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Chapter: Electrical machines - Electromechanical Energy Conversion and Concepts in Rotating Machines

Important Short Questions and Answers - Electromechanical Energy Conversion and Concepts in Rotating Machines

Electrical machines - Electromechanical Energy Conversion and Concepts in Rotating Machines - Important Short Questions and Answers - Electromechanical Energy Conversion and Concepts in Rotating Machines

ELECTROMECHANICAL ENERGY CONVERSION AND CONCEPT IN ROTATING MACHINES

 

28. What is an electromechanical system?

 

The system in which the electromechanical energy conversion takes palace via the medium of a magnetic or electric field is called electromechanical system.

 

29. Describe multiply excited magnetic field system.

 

The specially designed transducers have the special requirement of producing an electrical signal proportional to forces or velocities of producing force proportional to electrical signal. Such transducers requires two or more excitation called as multiply excited magnetic field system.

 

30. Define co energy.

 

Co energy is an energy used for a linear system computation keeping current as constant. It will not be applied to the non linear systems.

 

31. How energy is stored?

 

Energy can be stored of retrieved from the magnetic system by means of an exciting coil connected to an electric source.

 

32.         Write the equation for mechanical force.

L = N2 / S  where S=Reluctance

F = - ½ l i(x)/ (x)


33.         Write the equation that governs doubly excited magnetic field.

Force in a doubly exited system:


Where i1 and i2 are constants which are the stator and rotor current respectively.



34.         Define field energy.

 

The energy drawn by virtue of change in the distance moved by the rotor in electrical machines in field configuration is known as field energy.

 

35. Draw the graphical relation between field energy and coenergy



 

36. Define the term pole pitch

 

The distance between the centres of two adjacent poles idcalled pole pitch, one pole pitch is equal to 180 electrical degrees. It is also defined as the number of slots per pole.

 

 

37. Define pitch factor

 

It is defined as the ratio of resultant emf when coil is short pitch to the resultant emf when coil is full pitched. It is always less than one.Pitch factor is always termed as coil span (Kc) factor

 

kc = cos α/2 where α = angle of short pitch

 

38. Define the term breadth factor

 

The breadth factor is also called distribution factor or winding factor. The factor by which there is a reduction in the emf due to distribution of coil is called distribution

factor denoted as kd.

 

39.         Write down the advantages of short pitched coil.

 

(i)                       The length required for the end connection of coils is less i.e., inactive length of winding is less. So less copper is required. Hence economical.

 

(ii)                      Short pitching eliminated high frequency harmonics which distort the sinusoidal nature of emf. Hence waveform of an induced emf is motre sinusoidal due to short pitching.

 

(iii)                As high frequency harmonics get eliminated, eddy current and hysteresis losses which depend on frequency also get minimized. This increases the efficiency.

 

40.         What is distributed winding?

 

Id ‘x’ conductors per phase are distributed amongst the 3 slots per phase available under pole, the winding is called distributed winding.

 

41.         Explain the following terms with respect to rotating electrical machines.

a)                      Pole pitch

b)                      Chording angle.

 

Pole pitch: The distance between the centres of two adjacent poles is called pole pitch.One pole pitch is equal to 180 electrical degrees. It is also defined as the number of slots per pole.

 

Chording angle: It is defined as that angle by which the coil pitch departs from 180 electrical degrees.


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