JPS6241837B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a DC arc welding machine that uses a thyristor to adjust welding voltage by controlling the conduction angle and phase of the thyristor.

FIG. 1 shows an example of a three-phase double star rectification type DC arc welding machine with an interphase reactor that adjusts the welding voltage by controlling the conduction angle and phase of a thyristor, which has been commonly used in the past. In the figure, 1 is the primary winding of a three-phase AC main transformer. 2a-2f
is the secondary winding of the three-phase AC main transformer, and 2a,
Each phase voltage of 2b and 2c has a phase difference of 120° from each other, and each phase voltage of 2d, 2e, and 2f also has a phase difference of 120° from each other.
There is a phase difference of 120°. Also, the neutral points of each winding are connected, 2a and 2d, 2d and 2
The wires e, 2c and 2f are wound in winding directions such that the polarities are opposite to each other, and as a result, the phase voltages of each phase of the wires 2a to 2f have a phase difference of 60 degrees from each other. 3a to 3f are welding voltage adjusting thyristors whose cathodes are connected to each phase of the secondary winding of the main transformer, and the anodes of thyristors 3a to 3c and 3d to 3f are connected to each other. , an interphase reactor 4 is connected between them. A DC reactor 5 is connected to the neutral point of the interphase reactor 4, and the DC reactor 5 and the main transformer secondary windings 2a~
A welding load 6 is connected between the neutral point 2f and a double star rectifier circuit with an interphase reactor.
Further, the winding 8 connected to the primary input side via the protective fuse 7 is connected to a three-phase AC auxiliary transformer (single transformer) that serves to synchronize the firing of the thyristors 3a to 3f with the primary side three-phase AC voltage. 9a, 9
b and 9c are its secondary windings.

Reference numeral 10 denotes a gate firing circuit for controlling the conduction angles of the thyristors 3a to 3f, and is connected to the thyristors 3a to 3f by a gate wiring 11 (the connections are omitted in the figure for clarity). Further, 12 is an input switch that opens and closes the main transformer and the control circuit, and a protective fuse 7 protects the gate ignition circuit 10 and the three-phase AC auxiliary transformer.

Conventionally, in a DC arc welding machine in which a thyristor is applied to a three-phase AC main transformer and the welding voltage is varied by controlling the conduction angle of the thyristor, if one of the protective fuses 7 blows out or the input If the welding machine is not operated with a complete three-phase input due to a closing failure in one of the three contacts of the switch 12, it is relatively easy to detect because the welding arc becomes unstable during small current welding. However, during high current welding, the welding arc remains fairly stable, so operation can often be continued. In this case, two or four of the six thyristors are usually in conduction, although this varies depending on various trouble situations, such as a blowout of the protective fuse 7 or a failure to close the contact of the input switch 12.
At this time, the current that was being shared by the thyristor that has become non-conducting up to that point is divided and flows into the other thyristors that are conducting, so the current that is flowing through the thyristor that is conducting and the main transformer secondary connected to that thyristor. A current exceeding the rated value flows through the side windings, causing an abnormal temperature rise, and a simple melting of the protective fuse or failure to close the contact of the switch can lead to a chain reaction that destroys the thyristor and eventually burns out the main transformer. It often caused serious accidents that led to

To explain concretely with numerical values using Fig. 1, in a welding machine with a welding current rating of 300A,
When a welding current of 300A, which is the maximum rating, is flowing, the six thyristors 3a to 3f and the main transformer secondary windings 2a to 2f in Figure 1 each have a shared current of 50A (thyristors 3a to 3f and secondary windings). Next winding 2
For a to 2f, this 50A is the upper limit rating). And if 3
If one of the protective fuses 7 of the book blows out, the gate ignition circuit will malfunction, the gate ignition signal will be cut off, and the thyristor will become non-conductive. For example, if the thyristors 3a and 3d become non-conductive and we continue to weld 300A as before, the current load will be shared between the thyristors 3a and 3d and the main transformer secondary windings 2a and 2d. A total of 100 A current of 50 A each was transferred to other thyristors 3b, 3c, 3e, 3f and other main transformer secondary windings 2b, 2c, 2e,
2f has to share the extra burden. In that case, the conducting thyristors 3b, 3c, 3e,
3f and main transformer secondary windings 2b, 2c, 2
e and 2f do not equally share this 100A, but result in an extremely unbalanced share, but the waveform rate becomes extremely poor and the burden increases rapidly. Therefore, if welding continues, the temperature of the thyristors 3b, 3c, 3e, 3f and the main transformer secondary windings 2b, 2c, 2e, 2f will continue to rise abnormally, and the temperature will eventually exceed the allowable limit, causing the thyristors to fail. This caused a chain reaction of destruction and the main transformer was burnt out.

