Load Test On Dc Shunt Generator 15411j

6. LOAD TEST ON DC SHUNT GENERATOR AIM To plot the external ,internal and armature reaction characteristic of the given DC shunt generator. APPARATUS REQUIRED SL: NO:

ITEM

1

Voltmeter

2

Ammeter

3 4

Rheostat

5 6

Loading Rheostat Tachometer

7

SPST Switch

SPECIFICATION S 0-300 V MC 0-30 V MC 0-30 A MC 0-10 A MC 300 Ω ,1.7 A 570 ,1.7 A

QUANTITY

9 Ω , 1.2 A

1 NO.

7.65KW, 440V

PRINCIPLE For a dc shunt generator the induced emf is given by E = V + Ia Ra Ia = IL + Ish Ish = V / Rsh Where V – terminal voltage Ia – Armature Current Ra – Armature resistance Ish – shunt field current Rsh – shunt field resistance IL – load current

1NO. 1 NO. 1 NO. 1 NO. 1 NO. 1 NO. 1 NO. 1 NO. 1 NO.

CIRCUIT DIAGRAM

MOTOR SPECIFICATION

GENERATOR SPECIFICATION

TABULAR COLUMN Sl no.

Voltage (V)

Field current If (A)

Load current IL (A)

Armature current Ia (A)

E (V)

TO FIND THE ARMATURE RESISTANCE Sl No.

Voltage(V)

Current (I)

Resistance(Ω)

Mean R

Ea (V)

External characteristic is the plot of terminal voltage with load current at constant field resistance and speed. As the load on machine is varied ,the terminal voltage drop in it is due to 1. The drop in voltage across the armature resistance ie. IaRa drop. 2. Armature reaction the air gap flux decrease which will reduce the induced emf E0 3. Bjh Internal characteristic is the plot of induced emf with the armature current. It can be deduced from the external characteristics as from

PROCEDURE 1. Connections are done as per the circuit diagram. 2. Initially Motor field rheostat R1 is kept at minimum position and generator field rheostat R2 is kept at maximum position. Motor armature resistance at maximum position. 3. After giving the supply the motor is started using the starter. 4. The speed of the motor is made equivalent to the rated speed by adjusting the motor rheostats. 5. Field rheostat of the generator is adjusted and the voltage is made equivalent to the rated voltage. 6. Load switch is closed and the load current is changed by varying the load rheostat keeping the generator field rheostat R2 same. 7. Corresponding meter readings are taken and the tabulation is done at rated speed. 8. The load characteristics are plotted. RESULT

INFERENCE

SAMPLE CALCULATION ( SET NO. )