Paliyam Satyagraha (1947-48)

  * It is the first sathyagraha which took after the independence in Kerala.
* To get open the road surrounding of the main residence (at chendhamangalam) of Paliyath Achan ,the hereditary cheif minister of kochin for avarnas.
* Paliyam sathyagraha was officially inaugurated by C Kesavan on 4 December 1947 .
* Majority of Christian community supported the sathyagraha.
* Women played an important role in sathyagraha.
* Under the leadership of Yogakshema sabha,Namboothiri women P Priyadhatta,E S Saraswathi,I C Priyadhatta,Arya Pallam Arya thampuratti and Indira thampuratti played an important role.
* On 100 th day of sathyagraha in March 1948 A G Velayudhan was killed in a police lathi charge.
* In April 1948 temple entry proclamation was done by Kochi Raja.Then all temples where thrown open to all Hindus irrespective of cast.After that the avarnas and non Hindus get right to walk along the Paliyam road.

Previous questions in psa
# Arya Pallam related to which of the following?(foreman SIDCO 2015- PSC )
  1.Salt sathyagraha
  2.Guruvayur sathyagraha
  3.Vaikkom sathyagraha
  4.Paliyam sathyagraha

Ans) Paliyam sathyagraha

# The martyr of Paliyam sathyagraha? (Foreman SIDCO 2015)
   a.A K Goplalan
   b.Kunhapi
   C.Govidha Panikar
   d.A G Velayudhan

And) A G Velayudhan

Construction of dc machines

         The DC motors and generators have same general construction.Hence a DC generator can run as a DC motor and vice versa .The essential parts are.

1.Magnetic frame or Yoke.
        The outer frame or Yoke of DC machine provide for two functions.
         a) It gave mechanical support to the poles and acts as a protecting cover for the machine.
         b)It carries magnetic flux produced by the poles.
             The Yoke is usually made up of solid cast steel.
2.Pole Core and Pole Shoes.
        The field magnet consists of pole core and pole shoes.The field coils are supported on the pole core and pole shoe spread out the flux in the air gap.The large crossection of pole shoe reduce the reluctance of the magnetic path.
             the pole core and pole shoes are made up of thin steel lamination.
3.Field Coils.
         The field winding which consists of copper wire wound over the pole.When current is passes through this coils ,they electromagnetise the poles which produce the necessary flux that is cut by the revolving armature conductors.
4.Armature Core.
           It houses the armature coil and cause them to rotate in the magnetic flux produced by the field system.The armature core is keyed to the machine shaft and rotate between the field poles.Armature core is cylindrical shaped and made up of circular steel laminations and each laminations are coated with thin insulating film.The purpose of lamination is to reduce Eddy current loss.
5.Armature winding.
          The slots of the armature core holds insulated conductors that are connected in suitable manner.This is known as armature winding.In this winding working emf is induced.The armature winding of a DC machine is closed circuit winding.
6.Commutator.
          A commutator is a mechanical rectifier that converts the alternating voltage generated in the armature winding into direct voltage across the brushes.Commutator is made up of Copper segments and insulated from each other by mica sheets and mounted in the shaft of the machine.The armature conductors are soldered to the commutator segments in suitable manner.
7.Brushes.
           the brushes are used to ensure electrical connection between the rotating commutator and stationary external load circuits.The brushes are made up of Carbon and the rest on commutator.

Reason for rotation of rotor in induction motor

         When 3 phase stator winding is fed with 3 phase supply a magnetic flux of constant magnitude but rotating at synchronous speed is set up.This flux passes through the air gap and cut the stationary rotor conductors .Due to the relative speed between rotating flux and stationary conductors an e.m.f is induced in the rotor conductors according to Faraday's laws of electromagnetic induction.The frequency of induced e.m.f is same as that of supply frequency.
The magnitude of induced e.m.f is propotional to the relative velocity between flux and conductors.Its direction is given by Fleming's right hand rule.
     Since rotor bars or conductors form a closed circuit,  rotor current is rotating in such a way that it always opposes the very cause which produce it In this case the cause which produce the rotor current is relative velocity between flux and conductor .Hence to reduce the relative speed the rotor starts running as in same direction that of flux.

Advantages and Disadvantages of Swinburne's Test

Advantages of Swinburne's Test

The main advantages of this test are :
         1.This test is very convenient and economical because the power required to test a machine is small.ie,only no load input power.
         2.Efficiency can be pre-determined at any load because constant losses are known.

Disadvantages of Swinburne's Test

The main disadvantages of this test are :
           1. Iron loss is neglected though there is change in iron loss from no load to full load due to armature reaction.At full load ,due to armature reaction ,flux is distorted which increase the iron loss in some cases by as much as 50%.
           2. We cannot be sure about the satisfactory commutation on loaded condition because the test is done on no-load.
           3. We can’t measure the temperature rise when the machine is loaded. Power losses can vary with the temperature.
           4. In dc series motors, the Swinburne’s test cannot be done to find its efficiency as it is a no load test.Because in the case of dc series motors the speed is variable,when load increases speed decreases and when load decreases speed increases.hence at no load condition the speed will be extremely high.So this test cannot be applied to dc series machines.

Characteristics of an ideal operational amplifier

¥ Infinite voltage gain.

¥ Infinite input impedance so that any signal source can drive it.and it can avoid loading effect also.

¥ Zero output resistance so that the output can drive infinite number of other devices.

¥ Zero output voltage when input voltage is zero.

¥ Infinite bandwidth so that any frequency signal can be amplified without attenuation.

¥ Infinite slew rate. So that output voltage changes occurs simultaneously with the changes in input Voltage.

¥ Infinite CMRR then there will be no noises in the output.

Necessity of a compound generators

   In practical cases power circuits such as lighting require a constant voltage. Shunt and series generators cannot be used for such situations.Because, as load current of shunt generators increases its terminal voltage falls and as load current of series generator increases the terminal voltage also increases .

     In compound generators both series and shunt windings are placed in each field pole .The series winding so connected that flux produced by it aids the flux produced by the shunt winding. (Such generators are called Cumulatively compounded generators).So as load current increases , flux produced by series winding compensates the loss of flux due to armature reaction.Then the terminal voltage of the generator remains constant.

Disadvantages of using large number of poles in a DC machine

¥ Since the brush arms are closed together, chance of flash over increases.

¥ More commutator segments are needed

¥ Frequency is proportional to number of poles and core loss depents on frequency.

¥ Armature diameter increased.