ELECTRICAL MACHINES: PART 1 MCQ and Notes

  1. For a D.C Motor : :

V = E + Ia . Ra    . . . . (i)

T = ka . Φ . Ia    . . . . . (ii)

E = kn . Φ . N    . . . .(iii)

where V is the supply voltage to the motor.

E is the  Back e.m.f of the motor.

Ia is the Armature current.

Ra is the Armature resistance.

T is the torque produced in the motor.

ka and kare the proportionality constant for Torque and Back e.m.f. respectively.

Φ is the flux.

N is the rotation speed (in rpm i.e. revolutions per minute).

Based on these formulae , a lot of numerical can be framed where the values of few parameters will be given and the other(s) needs to be found out.

using (ii) and (iii) we can have an auxiliary formula as:

T1 . N1 = T2 . N2

where  Tis the torque at  Nrpm and  T2 is the torque at  N2 rpm.

  • 2. Series D.C. Generator cannot build up on Open-circuit .

 

  • 3. Series Generator has the poorest Voltage Regulation.

 

  • 4. D.C. Generator Ideal has ZERO(0) Voltage Regulation.

 

  • 5. D.C. Generator having negative Voltage Regulation is for over compound type.

 

  • 6. Transformer Core decreases the reluctance of the common magnetic circuits.

 

  • 7. DC Series motor : Φ ∝ Ia , which means that as the armature current increases so does the flux.

Hence, T = ka . Ia2  which is derived from point 1 equation (ii)    [look above]

 

  • 8. Transformer No Load test helps us to find out the No load losses and magnetizing current in the transformer

 

  • 9. Transformer has lagging power factor because of drawing magnetizing current for its working.

 

  • 10. Transformer cores are laminated in order to reduce eddy current losses.

Eddy current loss ∝ f2 . kf2 . Bm2 . t2 . V

where,  f is the frequency of reversal of magnetic field ( Hz )

kis the form constant.

Bis the maximum value of flux density ( wb/m)

t is the thickness of lamination ( meter )

V is the volume of magnetic material ( m)

A BRIEF MATLAB INTRODUCTION & 5 FREE ALTERNATIVES TO MATLAB

WHAT IS MATLAB ?   

 MATLAB (matrix laboratory) is a multi-paradigm numerical computing environment and fourth-generation programming language. A proprietary programming language developed by MathWorks. MATLAB was originally written to provide easy access to matrix software developed by the LINPACK and EISPACK projects.
MATLAB allows matrix manipulations, plotting of functions and data, implementation of algorithms, creation of user interfaces, and interfacing with programs written in other languages, including C, C++, Java, Fortran and Python.

The MATLAB system consists of five main parts:

  • The MATLAB language.
  • The MATLAB working environment.
  • Handle Graphics.
  • The MATLAB mathematical function library.
  • The MATLAB Application Program Interface (API).

For more information visit the website : http://in.mathworks.com

or refer Wikipedia: https://en.wikipedia.org/wiki/MATLAB

TOP 5 OPEN SOURCE ALTERNATIVES OF MATLAB:

1. GNU Octave: Octave language is quite identical to MATLAB, which makes for easy portability of most programs.It provides a convenient command-line interface for solving linear and nonlinear problems numerically, and for performing other numerical experiments.
https://www.gnu.org/software/octave/

2. Scilab: Scilab also comes with a free “Xcos” package analogous to MATLAB’s Simulink for effortless modeling and simulation). It was developed at INRIA. Scilab has been developed for system control and signal processing applications.
http://www.scilab.org/

3. FreeMat: FreeMat supports many MATLAB functions and features a codeless interface to external C, C++, and Fortran code, further parallel distributed algorithm development , and it has plotting and 3D visualization capabilities. FreeMat has been in development by Samit Basu over a period of four years with help from a number of contributers distributed throughout the globe.
http://freemat.sourceforge.net/

4. SageMath: SageMath is a robust numerical computing software that uses a Python like syntax. It builds on top of many existing open-source packages: like NumPy, SciPy, matplotlib, Sympy, Maxima, R and so on.
http://www.sagemath.org/

5. R: R is a language and environment for statistical computing and graphics. It is a free implementation of the S programming language, which was originally created and distributed by Bell Labs.

https://www.r-project.org/