SU854636A1 - Welding transformer idle voltage limiter - Google Patents

Description

(54) LIMITER OF TENDERING THE IDLE WELD OF WELDING TPAIICPOP iATOPA

This invention relates to a welding technique, in particular, to automatic voltage reduction devices in a chain of welding transformers used for manual arc welding. A voltage limiter containing a power supply unit, a current transformer in the welding circuit and Schmidt trigger 1 is known. The limitations of the limiter are low sensitivity and low speed. Small sensitivity is due to the presence of a diode in the current transformer and Schmidt trigger circuit. Low speed is explained by the method of connecting the trigger to the current transformer, in which the circuit operates only in positive half-periods, which determines the average response time of at least 0.01 s. In addition, the use of a contact switch increases the response time to 0.06 s. These disadvantages worsen the excitation of the arc, which leads to additional labor costs. A device containing a power thyristor komigiutator and a current transformer in the welding circuit 2 is known. However, this device is characterized by low sensitivity and insufficient stability of the circuit during welding. The sensitivity is explained by the presence of a current transformer with optocouplers of diodes in the circuit of the circuit, which have a high internal resistance at low currents. The lack of stability of the circuit during welding is explained by the lack of time lag, which leads to unstable arc burning. As a result, the device interferes with the work of the welder. It is also known a voltage limiting device containing a thyristor co-commutator and a current transformer in the welding circuit 3. However, this device has a low sensitivity and is not very fast. The low sensitivity is explained by the low input resistance of the optocouplers and the large control current, they. The lack of speed is explained by the presence of a relay in the circuit with a relatively large inertia. These limitations of the limiter also affect the work of the welder. The closest to the technical essence and the achieved result to the proposed is the no-load voltage limiter of the welding transformer, high sensitivity and speed of up to 5 ms, it can be used with all types of welding transformers. The limiter contains a thyristor switch in the supply circuit of the welding transformer, switch control unit, current limiting element in the form of an RC chain connected in parallel to the switch, power supply unit, current transformer in the welding circuit, Wuxi low frequency, two Schmidt triggers, a time relay, the amplifier input connected to the secondary winding of the current transformer, the amplifier output connected to the input of the first Schmidt trigger, the first output of which is connected to the time relay input, and the second output, the signal of which is inverse to the input the signal is free, the time relay output is connected with the input of the second Schmidt trigger, the second output of which is connected to the input of the control unit of switch 4. The disadvantage of this device is the influence of the Limiter on the work of the welder due to comparison tionary pain shogo incorporation time (up to 7 ms, depending on the sensitivity and time delay tripping). This disadvantage is explained by the fact that the second Schmidt trigger with the first one is carried out via a time relay, which is made on the basis of an emitter follower and an RC circuit connected to the emitter base, repeat. The base potential depends on the parameters of the discharge circuit, the time of the driving capacitor (resistor R 13, transition emitter-collector of transistor T 5, resistance of diode D 8 in direct direction and capacitor capacitance C 4): ps where TJ is the base potential of transistor T 7 relay time relative to the current pole of the power supply; E is the potential of the positive pole of the power source; veins 0; Y |, is the potential on the plates of the C 4 capacitor; J is the potential value on the capacitor plate. C 4 in the initial state until the first Schmidt trigger collapses (transistors T 5; T b, resistors R 10 - R 1 R 25, capacitor C 3); R is the circuit resistance of capacitor discharge C 4; C - capacitor capacitance C 4, Let U (5-.cp potential of the base of the transistor T 7 time relay, at which the second Schmidt trigger operates (transistors T 8; T 9, resistors R 17 - R 23). This potential has a minus sign , moreover (U jjp) Uo). Then from () we get an expression for the response time to turn on the time relay, and, respectively, the entire limiter (where and uj have a positive value. As can be seen from (2), the switching time depends on the capacitance of the capacitor C 4, the value of which is chosen as the outcome From the required time delay value for turning off the voltage of the idle run of the welding transformer. So, with a capacitor capacitance of microfarads, the time delay is 0.5 s, and the maximum turn-on time is 7.8 ms with an average value of 5.6 ms. The purpose of the invention is to reduce the influence of the limiter to the welding process by reducing the response time to switching on. The goal is achieved by the fact that the limiter circuit containing a thyristor switch in the power supply circuit of the welding transformer, switch control unit, current limiting element connected in parallel to the switch, current transformer in the welding circuit, to the secondary winding of which a low-frequency amplifier, two Schmidt triggers, a time relay, the amplifier output is connected to the input of the first Schmidt trigger, the first output of the last The output of the time relay is connected to the input of the second trigger, the second output of the latter is connected to the input of the control unit by the switch, an inverter is added, the input of which is connected to the second output of the first Schmidt trigger, and the output is connected to the input of the control block by the switch. The drawing shows the electrical circuit of the proposed device. The device contains a thyristor switch 1, a control unit 2 of a collimator 1, a current-limiting element 3, a power supply unit 4, a current transformer 5 in the welding circuit, a low-frequency amplifier 6, the first Schmidt trigger 7, a time relay 8, the second Schmidt trigger 9, made on a transistor 11, a resistor 12 and a zener diode 13, a welding transformer 14, an electrode 15, and a welded piece 16. The device is connected to the input terminals 17 and 18. The first Schmidt trigger 7 has transistors 19 and 20 and resistors 21 and 22. Time relay 8 is made on transistor 23, capacitor 24, resistor 25 and diode 26. Schmidt’s second trigger 9 includes transistors 27 and 28 and resistor 29.

