Blocking the rotor from rotating is equivalent to making s=1 so that R2?(1/s-1)=0. This test is conducted by applying a low voltage to the stator so as to limit the current drawn to its full load value. At this reduced voltage, the core loss can be neglected but the effect of Xm has to be taken into account, as its value is small as compared to that of the transformer. The slip of induction motor during normal operating conditions is low (2 to 8%). This leads to lower rotor frequency. So for obtaining more accurate value of the rotor resistance, this test is conducted at a lower frequency and then the reactance values are scaled upto 50Hz. Such kind of a test at low frequency is not necessary for motors of less than 25kw. 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. Squirrel cage induction motor 3HP 440V 1440rpm coupled with DC shunt generator 220V@1500rpm 2KW on a common base plate
2. DOL starter (ON line starter for 3? induction motor )
3. Suitable loading Rheostat single phase
4. Suitable Rheostat
5. Suitable Digital Voltmeter AC
6. Suitable Digital Ammeter AC
7. Suitable Wattmeter
8. Suitable Voltmeter DC
9. Suitable Digital Ammeter DC
10. Digital tachometer
11. 3? 6A capacity Variac 400V / 0-470V. |
