Dhanalakshmi Srinivasan Institute of Technology, Samayapuram, Trichy. Cycle 2 EE6512 Electrical Machines II Lab Manual

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1 Cycle 2 EE652 Electrical Machines II Lab Manual

2 CIRCUIT DIAGRAM FOR SLIP TEST 80V DC SUPPLY 350Ω, 2 A 3 Point Starter L F A NAME PLATE DETAILS: 3Ф alternator DC shunt motor FUSE RATING: Volts: Volts: 25% of rated current (full load current) For DC shunt motor :. Amps: Amps: For Alternator :. kva: RPM: kw: RPM: 2

3 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 Ammeter Ammeter Voltmeter Voltmeter Rheostat 3 Ф Auto transformer Tachometer Connecting wires FORMULAE USED:. Armature Resistance, R a =.6 X R dc V 2. Direct impedance per phase (Z d ) = I (0-5) A (0-5) A (0-50) V (0-50)V 300Ω,.5A min max in Ω 3. Quadrature axis impedance per phase (Z q ) = V I max min in Ω Direct axis reactance per phase (X d ) = Z d R a in Ω Quadrature axis reactance per phase (X q ) = E0 Vrated 6. Percentage Regulation = 00 V rated 7. E0 Vt cos IqRa Id X d (for Motoring) 8. E0 Vt cos IqRa Id X d (for Generating) 9. (for Generator) 0. (for Motor) Z in Ω q R a MI MC MI MC Wire wound As required Vt sin Ia X q. tan { + For generating mode; For Motoring mode} Vt cos IaRa 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

4 PRECAUTIONS:. 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:. 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 (Z d,z q ). TABULATIONS: a. To find Z d and Z q : S.No V max V min I max I min b. To predetermine % Regulation: S.No Powerfactor % 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

5 D P S T S 350Ω, 2A (0-300)V,MI T P S T S Dhanalakshmi Srinivasan Institute of Technology, Samayapuram, Trichy. Circuit Diagrams for Negative Sequence and Zero Sequence Impedances of Salient Pole Alternator 3 POINT STARTER + L F A F A R (0-0)A,MI V A 45V, 50Hz R 220V, DC F 2 A 2 M Y F F2 N B 45V, 50Hz Y B A - (0-2)A,MI N NEGATIVE SEQUENCE IMPEDANCE 45/(0-470)V, 3ϕ VARIAC Name Plate Details: D.C Shunt Motor kw :.. Speed: RPM Voltage:.V Current :.A Field Voltage:.V Field Current :.A 3 Phase Alternator kva :.. Speed: RPM Voltage:.V Current :.A Field Voltage:.V Field Current :.A 5

6 D P S T S 350Ω, 2A (0-300)V,MI T P S T S Dhanalakshmi Srinivasan Institute of Technology, Samayapuram, Trichy. 3 POINT STARTER + L F A F A R (0-0)A,MI V A 45V, 50Hz R 220V, DC F 2 A 2 M Y F F 2 N B 45V, 50Hz Y B A - (0-2)A,MI N ZERO SEQUENCE IMPEDANCE 45/(0-470)V, 3ϕ VARIAC TABULATION: Negative Sequence Zero Sequence S.No V I Z 2 =V/I S.No V I Z 0 =3V/I 6

7 MEASUREMENTS OF NEGATIVE SEQUENCE AND ZERO SEQUENCE IMPEDANCE OF ALTERNATORS. AIM: To measure the negative and zero sequence impedances of the given salient pole alternator. APPARATUS REQUIRED: S.NO NAME OF THE RANGE TYPE QUANTITY APPARATUS Ammeter Ammeter Voltmeter Rheostat 3 Ф Auto transformer Tachometer Connecting wires (0-5) A (0-2) A (0-300) V 300Ω,.5A MI MC MI Wire wound Digital As required THEORY: When a synchronous generator is carrying an unbalanced load its operation may be analyzed by symmetrical components. In a synchronous machine the sequence current produce an armature reaction which is stationary with respect to reactance and is stationary with respect to field poles. The component currents therefore encounter exactly same as that by a balanced load as discussed. The negative sequence is produced and armature reaction which rotates around armature at synchronous speed in direction to that of field poles and therefore rotates part the field poles at synchronous speed. Inducing current in the field damper winding and rotor iron. The impendence encountered by the negative sequence is called the ve sequence impedance of the generator. The zero sequence current produce flux in each phase but their combined armature reaction at the air gap is zero. The impedance encountered by their currents is therefore different from that encountered by + ve and ve sequence components and is called zero sequence impedance of generator. Negative sequence: The ve sequence impedance may be found by applying balanced ve sequence voltage to the armature terminals. While the machine is drive by the prime mover at its rated synchronous speed with the field winding short circuited. The ratio of v/ph and Ia/ph gives ve sequence Z/ph. The reading of the wattmeter gives I2 R losses. This loss /ph divided by Iph required gives the ve sequence R/ph from the impedance and reactance/ph. ve sequence can be calculated. Another method of measuring ve sequence reactance is found to be connect the arm 7

