Transformers for automatic welding

 
The transformers are manufactured in a stationary design, designed for continuous operation with forced air cooling. Technical data of transformers are given in table. 5.7
Order a transformer for automatic welding
Transformers TDF series... The design is based on a transformer with a magnetic shunt magnetized by direct current. In fig. 5.10 shows a simplified electrical diagram of the TDF-1001 transformer.

On each core of the main magnetic circuit of the transformer 77 are coils of the primary W1 and secondary windings. The secondary winding consists of two parts: main part W2Olocated at the upper yoke of the main magnetic circuit, and an additional part W2Dlocated together with the primary winding at the lower yoke of the main magnetic circuit. The magnetic shunt with the control winding W1 is located in the window of the main magnetic circuit between the windings W2Oand W1 in the path of the main leakage flux of the transformer. The transformers have a stepless welding current control.
                                                                                                                       
    Step regulation (two steps) is carried out by switching the turns of the secondary winding coils. When passing from a stage of lower currents to a stage of high currents, part of the turns of the main secondary winding is disconnected and an additional part of the secondary winding is connected, while the inductive resistance of the transformer decreases. Smooth current regulation within one step is performed by magnetizing the magnetic shunt. Higher control current corresponds to higher welding current.

The control winding of the magnetic shunt is powered by a single-ended thyristor rectifier consisting of an auxiliary transformer T2, a thyristor KS, a reverse diode VD and a thyristor phase control circuit made on a logic element M-403.
                                                                                                                         
    Welding transformers TDF are equipped with ballast and protective equipment. The possibility of local and remote (from the control panel of the welding machine) switching on and regulating the welding current is provided. Transformers have falling external characteristics. With such characteristics, good formation of the seam is obtained when working with automatic welding machines equipped with a system for automatically maintaining a given arc voltage (machines with an arc voltage-dependent electrode wire feed rate).
    Meanwhile, in recent years, simpler and more reliable automatic machines and automatic heads with a wire feed speed independent of the arc voltage have become widespread in the domestic industry.

Welding transformers TDF-1001 and TDF-1601 and other transformers with falling characteristics as part of automatic machines of this kind do not allow obtaining sufficient stability of the parameters of the weld in a number of welding modes. Insufficient output power of this series of transformers hindered the introduction of progressive and forced modes into production, especially in multi-arc welding of large diameter pipes. The production of TDF transformers was discontinued in 1980.

Transformers TDFZh series. The nominal parameters of TDFZh transformers correspond to the requirements of GOST 7012-77 for transformers for automatic submerged-arc welding. Transformers of this series have thyristor regulation and provide pulse stabilization of the welding process.

The magnetic core of the transformer is stacked, pinless design, made of steel grade 3414 with a thickness of 0.35 mm. The windings are made with a bus wound “on the edge”. In the transformer TDFZH-1002, an aluminum bus of the ADO brand is used, in TDFZH-2002 - a copper bus of the MGM brand.

A simplified schematic diagram of the TDFZh-1002 transformer is shown in Fig. 5.11, the appearance of the transformer is shown in Fig. 5.12.
                                                                                                                    
                                                                                                                         
      The primary 1,2 and secondary 3, 4 windings of the power transformer 77 each consist of two coils, separated for convenience and two sections connected in series. Pulse stabilization windings 5, 6 are installed between the sections of the secondary winding coils. In the transformer window there are two reactor winding coils 7, 8, which allows for step current regulation. In the TDFZh-1002 transformer, the full control range is divided into two, and in TDFZH-2002 - into three steps; the third stage of regulation in TDFZh-2002 transformers provides the possibility of welding at large (up to 40 V) voltage drops in the welding wires.

In the TDFZh-1002 transformer for welding in the range of low currents, the reactor winding coils are connected in series and in accordance with the primary winding; in the TDFZh-2002 transformer, the reactor winding coils are connected in series for welding in the range of low currents and in parallel - in the range of medium currents. When welding in the range of high currents, the reactor windings are not turned on.

Thyristors VS1 and VS2 regulate the voltage on the primary winding of the power transformer 77. The power thyristors VS1 and VS2 are protected from switching overvoltages by LS circuits (C1 and Rl). Protection of thyristor control transitions from random signals is carried out by resistors R2 and R3 and capacitors C2 and C3. Control pulses are fed to the thyristors from a phase-shifting device (FU), to the input of which the difference between the signals for setting the operating voltage and feedback is fed.
   The operating voltage setting circuit is powered from the T2.3 winding of the T2 auxiliary transformer. After rectification by the diode bridge VD1 and smoothing by the capacitor C4, the voltage is supplied through the resistor R4 to the Zener diode VD2. For parametric stabilization of the operating voltage of the transformer, a divider of resistors R5 and R6 is used. The potentiometer for setting the operating voltage R 7 is supplied with the difference between the stabilized voltage across the Zener diode VD2 and the non-stabilized voltage across the resistor R5. Thus, with an increase in the mains voltage, the reference signal on the potentiometer R 7 decreases, and with a decrease in the mains voltage, it increases. Resistors R8 and R9 are used to set the minimum and maximum values of the operating voltage of the transformer.

