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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

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ECE 4412

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3 For a Y-Connected Stator

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ECE 4414 For a Delta-Connected Stator

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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

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ECE 4416

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7 Simplified Equivalent Circuit Neglect the exciting current under blocked-rotor conditions – remove the parallel branch

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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.

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ECE 4419

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ECE 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.

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ECE 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.

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ECE Electrical connection for the No-Load Test is the same as for the Blocked-Rotor Test

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ECE 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.

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ECE The equivalent circuit for the no-load test is shown. Ignore

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ECE Substitute X 1 from the blocked-rotor test to determine the value of X M.

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ECE 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.

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ECE 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 = WP 3phase = W 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.

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ECE Convert the AC test data to corresponding phase values for a wye-connected motor.

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ECE Determine R 1 Determine R 2

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ECE Determination of X 1 and X 2 From Table 5.10, for a design B machine, X 1 = 0.4X BR,60 = 0.4(1.0182) = Ω/phase X 2 = 0.6X BR,60 = 0.6(1.0182) = /phase

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ECE Determination of X M

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ECE Determination of combined friction, windage, and core loss: b) Express the no-load current as a percent of rated current.

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