Transformers PDF - Module 3

Module 3 Electrical Fundamentals II Topic 3.15: Transformers  INTRODUCTION On completion of this topic you should be able to: 3.15.1 Describe the construction of transformers and their principles of operation 3.15.2 Desc...

Module 3 Electrical Fundamentals II Topic 3.15: Transformers  INTRODUCTION On completion of this topic you should be able to: 3.15.1 Describe the construction of transformers and their principles of operation 3.15.2 Describe transformer losses and methods used for overcoming them 3.15.3 Describe transformer action under load and no-load conditions 3.15.4 Describe the following regarding transformers: Power transfer Efficiency Polarity markings 3.15.5 Calculate line and phase voltages and currents 3.15.6 Calculate power in a three phase system continued... 30-03-2024 Slide No. 2  INTRODUCTION On completion of this topic you should be able to: 3.15.7 Describe the following with respect to transformers: Primary and secondary current Voltage Turns ratio Power Efficiency 3.15.8 Describe the construction and operation of auto transformers 30-03-2024 Slide No. 3  TRANSFORMER Typically – device composed of two or more coils wound on a former or core. Coils are linked by magnetic lines of force which transfer energy. Transformers come in many shapes and sizes. Very large, high voltage, high current transformers are used for power distribution in towns and cities. In contrast, miniature transformers are used in electronic equipment. 30-03-2024 Slide No. 4  TRANSFORMER CONSTRUCTION In its most basic form, a transformer consists of: A primary coil or winding - receives energy from AC source A secondary coil or winding - receives energy from primary winding and delivers it to load A core or former that supports the coils or windings - provides a path for magnetic lines of flux 30-03-2024 Slide No. 5  COMPONENTS OF A TRANSFORMER Two coils of wire (called windings) are wound on some type of core material. In some cases, coils are wound on a cylindrical or rectangular cardboard form. In effect, core material is air and called an air-core transformer. Low frequency transformers (50-400 Hz) require a low-reluctance core, usually iron. Most power transformers are iron-core transformers. 30-03-2024 Slide No. 6  CORE CHARACTERISTICS Composition of core depends on factors as voltage, current, and frequency. Commonly used core materials are air, soft iron, and steel. Air-core – usually used with high frequency voltage source (>20 kHz) Iron-core – usually used when source frequency is low ( Ep 30-03-2024 Slide No. 63  AUTO TRANSFORMERS If 200 volts is applied between B and C, secondary voltage of 100 V from A and B. 300 V will be available from points A and C. This is because primary field creates not only a back EMF of close to 200 V in turns between B and C, but also an EMF of 100 V in turns between A and B. Two EMFs are of same phase because they are induced in one winding by same field. Can therefore be added together to give a secondary voltage of 300 V (A to C). Alternately the 100 V induced between A and B can be taken as a secondary. 30-03-2024 Slide No. 64  CONCLUSION Now that you have completed this topic, you should be able to: 3.15.1 Describe the construction of transformers and their principles of operation 3.15.2 Describe transformer losses and methods used for overcoming them 3.15.3 Describe transformer action under load and no-load conditions 3.15.4 Describe the following regarding transformers: Power transfer Efficiency Polarity markings 3.15.5 Calculate line and phase voltages and currents 3.15.6 Calculate power in a three phase system continued... 30-03-2024 Slide No. 65  CONCLUSION Now that you have completed this topic, you should be able to: 3.15.7 Describe the following with respect to transformers: Primary and secondary current Voltage Turns ratio Power Efficiency 3.15.8 Describe the construction and operation of auto transformers 30-03-2024 Slide No. 66  This concludes: Module 3 Electrical Fundamentals II Topic 3.15: Transformers