Presentation on theme: "ECE 4411 Determination of Induction-Motor Parameters DC Test –Determines R 1 –Connect any two stator leads to a variable- voltage DC power supply –Adjust."— Presentation transcript:
ECE 4411 Determination of Induction-Motor Parameters DC Test –Determines R 1 –Connect any two stator leads to a variable- voltage DC power supply –Adjust the power supply to provide rated stator current –Determine the resistance from the voltmeter and ammeter readings
ECE 4415 Determination of Induction-Motor Parameters Blocked-Rotor Test –Determine X 1 and X 2 –Determines R 2 when combined with data from the DC Test –Block the rotor so that it will not turn –Connect to a variable-voltage AC supply and adjust until the blocked-rotor current is equal to the rated current
7 Simplified Equivalent Circuit Neglect the exciting current under blocked-rotor conditions – remove the parallel branch
ECE 4418 IEEE test code recommends that the blocked-rotor test be made using 25% rated frequency with the test voltage adjusted to obtain approximately rated current. A 60-Hz motor would use a 15-Hz test voltage. The calculated reactance is corrected to 60-Hz by multiplying by 60/15. Calculated resistance is correct.
ECE 44111 How Is the Blocked-Rotor Impedance Divided? If the NEMA-design letter of the motor is known, use Table 5.10 to divide the impedances. Otherwise, divide the impedances equally.
ECE 44112 Determination of Induction-Motor Parameters No-Load Test –Determine the magnetizing reactance, X M and combined core, friction, and windage losses. –Connect as for blocked-rotor test (next slide). –The rotor is unblocked and allowed to run unloaded at rated voltage and rated frequency.
ECE 44113 Electrical connection for the No-Load Test is the same as for the Blocked-Rotor Test
ECE 44114 Determination of Induction-Motor Parameters At no-load, the speed is very close to synchronous speed – the slip is =0, causing the current in R 2 /s to be very small, and will be ignored i the calculations. I M >>I fe, so I 0 = I M.
ECE 44115 The equivalent circuit for the no-load test is shown. Ignore
ECE 44116 Substitute X 1 from the blocked-rotor test to determine the value of X M.
ECE 44117 Example 5.16 The following data were obtained from no- load, blocked-rotor, and DC tests of a three-phase, wye-connected, 40-hp, 60-Hz, 460-V, design B induction motor whose rated current is 57.8A. The blocked-rotor test was made at 15 Hz.
ECE 44118 Blocked-Rotor No-Load DC V line = 36.2VV line = 460.0VV DC = 12.0V I line = 58.0AI line = 32.7AI DC = 59.0A P 3phase = 2573.4WP 3phase = 4664.4W a) Determine R 1, X 1, R 2, X 2, X M, and the combined core, friction, and windage loss. b) Express the no-load current as a percent of rated current.
ECE 44119 Convert the AC test data to corresponding phase values for a wye-connected motor.