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Lab Manuals for Electrical Machines 2 - EM2 By ANNA SUPERKINGS

  • Electrical Machines 2 - EM2
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  • Electrical and Electronics Engineering
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Dhanalakshmi Srinivasan Institute of Technology, Samayapuram, Trichy. Cycle 2 EE6512 Electrical Machines II Lab Manual 1

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Dhanalakshmi Srinivasan Institute of Technology, Samayapuram, Trichy. CIRCUIT DIAGRAM FOR SLIP TEST 3 Point Starter L F A 350Ω, 2A 180V DC SUPPLY NAME PLATE DETAILS: 3Ф alternator Volts: DC shunt motor Volts: Amps: Amps: kVA: kW: RPM: RPM: FUSE RATING: 125% of rated current (full load current) For DC shunt motor : ……………. For Alternator : ……………. 2

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Dhanalakshmi Srinivasan Institute of Technology, Samayapuram, Trichy. REGULATION OF THREE PHASE SALIENT POLE ALTERNATOR BY SLIP TEST AIM: The aim of the experiment is to predetermine the regulation of three phase salient pole alternator by conducting the slip test. APPARATUS REQUIRED: S.NO NAME OF THE RANGE TYPE QUANTITY APPARATUS 1. Ammeter (0-5) A MI 1 2. Ammeter (0-5) A MC 1 3. Voltmeter (0-150) V MI 1 4. Voltmeter (0-150)V MC 1 5. Rheostat 300Ω,1.5A Wire wound 1 6. 3 Ф Auto transformer 1 7. Tachometer 1 8. Connecting wires As required FORMULAE USED: 1. Armature Resistance, Ra =1.6 X Rdc 2. Direct impedance per phase (Zd) = Vmin in Ω I max 3. Quadrature axis impedance per phase (Zq) = 4. Direct axis reactance per phase (Xd) = Z d2 5. Quadrature axis reactance per phase (Xq) = 6. Percentage Regulation = I q Ra I d X d (for Motoring) 8. E0 Vt cos I q Ra I d X d (for Generating) (for Generator) 10. (for Motor) 11. tan 1 Vt sin Ia X q Vt cos I a Ra Ra2 in Ω Z q2 Ra2 in Ω E0 Vrated 100 Vrated 7. E0 Vt cos 9. Vmax in Ω I min {+ For generating mode; -- For Motoring mode} THEORY: In non salient pole alternators air gap length is constant and reactance is also constant. Due to this the MMFs of armature and field act upon the same magnetic circuit all the time hence can be added vectorically. But in salient pole alternators the length of the air gap varies and reluctance also varies. Hence the armature flux and field flux cannot vary sinusoid ally in the air gap. So the reluctance of the magnetic circuit on which mmf act is different in case of salient pole alternators. This can be explained by two reaction theory. 3

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Dhanalakshmi Srinivasan Institute of Technology, Samayapuram, Trichy. PRECAUTIONS: 1. The motor field rheostat should be kept in minimum resistance position. 2. The alternator field should be kept open throughout the experiment. 3. The direction of rotation due to prime mover and due to the alternator run as the motor should be same. 4. Initially all the switches are kept open. PROCEDURE: 1. Connections are given as per the circuit diagram and confirm that the alternator filed is in open condition. 2. Give the supply by closing the DPST switch. 3. Using the three point starter start the motor to run at the synchronous speed by varying the motor field rheostat. 4. Apply 20% to 30% of the rated voltage to the armature of the alternator by adjusting the autotransformer. 5. To obtain the slip and maximum oscillations of pointers, the speed is reduced slightly lesser than the synchronous speed. 6. Note down the maximum current, minimum current, maximum voltage and minimum voltage. Find out the direct and quadrature axis impedance (Zd,Zq). TABULATIONS: a. To find Zd and Zq : S.No Vmax Vmin Imax Imin b. To predetermine % Regulation: S.No Powerfactor 1 0.2 2 0..4 3 0.6 4 0.8 % Regulation Lagging Leading Unity GRAPH: i. Powerfactor Vs Percentage Regulation RESULT: Thus the percentage regulation of the given three phase alternator is predetermined using slip test. 4

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