Presentation on theme: "Induction Motor •Why induction motor (IM)?"— Presentation transcript:
1Induction Motor•Why induction motor (IM)?–Robust; No brushes. No contacts on rotor shaft–High Power/Weight ratio compared to Dc motor–Lower Cost/Power–Easy to manufacture–Almost maintenance-free, except for bearing and other mechanical parts•Disadvantages–Essentially a “fixed-speed” machine–Speed is determined by the supply frequency–To vary its speed need a variable frequency supply
6Example 5.1 A 3-phase, 460 V, 100 hp, 60 Hz, four‑pole induction machine delivers rated output power at a slip of Determine the:(a) Synchronous speed and motor speed.(b) Speed of the rotating air gap field.(c) Frequency of the rotor circuit.(d) Slip rpm.(e) Speed of the rotor field relative to therotor structure.Stator structure.Stator rotating field.(f) Rotor induced voltage at the operating speed, if the stator‑to‑rotor turns ratio is 1 : 0.5.Solution:(b) 1800 (same as synchronous speed)
17Example 4.2 A no‑load test conducted on a 30 hp, 835 r/min, 440 V, 3‑phase, 60 Hz squirrel‑cage induction motor yielded the following results:No‑load voltage (line‑to‑line): 440 VNo‑load current: 14 ANo‑load power: 1470 WResistance measured between two terminals: 0.5 The locked‑rotor test, conducted at reduced voltage, gave the following results:Locked‑rotor voltage (line‑to‑line): 163 VLocked‑rotor power: 7200 WLocked‑rotor current: 60 ADetermine the equivalent circuit of the motor.Solution:Assuming the stator windings are connected in way, the resistance per phase is:From the no‑load test:
18From the blocked‑rotor test The blocked‑rotor reactance is:
20Example 5.3 The following test results are obtained from a three-phase 60 hp, 2200 V, six‑pole, 60 Hz squirrel‑cage induction motor.(1) No‑load test:Supply frequency = 60 Hz, Line voltage = 2200 VLine current = 4.5 A, Input power = 1600 W(2) Blocked‑rotor test:Frequency = 15 Hz, Line voltage = 270 VLine current = 25 A, Input power = 9000 W(3) Average DC resistance per stator phase: 2.8 (a) Determine the no‑load rotational loss.(b) Determine the parameters of the IEEE‑recommended equivalent circuit(c) Determine the parameters (Vth, Rth, Xth) for the Thevenin equivalent circuit of Fig.5.16.
54Note that the equivalent circuit parameters are not given Note that the equivalent circuit parameters are not given. Therefore equivalent circuit parameters cannot be used directly for computation.)a) The synchronous speed is