EE6401 Important Questions Electrical Machines 1
EE6401 Important Questions Electrical Machines 1 Regulation 2013 Anna University
Sample EE6401 Important Questions:
1. Mention the types of electrical machines.
There are three basic rotating machines types, namely
a. The dc machines
b. the poly phase synchronous machine (ac), and
c. Poly and single phase induction machine (ac)and a stationary machine,
2. State Ohm’s law for magnetic circuit.
It states that the magneto motive force across the magnetic element is equal to the product of the magnetic flux through the magnetic element and the reluctance of the magnetic material. It is given by
MMF = Flux X Reluctance
3. Define leakage flux
The flux setup in the air paths around the magnetic material is known as leakage flux.
4. Define magnetic reluctance
The opposition offered by the magnetic circuit for the magnetic flux path is known as magnetic reluctance. It is analogous to electric resistance.
5. What is magnetostriction?
When ferromagnetic materials are subjected to magnetizing mmf, these may undergo small changes in dimension; this phenomenon is known as magnetostriction.
6. What is fringing?
In the air gap the magnetic flux fringes out into neighboring air paths due to the
reluctance of air gap which causes a non uniform flux density in the air gap of a
machine. This effect is called fringing effect.
7. State stacking factor.
The stacking factor is defined as the ratio of the net cross sectional area of a magnetic core to the gross cross sectional area of the magnetic core. Due to lamination net cross sectional are will be always less than gross cross sectional area. Therefore the value of stacking factor is always less than unity.
8.Mention some magnetic materials
Alnicos, chromium steels, copper–nickel alloy, nickel, cobalt, tungsten and aluminium.
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