descriptions
thereof may be omitted.

FIRST EXEMPLARY EMBODIMENT

The structure of the first exemplary embodiment of the present invention is described with reference to Fig. 1 and Fig. 2. Fig. 1 is a plan view showing a general structure of the transformer in accordance with the first exemplary embodiment of the present invention. Fig. 2 is a schematic view showing general circuitry of the transformer in accordance with the first exemplary embodiment of the present invention.

In Fig. 1 and Fig. 2, transformer 1 has first core 2, primary winding 3, first connecting sections 4a and 4b, secondary winding 5, second connecting sections 6a, 6b, 6c, and 6d, tertiary winding 7, and third connecting section 8. Primary winding 3 is wound around first core 2. First connecting sections 4a and 4b connect each end of primary winding 3 to other circuits. Secondary winding 5 is wound around first core 2. Second connecting sections 6a, 6b, 6c, 6d connect each end of secondary winding 5 to other circuits. Tertiary winding 7 is wound around first core 2. Third connecting section 8 connects the ends of tertiary winding 7 with each other. Tertiary winding 7 contains winding 7 a as the portion that is not wound around the first core 2. Winding 7a is wound around second core 9, and third connecting section 8 connects the one end with the other end of tertiary winding 7, so that tertiary winding 7 has a closed loop structure.
Such structured transformer 1 will be described.

Primary winding 3, secondary winding 5, and tertiary winding 7 shown in Fig. 1 may be formed of various materials: copper or aluminum formed into a square, a round, or a band shape; a Litz wire formed of many fine copper wires stranded with each other; and a vinyl wire. Insulating coating may be provided to these wirings or an insulating sheet may be inserted between primary wiring 3 and secondary wiring 5. Primary wiring 3 and second wiring 5 are wound around first core 2. At that time, primary wiring 3 and second wiring 5 are wound around first core 2 while a predetermined tension being applied, which increases connections between first core 2 and primary wiring 3, and between first core 2 and secondary wiring 5.

After the winding of primary winding 3 and secondary winding 5 around first core 2, a portion on the one-end side of tertiary winding 7 is wound around first core 2, and a portion on the other-end side of tertiary winding 7 is wound around second core 9. The one end and the other end of tertiary winding 7 are connected with each other at third connecting section 8, so that tertiary winding 7 has a closed loop structure. In the structure shown in Fig. 1, secondary-winding 5 has a thickness larger than, for example, primary winding 3, whereas tertiary winding 7 has a thickness smaller than, for example, primary winding 3. Primary winding 3 and secondary winding 5 are nearly adjacently wound on each position around first core 2. As for the connecting method used at third connecting section 8, soldering, pressure bonding, and screw fastening can be employed.

Generally, to change characteristics of a transformer, the core is divided into at least two parts, and a nonmagnetic, electrically insulated gap material is inserted between the cut-off edges that face each other of the divided parts of the core. The structure allows the core to have increased magnetic reluctance, suppressing the flow of magnetic flux. Besides, changing the material or the thickness of the gap allows the transformer to make a further change to characteristics.

Inserting a gap in the core, as described above, brings the effect of changing characteristics of the transformer. At the same time, in the structure where the primary winding of the transformer is determined to the input side of electric power and the secondary winding is determined to the output side, the increase in magnetic reluctance by gap insertion suppresses a sudden change in magnetic flux. Further, if the electric power on the input side changes suddenly, the magnetic flux has no sudden change, so that magnetic saturation—a phenomenon by which the core of a transformer becomes nonfunctional—can be suppressed. If magnetic saturation occurs, electric current on the input side rapidly increases, by which electric devices that are connected on the input side can be broken down. It is therefore critically important for a transformer to avoid magnetic saturation.

