previous post

RICH DAD POOR DAD BOOK REVIEW

-
  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 the difference between working
Post a Comment

Armature Reaction

-
Armature reaction

  • Due to relative motion between armature conductors and field mmf there is an emf induced in armature conductors. This emf causes flow of current in armature conductors which cause armature flux. This flux is produced as a reaction to field flux and hence is called as Armature Reaction.




  • Geometric Neutral Axis ( GNA ) is defined as the axis that is perpendicular to the field axis of the stator. Magnetic Neutral Axis ( MNA ) is defined as the axis perpendicular to the net flux that is flux due to field as well as armature mmf. The perpendicularity is taken in terms of electrical angle and not mechanical angle.
  • It is well known that the brushes are placed on the MNA to collect maximum emf and also to ensure that the undergoing commutation have zero rotational voltage to prevent serious commutation problems.
  • On no-load, the MNA coincides with the GNA because on no-load there is no armature current and armature reaction can be neglected so net flux is same as field flux.
  • However, when the machine is loaded then the armature MMF that is triangular in wave shape and along the brush axis causes a cross magnetizing effect on the main field resulting in to concentration of flux on the trailing pole tips in generator action and leading pole tips in motor action.
  • Leading Pole Tip is the tip of the pole encountered first by the armature in the direction of rotation and trailing pole tip is the tip which is encountered after the leading pole tip.




  • Flux is strengthened where armature and field flux lie along the same direction and weakened where armature and field flux lie in opposite directions.
  • So, magnetic field is strengthened at trailing pole tips and weakened at leading pole tips.




  • If strengthened effect = weakening effect, the average flux under the pole remains same and therefore no demagnetizing effect of Armature Reaction. But due to saturation, strengthening effect < weakening effect so average flux under each pole reduces and hence Armature Reaction is demagnetizing.
  • The Phasor Diagram for Armature Reaction is shown below :




  • Consequently, the MNA is no longer on the GNA but shifts in the direction of rotation for generator action and is a direction opposite to rotation for motor action.
  • Since, Armature Flux is perpendicular to Field Flux so the nature of Armature Reaction is cross magnetizing.

Effect of Cross Magnetizing Armature Reaction :-
  • MNA shifts in direction of rotation in case of generator and opposite to direction of rotation in case of motor. The amount of shift ∝ Ia
  • The iron losses are increased because Bmax is increased.
  • Due to presence of air gap flux along the brush axis, an emf is induced in coil which is undergoing commutation, so commutation process id delayed, so sparking at brushes occurs.
  • The ⲫ is maximum under trailing pole edge, so induced emf is maximum for conductors lying under this pole edge and if this induced emf increases beyond 30-40 V, the mica insulation fails, hence sparking takes place between adjacent commutator segments.
Read more>>> Methods of Reducing Armature Reaction

Comments

Post a Comment

If you have any doubts, please let me know

Popular posts from this blog

Ideal Transformer (1-phase) Operation Under Load

-
Image
 What is Ideal Transformer ? An ideal transformer is a transformer with the following assumptions: Permeability of transformer is infinite. Iron loss in the transformer core are zero. Resistance of transformer winding is zero. No magnetic leakage flux, so coefficient of coupling is  1 . Magnetization curve of transformer is linear. Operation of Ideal transformer under load Schematic diagram of an ideal, 1-phase transformer under load When a finite impedance load Z L   is connected across the secondary terminals of a 1-phase transformer as shown in above figure, the load current I 2   flows through the secondary winding and the load. load current I 2   is given by:- I 2  = V 2 / Z L How will MMFs Produce ? A voltage source V 1   is connected to the primary winding. Due to this voltage V 1  primary current I 1   flowing through N 1   number of turns in the primary winding produces an MMF  N 1 .I 1   which creates the flux Ⲫ in the core. This flux links with the secondary coil and induc
Read more

RICH DAD POOR DAD BOOK REVIEW

-
  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 the difference between working
Read more

Compensating Winding

-
Image
Compensating Winding The cross magnetizing armature reaction effect that causes concentration of flux under one pole tip is caused mainly by the conductors that lie under the pole are. When the machines are heavily loaded, the flux density at these tips become very high resulting in higher than normal induced voltage between concerned adjacent commutator segments. This may cause a spark over between adjacent commutator segments more so because these coils are physically close to the commutation zone where air temperature is high and favorable for spark over. This may lead to other segments also getting involved and resulting in fire over entire commutator segment. Also if load is rapidly fluctuating (e.g. rolling machine), L(di/dt) voltage of coils may became high enough to start a spark over between adjacent commutator segments. This phenomenon will start from the coil under the pole center and it would have maximum. This problem is more acute when load is decrea
Read more