The present invention is designed to prevent damage caused by such simple blowing of a protective fuse or failure to close a contact of an input switch.
To propose a circuit that prevents a major accident in which the thyristor is destroyed in a chain reaction and the main transformer is eventually burnt out if the welding machine continues to operate without a complete three-phase AC input. It is in.

The details of the present invention will be explained below with reference to the drawings. Second
The figure shows one embodiment of the present invention, and the numbers in the circuit diagram in Figure 2 correspond to those in the circuit diagram in Figure 1, where 1 is the primary winding of a three-phase AC main transformer. ,2
a to 2f are three-phase AC main transformer secondary windings having a phase difference of 60 degrees from each other, 3a to 3f are welding voltage adjustment thyristors, 4 is an interphase reactor, 5 is a DC reactor, 6 is a welding load, 7 is a protective fuse,
8 is the primary winding of the three-phase AC auxiliary transformer, 9a,
9b and 9c are the secondary windings of the three-phase AC auxiliary transformer, 10 is a gate ignition circuit that controls the conduction angle of the thyristors 3a to 3f, and 11 is the gate wiring connected to the gate of the thyristor (Fig. 2). 12 is an input switch that opens and closes the main transformer and the control circuit. Reference numeral 13 denotes a control circuit newly added according to the present invention, in which the normally closed contacts CRb of the relays CR inserted in the middle of the gate wiring 11 are used to melt the protective fuse 7 and close the contacts of the input switch 12. In the event of a failure, it opens immediately and stops all thyristors firing, stopping the welding machine from operating.

Let us now consider a case where the input switch 12 is turned on and voltage is applied to all three phase secondary windings 9a to 9c of the three-phase auxiliary transformer. Among the secondary voltages of the three phases, the secondary voltage generated in the secondary winding 9a is half-wave rectified through the diode _D1 and smoothed by the capacitor _C1 . This smoothed voltage is passed through the Zener diode ZD ₁ (3/ of the smoothed voltage
A Zener diode with a Zener voltage of about 4 is selected) and the base current is passed through the resistor _R1 to the transistor _Q1 as a switching element, so the transistor _Q1 turns on (the resistor _R2 stabilizes the transistor _Q1) . (This is a bias resistor that operates the

Similarly, the secondary voltages generated in the secondary windings 9b and 9c of the other two phases are also half-wave rectified and smoothed, and the base currents flow through the transistors Q ₁ ′ and Q ₁ ″ as switching elements, respectively. ,
Transistors Q ₁ ′ and Q ₁ ″ are turned ON. In this way, all transistors Q ₁ , Q ₁ ′, Q ₁ ″ are turned ON.
When the resistor R ₃ is connected from the DC voltage source Vc,
Since the currents flowing through R ₃ ′ and R ₃ ″ flow toward transistors Q ₁ , Q ₁ ′, and Q ₁ ″, respectively, the base current flowing into transistor Q ₀ through diodes D ₂ , D ₂ ′, and D ₂ ″ is zero. (Resistor R ₀ is a bias resistor that allows transistor Q ₀ to operate stably.) Therefore, transistor Q ₀ is OFF, no current flows through the coil of relay CR, and relay CR does not operate. When relay CR is not operating, normally closed contact CRb of relay CR is also closed, so the gates of thyristors 3a to 3f are connected to gate ignition circuit 10 through gate wiring 11 and normally closed contact CRb of relay CR. The thyristor fires normally.

However, if one of the protective fuses 7 blows out, or if one of the three contacts of the input switch 12 fails to close, the complete three-phase AC input will no longer enter the auxiliary transformer. For example, when the secondary voltage of the auxiliary transformer secondary winding 9a becomes zero or halved, the voltage smoothed by the capacitor _C1 through the diode _D1 also becomes zero or halved, so that the voltage applied to the transistor _Q1 No base current flows (Zener diode ZD ₁
Since the Zener voltage of is about 3/4 of the normal smoothed voltage of the capacitor _C1 , when it is reduced by half, the base current flowing into the transistor _Q1 is blocked by the Zener diode. ).

Therefore, at this time, transistor Q ₁ is OFF.
Therefore, the base current flows from the DC voltage source Vc through the resistor R ₃ and the diode D ₂ to the transistor Q ₀ , turning on the transistor Q ₀ .
When transistor Q ₀ turns on, current flows through the coil of relay CR, operating relay CR, and
The normally closed contact CRb opens and the thyristors 3a to 3f
Since the gate is cut off from the gate ignition circuit 10, the thyristors 3a to 3f immediately become non-conductive and welding stops.