According to the first exemplary embodiment of the present invention, as shown in Fig. 1, a portion on the one-end side of tertiary winding 7 is wound around first core 2, and a portion on the other-end side (that is not wound around first core 2) of tertiary winding 7 is wound around second core 9. The one end and the other end of tertiary winding 7 are connected with each other at third connecting section 8, so that tertiary winding 7 has a closed loop structure. With the structure above, tertiary winding 7 wound around second core 9 functions as a load on the magnetic flux in first core 2 and suppresses the flow of the magnetic flux. As is the same with the transformer having gap 106 inserted in core 105 described in Background Art, the structure above allows the transformer to offer the effect of changing its characteristics and of suppressing magnetic saturation.
According to the first exemplary embodiment, load characteristics of transformer 1 on magnetic flux can be determined by changing the followings: the number of turns of tertiary winding 7 wound around first core 2; the number of turns of tertiary winding 7 wound around second core 9; the turn ratio of the number of turns of tertiary winding 7 wound around second core 9 to the number of turns of tertiary winding 7 wound around first core 2; and the material of second core 9. Therefore, the structure of the first exemplary embodiment obtains the effects of changing the characteristics and suppressing magnetic saturation, without disposing a gap, as is the same with a transformer that obtains them by changing the material or thickness of a gap.

According to the structure of the first exemplary embodiment, transformer 1 has first core 2 and second core 9, and tertiary winding 7 is wound around the two cores so as to have a closed loop structure, by which the effects of changing characteristics and suppressing magnetic saturation are obtained. Therefore, with no need for using a complicated structure and a method, the structure above allows transformer 1 to change the characteristics and to be produced easily.

According to transformer 1 in which tertiary winding 7 is additionally disposed, tertiary winding 7 applies load on magnetic flux even though no gap is inserted in first core 2. As is the same with the structure having a gap inserted in the core described in Background Art, the structure of the embodiment offers the similar effects—changing the characteristics of transformer 1 and suppressing magnetic saturation in transformer 1.
When a gap is inserted in first core 2 of the structure above, not only the effect by the gap inserted in first core 2, but also the effect by tertiary winding 7 that works as a load on magnetic flux will be obtained.
The structure of the first exemplary embodiment, as described above, is applicable to both cases of gap-disposed first core 2 and first core 2 with no gap.

To facilitate easy winding of primary winding 3, secondary winding 5, and tertiary winding 7, first core 2 of transformer 1 may contain a bobbin (not shown in Fig. 1). It will be understood that the winding order and winding method of the windings on the core of transformer 1 depend on the shapes of the core and material used for the windings.

SECOND EXEMPLARY EMBODIMENT

The structure of the second exemplary embodiment will be described with reference to Fig. 1 and Fig. 2. As described in the first exemplary embodiment, the load characteristics of transformer 1 on magnetic flux can be determined by changing the followings: the number of turns of tertiary winding 7 wound around first core 2; the number of turns of tertiary winding 7 wound around second core 9; the turn ratio of the number of turns of tertiary winding 7 wound around second core 9 to the number of turns of tertiary winding 7 wound around first core 2; and the material of second core 9.

With the aforementioned structure where tertiary winding 7 is wound around first core 2 and second core 9 so as to have a closed loop structure, when a load is applied to magnetic flux from second core 9 toward first core 2, the number of turns of tertiary winding 7 wound around first core 2 has to be smaller than that wound around second core 9. The reason is as follows. If the number of turns of tertiary winding 7 wound around second core 9 is smaller than that wound around first core 2, the load on magnetic flux of first core 2 is too poor to change the characteristics of transformer 1.
According to the structure of the second exemplary embodiment, from the reason above, the number of turns of tertiary winding 7 wound around first core 2 is smaller than that wound around second core 9. With the structure above, tertiary winding 7 applies a load on magnetic flux so as to change the characteristics of transformer 1 and to suppress magnetic saturation. Therefore, even if a gap is not inserted in first core 2, the structure offers the effect as the same with a gap-inserted structure, allowing transformer 1 to change the characteristics and to suppress magnetic saturation.

