19–3 GENERATOR FIELD STRUCTURES DC generators can be classified by the method used for providing the magnetic field. This classification can be tabulated like this: 1. Permanent-magnet generators 2. Separately excited generators 3. Self-excited generators a. Shunt generators b. Series generators c. Compound generators Permanent-magnet generators are reserved for a few low-power applications where control […]
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Direct current fundamentals
Dc generators : generator field structures, armature reaction and buildup of self-excited fields
19–3 GENERATOR FIELD STRUCTURES DC generators can be classified by the method used for providing the magnetic field. This classification can be tabulated like this: 1. Permanent-magnet generators 2. Separately excited generators 3. Self-excited generators a. Shunt generators b. Series generators c. Compound generators Permanent-magnet generators are reserved for a few low-power applications where control […]
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Electromagnetic induction : lenz’s law , induction in rotating machines and summary of electromagnetic induction
18–4 LENZ’S LAW There is a more fundamental way of determining the current direction. As pointed out before, electrical energy is produced by mechanical energy; the hand that removes the magnet from the coil must do some work. The magnet does not push out of the coil by itself; the hand must pull it out. […]
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Electromagnetic induction : lenz’s law , induction in rotating machines and summary of electromagnetic induction
18–4 LENZ’S LAW There is a more fundamental way of determining the current direction. As pointed out before, electrical energy is produced by mechanical energy; the hand that removes the magnet from the coil must do some work. The magnet does not push out of the coil by itself; the hand must pull it out. […]
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Electromagnetic induction : moving coils—stationary fields, moving fields—stationary coils and fleming’s left-hand rule for generators
Electromagnetic Induction 18–1 MOVING COILS—STATIONARY FIELDS A simple way of demonstrating the induction process is shown in Figure 18–1. A piece of copper wire is connected to the terminals of a sensitive meter and moved downward through a magnetic field, the wire cutting across the lines of force. While the wire is moving, a voltage, […]
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Electromagnetic induction : moving coils—stationary fields, moving fields—stationary coils and fleming’s left-hand rule for generators
Electromagnetic Induction 18–1 MOVING COILS—STATIONARY FIELDS A simple way of demonstrating the induction process is shown in Figure 18–1. A piece of copper wire is connected to the terminals of a sensitive meter and moved downward through a magnetic field, the wire cutting across the lines of force. While the wire is moving, a voltage, […]
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Electrical measuring instruments (another application of electromagnetism) : clamp-on meters, digital multimeters and summary of electrical measuring instruments
17–9 CLAMP-ON METERS All the instruments discussed so far in this chapter operate on magnetic principles. Be aware, though, that modern technology provides meters that employ principles of electronics and induction. Induction, as you will learn in the following chapter, involves transfer of energy from one conductor onto another without physical contact. This energy transfer […]
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Electrical measuring instruments (another application of electromagnetism) : clamp-on meters, digital multimeters and summary of electrical measuring instruments
17–9 CLAMP-ON METERS All the instruments discussed so far in this chapter operate on magnetic principles. Be aware, though, that modern technology provides meters that employ principles of electronics and induction. Induction, as you will learn in the following chapter, involves transfer of energy from one conductor onto another without physical contact. This energy transfer […]
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Electrical measuring instruments (another application of electromagnetism) : megohmmeters, wattmeters and bridge circuits
17–6 MEGOHMMETERS An instrument called a megohmmeter is used for insulation testing and similar high-resistance tests. The megohmmeter contains a high-voltage generator that supplies current through the series resistors and the unknown resistance (R) to the two-coil assembly that operates the pointer; see Figure 17–13. Note in the figure that permanent magnets supply the field […]
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Electrical measuring instruments (another application of electromagnetism) : megohmmeters, wattmeters and bridge circuits
17–6 MEGOHMMETERS An instrument called a megohmmeter is used for insulation testing and similar high-resistance tests. The megohmmeter contains a high-voltage generator that supplies current through the series resistors and the unknown resistance (R) to the two-coil assembly that operates the pointer; see Figure 17–13. Note in the figure that permanent magnets supply the field […]
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