8 terminals. The machine is driven at synchronous speed and field current adjusted until rated current flows in the phases shorted through armature and current coil of wattmeter respectively Zero sequence: The sequence impedance may be determined by the connecting the armature windings of the three phase in series and then connecting them to the single phase source of power. If the machine is driven at synchronous speed with field winding shorted, then ZO=V/3I practically the same results will be obtained with rotor stationary. If windings are connected in parallel, then PROCEDURE: For Negative Sequence : i. Make connection as shown in circuit diagram. ii. Run DC motor with synchronous speed. iii. Keeping the speed constant, vary the excitation and measure the voltmeter, ammeter and wattmeter reading. iv. Take 3-4 readings for different excitation. v. The excitation should not be increased beyond the rated capacity of synchronous machine i.e. 6.9 A For Zero Sequence: i. Make connection as shown in circuit diagram. ii. Set the autotransformer output to zero volts and switch on the supply. iii. Gradually increase input voltage and note the ammeter reading for the voltage applied. iv. Repeat reading upto the rated current rating of the machine (i.e, 6.9A). RESULT: measured. Thus the negative and zero sequence impedances of the salient pole alternator is 8

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10 SEPARATION OF NO LOAD LOSSES OF THREE PHASE INDUCTION MOTOR AIM: To separate the no load losses of a 3 phase squirrel cage induction motor as iron losses and mechanical losses. NAME PLATE DETAILS: 3Ø Induction motor: HP: HP Speed: : RPM Voltage :..V Current :..A FUSE RATING: No load : 0% of rated current (full load current). APPARATUS REQUIRED: S.NO NAME OF THE APPARATUS Ammeter Voltmeter Wattmeter 3 Ф Auto transformer Tachometer Connecting wires RANGE TYPE QUANTITY (0-5) A (0-600) V 600Ω,5A 45/(0-470)V MI MI LPF Digital 2 As required PRECAUTIONS: i. The autotransformer should be kept in minimum voltage position. ii. The motor should not be loaded throughout the experiment. PROCEDURE: i. Connections should be made as per the circuit diagram. ii. Start the motor by giving three phase supply. iii. Vary the autotransformer till rated speed is attained and note the input power, voltage and current. iv. Repeat the same procedure for and tabulate the reading. 0

11 v. Find the stator copper loss and constant loss by respective formulas. vi. Draw the suitable graph to find the mechanical losses. vii. Obtain the core los by separating the mechanical loss from constant losses. GRAPH: The graph drawn between constant losses (watts) and input voltage(volts). MODEL CALCULATIONS:. Input power (W) =(W+W2)in watts 2. Stator copper loss =3I 2 R s in watts 3. Constant loss/phase (W c )= (W-3I 2 R s )/3 in watts 4 Core loss/phase (Wi)= (constant loss/phase)-mechanical loss TABULTAION: S.No V I W W 2 W Stator Cu Loss Constant Loss per Phase (W c ) Core Loss per Phase (W i ) RESULT: Thus the no load losses of 3-phase squirrel cage induction motor was separated as core losses and mechanical losses.

12 NO LOAD TEST 2

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14 NO LOAD AND BLOCKED ROTOR TEST ON SINGLE PHASE INDUCTION MOTOR AIM: To draw the performance characteristics of a single phase induction motor by conducting the no-load and blocked rotor test. APPARATUS REQUIRED: S.No Name of Apparatus Range Type Qty. Voltmeter (0-300)V MI 2 Voltmeter (0-50)V MI 3 Ammeter (0-0)A MI 4 Ammeter (0-2)A MI 5 Wattmeter (330V,0A) UPF 6 Wattmeter (300V,5A) LPF 7 Connecting wires As reqd. FUSE RATING: 25% of..a=..a THEORY: A -Ф induction motor consists of stator,rotor and other associated parts.in the rotor of a single phase winding is provided.the windings of a - Ф winding(provided) are displaced in space by 20º.A single phase current is fed to the windings so that a resultant rotating magnetic flux is generated.the rotor starts rotating due to the induction effect produced due to the relative velocity between the rotor winding and the rotating flux. PRECAUTIONS: No load test: Initially TPST Switch is kept open. Autotransformer is kept at minimum potential position. The machines must be started on no load. BLOCKED ROTOR TEST: Initially the TPST Switch is kept open. Autotransformer is kept at minimum potential position. The machine must be started at full load (blocked rotor). PROCEDURE: NO LOAD TEST:. Connections are given as per the circuit diagram. 2. Precautions are observed and the motor is started at no load. 3. Autotransformer is varied to have a rated voltage applied. BLOCKED ROTOR TEST: 4

15 . Connections are given as per the circuit diagram. 2. Precautions are observed and motor is started on full load or blocked rotor position. 3. Autotransformer is varied to have rated current flowing in motor. 4. Meter readings are the noted. FORMULAE USED: R e =.6XR dc. No Load Test: cos Ф = W 0 /V 0 I 0 Iw = I 0 cosф Im = I 0 sin Ф R 0 = V 0 /I w X 0 = V 0 /I m 2. Blocked Rotor Test: o Z sc = V sc /I sc Ω o R sc = W sc /I 2 sc Ω o X sc = (Z 2 sc R 2 sc ) Ω TABULATION NO LOAD TEST S.No. Vo(volts) Io(amps) Wo(watts) m.f Observed Acual BLOCKED ROTOR TEST S.No. Vsc(volts) Isc(amps) Wsc(watts) m.f Observed Actual RESULT: Thus the no load and blocked rotor test on the single phase induction motor has been conducted and the equivalent circuit has been drawn. 5

DEPARTMENT OF ELECTRICAL & ELECTRONICS ENGINEERING 1

DEPARTMENT OF ELECTRICAL & ELECTRONICS ENGINEERING 1 OC & SC TESTS ON SINGLE PHASE TRANSFORMER Circuit Diagram: (a) OC Test (b) SC Test Name Plate Details 1 Φ T/F: KVA = LV Voltage = HV Voltage = Frequency