Compare Lap Winding & Wave Winding

Compare Lap Winding and Wave Winding

In this post, comparison between lap winding and wave winding is given on the basis of parallel path, current in each path, equalizer rings, commutation difficulty and on the basis of conductors.

Voltage build up in the Generator

 

• When the mechanical input power is given to the DC Generator, some emf and therefore current would be generated due to residual magnetism in the poles. 
• This current while passing through field coils, it will strengthen the magnetism of the poles which further generates emf. 

Reactance Voltage

• The rate of change of current during commutation period is from + Ia to – Ia. 
• We have taken it + 25 Amp to – 25 Amp.
• The rapid reversal of current in the armature coil is delayed as a result coil undergoing commutation do not in a position to attain full value of current by the end of short circuit.   

DC Generator : Condition For maximum efficiency

The power stages of DC Generator is shown in the Figure

Characteristics of DC Shunt, DC Series and DC Compound Generator

The most important characteristics of DC generators are given below.

Magnetizing or open circuit characteristics ( O.C.C ) ( E_o – I_f )

• It shows the relation between no load emf in armature for different value of field current. 
• The magnetizing characteristic is practically same for all types of generators.

Commutation in the DC Machines

• The function of the commutator is to make alternating current into unidirectional. 
• The direction of armature conductors are in one direction when conductors pass through N – poles and in opposite direction when they are under S – poles and vice versa.  
• The reversal of current takes place when conductors pass out under influence of the N – poles and enter that of S – poles. 

Losses in the DC Machines

The various losses occurring in DC machines can be given as follows.

• Iron loss (Magnetic or Core Loss) : Hysteresis Loss and Eddy Current Loss
• Copper Losses : Armature Copper Loss, Shunt Field copper loss and Series field copper loss

Armature Reaction in the DC Generator

• The flux which is produced by field winding is called as main flux or field flux.
•  The armature conductors produce armature flux. 
• The effect of armature flux on main flux or field flux is known as armature reaction. 

Types of DC Generator

The DC Generators are classified according to the way their field windings are connected and excited.

(A) Separately excited Generator

(B) Self excited Generator : There are two types of self excited generator

Equalization Ring or Equalization connection

• All the Conductors lay in any parallel path under one pair of poles in the Lap winding. 
• If the flux from all the poles is exactly same, the induced elf and hence current carried by each path will be equal in the ideal condition. 

Dummy coils

• The wave winding is possible only with particular number of conductor or coils.
• But sometimes the armature slots available in the armature winding do not meet the requirement of the winding. ( It means that the available number of slots is more than the required number of conductors ). 

EMF Equation of the DC Generator

Let P = Numbers of poles

     Ф = Flux / pole in weber

      Z = Total numbers of armature conductors

         = Numbers of slots × Numbers of Conductors / Slot

Parts of DC Machines

The following are main parts of DC machine. Figure A shows the construction of the 2 – Pole DC machine.

•  Yoke or Frame
•  Pole cores and pole – shoes

Practical DC Generator

• There are basic following elements of an electrical generator

Stationary part

• Field system which produce magnetic field

Rotating part

Principle of DC Generator

Principle of DC Generator

• It is an electrical machine which converts mechanical energy into electrical energy. 
• The principle of operation of the dc generator is based on dynamically induced emf.