Electrical Machines-II TE Electrical EXPERIMENT NO. 1 O. C. And S. C. Test on alternator AIM: Determination of regulation of cylindrical rotor alternator by o.c. and s.c. test APPRATUS: Ammeter (0-5A) A.C,(0 – 2)A D. C. Voltmeter (0 – 600V) A. C. Alternator 3.5 KVA, 415V, 4.5A, 1500 rpm, 50Hz D.C. Motor 5 BHP, 220 V, 1500 rpm, 19A Rheostat - 2 750 ohm, 1.4A Tachometer 0 – 3000 rpm Multimeter PROCEDURE: Connect the circuit as shown in the circuit diagram. Make sure the rheostat in d c motor field is at minimum position and rheostat in alternator field is at maximum position. Start D. C. Motor Set the speed of d. C. Shunt motor to 1500 rpm by field rheostat of d. C. Motor. For O.C. test Note down the voltmeter reading when switch in field of alternator is open. This is voltage due to residual magnetism when field current is zero. Close the switch in field circuit (single pole), take down readings of D. C. Ammeter (If) and A. C. Voltmeter (VOC) by gradually reducing resistance in the field circuit of alternator. Take down readings upto VOC = 440 V. Field current of alternator should not exceed its rating. Increase resistance gradually, then directly switch off d. c. Supply. PES Modern college of engineering Department of Electrical Engineering Page 1 Electrical Machines-II TE Electrical For S. C. Test Connect Ammeter in R and Y terminal of alternator, Short Y and B terminals Make sure rheostat positions of both machine fields a.Motor field rheostat - minimum, b. Alternator field rheostat – maximum position. Switch on D.C. supply, start d. C. Motor by 3 point starter. Adjust speed of d.c. motor at 1500 rpm by field rheostat. Close the single pole switch, d.c. ammeter will be at minimum reading. Take down d. C. Ammeter reading (If) and a.c. ammeter (ISC)reading by gradually reducing field resistance of alternator. Short circuit current of alternator must be below 4.2A that is rated current of alternator. Increase resistance to max of alternator field and switch off d.c. supply. Remove connections. OBSERVATION TABLE: 1. D. C. Resistance test Measure resistance across R and N of alternator RDC = ............ ohm RAC = 1.2 * RDC = ...............ohm 2. O. C. Test Sr. No. If amps VOC Volts 1 0 2 3 4 5 6 PES Modern college of engineering Department of Electrical Engineering Page 2 Electrical Machines-II TE Electrical 3. S. C. Test Sr. No. If amps ISC Volts 1 2 3 4 5 CALCULATIONS: Synchronous Impedance (EMF) method 1. Plot graph of OCC and SCC 2. From the graph of OCC, find If for rated voltage 400V. 3. For the same If, find SC current = ISC1 /√ 4. Calculate Synchronous Impedance = ohm 5. Stator winding is star connected. 6. = − ohm. 7. = = √× 8. / = cos∅ + + sin∅ + = Volts/ph. Since we have to calculate regulation at full load, so, Vph is rated voltage / √3 and rated current is calculated from step 7. 9. Calculate % = / × 100 10. for leading p.f., IaXS is negative in above formula. PES Modern college of engineering Department of Electrical Engineering Page 3 Electrical Machines-II TE Electrical Mmf method. 1. Draw mmf triangle as per procedure in theory. 2. Find Eg corresponding to IFR from graph of OCC. 3. Calculate % = × 100 RESULT TABLE: Power Regulation by Emf method Regulation by mmf method factor 0.8 lagg 0.8 lead Unity CONCLUSION: PES Modern college of engineering Department of Electrical Engineering Page 4 Electrical Machines-II TE Electrical EXPERIMENT NO. 2 Regulation of cylindrical rotor alternator by Potier triangle method AIM: To study the regulation of Alternator by Potier Method. APPRATUS: Ammeter (0-5 A) AC,( 0-2 A) DC Voltmeter (0-600V) AC. Alternator 3.5kVA, 415 V , 4.5A,1500rpm, 50 Hz. DC Motor 5HP, 220 V , 20A , 1500 rpm. Inductive load bank 3 ɸ star connected. PROCEDURE: Connect the circuit as per the circuit diagram. Make sure positions of field rheostat of motor and alternator. Make sure load is at zero position. Start d.c. shunt motor adjust its speed to 1500 rpm. Increase voltage of alternator by field rheostat to slightly more than rated value i.e. 440 V. Switch on load bank. Adjust the load current to rated value nearly equal to 4 Amps. Voltage will drop, for rated armature current, take down field current and terminal voltage of alternator. increase field excitation, (keeping an eye on field current) also maintain full load current of alternator and take down correspondong load voltage readings. Increase field current upto rated value and take voltage readings by maintaing load current constant. Reduce load to zero vale, simulaneously reduce voltage of alternator. 