CIRCUIT DIAGRAM FOR HOPKINSON’S TEST

DROP TEST for Ra GENERATOR

DROPTEST FOR Ra MOTOR

EM1 LAB,BVCR,RAJAHMUNDRY Prepared by K. Nagesh & V.D.Neelima

HOPKINSON’S TEST DC SHUNT MACHINE

AIM:- To conduct Hopkinson’s Test on two identical D.C. Shunt Machines and to determine their efficiencies at different loadings.

APPARATUS:

THEORY:

Kapp’s modified Hopkinson’s test, usually called the hopkinson test, is used to determine the losses and efficiency of two identical D.C. shunt machines. To perform this test one machine is run upto speed of shunt motor and the other one is to be excited to such a level that it generates an e.m.f. exactly equal to the voltage of the supply feeding the motor. Both the machines are mechanically coupled with each other. Then the generator is put in parallel with the supply system and called the floating state of the generator. Now any desired load can be given to the generator. The difference between the generator output and motor input i.e. all the losses will be equal to the total current taken from the supply system and the current generated by the generator.

PROCEDURE:

1. Make the connections as per the circuit diagram.2. Give supply to the motor by closing DPST switch.3. Start the motor with the help of 3-Point starter.4. Adjust the speed of the motor by first varying armature rheostat and then field rheostat.5. Vary the field rheostat of the generator until voltmeter shows zero reading.6. After voltmeter shows zero deflection close DPST switch.7. Adjust the field regulator of the generator such that a current flows through the generator to the

motor.8. Take the readings of all meters.9. Do the necessary calculations and draw the graphs.

Tabulation:

S.No V IL IFM IFG ILG Motor I / P

V(IG+IL)

Gentr.O / PVILG

WG

(W/2)MotorLosses

GeneratorLosses

ηM =

O/PI/P

ηG =

O/PI/P

1

2

3

EM1 LAB,BVCR,RAJAHMUNDRY Prepared by K. Nagesh & V.D.Neelima

S. No

Name of the Equipment Type Range Qty.

1 Ammeter M.C 0 – 2 A 2No.2 Ammeter M.C 0 – 20A 2No.3 Voltmeter M.C 0 – 300V 2No.4 Voltmeter M.C 0 – 30V 1No.5 Rheostat Wire

wound 50 Ω/ 5A 1No.

6 Rheostat Wire wound

360 Ω/ 1.2A 2No.

7 Tachometer Digital 0 – 10,000 rpm 1No.

4

5

For Drop Test For RAG:

S.No.

Voltage ( V ) Current in ( A ) Armature Resistance Ra = V / I

1234

For Drop Test For RAM:

Model Calculations:

RAM =__________ RAG = __________ V=____________

MOTOR INPUT = ( I LG + I LM ) *V

GENERATOR OUTPUT = V* ILG

MOTOR :

ARMATURE CU LOSSES = I2 ARAM

IA= I LG+ I LM-I FM

GENERATOR:

ARMATURE CU LOSSES = I2 ARAG

IA= I LG+ I FG

CONSTANT LOSSES :

INPUT = V*IL

W (CONSTANT LOSSES) = INPUT – [ GEN CU LOSSES + MOT CU LOSSES ]

= V*IL – [I2 AR AG + I2 AR AM ]

MOTOR EFFICIENCY ( η M ) = Input - Losses*100

Input

= ( I LG + I LM ) *V – [ W/2 + I2 A R AM ] / I LG + I LM

EM1 LAB,BVCR,RAJAHMUNDRY Prepared by K. Nagesh & V.D.Neelima

S.No.

Voltage ( V ) Current in ( A ) Armature Resistance Ra = V / I

1234

GENERATOR EFFICIENCY ( η G) = Output

Out put +Losses

= ( V *I LG) /( V *I LG + [ W/2 + I2 A R AG ] )

MODEL GRAPH:

PRECAUTIONS:

1. Connections should be tight.2. Take the readings without parallax error.3. Fuses should be properly rated.4. The operation of the 3 – Point starter should be slow and uniform,5. Armature rheostat should be connected in maximum position initially.6. Field rheostat should be connected in minimum resistance position.

RESULT:-

Hopkinson’s test is conducted on two identical D.C. Shunt Machines and their efficiencies at different loadings are calculated.

VIVA QUESTIONS

1. What is the other name of Hopkinson’s test?

2. What is the principle of a generator, motor?

3. What is commutation?

4. How can the direction of a D.C shunt motor reversed?

EM1 LAB,BVCR,RAJAHMUNDRY Prepared by K. Nagesh & V.D.Neelima