LOAD TEST OF A D.C. SERIES GENERATOR
OBJECT : To determine the external and internal characteristics of a d.c. series generator.
APPARATUS :
Sr No. Name Range No. Reqd. Remarks
1. D.C.Series Generator
2. D.C. Shunt Motor
3. D.C. Shunt Motor Starter And Regulator
4. Rheostates
5. Ammeters
6. Voltmeters
7. Loading Rheostate
8. Techometer
THEORY :
The external characteristics is the graph of terminal voltage of a generator plotted against load current. The internal characteristics is the graph of induced e.m.f. of a generator plotted against load current.
In a series generator armature and field winding are connected in series. The load is also connected in series with the field winding. Since the load current passes through the field winding, flux produces increases as the load current increases. As the flux increases, the e.m.f. induced in the armature also increases. In short as the load current increases, the induce e.m.f. also increases.
In a series generator,
E = V + Ia Ra + Ia Rse
= V + Ia (Ra + Rse)
Where,
E = induced e.m.f.
V = terminal voltage
Ia = current through armature
Ra = armature resistance
Rse = resistance of series field winding
Ia Ra = armature voltage drop
Ia Rse = voltage drope in series field winding
Initially, when load current is zero, very small voltage is induced in the armature. This is because of residual magnetic flux.
As the terminal voltage of series generator changes, with the change in load. It is also used for practical purposes where cnstant voltage is required.
PROCEDURE :
1. Set up the connections as per the circuit diagram.
2. Start the supply and set up the normal speed of motor. Measure speed of D.C. shunt motor at 1000 r.p.m. by Techometer.
3. Generally increase the load current of generator with the help of rheostate. Keeping the speed to normal value.
4. Note down the readings of terminal voltage with help of voltmeter.
5. Make calculations.
6. Draw graphs:
a. Terminal voltage (V) v/s load current IL.
b. Induce e.m.f. (E) v/s load current IL.
c. Voltage drop in armature and field winding Ia (Ra + Rse) v/s load current IL.
OBSERVATION TABLE : Take Ra + Rse = 3 ?
Sr No. Load current in amps. IL Terminal voltage at normal speed V Armature and field voltage drop Ia(Ra+Rse) Induce e.m.f. in volts E=V+Ia(Ra+Rse)
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
CALCULATIONS :
CONCLUSION :