## EE6365 ELECTRICAL ENGINEERING Lab Manual

Anna University Regulation 2013 Mechanical Engineering (MECH) EE6365 EE LAB Manual for all experiments is provided below. Download link for MECH 3rd SEM EE6365 ELECTRICAL ENGINEERING Lab Manual is listed down for students to make perfect utilization and score maximum marks with our study materials.

LOAD TEST ON DC SHUNT MOTOR

AIM:

To conduct a direct load test on the given dc shunt motor and to plot the following performance characteristics: 1) Efficiency vs Output power (2) Torque vs Output power (3) Speed vs Output Power (4) Line current vs Output Power (5) Torque vs Speed.

THEORY:

Load test on motors are performed to know about the efficiency, torque and speed characteristics, which enable us to select an appropriate motor for an application. The torque equation of a DC Motor is given by Ta = 0.159 (IxPxZ / A) * Ia N-m, where I=Flux per pole (Wb), P= No. of poles, Z= No. of armature conductors, A = no. of parallel paths. As P, Z, A being constant, the above equation reduces to Ta=K I Ia. In a DC Shunt motor as I is constant, the torque is directly proportional to armature current.

The speed of a DC motor is given by, N = K (V – IaRa) /I. Since I is constant, the speed is directly proportional to (V-Ia Ra). As the load on the motor increases, the drop IaRa becomes negligible as `Ra ‘ is very small and the speed is nearly constant.

Hence a DC shunt motor is considered as a constant speed motor. If a DC shunt motor is started on load, it draws a heavy armature current which in turn will damage the machine itself. Hence DC shunt motors are always started on no-load condition

PRECAUTIONS: (Not to be included in the Record)

1. Remove the fuse carriers before wiring and start wiring as per the circuit diagram.

2. Check the position of the rheostat as specified in the procedure.

3. The load on motor must be released initially.

4. Fuse calculations: As this is a load test, the required fuse ratings are 120% of the rated current of the motor.

5. Replace the fuse carriers with appropriate fuse wires after the circuit connections are checked by the Staff-in-charge.

PROCEDURE:

1. The circuit connections are made as per the circuit diagram.

2. Keeping the motor field rheostat in its minimum position and the starter in its OFF position the main supply is switched ON by closing the DPSTS.

3. The motor is started using the three-point starter by slowly and carefully moving the starter handle from its OFF to ON position.

4. The motor is brought to its rated speed by gradually adjusting the field rheostat and checked with the help of a tachometer.

5. Under this no load condition, one set of readings namely, applied voltage (VL), armature current (Ia), field current (If), the two spring balance readings (F1and F2) and motor speed (N) are noted down in the tabular column.

6. The load on the motor is increased in steps gradually and at each step, all the meter readings and the motor speed are recorded in the tabular column. The above procedure is repeated until the motor is loaded to 120% of its rated current.

7. After the experiment is completed, the load on motor is gradually decreased to minimum and the rheostat is brought back to its original position and then the main supply is switched OFF.

8. After completing the experiment, calculate the Torque, Armature current, Input power, Output power and Efficiency using the formulae given.

9. The plots of Efficiency vs Output Power, Torque vs Output Power, Line Current vs Output Power and Speed vs Output Power are plotted in the same graph sheet and also the Speed vs Torque response is plotted in a separate graph sheet.

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