When a gap is inserted in first core 2 of the structure above, in addition to the effect by the gap inserted in first core 2, tertiary winding 7 applies a load on magnetic flux, allowing transformer 1 to change the characteristics and to suppress magnetic saturation.

THIED EXEMPLARY EMBODIMENT

The structure of the third exemplary embodiment will be described with reference to Fig. 1 through Fig. 3. Fig. 3 shows an amount of heat generation of second core 9 for a turn ratio of the number of turns of tertiary winding 7 wound on second core 9 to the number of turns of tertiary winding 7 wound on first core 2 of transformer 1 in accordance with the third exemplary embodiment of the present invention. The horizontal axis of Fig. 3 represents the turn ratio of the number of turns of tertiary winding 7 wound on second core 9 to the number of turns of tertiary winding 7 wound on first core 2. The vertical axis of Fig. 3 represents an amount of heat generation on the surface of second core 9 when first connecting sections 4a and 4b input a predetermined AC power and second connecting sections 6a, 6b, 6c, and 6d output converted AC power.

As shown in Fig. 3, when the turn ratio is smaller than 15, the amount of heat generation of second core 9 tends to become larger. The reason of the increase in the amount of heat of second core 9 is as follows. As the turn ratio of the number of turns of tertiary winding 7 wound around second core 9 to the number of turns of tertiary winding 7 wound around first core 2 becomes small, the flow of electric current in tertiary winding 7 increases. The increase in the current causes increase in magnetic flux that flows in second core 9, increasing the amount of heat generation of second core 9.
The smaller the turn ratio of the number of turns of tertiary winding 7 wound around second core 9 to the number of turns of tertiary winding 7 wound around first core 2, the larger the effect of changing the characteristics of transformer 1 and suppressing magnetic saturation in transformer 1. However, if heat generation of second core 9 becomes high and the temperature exceeds Curie temperature, second core 9 no longer functions as a core, so that the effect of additionally disposed tertiary winding is not expected.

Besides, the amount of heat generation has to be suppressed so as not to exceed a heat-resistant temperature of insulating coating on tertiary winding 7 wound around second core 9.

If the turn ratio is greater than 20, the current that flows through tertiary winding 7 decreases and the magnetic flux that flows through second core 9 also decreases. This is effective in suppressing heat generation of second core 9; however, the effects of changing characteristics of transformer 1 and suppressing magnetic saturation are decreased. Therefore, the magnetic saturation easily occurs in transformer 1.

As described above, in transformer 1 having a closed loop structure of tertiary winding 7 whose one side is wound around first core 2 and the other side is wound around second core 9, the turn ratio has an optimum range. That is, in the structure above, the turn ratio of the number of turns of tertiary winding 7 wound around second core 9 to the number of turns of tertiary winding 7 wound around first core 2 may be determined not less than 15 but not more than 20. The structure above offers the effects of changing characteristics of transformer 1 and suppressing magnetic saturation, and at the same time, the structure suppresses heat generation of second core 9.

With the structure above, tertiary winding 7 applies a load on magnetic flux so as to change the characteristics of transformer 1 and to suppress magnetic saturation. Therefore, even if a gap is not inserted in first core 2, the structure offers the effect as the same with a gap-inserted structure, allowing transformer 1 to change the characteristics and to suppress magnetic saturation.

When a gap is inserted in first core 2 of the structure above, in addition to the effect by the gap inserted in first core 2, transformer 1 further offers the effect brought by tertiary winding 7 that functions as a load on magnetic flux in first core 2.

