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Unit 51: Electrical Technology The Characteristics and Principles of AC and DC Generators and the features of a Range of difference Power Station Course Aims • NDGTA At the end of this course the learner will be able to… 1. Know the methods used to produce electrical energy 2. Know the properties and applications of conductors, insulators and magnetic materials 3. Know the physical arrangements of supply, transmission and distribution equipment 4. Know how electrical energy is used to support applications of electrical technology Agenda NDGTA • At the end of the session the learner will be able to… – Describe DC Generators D.C. Generation • NDGTA DC Generator - Molecular Expressions Florida State University D.C. Generators NDGTA D.C. Generators NDGTA • A rotating armature coil passes through a magnetic field that develops between the north and south polarities of permanent magnets or electromagnets. • As the coil rotates, electromagnetic induction causes a current to be induced into the coil. • The current produced is an alternating current. • However it is possible to convert the alternating current into a form of direct current (DC) D.C. Generators NDGTA • This AC to DC conversion is accomplished though the use of a split-ring commutator. • The purpose of the split-ring commutator is to reverse the armature-coil connection to the external load circuit at the same time that the current induced in the armature coil reverses. • This causes DC of the correct polarity to be applied to the load at all times D.C. Generators NDGTA Peak Voltage 0o 90o 180o 270o 360o 90o Coil Rotation Pulsating DC developed by a simple single-coil generator 0o 90o 180o 270o 360o 90o Pure DC developed by a more complex generator using many turns of wire and many commutator segments Factors affecting the voltage developed NDGTA • The voltage developed by a DC generator depends upon… – The strength of the magnetic field – The number of coils in the armature – The speed of rotation of the armature • The voltage can be increased by increasing any of these factors The Voltage Developed by a DC Generator NDGTA • Vo = (Z x n x Ф) / 60 • Where Vo is the voltage developed across the generator brushes in volts • Z = the total number of armature conductors • N = speed of rotation in r.p.m. • Ф = magnetic flux per pole in webers • Given: A 4-pole DC generator rotates at 1200 r.p.m. The armature has 36-slots and each coil has 4-turns of wire. The magnetic flux per pole is 0.05 webers. Find the voltage output of the DC generator? The Voltage Developed by a DC Generator • Note each turn of the wire has two conductors, thus… • Z = 2 x 36 x 4 = 288 • Thus Vo = (288 x 1200 x 0.05) / 60 • Vo = 288 volts NDGTA