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Download Lesson 15: Induction Motor Testing: Lock-Rotor and No
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4/11/2016 Lesson 15: Induction Motor Testing: Lock-Rotor and No-load Tests ET 332b Ac Motors, Generators and Power Systems Lesson 15_et332b.pptx 1 Learning Objectives After this presentation you will be able to: Conduct locked rotor tests on 3-phase induction motors Conduct no-load tests on 3-phase induction motors Use measurements from lock rotor and no-load tests to find motor circuit parameters Lesson 15_et332b.pptx 2 1 4/11/2016 Finding Induction Motor Parameters Dc Test - finds R1, the stator conductor resistance Procedure: Formulas V R dc dc I dc 1.) Apply dc voltage to stator 2.) Adjust dc source until rated current flows R dc 2 For wye connected stator R1 For delta connected stator R1 1.5 R dc Lesson 15_et332b.pptx 3 Finding Induction Motor Parameters Locked rotor test - finds the rotor parameters (R2, x2) and stator reactance (x1) . Locked-Rotor Test Procedure 1.) connect ammeters wattmeters and voltmeters as shown above 2.) mechanically lock the motor rotor 3.) adjust the supply voltage until rated current flows 4.) measure V P and I (line-to-line voltage, line current and total active power) Recommended practice is to perform test at 25% rated f (15 Hz) Minimizes errors due to saturation (X's) and skin effects (R's) Lesson 15_et332b.pptx 4 2 4/11/2016 Per Phase Circuit Model For Lock-Rotor Test Finds rotor resistance R2 and rotor and stator leakage reactances x1 and x2 Calculations Define Test Quantities IBR15 = blocked rotor test current (15 Hz) PBR15 = blocked rotor test power (15 Hz) VBR15 = blocked rotor voltage (15 Hz) Find total impedance at 15 Hz ZBR15 VBR15 I BR15 R BR15 PBR15 I 2BR15 R BR15 R1 R 2 Find rotor R R 2 R BR15 R1 Lesson 15_et332b.pptx 5 Locked-Rotor Test Calculations Find the rotor and stator leakage reactances from locked rotor resistance and reactance X BR15 Z2BR15 R 2BR15 60 Hz X BR60 X BR15 15 Hz Change to 60 Hz X BR60 x1 x 2 Divide the leakage reactances based on the NEMA design types. Use the following table. Design Type A, D B C x1 0.5∙XBR60 0.4∙XBR60 0.3∙XBR60 0.5∙XBR60 x2 0.5∙XBR60 0.6∙XBR60 0.7∙XBR60 0.5∙XBR60 Lesson 15_et332b.pptx Wound Rotor 6 3 4/11/2016 Induction Motor No-Load Test No-load Test - Finds magnetizing reactance and combined friction, core and windage power losses. No-Load Test Procedure 1.) Apply rated voltage and frequency with no mechanical load. 2.) Measure current voltage and power. 3.) Uses same test instrument setup as locked-rotor test. Measure IL, VL and PT. Since IM >>> Ife it is neglected in this test so Rfe omitted Model for No-load test Measure PNL = No-load power losses INL = No-load current VNL = No-load voltage Lesson 15_et332b.pptx 7 Induction Motor No-Load Test Formulas Find apparent and reactive power into unloaded motor SNL VNL I NL Q NL SNL PNL 2 2 Use reactive power to find total reactance X NL Q NL I 2NL No-load reactance is the sum of the magnetizing reactance and stator leakage X NL x1 x M x M X NL x1 Use no-load power to find rotational losses PNL I 2NL R1 Pcore Pstray Lesson 15_et332b.pptx 8 4 4/11/2016 Example 15-1: Following data is taken from no-load, locked rotor, and DC tests of a 3-phase, wye connected 40 HP, 60 Hz, 460 V, induction motor with a rated current of 57.8 A. The locked-rotor test is made at 15 Hz to minimize the errors due to saturation and skin effects. Determine the motor parameters and the total core, friction and windage losses. Draw the approximate equivalent circuit for the motor Lock-rotor Vline = 36.2 V Iline = 58.0 A PT = 2573.4 W No-load 460.0 V 32.7 A PT = 4664.4 W DC Test Vdc = 12.0 V Idc = 59.0 A Lesson 15_et332b.pptx 9 Example 15-1 Solution (1) Convert line voltages, currents and total power to per phase quantities Lesson 15_et332b.pptx 10 5 4/11/2016 Example 15-1 Solution (2) For a wye connected motor Stator winding resistance Lesson 15_et332b.pptx 11 Example 15-1 Solution (3) Use locked-rotor test values to find rotor resistance, R2 and stator/rotor leakage reactance x1, x2 Find the rotor resistance Lesson 15_et332b.pptx 12 6 4/11/2016 Example 15-1 Solution (4) Now find XBR at test frequency of 15 Hz Convert this result to 60 Hz Lesson 15_et332b.pptx 13 Example 15-1 Solution (5) Now find Xm and power losses from no-load test data Lesson 15_et332b.pptx 14 7 4/11/2016 Example 15-1 Solution (6) Need to find x1 and x2 to find the xm value. Assume the motor is NEMA design B Lesson 15_et332b.pptx 15 Approximate Equivalent Circuit 0.1020 Ω j0.4073 Ω j0.6110 Ω 0.1530/s Ω Omit Rfe j7.58 Ω Lesson 15_et332b.pptx 16 8 4/11/2016 ET 332b Ac Motors, Generators and Power Systems END LESSON 15: INDUCTION MOTOR TESTING: LOCK-ROTOR AND NO-LOAD TESTS Lesson 15_et332b.pptx 17 9