JP4935679B2 - Welding equipment - Google Patents

Description

  The present invention relates to a welding apparatus that uses a semiconductor element, and relates to a welding apparatus that detects a failure of the semiconductor element.

  In recent years, efforts for equipment safety have been strengthened worldwide. When a semiconductor element such as a thyristor used in a welding apparatus is short-circuited, not only the failure of the semiconductor element but also components such as a transformer may be burnt out at the same time.

  In the conventional welding apparatus, the following are generally known as a protection method in the case where a semiconductor element fails and is short-circuited.

  For example, a fuse or a circuit breaker is provided in a power distribution facility or an input power supply circuit that supplies power to the welding apparatus. And when a semiconductor element is short-circuited, an excessive input current flows, so the fuse blows, or the circuit breaker trips, preventing the transformers that make up the welding equipment from burning out and preventing the expansion of the failure. (For example, refer to Patent Document 1).

  FIG. 3 shows a schematic configuration of the conventional welding apparatus.

  In this conventional welding apparatus, when the input switch 101 is closed, the input power (U, V, W) is supplied to the primary winding 121 of the three-phase AC main transformer 122. The output voltages of the secondary windings 102a to 102f are rectified by thyristors 103a to 103f and supplied to the welding load 106 as a welding output current via the interphase reactor 104 and the DC reactor 105. At this time, a current obtained by dividing the welding output current into six flows through the thyristors 103a to 103f.

  A protective fuse 107 is provided to prevent the influence on other parts when the control circuit 110 that controls them is abnormal.

  Here, when one or a plurality of thyristors 103a to 103f are short-circuited for some reason, the output of the secondary windings 102a to 102f of the welding transformer is short-circuited via any of the failed thyristors 103a to 103f. Excessive current flows. When this excessive current flows, the protective fuse (not shown) provided in the power distribution device connected to this welding device blows, or the circuit breaker (not shown) trips and the welding device Protect.

  However, if a fuse or circuit breaker larger than the specified value is connected, the fuse or circuit breaker does not operate even if the thyristors 103a to 103f are short-circuited, and the secondary winding 102a of the three-phase AC main transformer 122 is not operated. ˜102f and the primary winding 121 may be burned out.

  In addition, even if the fuse attached to the distribution box or the like is melted to protect the welding apparatus, there are problems such as troublesome replacement and expensive replacement parts due to the large capacity fuse.

  Thus, in the conventional welding apparatus, when the welding apparatus does not have a fuse or a circuit breaker, it is necessary to provide a fuse or a circuit breaker in a distribution box or the like that supplies electric power to the welding apparatus. In addition, it is necessary to specify a fuse or circuit breaker with a value that can prevent burnout of the device when a semiconductor element has a short circuit failure. There was a problem that it could not be protected.

Even when a fuse or a circuit breaker is provided in the welding apparatus, the space for arranging the welding apparatus becomes large. In addition, since a fuse or a breaker for passing a large current is required, there is a problem that the cost is high.
Japanese Examined Patent Publication No. 62-41837

  In order to solve the above-described problems, the present invention is intended to easily and inexpensively cut off the input power supply of a welding apparatus when a semiconductor element breaks down, thereby preventing the failure from spreading.

  In order to solve the above problems, a welding apparatus of the present invention includes a transformer, a switch unit provided on the primary side of the transformer, for supplying or cutting off AC power to the transformer, and a transformer. A semiconductor element for controlling the welding output, and a voltage detection unit for detecting a voltage across the semiconductor element, and both ends of the semiconductor element when AC power is supplied to the transformer When the voltage detecting unit detects that the voltage is lower than the normal voltage or zero, the switch unit is opened to cut off the supply of AC power to the transformer.

  In the welding apparatus of the present invention, a plurality of semiconductor elements are provided, the plurality of semiconductor elements are connected in parallel, and a voltage detection unit is provided for each of the plurality of semiconductor elements. When one voltage detection unit detects that the voltage across the semiconductor element is lower than the normal voltage or zero, the switch unit is opened to cut off the supply of AC power to the transformer.