FOURTH EXEMPLARY EMBODIMENT

The structure of the fourth exemplary embodiment is described with reference to Fig. 1 and Fig. 2. The description is given on the structure where transformer 1 has first core 2 of a ring-shaped toroidal core, as is shown in Fig. 1. To insert a gap in the toroidal core in the structure above, the core is cut at a part and gap material is inserted and fixed between the both cut-off surfaces. In such a fixing method above—the toroidal core is partly cut and a gap is inserted between the facing cut-off surfaces, the strength of the structure may be lowered in some fixing methods. In addition to decrease in strength, variations in cutting accuracy affect gap thickness, causing inconsistency in an intended effect by changing characteristics. This causes difficulty in producing transformers having same characteristics and in simplifying the production method. Besides, a transformer as a completed product has difficulty in changing its characteristics. That is, to change the material or the thickness of the fixed core, the already wound first and second windings need rewinding.

According to the structure of the fourth embodiment, even when the core to be used for transformer 1 has a ring shape such as a toroidal core, no need to cut a part of the toroidal core. Further, even after the completion of winding of primary winding 3 and secondary winding 5 on first core 2, tertiary winding 7 can be added or removed to change the characteristics of transformer 1 and to suppress magnetic saturation. Besides, the characteristics of transformer 1 as a completed product can be changed, without rewinding primary winding 3 and secondary winding 5, by changing the followings: the number of turns of tertiary winding 7 wound around first core 2, the number of turns of tertiary winding 7 wound around second core 9, the turn ratio of the number of turns of tertiary winding 7 wound around second core 9 to the number of turns of tertiary winding 7 wound around first core 2, and the material of second core 9. The structure above allows transformer 1 to have easy change in characteristics and to suppress magnetic saturation.

FIFTH EXEMPLARY EMBODIMENT

The structure of the fifth exemplary embodiment is described with reference to Fig. 1 and Fig. 2. When an amorphous metal is employed for the material of first core 2 of transformer 1 shown in Fig. 1, the following advantages are obtained.

- An amorphous metal has a magnetic permeability greater than ferrite, enhancing conversion efficiency of converting electric current to intensity of a magnetic field.

- An amorphous metal has a low iron loss, suppressing heat generation of first core 2.

- An amorphous metal has high Curie temperature—the temperature beyond which the core no longer functions as a core, maintaining the characteristics as transformer 1 even in a high-temperature environment.
These advantages suppress breakage of components of an electric device having transformer 1 thereon, enhancing reliability of the device.
When a dust core is employed for second core 9 of transformer 1 shown in Fig. 1, it is greatly effective in suppressing magnetic saturation. However, a ferrite core is employed for second core 9, compare to the dust core, the effect of suppressing magnetic saturation decreases.

Considering above, in transformer 1 of the fifth exemplary embodiment, first core 2 is formed of the amorphous core of an amorphous metal and second core 9 is formed of the dust core. With the structure above, even if a gap is not inserted in first core 2, tertiary winding 7 applies a load on magnetic flux. As a result, the structure offers the effect as the same with a gap-inserted structure, allowing transformer 1 to change the characteristics and to suppress magnetic saturation.

When a gap is inserted in first core 2 of the structure above, in addition to the effect by the gap inserted in first core 2, transformer 1 further offers the effect brought by tertiary winding 7 that functions as a load on magnetic flux in first core 2.

SIXTH EXEMPLARY EMBODIMENT

The structure of the sixth exemplary embodiment is described with reference to Fig. 1, Fig. 2, and Fig. 4 through Fig. 7. Fig. 4 is a circuit diagram showing a general structure of arc-discharge processing machine 10, such as an arc welding machine and an arc cutting machine, in accordance with the sixth exemplary embodiment of the present invention. Fig. 5 is a waveform chart of driving signals that have temporal change with variations in arc load 24 (described later) in accordance with the sixth exemplary embodiment of the present invention. Fig. 6 is a waveform chart showing temporal change in the electric current that flows through primary winding 3 of transformer 1 in the structure where tertiary winding 7 is not disposed and a gap material is not inserted in first core 2 in accordance with the sixth exemplary embodiment of the present invention. Fig. 7 is a waveform chart showing temporal change in the electric current that flows through primary winding 3 and tertiary winding 7 in the structure shown in Fig. 1 where, unlike the structure shown in Fig. 6, the tertiary winding is added in accordance with the sixth exemplary embodiment of the present invention.

