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It was rather common practice to use excessive amounts of copper in the secondaries and a very small amount of primary copper.
There was no logical reason for this except perhaps that the secondaries could be seen while the primaries were covered. In general, confusion existed, no standard ratings were used, and it was extremely difficult for power companies or users to determine actual ratings and demand figures.
Article :. Date of Publication: Dec. Need Help?These are some of the basic calculations you should become familiar with if you are shopping for equipment or learning about the resistance welding process.
The first resistance welders were tied to the utility frequency of the power supply to the machine. For this reason, you will still see Weld Cycles quite commonly in resistance welding documentation. In North America, line frequency is 60Hz.
In many other parts of the world, utility frequency is 50Hz. World map showing frequency for public mains power, by country. Not all colored areas have mains power available.
Japan uses both 50Hz and 60Hz. Single-phase AC machines still count the number of cycles of the utility frequency to control the time of a weld. Duty Cycle is used to mathematically derate a welding transformer. They are often turned on for only brief periods of time.
Care must be taken when shopping for a welder, as Duty Cycle calculations can be manipulated to make machinery sound more powerful than other equipment. The Power into a transformer should be roughly the same going in as going out.
Search for:. Request a quote. Equations and Calculations related to Resistance Welding. Request a Quote. Welding Related Math These are some of the basic calculations you should become familiar with if you are shopping for equipment or learning about the resistance welding process.
Time calculations Weld Cycles The first resistance welders were tied to the utility frequency of the power supply to the machine.Automotive and robotic lines use MFDC to take advantage of the weight savings not to mention power reductions and in house primary feed reductions, power factor improvements and others.
MFDC does cost more and it is not forgiving if pushed beyond its rated limit. Its electrical features are excellent in that it heats quickly and does not produce the sine way stitching with the zero cross over cooling.
Since it is DC it has virtually no inductance loss when magnetic material enters the throat. Depending upon the equipment the initial period from initiation of the current till the full current flow is reached takes milliseconds ms in MFDC. Hanging transformers are used with portable weld guns. They generally have long conductors to the guns. The transformers tend to be large to drive the power over these long cables.
The question is what type of core material is suitable for a hanging transformer. This is a machine design question and is beyond the scope of this forum. Resistance welding transformer primaries are wound with many turns in order to produce the desired turns ratio.
This in turn produces the conversion of the high voltage and low amperage in the primary to the desired low voltage and high amperage in the secondary. The winding material is copper and is required to conduct both current and heat at the amperage the transformer is designed for. Calculation of the winding gauge size is a manufacturing question and is beyond the scope of this forum.
The turns ratio for all resistance welding transformers is calculated in the same manner no matter the KVA size. Turns ratio is the ratio of the number of coil turns in the primary vs the secondary. In AC transformers, there are many turns in the primary. The secondary has one turn. The equations for this are:.
This is correct once the current is at steady state. Impedance is a combination of reactance and resistance in the welding circuit.
Inductance is a property of a conductor that resists the change in current over time. This occurs at the beginning and end of a weld, when the current starts and stops flowing. In the initial and final cycles when the current is changing, inductance does have an effect upon the process of MFDC.
As the weld initiates the control measures the current each half cycle and realizes that it did not reach its desired current due to the inductance.
The control will fire at full conduction during this time. This repeats until the desired current is reached. This is called rise time and is milliseconds for MFDC. At this point the current is at steady state and the inductance goes to zero and the current levels off until the control turns the current off. When the control turns off, the inductive energy that was stored in the circuit will now bleed off. There will be a decreasing current flow until all is bled off. This is called decay time and is about milliseconds.
welding transformer design
DC equipment which operated at 60 HZ operates similarly but will have a different curve and take longer to reach steady state. These ripples reflect the electrical sine wave which has been rectified to HZ or 60 HZ. These inductive losses can be compared to a fly wheel. To get it started, extra energy must be put into the flywheel to get it turning, rise time.Welding inverter is an alternative to a conventional welding transformer.
Modern semiconductors allow to replace the traditional mains transformer with a switching power supply, which is much lighter, smaller and allows easy current adjustment via a potentiometer. The advantege is also that the output current is DC. DC current is less dangerous than AC and prevents arc extinction. For this inverter i chose topology, which is the most common in welding inverters - forward converter with two switches.
In my article about switchning supplies it is a topology II. Input mains voltage passes through an EMI filter and is smoothed with high capacity capacitors. Since the inrush current of those capacitors would be too high, there's a softstart circuit. After switching ON, the primary smoothing capacitors are charging via resistors, which are later bypassed by the contact of a relay. The control integrated circuit is UC Working frequency is 42kHz. Control circuit is powered by an auxiliary power supply of 17V.
Current feedback, due to high currents, is using a current transformer Tr3. Output current can be controlled by potentiometer P1, which determines the threshold of the current feedback.
Threshold voltage of the pin 3 of UC current sensing is 1V. Power semiconductors require cooling. Most of the heat is dissipated in output diodes.
Upper diode, consisting of 2x DSEIA, must in worst case handle the average current of 50A and the dissipation of 80W total of both diodes. Lower diode STTHL06TV1 doube diode package with both internal diodes connected in parallel must in worst case handle an average current of A and the dissipation of nearly W.