  In addition, the welding apparatus of the present invention opens the switch unit when the voltage detection unit detects that the voltage across the semiconductor element is lower than or equal to the normal voltage continuously for a predetermined time or longer. The AC power supply to the transformer is cut off.

  The welding apparatus of the present invention opens and closes the second relay based on the first relay, the second relay, the capacitive element connected in parallel to the second relay, and the detection result of the voltage detection unit. And a switching element such as a transistor to be operated. When the first relay operates, the second relay closes for a predetermined maintenance time corresponding to the energy stored in the capacitive element, and the first relay and the first relay When the relay of No. 2 is closed, the switch unit is closed and AC power is supplied to the transformer. When the voltage detection unit detects that the voltage across the semiconductor element is a normal voltage, the switching element is closed. By operating, the second relay is kept closed even after a predetermined maintenance time has elapsed, and the supply of AC power to the transformer is maintained, and the voltage detector has a voltage across the semiconductor element lower than the normal voltage. Or after a predetermined holding time elapses by detects switching elements operate to open that it is zero in which supply of AC power is shut off from the transformer a second relay and opening operation.

  With such a configuration, the welding apparatus of the present invention monitors the voltage of the semiconductor element, cuts off the input power when the voltage across the semiconductor element is zero or lower than the normal voltage, and inputs to the welding apparatus. By shutting off the supply of power, it is possible to prevent the expansion of failure at a simple configuration and at a low cost.

  FIG. 1 is a diagram showing a schematic configuration of a welding apparatus according to an embodiment of the present invention. The present embodiment is an example in which the present invention is applied to a double star rectifier circuit using a thyristor often used in a welding apparatus.

  As shown in FIG. 1, this double star rectifier circuit has an input switch 1 and a welding transformer 2 for opening and closing an input power source of the welding apparatus, and the welding transformer 2 includes primary windings 2a and 2. And a secondary winding 2b. Furthermore, since the thyristors 3a to 3f, which are power semiconductor elements for rectifying the output of the welding transformer 2, are provided and have a double star rectifier circuit configuration, the six thyristors 3a to 3f are connected in parallel.

  The light-emitting side elements 4a to 4f of the photocoupler connected in series with the current limiting resistor and the diode are connected in parallel or antiparallel to the thyristors 3a to 3f. In addition, the code | symbol K1-K6 attached | subjected to the arrow in FIG. 1 has shown that the arrow of the same code | symbol is connected, respectively.

  Further, the outputs of the light-receiving side elements 5a to 5f of the photocoupler are connected to inputs of AND elements 6a to 6c constituting a sequence circuit via a voltage adjustment resistor. The structure of the control part 9 of the input switch 1 in the welding apparatus of this Embodiment is shown in FIG. In addition, the code | symbol m1-m3 attached | subjected with the arrow in FIG. 1 and FIG. 2 has shown that the arrow of the same code | symbol is connected, respectively.

  As shown in FIG. 2, the control unit 9 includes a first relay 7 and a second relay 8 having a normally open contact and a normally closed contact. The first relay 7 can simultaneously turn on and off the two systems of the first system 71 and the second system 72.

  The normally open contact of the first relay 7 is connected to the connection point 1a. The normally open contact of the second relay 8 is connected to the connection point 1b via the coil portion 1c of the input switch 1 for operating the contact of the input switch 1. The normally open contact of the first relay 7 and the normally open contact of the second relay 8 are connected in series. When the normally open contact of the first relay 7 and the normally open contact of the second relay 8 are turned on (contacts are closed), the connection point 1a and the connection point 1b are connected to each other. Current flows, and the input switch 1 is closed. That is, the input power is supplied to the welding transformer 2. On the other hand, when the normally open contact of the first relay 7 or the normally open contact of the second relay 8 is turned off (the contact is opened), the connection point 1a and the connection point 1b are not connected via the coil portion 1c. As a result, no current flows through the coil portion 1c and the input switch 1 is opened. That is, the input power is not supplied to the welding transformer 2.