Similarly, when the secondary voltage of the auxiliary transformer secondary winding 9b becomes zero or halved, the transistor Q ₁ '
It turns OFF and transistor Q ₀ turns ON. Similarly, even if the secondary voltage of the auxiliary transformer secondary winding 9c becomes zero or halved, the transistor Q ₁ '' is turned off and the transistor Q ₀ is turned on. If the transistor Q ₀ is turned on, Current flows through the coil of relay CR, operating relay CR, and the normally closed contact CRb of relay CR opens, and the gates of thyristors 3a to 3f are cut off from gate ignition circuit 10, so thyristors 3a to 3f are activated immediately. There will be no continuity and welding will stop.

Therefore, the auxiliary transformer secondary windings 9a, 9b,
When the voltage on the secondary side _of either of
The CR operates to cut off the gate ignition circuits of the thyristors 3a to 3f, thereby stopping the operation of the welding machine.

In this way, the present invention can prevent damage caused by a simple blowing of a protective fuse or a failure to close the contact of an input switch.
If the welding machine continues to operate without a complete three-phase AC input, it can prevent a major accident that could lead to a chain reaction of destruction of the thyristor or even burnout of the main transformer. Therefore, it greatly contributes to the reliability and safety of equipment.

In Figure 2, complete three-phase AC input cannot be applied to the auxiliary transformer due to one of the protective fuses 7 blowing out, or one of the three contacts of the input switch 12 failing to close. Considering that even if the secondary voltage of one phase among the three phases of the auxiliary transformer is completely unaffected, D of the control circuit 13 in FIG. ₁ ″，ZD ₁ ″，C ₁ ″，
By omitting R ₁ ″, R ₂ ″, Q ₁ ″, R ₃ ″, and D ₂ ″ and detecting the secondary voltage of only two phases, the relay
It is also possible to operate CR. In addition, in FIG. 2, the gates of the thyristors 3a to 3f and the gate ignition circuit 10 can be cut off by directly shorting the gate signal of the gate ignition circuit 10 with the transistor Q ₀ without going through the contacts of the relay CR. It is possible.

FIG. 3 shows the present invention applied to a DC arc welding machine that adjusts the secondary voltage by connecting a thyristor to the primary side of a three-phase AC main transformer. The numbers correspond to those in the circuit diagram of FIG. However, 2 is a main transformer secondary winding, and 4' is a diode for full-wave rectification of the main transformer secondary voltage. Since the operation is exactly the same as that shown in FIG. 2, the explanation will be omitted.

According to the DC arc welding machine of the present invention having the above-described configuration, the welding machine continues to operate without a complete three-phase AC input due to a mere blowing of a protective fuse or a failure to close the contact of the input switch. When the welding voltage is adjusted by controlling the conduction angle and phase of the thyristor, the reliability of the equipment and This can be done with improved safety.

[Brief explanation of the drawing]

Figure 1 is an electrical circuit diagram of an example of a conventional DC arc welding machine that connects a thyristor to the secondary side of a three-phase AC main transformer to adjust the welding voltage. An electric circuit diagram of an embodiment of a DC arc welding machine to which the present invention is applied to the DC arc welding machine shown in Figure 3. Figure 3 shows a thyristor connected to the primary side of a three-phase AC main transformer to adjust the welding voltage. FIG. 2 is a circuit diagram of another embodiment of a DC arc welding machine to which the present invention is applied. 1... Three-phase AC main transformer primary winding, 2, 2a
~2f... Secondary winding, 3a to 3f... Thyristor, 6... Welding load, 7... Protective fuse, 8
...Primary winding of three-phase AC auxiliary transformer, 9a, 9
b, 9c... Secondary winding, 10... Gate ignition circuit, 12... Input switch, 13... Control circuit.

Claims (1)

[Claims] 1. A thyristor connected to the secondary or primary side of a three-phase AC transformer, a gate ignition circuit that controls the conduction angle of this thyristor to adjust the welding voltage, and the three-phase AC main transformer. A three-phase AC auxiliary transformer used as a power source for driving the gate circuit connected in parallel, and a half-wave or half-wave or A rectifier circuit that performs full-wave rectification, a switching element that is connected to each of the rectifier circuits via a Zener diode and turns on and off depending on the magnitude of the secondary voltage that is separately rectified by the rectifier circuit, and this switching element. ON−
A DC arc welding machine comprising a switching circuit that cuts off the thyristor from the gate ignition circuit when in an OFF state.