© COPYRIGHT 1999 THE ESAB GROUP, INC. LESSON I, PART B The transformer in a welding machine performs much the same as a large power plant transformer.  The primary voltage coming into the machine is too high for safe welding.  Therefore, it is stepped down to a useable voltage.  This is best illustrated with an explanation of how a single transformer works. In the preceding paragraphs, we have found than an electrical current can be induced into a conductor when that conductor is moved through a magnetic field to produce alternating current.  If this alternating current is passed through a conductor, a pulsating magnetic field will surround the exterior of that conductor, that is the magnetic field will build in intensity through the first 90 electrical degrees, or the first cycle.  From that point, the magnetic field will decay during the next quarter cycle until the voltage or current reaches zero at 180 electrical degrees.  Immediately, the current direction reverses and the magnetic field will begin to build again until it reaches a maximum at 270 electrical degrees in the cycle.  From that point the current and the magnetic field again begin to decay until they reach zero at 360 electrical degrees, where the cycle begins again. If that conductor is wound around a material with high magnetic permeability (magnetic permeability is the ability to accept large amounts of magnetic lines of force) such as steel, the magnetic field permeates that core.  See Figure 14.  This conductor is called the primary coil, and if voltage is applied to one of its terminals and the circuit is completed, current will flow.  When a second coil is wound around that same steel core, the energy that is stored in this fluctuating magnetic field in the core is induced into this secondary coil. It is the build-up and collapse of this magnetic field that excite the electrons in the secondary coil of the transformer.  This causes an electrical current of the same frequency as the primary coil to flow when the secondary circuit is completed by striking the welding arc.  Remember that all transformers operate only on alternating current. A simplified version of a welding transformer is schematically shown in Figure 15. This welder would operate on 230 volts input power and the primary winding has 230 turns of wire on the core.  We need 80 volts for initiating the arc in the secondary or welding circuit, thus we have 80 turns of wire in the secondary winding of the core.  Before the arc is struck, the voltage between the electrode and the work piece is 80 volts.  Remember that no current (amperage) flows until the welding circuit is completed by striking the arc. FIGURE 14 STEEL CORE PRIMARY COIL SECONDARY COIL 80 V 80 TURNS 460 V 460 TURNS BASIC TRANSFORMER

Lesson 1
The Basics of Arc Welding
Lesson 2
Common Electric
Arc Welding Processes
Lesson 3
Covered Electrodes for Welding
Mild Steels
Lesson 4
Covered Electrodes for Welding Low Alloy Steels
Lesson 5
Welding Filler Metals for Stainless Steels
Lesson 6
Carbon & Low Alloy
Steel Filler Metals -
Lesson 7
Flux Cored Arc Electrodes Carbon Low Alloy Steels
Lesson 8
Hardsurfacing Electrodes
Lesson 9
Estimating & Comparing Weld Metal Costs
Lesson 10
Reliability of Welding Filler Metals


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