  As can be seen from FIG. 2, when the activation switch 10 is off, no current flows through the coil of the first relay 7, and the first relay 7 is off, and the connection between the connection point 1a and the connection point 1b is performed. Will be disconnected. Accordingly, the input switch 1 is opened. In this state, a predetermined current flows through the coil of the second relay 8 via the normally closed contact of the second system 72 of the first relay 7, and the second relay 8 is turned on. ing.

  When the activation switch 10 is turned on in this state, a predetermined current flows through the coil of the first relay 7, the first relay 7 is turned on, and the second relay 8 is also turned on. And the connection point 1b is connected via the first relay 7, the second relay 8, and the coil portion 1c of the input switch 1. At this time, the normally closed contact is opened in the second system 72 of the first relay 7. However, the second relay 8 remains on. The reason will be described in detail later.

  In this way, the connection point 1a and the connection point 1b are connected, and a current flows through the coil part 1c to close the input switch 1. Then, a voltage is applied to the thyristors 3 a to 3 f via the welding transformer 2. The thyristors 3 a to 3 f rectify the applied voltage and supply a DC voltage to the welded part 20. Note that the AC output voltage of the welding transformer 2 is applied between the anode and the cathode of the thyristors 3a to 3f.

  Here, if one or more of the thyristors 3a to 3f fail and the anode and cathode of the failed thyristors 3a to 3f are short-circuited, the short-circuited thyristors 3a to 3f are applied to the cathode. It becomes impossible to block the voltage. A short circuit is formed in the secondary winding 2b of the welding transformer 2 by the failed thyristors 3a to 3f and the other thyristors 3a to 3f connected to the secondary winding 2b, and the thyristors 3a to 3f and An excessive current flows through the welding transformer 2.

  Furthermore, when the state continues, the secondary winding 2b and the primary winding 2a of the welding transformer 2 are burned out. In addition, not only in the case of any one of thyristors 3a-3f, but also when a plurality of thyristors 3a-3f fail, a short circuit is formed in the same manner, and an excessive current flows.

  In order to prevent such a state, the welding apparatus according to the present embodiment is configured to monitor the anode-cathode voltages of the thyristors 3a to 3f. In order to monitor the anode-cathode voltage of the thyristors 3a to 3f, the light emitting side elements 4a to 4f of the photocoupler, a diode and a current limiting resistor are connected in series so as to be parallel or anti-parallel to the thyristors 3a to 3f. Connect the circuit. The diode is for preventing overvoltage of the light emitting side elements 4a to 4f of the photocoupler, and the resistor is for current limiting.

  When the welding apparatus is operating normally, a voltage is applied between the anode and cathode of the thyristors 3a to 3f, so that the current flows to the light emitting side elements 4a to 4f of the photocoupler due to the voltage, and light is emitted. Light is transmitted to the light receiving side elements 5a to 5f of the photocoupler. Then, the light receiving side elements 5a to 5f of the photocoupler are turned on, and these signals set the output terminal 6f of the AND element 6e to the high state via the sequence circuit composed of the AND elements 6a to 6e.

  The output terminal 6f of the AND element 6e is input to the base terminal 11a of the transistor 11 which is a switching element, and turns on the transistor 11.

  Since the transistor 11 is turned on, a predetermined current continues to flow through the coil of the second relay 8, and the second relay 8 is kept on. Therefore, the state where the connection point 1a and the connection point 1b are connected is maintained, and the input switch 1 is maintained in the closed state.

  Next, an operation when one or a plurality of thyristors 3a to 3f among the six thyristors 3a to 3f is short-circuited will be described.

  When any one or a plurality of thyristors 3a to 3f out of the thyristors 3a to 3f are short-circuited, the anode-cathode voltage of the thyristors 3a to 3f is zero or lower than the normal voltage. Then, no current flows to the light emitting side elements 4a to 4f of the photocoupler connected between the anode and the cathode of the thyristors 3a to 3f, and the light receiving side elements 5a to 5f of the corresponding photocoupler are turned off.

  As a result, any of the corresponding input terminals of the AND elements 6a to 6c is in a low state, and the output terminal 6f of the AND element 6e is also in a low state. Since the output terminal 6f of the AND element 6e is connected to the base terminal 11a of the transistor 11, the transistor 11 is turned off.

