Monday, June 27, 2011
Friday, June 17, 2011
Wednesday, June 15, 2011
Tuesday, June 14, 2011
Principle of Operation of DC motor & Generator
Dc motors
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Monday, June 13, 2011
vector control of Induction motor drive
In applications where high performance variable speed operation is required, only
dc motors were extensively used due to the ease speed control. Separately excited dc
motors were particularly popular in applications where fast torque response was required.
However, dc motors have some generic disadvantages like, requirement of periodic
maintenance. Unusable in explosive or corrosive environments due to sparking problem.
Commutation is difficult at high currents and voltages and hence its use is limited to low
power, low speed motors.
These problems can be overcome by using induction motors, which have a simple
and rugged structure. Further, they have a high torque weight ratio as compared to their
dc counterparts.
The field and the armature currents respectively can control the flux and torque,
independently in the case of dc motors. It is because of this inherent decoupling between
the field flux and the armature current, one is able to achieve very good torque dynamics
from dc machines. Unlike dc machines, there is no inherent decoupling between flux and
torque producing components of the stator currents in the induction machines. Therefore,
achieving good torque dynamics in ac machines is not easy. However, nowadays, field
oriented control or vector control techniques have been employed, which results in good
torque dynamics of induction motors.
In this dissertation work all discussions relating to induction motors are with
respect to squirrel cage type induction motors only. The operation of the 3phase induction
motor is based on Faraday’s law and Lorentz force on a conductor. According to
Faraday’s law, if the flux linking a conductive loop varies as a function of time, then an
e.m.f, which is proportional to the rate of change of flux, is induced in the loop there by
forcing a current to flow in the conductive loop. In the case of induction motor, the induced current in the rotor conductors interact with the air gap flux to produce the
torque. As the rotor tries to catch up with the magnetic flux in accordance with the Lenz’s
law, the rate at which conductors are cut by the magnetic flux is reduced. As a
consequence the induced rotor currents decrease and the Lorentz force on the rotor
conductors reduce. Evidently if the rotor conductors were to catch up with the magnetic
flux then there would be no relative motion between the conductors and the flux, and this
would result in zero rotor currents and zero torque. Therefore, for the induction motor to
operate there must exist some relative speed between the flux and conductors, which is
called the slip speed ωsl.
for more click here VECTOR CONTROL
for more click here VECTOR CONTROL
Political Satire cartoon1
cartooinst sridhar known for his cartoons sketched one good political satire cartoon in eenadu newspaper dated 12th june 2011.
Sunday, June 12, 2011
Support to Lokpal Bill
As you are aware that Govt. of India has put a condition that 25 Crores of People support is needed to implement The Lokpal Bill. For this we just have to give a Toll Free Call to +91-22-61550789. The Call gets disconnected automatically after 1 ring. After giving a call to this number, you will receive a Thanks Message. Request to forward this mail to as many as possible to make our nation corruption free. Please do it once, Call the above number with NO CHARGES I did it.
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