Questions (1 Viewer)

[Sirius Black]

q1.The windings of a large electric motor may be protected by placing a variable resistance in series with the windings. The resistance is set to be maximum before the motor is switched on. After switching on, the resistance is reduced to zero as the motpr gathers speed.

Outline why this protections is unlikely to be needed for an A.C. motor

Q2. A soft ion core is placed inside a transformer and layered core with hin ceramic layers. explain the purpose of this. (apart from intense the magnetic field strength)

 

[Budz]

Wow.. good question.
OK u need to talk about current surges which is a high amount of current passing through a conductor with no opposing force,
If minimum resistance is applied initially current will flow immediatly with No Back Emf "the coild has not yet begun to turn as electrical energy moves faster than the K.E of the loop" this can cause a current surge..

Why not need for AC, the current alternates before a surge can occur, The rotation must of course be sychronized so that the loop rotates 90 degrees 50 times a second.

Soft iron core increases 'B' field, Why does it need to be layered with ceramics, So eddy currents are minimised not allowing heat to build up which could melt wires, also to reduce energy losses.