Maximum total dissipation of the secondary rectifier is W. The heatsink must be able to handle it. To the thermal resistance you must include the junction-case Rth, case-sink Rth and sink-ambient Rth.
DSEIA diodes don't have insulation pads and the cathode is connected to the the heatsink. Output choke L1 is therefore in the negative rail. It is advantageous because in this configuration, there's no high-frequency voltage on the heatsink. You can use another type of diodes, for example a parallel combination of a sufficient number of the most accessible diodes, such as MUR or FES16JT.
Note that the maximum average current of the lower diode is twice the current of the upper diode. Calculation of the power dissipation of the IGBTs is more complicated because in addition to conductive losses there are also switching losses.A premium membership for higher-level suppliers. Relevancy Transaction Level Response Rate. Supplier Types Trade Assurance. Supplier A premium membership for higher-level suppliers.
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Devotes to the development of I nverter resistance welding transforme r with high quality and efficiencyto help customers improve product value.This photograph shows the construction of the transformer used in a small ampereinexpensive electric arc welding unit. You see that it is essentially a shell type of core.
The windings are on separate bobbins, with the primary on the right and the secondary on the left. Between them however, is an important modification to the magnetic design. Observe the separate bar protruding from the back of the transformer.
This bar, comprising a set of stacked laminationsis linked by a lead screw to the current adjustment control on the front panel. By turning the current control wheel the position of the bar may be altered. With the bar out in the position shown, the core behaves in much the same way as an ordinary mains transformer. That is, the primary and secondary share the same magnetic flux path. This strong linkage results in the highest current being available to the welding electrode.
When the control wheel is rotated so that the bar is withdrawn back into the core then the flux generated by the primary winding need no longer travel through the secondary in order to form a closed loop. It instead has the option of following the shorter path through the bar; and this is what most of it will decide to do.
There are three effects as a result of this change in the flux path due to this 'magnetic shunt':. E-mail: R. Clarke surrey.Practical transformer design requires knowledge of electrical principles, materials, and economics. Small transformers, under 10 kVA, may be designed using handbook data and pencil-and-paper calculations, but larger or mass-produced units are often designed with extensive computer aided modeling CAM.
Ref:  . Other computer aided design CAD software exists that use the basic equations, and it is used by smaller manufacturers. The designer first needs several known factors to design a transformer. For a transformer using a sine or square wave, one needs to know the incoming line voltage, the operating frequency, the secondary voltage sthe secondary current sthe permissible temperature rise, the target efficiency, the physical size one can use, and the cost limitations.
Once these factors are known, design can begin. The designer first starts with the primary voltage and frequency. Since they are a known factor, they are the first numbers to be plugged into the equations. One then will find the power in watts or volt-amperes of each secondary winding by multiplying the voltage by the current of each coil. These are added together to get the total power the transformer must provide to the load s. The transformer losses in watts are estimated and added to this sum to give a total power the primary coil must supply.
The losses are from wire resistance I 2 R lossloss in the core from magnetic hysteresis and from eddy currents. These losses are dissipated as heat.
Here, the permissible temperature rise must be kept in mind. Each type of core material will have a loss chart whereby one can find the loss in watts per pound by looking up the operating flux density and frequency. Next, one selects the type of iron by what efficiency is stated, and the value of losses to the user. Once the iron is selected, the flux density is selected for that material.
In this case, one looks for a core material with high permeability and a high flux density. Of course, the better each become, the material goes up in price due to the manufacturing cost of the material, and their different compositions.
Some basic values of relative permeability for electrical steel are: SiFe unorientedSiFe orientedNiFe orientedand 79 Permaloy 12, toIn other words, a grain-oriented silicon steel conducts magnetic flux times better than a vacuum.
Ref: . Each type of iron steel has a maximum flux density it can be run at without saturating. The designer refers to B-H curves for each type of steel. They select a flux density where the knee either starts on the curve, or slightly up on it. The start of the knee is where saturation starts and permeability is at its highest. As saturation starts, the permeability curve starts dropping off rapidly to zero, and the primaries inductance falls rapidly.
By selecting this point on the knee, it will give a transformer with the lowest weight possible for that material. The curve shows that as saturation begins, the magnetic field strength in Oersteds H raises rapidly as compared to any increase in flux density Band so will the ampere turns.
When using the equations, the two most important are the number of turns Nand the core area a. One needs to find the core area in square centimeters or inches, and match it to the total power in watts or volt-amperes. The larger the core, the more power it will handle.
Once this core size is calculated, one then finds the number of turns for the primary. For sine wave operation, the designer then uses either the two short formulas, or they begin using the long formulas which are more exact, and whereby all the factors can be changed. For square wave operation, refer to the notes at the end of the equations section. Either way, it's time to use a transformer design sheet. The design sheet has places to write the details such as the flux density, the number of turns, calculate the turns per layer, and thickness of the coil.
Once the number of turns of the primary are calculated, the secondary windings numbers can be calculated with the same turns per volt figure. If the primary has turns for volts input, we would have 1 turn per volt.