Theory: No load Test of Three-phase Induction Motor The no load test is similar to the open circuit test on a transformer. It is performed to obtain the magnetizingbranch parameters (shunt parameters Rc and Xm) in the induction machine equivalent circuit. In this test, the motor is allowed to run with no-load at the rated voltage of rated frequency across its terminals. Machine will rotate at almost synchronous speed, which makes slip nearly equal to zero. This causes the equivalent rotor impedance to be very large (theoretically infinite neglecting the frictional and rotational losses). Therefore, the rotor equivalent impedance can be considered to be an open circuit which reduces the equivalent circuit diagram of the induction machine Fig. 1 (a) to the circuit as shown in Fig. 1 (d). Vph R1 jX lo > Ic Rc Ic Vph Rc ник чик lo R2' jx 2' Im R2" ((1-s)/s). jXm (a) lo R1+R2' j(X1+X2') www. Vph R1 R2' jX2' jX 1 lo ပ Ic Rc www (b) /lo Im jXm lo Im Ic Vph jXm Rc www Im E jXm (c) (d) Fig.1. Development of equivalent circuit of induction motor in open circuit test 1. Connect the circuit as shown in the connection diagram in Figure 2. 127v U 11 U A IM 127v > VLL1 V V No- Shaft 127v VLL2 W 12 W A Fig. 2. Induction motor open circuit test 2. Start the motor by ensuring the shaft is at no load condition. 3. For starting, increase the voltage to reach rated voltage. 4. Note the readings of voltmeter, ammeter and wattmeter by carefully and fill them in table 1 5. Reduce the voltage to zero and turn the main switch off. Table 1: The measured parameters during open circuit test of the induction motor Parameter Measurement Value VLL 240 IL P1 P2 Pinput Report 1. Draw the circuit diagram of open circuit test. Give some explanations 2. Calculate the machine parameters that is can be obtained from No-Load test (Rc and Xm). 3. What is the power factor of the machine? Comment on its value. 4. Comment on the slip of the machine in this case. 5. What are the different losses that are present in an induction machine in this case?

Why is it necessary to conduct polarity tests on transformers?

T-a. The direction of rotation of a single-phase split-phase motor can be change by........ a) reversing the connection of the start winding b) reversing the connection of the run winding c) reversing the connection of the start and run winding at the same time d) "a" or "b", not "c" T-b. Single-phase split-phase motors using an electrolytic capacitor in the start winding circuit should not be cycled more than about__________ time per hour. a) 8 b) 12 c) 24 d) none of the above T-c. When replacing the capacitor in a capacitor-start induction-run motor, one must be sure to replace the bad capacitor with__________ . a) a smaller one b) one of the same size c) a larger one d) none of the above

The shunt field winding of a shunt generator has a resistance of 80 ohms at 20⁰C. After several hours of continuous operation, the winding temperature rises to 50⁰C. How much is the winding resistance under this condition, Assume the resistance temperature coefficient of copper to be 0.004 ohm per degree at 0⁰C.