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RICH DAD POOR DAD BOOK REVIEW

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  RICH  DAD  POOR  DAD  BOOK REVIEW This is amazing book.   • Explodes the myth that you need to earn a high income to become rich • Challenges the belief that your house is an asset • Shows parents why they can't rely on the school system to teach their kids about money • Defines once and for all an asset and a liability • Teaches you what to teach your kids about money for their future financial success It's been nearly 25 years since Robert Kiyosaki’s  Rich Dad Poor Dad  first made waves in the Personal Finance arena. It has since become the #1 Personal Finance book of all time... translated into dozens of languages and sold around the world. Rich Dad Poor Dad  is Robert's story of growing up with two dads — his real father and the father of his best friend, his rich dad — and the ways in which both men shaped his thoughts about money and investing. The book explodes the myth that you need to earn a high income to be rich and explains...
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Characteristic of DC Motor ( Shunt, Separately and Series)

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 The following characteristics are plotted in case of DC Motors:
  • Speed- Armature current characteristics ( N or Ꞷ  vs  Ia )
  • Torque- Armature current characteristics ( T  vs  Ia )
  • Speed- Torque characteristics ( N or Ꞷ  vs  T )

NOTE:- For Shunt Excited DC Motor all characteristics are same as that of Separately Excited DC Motor.

Shunt and Separately excited DC Motor


The set-up of a Separately Excited motor is shown in the figure below:

Shunt Excited DC Motor

Separately Excited DC Motor




Torque- Armature current characteristics

Developed Torque in a DC Machine depends on Armature Current as shown
below.
We assume that field excitation is kept constant and hence flux is constant.
T = K Ⲫ Ia  ∝  Ia    ,   if  Ⲫ = Constant 


   

Speed- Armature current characteristics

The performance equation of a separately excited DC Motor is given by,

Eb = (Vs - Ia Ra) = K Ⲫ N

⇒ N = (Vs - Ia Ra) /K Ⲫ





Speed- Torque characteristics

In the Speed- Current characteristics, Armature Current (Ia = T / KⲪ) can be replaced by Torque as shown below,

N = (Vs/K Ⲫ) - (Ra T/(K Ⲫ)^2)

Due to Armature Reaction, flux reduces and so drop in Ꞷm increases





Series Excited DC Motor

Series Excited DC Motor


Speed-Armature Current Characteristics


In a Series Excited DC Motor, field current is same as Armature Current and so flux in the machine is proportional to Armature Current.
So, flux  Ⲫ = K1 Ia

Eb = K Ⲫ N = Vs - Ia (Ra + Rse)

N = {Vs /KⲪ} - {Ia (Ra + Rse) /KⲪ}

N = {Vs /K K1 Ia} - {(Ra + Rse) /K K1}-------(1)

Armature and series field resistance being very low, (Ra + Rse) can be neglected and we can obtained:

N Ia = VS /K K1 --------(2)

Thus, at lower currents, the N vs Ia characteristics resembles rectangular hyperbola ( according to equation 2 ). In this region, the speed decreases abruptly with increase in input current.

with larger currents, the magnetic circuit gets saturated and flux Ⲫ tends to approach a constant value. In that case, speed and armature current can be related by using equation 1. 
This represents a slightly drooping straight line nature of N vs Ia characteristics for larger values of armature current. 
The speed becomes zero when the input current is equal to short-circuit current of the motor, i.e.
Ia = Isc = Vs /(Ra + Rse)



Torque-Armature current characteristics

In a series Excited DC Motor, flux is proportional to Armature Current as given below,
Ⲫ = K1 Ia

Torque,  T = K Ⲫ Ia = K K1 Ia^2 = K' Ia^2

Again for large armature current Ia, Ⲫ ≈ constant   so,  T ∝ Ia


Speed-Torque characteristics

Armature Current can be expressed as a function of Torque as shown below,

Ia = {T/K K1}^1/2

Substituting this value in Speed Armature Current Characteristics,

N = {Vt /(K K1 T)^1/2} - {(Ra + Rse) /K K1}

When saturation sets in , Ⲫ = constant

N ={Vt /(K Ⲫ} - {(Ra + Rse)T /K^2 Ⲫ}


Some points:-
  • Ideally suited for traction load, locomotives
  • Series motors are never belt loaded or chain loaded it must be directly coupled to load.
  • Series Motors must never be run under No-Load conditions else speed can be dangerously high.



                                          

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