The reference voltage from potentiometer R 7 is compared with the operating voltage feedback signal. The feedback circuit consists of a rectifier bridge VD3, feedback voltage divider resistors R10 and R11 and a smoothing capacitor Sb. In its fully formed form, the feedback voltage is allocated across the resistor R11.

The difference between the voltages of the reference and feedback through the filter (resistor R12, capacitor C5) is fed to the input of the FU.

A decrease in the voltage at the output terminals of the transformer as a result of the action of any disturbance in the process (for example, a decrease in the stickout of the electrode) causes a decrease in the feedback signal. Since the reference voltage has not changed, the difference signal at the input of the FU increases. The charge of the time-setting capacitor of the FU is accelerated, the time from the beginning of the half-period of the supply voltage to the moment of the capacitor discharge and the arrival of control pulses to the power thyristors decreases. As a result, the voltage on the windings of the power transformer rises to the previous value.
  The transformer is switched on for welding with the K1 switch. In this case, the supply voltage is supplied to the FU, to the unit for setting the operating voltage (winding T2.3) and to the output device of the FU (windings T2.4 and T2.5). The open circuit voltage is set at the output terminals of the power transformer, corresponding to the setting of the potentiometer R 7.

In the event of a breakdown of the power thyristors VS1 and VS2 in the absence of welding, the full open-circuit voltage will appear on the secondary winding of the transformer. To ensure the safety of the operating personnel, an automatic protection is provided. For this purpose, the terminals of the HP shunt release of the Q1 circuit breaker installed at the input of the transformer are connected to the output terminals of the transformer through the opening contact of the magnetic starter K2, which ensures almost instantaneous disconnection from the mains when the no-load voltage appears during the adjustment work.

In fig. 5.13 shows the external characteristics of the TDFZh-2002 transformer for the ranges of high and low currents; the dashed lines indicate the limiting natural external characteristics of the power transformer for these ranges. The rigidity of the external characteristics ensures the maintenance of a constant arc voltage. The welding current is determined by the wire feed speed. The parallelism of the external characteristics of TDFZh transformers allows you to roughly set the operating voltage at the no-load of the transformer. When the electrode wire is closed to the product at the moment of arc ignition, the voltage at the output of the transformer drops sharply, the thyristors of the phase regulator fully open. This means that regardless of the welding mode, the arc is always ignited at the maximum current of the set range.

In fig. 5.14 shows the current and voltage of the first arc of a three-arc mill for welding large diameter pipes recorded by the recorder when the arc is fed from the TDFZh-2002 transformer (Figure 5.14, a) and TDF-1601 (Figure 5.14, b). When welding from a TDFZh-2002 transformer with rigid external characteristics, the process of self-regulation of the arc proceeds more actively: the constancy of the arc length is ensured by continuous fluctuations of the welding current.
                                                                                     
  In some automatic welding applications, such as submerged arc welding with a voltage-dependent arc feed rate, the welding transformer must have steep external characteristics. In transformers of the TDFZh series, such characteristics can be obtained by a relatively simple alteration of the control circuit. The alteration boils down to replacing the negative voltage feedback of the load with the current feedback.

In chapter three, it was noted that in a CT with an air reactor winding in the power transformer window, the current feedback signal can be removed directly from the reactor winding, the EMF of which is proportional to the welding current. For galvanic isolation of control elements from the supply network, an isolation transformer should be used, the primary winding of which is connected to either of the two coils of the reactor winding, and the secondary winding to the input terminals of the rectifier bridge of the feedback circuit (bridge VD3 in the diagram in Fig.5.11). Since the multiplicity of welding current regulation is higher than the voltage regulation multiplicity, to form a linear current control scale, it is necessary to re-select the resistances of the resistors in the reference potentiometer circuit (resistors R8 and R9 in Fig. 5.11). In cases where it must be ensured the possibility of welding as hard; and on falling characteristics, in various ranges of welding current and with high-quality stabilization in terms of the supply voltage, the need for a switch of the type of external characteristics is obvious.

