How to set trip point in overload relay of starter?

Well, most of the engineers, who use the motors find sometimes get quizzed that how they should find right trip point on the overload relay in the starter for the motor.

For this, one must find the current rating provided on the motor. This is usually the safe current which the winding of the motor can work with out failure. Usually the winding of motor can withstand high current also based on the time. If the motor curve is available it is easy to find out the required trip current based on the trip time.

or else, one has to consider the 1.5 times of the rated current of motor. When we set the trip point on the relay at the required current, the next step is to ensure the trip time. Trip time could be find out by using equivalent load.

The final step to ensure that you have used the proper relay is to perform rotor lock test
of the motor.        

What is rotor lock test?

The name itself gives and idea that it is locking of the shaft or rotor. One has to lock the rotor and switch on the motor.
This will lead to high current passage through winding. The relay should get tripped within prescribed time by manufacturer
to stop damage to the winding. This is the worse condition of failure and thus, suitable use of relay and trip set point, will always protect the motor.

Any queries are welcome.

Polar Dielectric in Uniform Electric Field

 i) There are permanent dipoles present in Polar Dielectric which are randomly aligned in such a way that there exists permanent dipole moment  Pp.

ii) When a dipole is present in an uniform electric field the dipole tries to align itself in the direction of electric field.

iii) Because of this all dipoles in polar dielectric are partially aligned in the direction of the field. This partial alignment is responsible for the induced dipole moment Pi.

Therefore the electric dipole moment is increasing.

P = Pp + Pi

iv) The electric dipole moment of a polar dielectric increases

      a) by increasing the applied electric field

      b) by decreasing the temperature