First, the general structure of arc-discharge processing machine 10 is described with reference to Fig. 4. As is shown in Fig. 4, arc-discharge processing machine 10 has first rectifier 11 to rectify a three-phase, or a single-phase AC input power source. First switching section 12 is connected in series with second switching section 13, forming a first switching circuit.

Third switching section 14 is connected in series with fourth switching section 15, forming a second switching circuit. The first switching circuit and the second switching circuit are connected between output terminals of first rectifier 11. With the connection above, switching operation of first switching section 12 and fourth switching section 15 allows primary current to flow in a first direction; and switching operation of second switching section 13 and third switching section 14 allows primary current to flow in a second direction that is opposite to the first direction. To determine the flowing direction of primary current described above, connecting sections 4a and 4b are connected to the first switching circuit and the second switching circuit, respectively. The first switching circuit and the second switching circuit form an inverter section for converting the output rectified by first rectifier 11 into AC.

Second connecting sections 6a and 6d of secondary wiring 5 of transformer 1 shown in Fig. 1 and Fig. 2 are connected to second rectifier 16 shown in Fig. 4. Second connecting sections 6b and 6c shown in Fig. 1 and Fig. 2 are connected to output terminal 17 shown in Fig. 4. With the connection above, the electric current rectified by second rectifier 16 is fed to the outside of arc-discharge processing machine 10 via output terminal 17.

Arc-discharge processing machine 10 of the sixth exemplary embodiment is formed of first rectifier 11 to rectifying AC power fed from outside, the inverter to change the output of first rectifier 11 into AC, transformer 1 to transform the output of the inverter, and second rectifier 16 to rectify the output of transformer 1 to DC.

The structure above allows arc-discharge processing machine 10 to have easy change in characteristics and easy production with no need to employ a complicated structure and a method.

Besides, arc-discharge processing machine 10 has output detector 18, output setting section 19, and controller 20. Output detector 18 detects the voltage across output terminals 17 and detects the output current fed from output terminal 17. Output setting section 19 appropriately determines output voltage and output current. Controller 20 compares between the outputs of output detector 18 and output setting section 19 and then outputs driving signals to first switching section 12, second switching section 13, third switching section 14, and fourth switching section 15.

As is shown in Fig. 4, one side of output terminals 17 is connected to welding torch 21, and the other side of output terminals 17 is connected to welding object 23. Welding torch 21 supplies welding wire 22 with electric power fed from output terminal 17. Welding wire 22 is fed to welding object 23 by a feeding motor (not shown). Welding is thus carried out.
The workings of arc-discharge processing machine 10 structured above is described. As shown in Fig. 1 and Fig. 4, first connecting section 4a as an end of primary winding 3 is connected to first switching section 12 and second switching section 13; on the other hand, first connecting section 4b is connected to third switching section 14 and fourth switching section 15. Second connecting sections 6a and 6d as the both ends of secondary wiring 5 are connected to second rectifier 16. Second connecting sections 6b and 6c are connected to output terminal 17. Tertiary winding 7 is wound around first core 2 and second core 9, and after that, the both ends of tertiary winding 7 are connected with each other at third connecting section 8 so as to form a closed loop structure. First switching section 12 through fourth switching section 15 are formed of, for example, IGBTs (Insulated Gate Bipolar Transistors) or MOSFETs (Metal-Oxide Semiconductor Field Effect Transistors). Second rectifier 16 is formed of a diode, for example.
Output setting section 19 shown in Fig. 4, which is formed of a volume, a jog dial, and a switch (not shown), determines output voltage and output current. Output detector 18 detects output voltage and output current. Controller 20, which is formed of a CPU or an operational amplifier, outputs driving signals to first switching section 12 through fourth switching section 15 so as to agree the output setting value determined by output setting section 19 with the detected value detected by output detector 18. The driving signals fed from controller 20 are, for example, for PWM (Pulse Width Modulation) operation or phase shift operation.

