Sphoorthy Engineering college

Dept of EEE

EXPERIMENT NO-5

SWINBURNE’S TEST AND SPEED CONTROL OF DC SHUNT MOTOR. PREDETERMINATION OF EFFICIENCIES. (a) SWINBURNE’S TEST Aim:-

To predetermine the efficiency of a DC shunt Machine at any desired load both as a motor and also as a generator Using Swinburne’s Test. Apparatus:S.No

Equipment

Range

Type

Quantity

Name plate details:Terminal Voltage: Rated current: Field Current: Power: Speed:

1|Page ET lab manual

Sphoorthy Engineering college

Dept of EEE

Theory:-

It is a simple indirect test which is applicable where flux is constant like shunt machine. The machine is run as motor at no load at its rated speed with the help of shunt field resistance. The supply voltage, no load input current and field current are measured by ammeters. Then the no load armature current Ia0 = Io-Ish amps. Where Ia0 = No load input current Ish = Shunt field current No load input power = V * Io watts Constant losses (WC) = input - Ar. cu. losses = V Iao – (Iao)2Ra Where Ra = armature resistance

Efficiency of Machine as a motor:

Let motor input Current = I amps Terminal voltage Input Power

= V volts

= V IL watts

Output power =Input - Losses = V IL - (WC + Ia2Ra) watts Where Ia = IL - Ish Amps % Efficiency = (output/input) x100

2|Page ET lab manual

Sphoorthy Engineering college

Dept of EEE

Efficiency of machine as a generator:

Let output current supplied by the generator = IL Amps Terminal voltage = V volts Output of the generator = V IL watts Input = Output + Losses = V IL + (Wc + Ia2Ra) watts, where Ia = IL + Ish % Efficiency of generator = (output/input) x 100

Circuit Diagram:-

Procedure:-

1. Connections are made as per the circuit diagram

2. At the time of starting the armature rheostat is kept in maximum resistance position and field rheostat in minimum resistance position. 3|Page ET lab manual

Sphoorthy Engineering college

Dept of EEE

3. The motor is started with no load by using starter after closing the main switch. 4. The machine is brought to the rated speed by cutting off fully the armature Rheostat resistance and by increasing the field rheostat resistance. The readings of the ammeters and the voltmeter are noted after free-running the Machine for about half an hour. 5. The machine is stopped by switching-off the supply. 6. The armature resistance of the machine is measured with the help of multimeter. Observations:-

Terminal voltage (V)

No load current (Io):

Field current(If)

To predetermine the efficiency of motor:S.No Load (%)

1

10%

2

20%

3

25%(1/4 th

IL(amp

Ia(am

(Ia)2*Ra

WC+(Ia)2*Ra

Input

Output Efficiency

s)

ps)

(copper

(Total

Power

power

losses)

losses)

(VIL)

load)

4

40%

4|Page ET lab manual

Sphoorthy Engineering college

5

Dept of EEE

50%(Half load)

6

75%

7

90%

8

100%(full load)

To predetermine the efficiency of generator:S.No Load (%)

1

10%

2

20%

3

25%(1/4 th

IL(amp

Ia(am

(Ia)2*Ra

WC+(Ia)2*Ra

output

Input

s)

ps)

(copper

(Total

Power

power

losses)

losses)

(VIL)

Efficiency

load)

4

40%

5|Page ET lab manual

Sphoorthy Engineering college

5

Dept of EEE

50%(Half load)

6

75%

7

90%

8

100%(full load)

Model Graphs:-

A graph is drawn between Output Vs efficiency as a motor and generator.

Precautions:-

1. Do not make loose connections. 2. At the time of starting, the field rheostat should be in minimum Resistance position and armature rheostat in maximum resistance position. 3. While doing the experiment load should not be applied.