  At this time, since the activation switch 10 is in the on state, the first relay 7 is in the on state, and the normally closed contact of the second system 72 of the first relay 7 is in the open state. Yes. Therefore, no current flows through the coil of the second relay 8, and the second relay 8 is turned off.

  Thereby, the connection point 1a and the connection point 1b are not connected, the current does not flow through the coil portion 1c, the input switch 1 is opened, and the input power to the welding apparatus is shut off.

  As the first relay 7 and the second relay 8 in the control unit 9, an electromagnetic contactor or a switch equivalent to this, a semiconductor switch such as a triac, or the like may be used.

  As described above, the voltages of the thyristors 3a to 3f are monitored, and when the thyristors 3a to 3f are short-circuited, the voltage between the anode and the cathode of the thyristors 3a to 3f becomes smaller than that during normal operation or becomes zero. Therefore, by detecting this, the input power source is shut off by the input switch 1, thereby preventing the failure of the constituent members of the welding apparatus such as the welding transformer 2.

  Note that the voltage of each thyristor 3a to 3f is detected, and the ON / OFF state of the input switch 1 is maintained by the plurality of AND elements 6a to 6e corresponding to the respective thyristors 3a to 3f that receive the detection result. Since the sequence circuit for turning off (opening) is configured, the input switch 1 can be turned off (opened) when at least one of the thyristors 3a to 3f fails.

  Moreover, although the voltage of the monitored thyristors 3a to 3f becomes smaller than that during normal operation or becomes zero, an example in which the input switch 1 is turned off (opened) to shut off the input power supply has been shown. Although the thyristors 3a to 3f are not malfunctioning and are operating normally, the voltage of the thyristors 3a to 3f is prevented from being erroneously detected that the voltage of the thyristors 3a to 3f has dropped due to some cause such as noise. The input switch 1 may be turned off (opened) to shut off the input power supply when the state that becomes smaller than the normal operation or becomes zero is continued for a predetermined time.

  Next, the operation when starting the welding apparatus of the present embodiment will be described.

  Before the welding apparatus is started, the input power supply is cut off, so that no voltage is applied to the welding transformer 2 and voltage is also applied to the thyristors 3a to 3f connected to the secondary winding 2b of the welding transformer 2. Is not applied. Therefore, no current flows through the light emitting side elements 4a to 4f of the photocoupler, and it is erroneously determined that the thyristors 3a to 3f are short-circuited, so that the output terminal 6f of the AND element 6e is in a low state and the transistor 11 is also in an off state. It becomes.

  In this state, if the start switch 10 is off, the first relay 7 is off and the second relay 8 is on.

  However, when the activation switch 10 is turned on from this state, the first relay 7 is turned on, and the normally closed contact of the second system 72 of the first relay 7 is opened. Further, at this stage, since no current flows through the thyristors 3a to 3f, the output terminal 6f of the AND element 6e remains in the low state, and the transistor 11 is not turned on. Therefore, no current flows through the coil of the second relay 8, and the second relay 8 cannot be turned on. In other words, the input switch 1 cannot be turned on (closed) indefinitely.

  Therefore, a series circuit of a capacitor 91 and a resistor 92 is connected in parallel to the coil of the second relay 8, the start switch 10 is turned on, and the normally closed contact of the second system 72 of the first relay 7 is opened. Even if it becomes a state, the current charged in the capacitor 91 continues to flow through the coil of the second relay 8 for a certain period, and the second relay 8 is kept on. In this way, a certain delay time is allowed from when the activation switch 10 is turned on to when the second relay 8 is turned off.

  That is, in the standby state before the welding apparatus is activated, the second relay 8 is in the on state.

  When the start switch 10 is turned on to turn on the input switch 1 and the first relay 7 is turned on, the normally closed contact is opened, but the capacitor 91 is charged. The second relay 8 keeps the ON state for that period.

