brake test on dc compound motor

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

EM1LAB,BVCR,RAJAHMUNDRY ,Prepared by K. Nagesh & V.D.Neelima

BRAKE TEST ON D.C. COMPOUND MOTOR

AIM: To conduct brake test on D.C. Compound 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:

The series field may be connected in the circuit so as to help the shunt field or oppose.,in first case the motor is cumulatively compounded and in the second case differentially compounded. If the series field of the differentially compounded motor is so adjusted that at full load, the decrease in flux produced by it is just sufficient to make the full load speed and to no-load speed, then for and other load with in its range, it’s speed will be approximately constant. The cumulative compounded motor experiences an increase in flux so that, as load increase, the speed decreases, the fall in speed affords relief to the motor. When differentially compounded motor is started. First series field flux will be established and the motor start is wrong direction, when the shunt field is fully established, the total flux is so small that the motor draws a large current from the supply. When the motor is overloaded speed will increase like a series motor on no-load. 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. One end of the band is fixed to earth via a spring balance S1 and the other is connected to a suspended weight W1. The motor is running and the load on the motor is adjusted till it carries its full load current. The net pull on the band due to friction at the pulley is ( S1 – S2 ) Kg Wt.Shaft torque T sh = 9.81 ( S1 - S2 ) R N- MR = Radius of brake drum in MtMotor output Power = T sh x 2πN Watt.Efficiency = Output

Input PROCEDURE:

1. Make the connections as per the circuit2. Give Supply to the motor, by closing DPST switch3. 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 tighting the belt of the pulley.7. Note down the readings.8. Take the readings for different loads.9. Do the necessary calculations and draw the graphs.


TABULATION:

S.NoLineCurre

ntIL ( 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) Readings must be noted without any parallax error.

2) The pulley of the brake drum must be filled with cool water.

3) Before stop the motor, load should be removed.

4) Connections must be tight.

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 Compound Motor is conducted and its performance curves are drawn.

VIVA QUESTIONS

1) What is the difference between cumulative and differential compound motor connections?

2) What happen, if the field circuit of a loaded cumulative compound motor is suddenly opened?

3) At the time of starting of motor the rheostat of the field circuit kept, in which position (maximum or

minimum)?

4) What are the applications of DC compound motor?

5) What is the necessity of the starter?


brake test on dc compound motor

Documents