Controller 20 outputs the driving signals to first switching section 12 through fourth switching section 15, by which primary current flows into transformer 1, and electric power converted by first core 2 is fed to second rectifier 16 and rectified there. The rectified electric power is supplied, via output terminal 17, to welding wire 22 and welding object 23 to generate an arc between them for welding.

Welding torch 21 feeds welding wire 22 fed by a feeding motor (not shown) so as to position it properly to welding object 23, and at the same time, welding torch 21 supplies welding wire 22 with output electric power.
In a welding method where a welding electrode is fed by the feeding motor and an arc is generated between the welding electrode and welding object 23, welding wire 22 as a welding electrode is called a consumable electrode. In contrast, in a welding method where an arc is generated between a welding electrode fixed to welding torch 21 and welding object 23, the welding electrode is called non-consumable electrode. In the sixth exemplary embodiment, the description is given on a non-consumable electrode type arc-discharge processing machine 10 as an example, more specifically, given on a non-consumable electrode type welding machine.
Arc load 24 shown in Fig. 4 causes arc generation between welding object 23 and welding wire 22 fed by the feeding motor (not shown) to carry out welding. Welding wire 22 is fed at a constant speed during the welding operation, and a short-circuit condition and an arc condition are repeatedly generated between welding wire 22 and welding object 23. As described above, on the output side of non-consumable electrode type arc-discharge processing machine 10, arc load 24 widely varies due to repeatedly generated the short-circuit condition and the arc condition.

Fig. 5 shows, on its vertical axis, a load amount that represents magnitude of arc load 24 of Fig. 4. The larger the load amount becomes, the higher the graph shifts along the up arrow.

In Fig. 5, driving signal A represents driving signals applied to first switching section 12 and forth switching section 15, and driving signal B represents driving signals applied to second switching section 13 and third switching section 14. The waveform chart of Fig. 5 shows an example in which first switching section 12 through fourth switching section 15 work on the PWM operation. The on-state is represented by the high level (of the pulse) and the off-state is represented by the low level.

The description below is given on a case where controller 20 (Fig. 4) controls the width of a driving signal applied to first switching section 12 through fourth switching section 15 according to the output detected by output detector 18 so as to agree with a predetermined output voltage and a predetermined output current determined by output setting section 19 (Fig. 4).

Under the lightly loaded condition of arc load 24 (i.e. in section El of Fig. 5), the width of each driving signal applied to first switching section 12 through fourth switching section 15 is narrowed. In contrast, under the heavily loaded condition of arc load 24 (i.e. in section E2), the width of each driving signal applied to first switching section 12 through fourth switching section 15 is widened. Further, under the condition where arc load 24 has wide variations in magnitude (i.e. in section E3), the width of the driving signal may change between a narrow state and a wide state.

The AC fed into transformer 1 depends on use, having a wide range of frequencies—from 50-60 hertz (for commercial use and households) to several megahertz or higher (for communications equipment). For example, when high-frequency AC is continuously applied to a low-frequency core, abnormal heat can occur in the core due to heat generation caused by iron loss, such as eddy-current loss and magnetic hysteresis loss. On the other hand, when low-frequency AC is applied to a high-frequency core, magnetic saturation occurs. This is because the time for one cycle of a low frequency is longer than that of a high frequency, and accordingly, the time in which input current flows in one direction increases. As a result, primary current becomes abnormally high, which can cause breakdown the circuits of first switching section 12 through fourth switching section 15.

Transformer 1 works with stability by not only selecting the material of a core having characteristics suitable for each frequency but also inserting a gap in the core so as to suppress the flow of magnetic flux. The AC frequency (hereinafter, carrier frequency) of arc-discharge processing machine 10 of the sixth exemplary embodiment generally has a range from several kilohertz to hundreds of kilohertz.