The device works as follows.

When voltage is applied to the clamps 17 and 18, all circuit elements are supplied with power from block 4. Welding transformer 14 is powered through current-limiting element 3, therefore, the voltage in the welding circuit is reduced to acceptable values. The input voltage of the low-frequency amplifier 6 is missing, so there is no signal at the input of the trigger 7. The latter is in the off state, 5.f. the transistor 19 is closed and the transistor 20 is open. Time relay 8 is in the initial state when the transistor 23 is open and the capacitor 24 is charged. The transistor 27 of the second trigger 9 is also open, and the transistor 28 is closed. The voltage at the output of the second trigger 9, taken from the resistor 29, is equal to O, which corresponds to the absence of a signal at the input of the control unit 2 of the thyristor switch 1. In this mode, the inverter

10 also has no output voltage, since the zener diode 13 closes the base current of the transistor 11 is small, and the latter is in the off state. This state of the circuit may continue indefinitely.

When the electrode 15 is closed, the current in the welding circuit appears on the welding part 16, a signal appears at the output of the current transformer 5, which is amplified by the amplifier 6. The transistor 19 of the trigger 7 opens, and the transistor 20 closes, resulting in a signal input relay 8, time and the disappearance of the signal at the input of the inverter10. In this case, the capacitor 24 of the time relay 8 is discharged through the resistor 22, the transistor 19, the diodes 26, and the voltage on the capacitor 24 begins to decrease exponentially. At this time, when the transistor 20 is locked, the Zener diode 13 of the inverter 10 is punched, the transistor

11 is energized by applying a voltage to the input of control unit 2. The latter opens the thyristor switch 1, which leads to the supply voltage of the network to the primary winding of the welding transformer 14. A welding current occurs in the welding circuit. During the operation of the inverter 10, the discharge process of the capacitor 24 continues.

At the same time, the potential of the base of transistor 23 rises and when a certain value is reached, the transistor 23

is closed, which causes the transistor 27 to close and the transistor 28 to open. The flip-flop 9 tilts. At resistor 29, the voltage from transistor 28 appears, i.e.

a duplication of the signal occurs at the input of the control unit 2.

In this state, the circuit is all the time welding.

When the welding arc is broken, the signal at the input of the low-frequency amplifier 6 disappears and, accordingly, at the input of the trigger 7. At the same time, the transistor 19 is closed and the transistor 20 is opened. The transistor 11 of the inverter 10 is closed, the signal at its output

to disappears, however, the signal at the input of control unit 2 remains, since transistor 28 remains open. Capacitor 24 begins to charge through resistor 25 of time relay 8 and resistor of trigger 7. Transmitter 23 decreases its potential according to the law of exponentials until at a certain time, the transistor 27 opens and the transistor 28 closes. The signal at the input of the control unit 2 disappears, and the thyristor switch 1 is closed, breaking the supply circuit of the welding transformer 14. The circuit returns to its original state.

five

The acceleration of switching on the circuit (increase in speed) occurs due to the fact that the input signal of the trigger 7 is transmitted to the input of the control unit 2, the inertia element — the time relay 8 — because the response time of the transistor 11 of the inverter 10 is much less than the discharge time yes capacitor 24 and transistor response time

5 23 and 27. Connecting the inverter 10 to the output of the trigger 7, independent of the discharge circuit of the capacitor 24, eliminates the influence of this circuit on the operation of the inverter 10,

0

The positive effect of the application of the proposed device is to reduce the device turn-on time and, accordingly, to reduce its effect on the work of the welder, which leads to an increase in

5 labor productivity of the latter. So, with the device sensitivity to the circuit resistance of the electrode part 120 ohms and the turn-on time of 5.6 ms excitation reliability factor

0 arc is 0.64. The application of the proposed device with the same sensitivity allows to reduce the turn-on time to 2.8 ms, while the excitation reliability factor

5 ARCS rises to 0.82. A decrease in the number of attempts to initiate the arc leads to a decrease in the psychophysiological load on the welder, which ultimately leads to an increase in the productivity of his labor.

Claims (4)

1. Accepted for Japan No. 50-8699, Cl, B 23 K 9/10, 07.04,75. 2, For the application of the Federal Republic of Germany No. 2504870, 0 Cl, B 23 K 9/10, 1976, 3, USSR author's certificate yes 647076, cl. At 23 K 9/10, 1974. 4. Thyristor voltage limiter for no-load operation of welding transformers TONH-6.-Ikformatsnonny leaflet f 83-78 of the Kemerovo inter-branch territorial CNTI, 1978 (prototype),