12. Switch off d.c. supply. OBSERVATION TABLE: Sr.No. PES Modern college of engineering Department of Electrical Engineering Page 5 Electrical Machines-II TE Electrical Graph:- 1. Plot OCC from OC test 2. Plot ZPF curve i.e. If on X axis and VL on Y axis 3. Draw potier triangle as per theory and calculate regulation. RESULT :- % regulation at zero p.f. lagging = CONCLUSION: PES Modern college of engineering Department of Electrical Engineering Page 6 Electrical Machines-II TE Electrical EXPERIMENT NO. 3 Direct loading test on alternator AIM: To determine regulation of alternator by direct loading APPRATUS: Voltmeter (0 – 600V) A. C. D. C. Motor coupled to Motor : 5 BHP, 220 V, 1500 alternator set rpm, 19A, with three point starter Alternator 3.5 KVA, 415V, 4.2A Rheostat – 2 750 ohm, 1.4A Tachometer 0 – 3000 rpm Ammeter (0-2)A d.c. Frequency meter Digital frequency meter. Ammeter - three (0 – 5A) A.C. Three phase lamp 415V, 10A, star connected bank PROCEDURE: Connect the circuit as per the circuit diagram. Keep the field rheostat of d.c. motor at minimum position and field rheostat of alternator at maximum position. Switch on d.c. supply and start d.c. shunt motor. Adjust the speed of d.c. motor to 1500 r.p.m. Adjust rheostat in field circuit of alternator such that it gives rated voltage i.e. 400V. Take down voltmeter reading. This is no load voltage of alternator. Switch ON load suct that ammeter of each phase indicate same reading. Check speed of motor, if it is reduced, adjust the speed to 1500 r.p.m. at this loading condition. Take down readings of ammeter and voltmeter by gradually increasing load. At each loading condition, speed should be adjusted to 1500 rpm. Switch off load bank. PES Modern college of engineering Department of Electrical Engineering Page 7 Electrical Machines-II TE Electrical Adjust rheostat of alternator field to maximum position and switch off d.c. supply. OBSERVATION TABLE: Sr. Ia amps VL (volts) N rpm No. CALCULATIONS: √ % Regulation = × 100 = VNL = Eg Plot graph of V Vs IL. RESULT TABLE: Sr. Ia % R No CONCLUSION: PES Modern college of engineering Department of Electrical Engineering Page 8 Electrical Machines-II TE Electrical EXPERIMENT NO. 4 Slip Test on alternator AIM: Determination of regulation of salient pole alternator by slip test. APPRATUS: Ammeter (0-5A) A.C Voltmeter (0 – 600V) A. C. (0 – 100)A.C. Alternator 3.5 KVA, 415V, 4.5A, 1500 rpm, 50Hz D.C. Motor 5 BHP, 220 V, 1500 rpm, 19A Rheostat 750 ohm, 1.4A Tachometer 0 – 3000 rpm Ammeter (0-5A) A.C PROCEDURE: Connect the circuit as per the circuit diagram. Make sure rheostat in d c motor field circuit is at minimum position. Switch On d. C. Supply and start d. C. Shunt motor. Adjust speed of d.c. motor less than synchronous speed nearly equal to 1485 rpm. Apply low three phase voltage through auro transformer to stator of alternator. As rotor speed is near synchronous speed, stator voltmeter and ammeter indicate minimum and maximum values. Note down these stator voltage and current minimum and maximum values. Reduce a. c. Voltage to zero, switch off a.c. supply, switch off d.c. supply. Remove connections. PES Modern college of engineering Department of Electrical Engineering Page 9 Electrical Machines-II TE Electrical OBSERVATION TABLE: Sr. Stator voltage Stator current Field Voltage No. Vmax Vmin Imax Imin Vf min Vmax (Volts) (Volts) (Amps) (Amps) (volts) (volts) 1 CALCULATIONS: D. c. resistance of stator winding = RDC = 4 ohms, RAC = 1.2 * RAC = ...... ohms. 1. = ℎ 2. = ℎ 3. = = ............... Volts √ 4. = = .............. √× 5. cos∅ = 0.8 6. sin∅ = 0.6 7. tan = ∅ = ∅ 8. ∴ = 9. = −∅ = 10. = sin = 11. = cos = 12. = cos + + = 13. % Regulation = × 100 = RESULT TABLE: Sr. No Xd Xq Egph % Regulation CONCLUSION: PES Modern college of engineering Department of Electrical Engineering Page 10 Electrical Machines-II TE Electrical EXPERIMENT NO. 5 V and inverted V curve of Synchronous Motor AIM: To plot variation of power factor and input current of a synchronous motor with respect to field current at constant load. APPRATUS: Ammeter (0-5A) A.C , (0-2)A D.C. Voltmeter (0 – 600V) A. C. Alternator 3.5 KVA, 415V, 4.5A, 1500 rpm, 50Hz Synchronous Motor 5 BHP, 415 V, 50Hz, 1500 rpm, 4.5A Rheostat 750 ohm, 1.4A Tachometer 0 – 3000 rpm 3 phase 0 – 450V, 3 phase. autotransformer Wattmeter (0 – 10)A, (0 – 600)V Single pole switch PROCEDURE: Connect the circuit as per the circuit diagram. Make sure rheostat in field circuit of synchronous motor is at mid position and switch is open. Autotransformer variable pot should be at minimum position. Switch on 3 ph a.c. supply, increase input voltage gradually, check direction of rotation, motor is now started as induction motor. Increase voltage upto 290V, check speed of motor.