  During that period, the first relay 7 and the second relay 8 are turned on simultaneously, the input terminals 1a and 1b of the control unit 9 are connected, the control unit 9 is turned on, and the input switch 1 is turned on ( Closed).

  In this way, when the input switch 1 is turned on, a voltage is applied between the anode and the cathode of the thyristors 3a to 3f. By detecting the voltage, the output terminal 6f of the AND element 6e becomes high. It becomes a state. This is input to the base terminal 11a of the transistor 11, the transistor 11 is turned on, the second relay 8 is kept on, and the input switch 1 can also be kept on (closed).

  In the present embodiment, an example of a circuit using a relay as a circuit for starting the welding apparatus is shown. However, the present invention is not limited to this, and can be realized by using other components such as a logic IC and a transistor circuit. be able to.

  Although the present embodiment has described a double star rectifier circuit using a three-phase input thyristor, it is also applicable to other rectifier circuit configurations, single-phase input rectifier circuits, and semiconductor circuits including other control elements. be able to.

  INDUSTRIAL APPLICABILITY The present invention can prevent damage expansion due to a failure of a semiconductor element used in a welding apparatus with a low cost and simple configuration, and is industrially useful as a welding apparatus that improves safety.

The figure which shows schematic structure of the welding apparatus in one embodiment of this invention The figure which shows the structure of the control part of the input switch of the welding apparatus in one embodiment of this invention The figure which shows schematic structure of the conventional welding apparatus

Explanation of symbols

1,101 Input switch 10 Start switch 11 Transistor (switching element)
11a Base terminal 2 Welding transformer 2a, 121 Primary winding 2b, 102a, 102b, 102c, 102d, 102e, 102f Secondary winding 3a, 3b, 3c, 3d, 3e, 3f, 103a, 103b, 103c, 103d , 103e, 103f Thyristors 4a, 4b, 4c, 4d, 4e, 4f Photocoupler light emitting side elements 5a, 5b, 5c, 5d, 5e, 5f Photocoupler light receiving side elements 6a, 6b, 6c, 6d, 6e AND elements 7 First relay 71 First system 72 Second system 8 Second relay 9 Control unit 91 Capacitor 92 Resistance

Claims (3)

A transformer,
A switch unit provided on the primary side of the transformer for supplying or cutting off AC power to the transformer;
A semiconductor element provided on the secondary side of the transformer for controlling the welding output;
A voltage detection unit for detecting a voltage across the semiconductor element;
When the voltage detection unit detects that the voltage across the semiconductor element is lower than the normal voltage or zero when the AC power is supplied to the transformer, the switch unit is opened to open the switch. A welding device for cutting off the supply of the AC power to the transformer,
A first relay;
A second relay;
A capacitive element connected in parallel to the second relay;
A switching element that opens and closes the second relay based on a detection result of the voltage detector;
When the first relay operates, the current charged in the capacitive element continues to flow to the coil of the second relay for a certain period, and the second relay closes for this certain period ,
When the first relay and the second relay are closed, the switch unit is closed and the AC power is supplied to the transformer.
When the voltage detecting unit detects that the voltage across the semiconductor element is a normal voltage, the switching element is closed to maintain the closing operation of the second relay even after the predetermined maintenance time has elapsed. The supply of AC power to the vessel is maintained,
When the voltage detection unit detects that the voltage across the semiconductor element is lower than the normal voltage or zero, the switching element is opened, so that the second relay is opened after the predetermined maintenance time. A welding apparatus in which the supply of the AC power is cut off to the transformer. A plurality of the semiconductor elements are provided, the plurality of semiconductor elements are connected in parallel, the voltage detection unit is provided for each of the plurality of semiconductor elements, and at least one voltage detection unit 2. The welding according to claim 1, wherein when detecting that a voltage across the semiconductor element is lower than a normal voltage or zero, the switch unit is opened to cut off the supply of the AC power to the transformer. apparatus. When the voltage detection unit detects that the voltage across the semiconductor element is continuously lower than a normal voltage or zero after continuing for a predetermined time or longer, the switch unit is opened to open the switch to the transformer. The welding apparatus according to claim 1, wherein the supply of AC power is cut off.

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