Hereinafter, with reference to Fig. 6, the description will be given on temporal change in the waveform of primary current in the structure where tertiary winding 7 and a gap are not disposed in first core 2. In Fig. 6, the descriptions of like reference marks the same as those in Fig. 5 are omitted. The primary current shown in Fig. 6 represents the current that flows through primary winding 3 of transformer 1 disposed in a circuit of arc-discharge processing machine 10 of Fig. 4.

The description below is given on an example where an amorphous metal is employed for first core 2 of transformer 1. In general, amorphous metal offers stability at a carrier frequency of 50 kHz. First switching section 12 through fourth switching section 15 operates in a limited range due to electric characteristics, such as a switching speed and on-resistance. When a soft-switching control is employed for the driving system of controller 20, switching loss is decreased, but it is difficult to obtain a leap upward in the carrier frequency. Generally, the lower the product cost of a switching section is, more difficult the increase in the carrier frequency gets. For driving at 50 kHz, an expensive switching section formed of, for example, MOSFET has to be used. When relatively low-cost, easily-available IGBTs are used, the switching sections may work at a high frequency by employing an inverter driving system capable of reducing switching loss. However, a switching section of IGBT offers the greatest efficiency at carrier frequencies of 20 kHz to 30 kHz.

The description below is on a case where the structure is driven at a carrier frequency lower than the optimum carrier frequency—so as to use low-cost switching sections—with respect to the most suitable frequency band for first core 2 of transformer 1. For example, in the structure driven at a carrier frequency of 20 kHz (i.e., lower than 50 kHz), magnetic saturation hardly occurs as long as the on-state of a driving signal is kept at a constant width. However, in the condition with a large variations in the load amount (as shown in section E3 of Fig. 6), when tertiary winding 7 of the sixth exemplary embodiment is not disposed and a gap is not inserted in first core 2, magnetic saturation can occur (see the waveform change of primary current in section E3). To avoid the phenomenon, a non-magnetic, electrically insulated gap is inserted between the cut-off surfaces facing each other at which the core is separated. Inserting a non-magnetic, electrically insulated gap into the core allows the structure to have an increased magnetic resistance, suppressing the flow of magnetic flux. As a result, magnetic saturation is suppressed.

Next description is given on arc-discharge processing machine 10 of the sixth exemplary embodiment in which tertiary winding 7 is disposed on first core 2 of transformer 1.

According to arc-discharge processing machine 10 of the sixth exemplary embodiment, a portion on a one-end side of tertiary winding 7 is wound around first core 2, and a portion on the other-end side of tertiary winding 7 (that is not wound around first core 2) is wound around second core 9. The one end and the other end of tertiary winding 7 are connected with each other by third connecting section 8, so that tertiary winding 7 has a closed loop structure. In the structure above, tertiary winding 7 wound around second core 9 functions as a load on the magnetic flux.

With the structure above, even though no gap is inserted in first core 2, tertiary winding 7 applies load on magnetic flux in first core 2. As is the same with a structure in which a gap is inserted in the core, the structure of the embodiment offers the similar effects—changing the characteristics of transformer 1 and suppressing magnetic saturation in transformer 1. When a gap is inserted in first core 2 of the structure above, not only the effect by the gap inserted in first core 2, but also the effect by tertiary winding 7 that works as a load on magnetic flux will be obtained.

Next, how primary current and tertiary-winding current flow when tertiary winding 7 is disposed on first core 2 will be described with reference to Fig. 7.

In Fig. 7, the descriptions of like reference marks the same as those in Fig. 6 are omitted. The tertiary-winding current in Fig. 7 represents the electric current that flows through tertiary winding 7 in transformer 1 disposed on a circuit of arc-discharge processing machine 10 shown in Fig. 4. The waveform of the tertiary-winding current of Fig. 7 shows a temporal change when tertiary winding 7 of the sixth exemplary embodiment is additionally disposed.

