Table of Contents
Why DC is used for excitation?
Originally Answered: Why dc is used as excitation of alternator? Its because you need a constant field. If you give ac it produces a time varying field. In a constant field the armature cuts the flux, hence a time varying emf is induced.
What is the purpose of field winding in DC machine?
The field winding’s sole purpose is to provide a magnetic field for an armature, or rotor, to work in. For motors, a current is supplied to both the field windings and the armature windings to induce motion in the armature.
How is the field excited in a DC alternators?
The DC generator converts mechanical power into electrical power. The magnetic flux in a DC machine is produced by the field coils carry current. The circulating current in the field windings produces a magnetic flux, and the phenomenon is known as Excitation.
Is the rotor excitation current AC or DC?
1. Magnetic flux: Magnetic circuit is placed in the rotor. Required magnetic flux is created in the rotor by supplying DC (Direct Current) to the rotor circuit. This Direct Current (DC) is called excitation current.
What is the purpose of field flashing?
Field flashing is used on self-excited generators, where the residual magnetism is not high enough to build up the terminal voltage when starting. What is done is to connect an external DC source to the field winding to start the voltage build up; the flashing source is removed for normal operation.
What is separately excited DC machine?
A separately excited dc motor is a motor whose field circuit is supplied from a separate constant-voltage power supply, while a shunt dc motor is a motor whose field circuit gets its power directly across the armature terminals of the motor. Hence, the motor speed will slow down.
How would you define separately excited DC generator and self excited DC generator?
In a separately excited (S.E.) machine, the field winding is connected to a separate voltage source while, in a self excited generator field winding is connected across the armature terminals (provides its exciting current) . Hence, the field winding has a large number of turns with a thin conductor.
What is the function of exciter?
A Exciter. The exciter supplies direct current to the field winding of the generator, at whatever voltage is required to overcome the resistance of the winding.