Open Circuit Test
Objective: To obtain the magnetization characteristic and therefrom determine the critical field resistance and critical speed of the given dc shunt generator.

Preview:
The EMF induced in a DC machine is proportional to the flux per pole, the number of conductors and speed. This EMF depends on speed and flux. As the flux increases the EMF increases beyond a point the flux gets saturated. The BH curve of the core depicts the magnetization curve of the machine.

(A) Critical Speed of a DC Shunt Generator

Objective: To determine the critical speed of a dc shunt generator. With the fixed excitation and variable speed, as the speed reduces the OCC proportionally slides down so that the no load voltage reduces. At a particular speed, called the critical speed, the OCC is tangential to the Rf line and as a result the generator fails to excite.

Preview :
With the fixed excitation and variable speed, as the speed reduces the OCC proportionally slides down so that the no load voltage reduces. At a particular speed, called the critical speed, the OCC is tangential to the Rf line and as a result the generator fails to excite.

Equipment Required: All the measuring instruments associated with each experiment are industrial grade. These instruments are housed in an elegant cabinet as a package. Range of instruments and accessories (standard format)
1. 2HP Shunt machines mechanically coupled both are identical 220V 2HP 1500rpm.
2. 3-4 point DC Starter for the above
3. Suitable Loading rheostat
4. Digital tachometer
5. Suitable Double tube rheostat
6. Suitable Single tube rheostat
7. Suitable Digital Voltmeter DC
8. Suitable Digital Voltmeter DC
9. Suitable Digital Ammeter DC
10. Rectifier Unit 0-240V DC @ 1.5KVA with power failure protection.