In the condition with a large variations in the load amount (as shown in section E3 of Fig. 7), a large current flows through tertiary winding 7, suppressing the flow of magnetic flux in first core 2, and accordingly, suppressing magnetic saturation. The amount of the current flowing through tertiary winding 7 increases with large variations occurred in width of a driving signal. In the condition where first core 2 has a great change in the amount of magnetic flux, magnetic flux also flows in second core 9 and serves as a load on first core 2, suppressing the flow of magnetic flux in first core 2. With the structure above, in transformer 1, even though no gap is inserted in first core 2, tertiary winding 7 applies load on magnetic flux in first core 2. As is the same with a structure in which a gap is inserted in the core, the structure of the embodiment offers the similar effects—changing the characteristics of transformer 1 and suppressing magnetic saturation in transformer 1. When a gap is inserted in first core 2 of the structure above, not only the effect by the gap inserted in first core 2, but also the effect by tertiary winding 7 that works as a load on magnetic flux will be additionally obtained.

The aforementioned advantage of the structure of the sixth exemplary embodiment is evidently shown in the comparison between waveforms of primary current of Fig. 6 and Fig. 7. That is, under the condition of similar change in the amount of load, primary current reaches saturation in section E2 of Fig. 6, whereas no saturation occurs in primary current in section E2 of Fig. 7.

It will be understood that first switching section 12 through fourth switching section 15 may contain backward diodes each of which disposed in parallel with each IGBT.

The second core may contain a gap therein. Further, a gap may be disposed in either the first core or the second core, or disposed in both of them.

INDUSTRIAL APPLICABILITY

The present invention provides a transformer capable of changing characteristics, with no Change in the material and thickness of the first core, by changing the number of turns of the tertiary winding wound on the first core and on the second core. Further, an additionally disposed tertiary winding enables the transformer to change the characteristics even when a gap is not inserted in the core. The present invention is therefore useful for a built-in transformer in equipment.

REFERENCE MARKS IN THE DRAWINGS
1 transformer
2 first core
3 primary winding
4a, 4b first connecting section
5 secondary winding
6a, 6b, 6c, 6d second connecting section
7 tertiary winding
7a winding
8 third connecting section
9 second core
10 arc-discharge processing machine
11 first rectifier
12 first switching section
13 second switching section
14 third switching section
15 fourth switching section
16 second rectifier
17 output terminal
18 output detector
19 output setting section
20 controller
21 welding torch
22 welding wire
23 welding object
24 arc load

CLAIMS

1. A transformer comprising:

a first core;

a primary winding wound around the first core;

a secondary winding wound around the first core;

a tertiary winding wound around the first core; and

a second core, wherein, a portion of the tertiary winding that is not wound around the first core is wound around the second core so as to form a closed loop structure of the tertiary winding.

2. The transformer according to claim 1, wherein the number of turns of
the tertiary winding wound around the first core is smaller than the number of turns of the tertiary winding wound around the second core.

3. The transformer according to claim 2, wherein a turn ratio of the number of turns of the tertiary winding wound around the second core to the number of turns of the tertiary winding wound around the first core is not less than 15 but not more than 20.

4. The transformer according to claim 1, wherein the first core is an amorphous core and the second core is a dust core.

5. The transformer according to claim 1, wherein each of the first core and the second core is a toroidal core with a no gap.

6. The transformer of according to claim 1, wherein at least any one of the first core and the second core has a gap.

7. An arc-discharge processing machine comprising:

a first rectifier to rectify AC power fed from outside; an inverter to convert output from the first rectifier to AC output; a transformer to transform the AC output from the inverter, the transformer according to any one of claim 1 through claim 6; and

a second rectifier to rectify output from the transformer to DC.