6|Page ET lab manual

Sphoorthy Engineering college

Dept of EEE

4. After starting the motor the armature rheostat resistance should be cut off fully before bringing the motor to its rated speed Results:1. Constant losses of the machine: 2. Maximum efficiency of the motor: 3. Maximum efficiency of the generator: 4. Current corresponding to maximum efficiency of the motor: 5. Current corresponding to maximum efficiency of the generator:

7|Page ET lab manual

Sphoorthy Engineering college

Dept of EEE

(b)SPEED CONTROL OF DC SHUNT MOTOR

Aim:To determine the speed characteristics of a DC shunt motor. Apparatus Required :S.NO

Equipment

Type

Range

Qty

Name plate details :Terminal voltage : Rated current : Field current : Power : Speed : 8|Page ET lab manual

Sphoorthy Engineering college

Dept of EEE

Theory:The speed of a D.C. motor is given by the relation 

b



( V- Ia . Ra) N = K ---------------- ………………… ( 1 ) Φ

Where Ia = Armature current Ra = Armature Resistance Φ = Flux per pole It is obvious that the speed can be controlled by varying (i) field flux ( field control ) (ii) resistance in the armature circuit (armature voltage control ) (iii) applied voltage V ( voltage control ).

9|Page ET lab manual

Sphoorthy Engineering college

Dept of EEE

In the flux control method the speed of a DC motor varies with the field current (Φ α If). This can be achieved by providing a rheostat in series with the field resistance. From the above equation (i) the speed of a DC motor is inversely proportional to the field flux. If the resistance in the field circuit increases then the field current decreases accordingly. Obviously the flux in the air gap decreases and hence speed will increase. This method is used for speeds above the no load speed. In armature control method, as the supply is constant, the voltage across the armature is varied by inserting a variable rheostat in series with the armature circuit. If the controller resistance is increased, the potential across the armature is decreased. There by decreasing the speed of the motor. From above equation (I) the speed of the motor is directly proportional to the back Emf (Eb) and hence to the P.d across the armature. This method is used when speeds below the no load speed are required.

Circuit Diagram:3 POINT STARTER

10 | P a g e ET lab manual

Sphoorthy Engineering college

Dept of EEE

Armature resistance test:-

Procedure:-

1. Connections are made as per the circuit diagram. 2. The field rheostat is kept in minimum resistance position and armature rheostat in maximum position. The motor is started by closing the main switch.

11 | P a g e ET lab manual

Sphoorthy Engineering college

Dept of EEE

Field control method:-

3. For field control method, the armature rheostat is kept in a minimum Position corresponding to constant voltage at v = 200 or 180 volts (near rated voltages) and the field rheostat resistance is increased in steps. 4. The field current and the corresponding speed in each step at constant voltage (200 V or 180 V) are tabulated.

Armature control method:-

5. For armature control method, the field current is kept at selected values (0.8 or 0.6 amps) near the rated fixed current or normal excitation and the armature rheostat resistance is decreased in steps from its maximum value. 6. The reading of voltmeter and speed at constant field ammeter Reading ( 0.8 or 0.6 amps ) are tabulated. 7. The armature resistance of the machine is measured by voltmeter Ammeter method.

12 | P a g e ET lab manual

Sphoorthy Engineering college

Dept of EEE

Observations:Field control method: S.NO

Field Current(If)

Speed(N)

Armature voltage(V)

Speed(N)

Armature control method: S.NO

13 | P a g e ET lab manual

Sphoorthy Engineering college

Dept of EEE

Armature Resistance test: S.No

Voltage

Current

Calculations:-

Model Graphs :The curve If Vs N for a constant V and the curve Eb Vs N for constant If are plotted. Precautions:1. Avoid loose connections. 2. Make sure that the rheostats (field and armature) are in their proper initial positions before starting the motor. 3. Take the voltmeter readings and note the speed after the voltmeter 14 | P a g e ET lab manual

Sphoorthy Engineering college

Dept of EEE

pointer settles. Review Questions:What are the factors which influence the speed of the shunt motor and how? 2. When will we use field control and armature control methods? 3. Can you start the dc motor with out a starter? If you can, then How ?

Results:-

Inference:-

15 | P a g e ET lab manual