Below are schematic diagrams, types and parameters of components required for converting the TDFZh-2002 transformer into a universal transformer with three ranges of welding current regulation in the welding mode with an independent electrode feed rate and with two ranges of welding current regulation in the welding mode with a dependent electrode feed rate ... In fig. 5.15, c shows a diagram for switching on an isolation transformer 77 for a welding current feedback. The primary winding of the transformer is connected to the coil of the reactor winding, wires A1 and 9 are connected according to the schematic diagram of the transformer (passport IEGV.672.222.022.00PS). The isolation transformer is made on a Ш16 X 16 magnetic core, the primary and secondary windings each contain 700 turns of PEV-2 wire with a diameter of 0.2 mm. The secondary winding of the transformer is connected according to the diagram in Fig. 5.15, and to the switch of the type of external characteristics S1 (PGK-ZP6N-8-A). In positions 2 and 3 of switch S1, the secondary winding of the current feedback transformer is connected to contacts X3: 14 and X3: 15 of the connector of the 8ДЯ.577.201 element block and further to the input terminals of the rectifier bridge of the feedback circuit. In position 1 of the switch S1, the voltage from the output terminals of the TDFZh-2002 transformer is applied to contacts X3: 14 and X3: 15, i.e., this position corresponds to welding with rigid characteristics. The linearity of the welding current control characteristics and the stabilization of the current relative to the mains voltage fluctuations are ensured by the use of resistors Rl, R2, R3 and a Zener diode VD1, installed directly on the SI switch according to the diagram in Fig. 5.15, b. The R18 control potentiometer is standard, located on the front panel of the TDFZh-2002 transformer. Resistors RI, R2 and R3 of MLT-0.5 type with nominal values of 1.1 kOhm, 680 Ohm and 2.4 kOhm, respectively, zener diode type D814G. Wires numbered 40 and 43 must be unsoldered from potentiometer R18 and connected to the terminals of the movable contacts of the switch S1 according to the diagram in Fig. 5.15, b; wire 38 is additionally connected to the switch. In position 2 of the switch S1, welding is carried out in the current range of 600-1200 A, while the power switch for the ranges of welding current Q2 (see Fig. 5.11) should be in the "low currents" position. In position 3 of switch S1, welding is performed at currents of 1100-2200 A, switch Q2 - in position "average currents".
                                                                                                    

The steeply dipping external characteristics of the TDFZh-2002 transformer, subjected to the considered alteration, are shown in Fig. 5.16. The ratio of short-circuit current to operating current in transformers does not exceed 1.1. When the supply voltage fluctuates in the range from +5 to -10% from the rated value, the welding current changes by no more than 2%.
                                                                                                        
      Autotransformer welding ATC-01. Welding autotransformer АТС-01 is intended for switching on welding transformers according to a two-phase symmetric circuit (Scott's circuit). Such inclusion allows, when supplying powerful single-phase transformers TDFZh-2002, to ensure uniform loading of a three-phase network, as well as to obtain a phase shift between the currents of two arcs 90 ° el. In two- and three-arc welding, which gives a certain technological effect when welding pipes under flux.
                                                                                      
       The principle of operation of the ATC-01 autotransformer is as follows. One of the line-to-line voltages of the supply network (for example, UABin the diagram in Fig. 5.17, a) is divided into two equal parts: the voltage between the division point 0 and phase C is equal in value 3/2 • UAvand is phase-shifted relative to UAB90 ° (270 °). This voltage is transformed to the nominal value UOH= UABused for the power supply day of the welding transformer 77 (Figure 5.17, b). Transformer T2 is switched on for voltage UAB With this connection, the currents of the secondary windings of the transformers are shifted by 90 ° el.

The voltage divider in the ATC-01 autotransformer and the autotransformer itself are made on a single three-rod magnetic circuit. On one of the extreme rods there are voltage divider coils, on the other - autotransformer coils. The middle rod serves to decouple the magnetic fluxes of the divider and the autotransformer, its cross-section is 2 times the cross-section of the extreme rods.

The design of the ATS-01 autotransformer is stationary, with natural air ventilation. Autotransformer technical data

are given below:

Three-phase power supply voltage, V ………………. 380

Load voltage, V, not less ………………………… 380

Load current, А …………………………………………… .630

Operating mode, PV, % ……………………………………… .100

Consumption current, A;

phase A …………………………………………………… 375

 phase B ………………………………………………… .375

phase C ………………………………………………… .750

Weight, kg, no more than ………………………………………… ..700

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Total comments: 2

  • Марина
    By Marina Added on August 29, 2019 at 11:49 am

    We need an invoice for the TDF-1001 380 / 75-3 transformer.
    account at PJSC "Kryukovsky Carriage Works", Kremenchug, tel. 0679577556 Marina
    mail uzim1@kvsz.com

    To answer
  • Алексей
    By Alexey Posted on April 29, 2021 at 09:46

    Good day! Is there a phase imbalance during the operation of the TDFZh-2002 welding transformer?

    To answer

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