brake test on dc shunt motor

CIRCUIT DIAGRAM FOR BRAKE TEST ON D.C.SHUNT MOTOR

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

BRAKE TEST ON D.C. SHUNT MOTOR

AIM: To conduct brake test on D.C. Shunt Motor and to draw its performance curves.

APPARATUS REQUIRED:

S. No Name of the Equipment Type Range Qty.1 Ammeter M.C 0 – 2 A 1No.2 Voltmeter M.C 0 – 300V 1No.3 Ammeter M.C 0 – 20 A 1No.4 Rheostat Wire wound 50 Ω/ 5A 1No.5 Rheostat Wire wound 360 Ω/ 1.2A 1No.6 Tachometer Digital 0 – 10,000 rpm 1No.

THEORY:

It is a direct method and consists of applying a brake to a water – cooled pulley mounted on the motor shaft. The brake band is fixed with the help of wooden blocks gripping the pulley.

The sample brake test described above can be used for small motors only. Because in the case of large motors. It is difficult to dissipate the large amount of heat generated at the brake.The load test can be conducted by using a belt brake or rope brake. For a constant applied voltage, the field current is constant for a D.C. Shunt motor. The flux will, therefore have its maximum value at no-load, and because of armature reaction will decrease slightly as the load increases. For most purpose this decrease can be

neglected, and the flux per pole ‘φ ’ can be regarded as constant.

The speed N is proportional to

V − I aRaφ . The speed of shunt motor from no load to any other load

is proportional to the armature drop at that load. The fall in speed will not be quite so great. Since the full load drop in the armature is small compared with applied voltage, the speed curve of a D.C. Shunt motor is a

slightly drooping curves. Torque (T) is proportional to φ Ia, since φ is approximately constant,. The torque is proportional to (Ia) the armature current. Hence the torque characteristic is a straight line through the origin.

PROCEDURE:

1) Make the connections as per the circuit

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 to its rated value by varying either field or armature Rheostat as per

the requirement.

5) Note down the no load readings.

6) Apply load on the motor by tightening the belt of the pulley.

7) Note down the readings till rated current of motor.

8) Take the readings for different loads.

9) Do the necessary calculations and draw the graphs.


TABULATION:

S.NoLineCurrent

IL ( A )

Voltage(v )

FieldCurrentIf (A)

Ia= IL+If

N(rpm)

SpringBalance

NetBalance

S=S1 – S2

Torque =

S x Rx 9.81

Power( O/P)2πNT

60

Power(I/P)

VIL

Efficiency= O/P I/ PS1 S2

R=0.1034M

Model Graph:-

PRECAUTIONS:

1) The pulley of the brake drum must be filled with cool water.2) Before stop the motor, load should be removed.3) Connections must be tight.4) Readings must be noted without any parallax error.5) Fuses should be properly rated .6) The operation of the 3-Point starter. Should be slow and uniform.7) Armature rheostat should be connected in maximum position initially.8) Field rheostat should be minimum resistance position.


RESULT:-

Brake Test on D.C Shunt Motor is conducted and its performance curves are drawn.

VIVA QUESTIONS

1) What will happen if the field circuit gets opened during the experiment?

2) What is the variation of speed of the D.C shunt motor when the load increases?

3) How can you adjust the speed of the D.C shunt motor under no load conditions?

4) What is the necessity of three point starter during this experiment?

5) While starting, if the motor rotates in the reverse direction then what you have to do?


brake test on dc shunt motor

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