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- 1. March 5, 2009 1 Elektrische Aandrijvingen WTB Lokatie/evenement P.BAUER
- 2. March 5, 2009 2 FIGURE 15-1 Equivalent circuit of a wound-rotor induction motor at standstill. Equivalent circuit of the IM
- 3. March 5, 2009 3 FIGURE 15-2 Approximation of the equivalent circuit is acceptable for motors above 2 hp. Equivalent circuit of the IM • Locked rotor
- 4. March 5, 2009 4 FIGURE 15-3 Equivalent circuit of a wound-rotor motor when it is running at a slip s. The frequency of the voltages and currents in the stator is f. But the frequency of the voltages and currents in the rotor is sf. • E2 = s E1 Equivalent circuit of the IM
- 5. March 5, 2009 5 FIGURE 15-4 a. Equivalent circuit of the rotor; E2 and I2 have a frequency sf. b. Phasor diagram showing the current lagging behind the voltage by angle β. • I2 = s E1 / (R2+js x2) • I1 = I2 = s E1 /(R2+js x2)= E1 /z2
- 6. March 5, 2009 6 FIGURE 15-6 Equivalent circuit of a wound-rotor motor referred to the primary (stator) side.
- 7. March 5, 2009 7 FIGURE 15-7 The primary and secondary leakage reactances x1 and x2 are combined to form an equivalent total leakage reactance x. • P = Eg 2 / Rm+ I1 2 r1 +.. • Q = Eg 2 / xm+ I1 2 x. • S = Sqrt( P2 + Q2 ) • Pr = I1 2 R2./s • Pjr = I1 2 R2 • Pjr = s Pr • Pm = Pr- Prj
- 8. March 5, 2009 8 Simpler phasor diagram
- 9. March 5, 2009 9 . Maximum torque • Tb= 9,55 Eg 2 /(nsz1cos2 alpha/2)
- 10. March 5, 2009 10 FIGURE 15-12 Equivalent circuit of a 5 hp, squirrel-cage induction motor. Because there is no external resistor in the rotor, R2 = r2.
- 11. March 5, 2009 11 FIGURE 15-13 Equivalent circuit of a 5000 hp, squirrel-cage induction motor. Although this motor is 1000 times more powerful than the motor in Fig. 15.12, the circuit diagram remains the same.
- 12. March 5, 2009 12 FIGURE 15-14 Torque-speed curve of a 5 hp motor.
- 13. March 5, 2009 13 FIGURE 15-15 Torque-speed curve of a 5000 hp motor.
- 14. March 5, 2009 14 Properties of Asynchr. generator • s = • R2/s = - 48 ohm • Z = • I1 = E/Z • Pjr = I1 2 r2 • Pm = Pr+ Prj • Pr = -1410 W
- 15. March 5, 2009 15 FIGURE 15-17 A no-load test permits the calculation of Xm and Rm of the magnetizing branch. No load test • r1 = RLL/2 • ENL PNL INL • SNL=ENL INLsqrt(3) • QNL=Sqrt( SNL 2 – PNL 2) • PfV PNL-3r1INL 2 • RM=ENL 2 /(Pf +Pv)
- 16. March 5, 2009 16 FIGURE 15-18 A locked-rotor test permits the calculation of the total leakage reactance x and the total resistance (r1 + r2). From these results we can determine the equivalent circuit of the induction motor. Locked rotor test • SLR=ELR ILRsqrt(3) • QLR=Sqrt( SLR 2 – PLR 2) • x =QLR / 3ILR 2 • 3ILR 2(r1+r2 )= PLR
- 17. March 5, 2009 17 FIGURE 15-19 Determining the equivalent circuit of a squirrel-cage induction motor (see Example 15-1).

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