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1. SAFETY is of paramount importance in the Electrical Laboratories.
equipment and follow safety practices in the laboratory. (Electricity is a good servant but a bad master).
subject you to electrical shock).
current will not flow through your body to earth and hence you will be protected from electrical shock).
6. Girl students should have their hair tied firmly or have it in a knot.
approved circuit diagram. You can use equipment issue slip available in Lab for this purpose.
the safety feature of these plugs by using underground plugs.
13. Do not defeat any safety devices such as fuse or circuit breaker by shorting across it.
Safety devices protect YOU and your equipment.
16. Do not make any change in the connection without the approval of the staff member.
switch off the power to your circuit immediately and inform the staff member.
circuit after getting approval from the staff member.
WHO HAS DAMAGED IT IN SUCH A MANNER.
Observe the safety rules yourself and help your friends to observe. EM Lab Page 4 . IITBBS.
Mr. Mr. Brajamohan Mohapatra. Reports: 20 Marks.in Course Contents: Theory Components: 100 Marks Teacher Assessment: Teacher Assessment: Laboratory Components: 100 Marks Attendance: 10 Marks. C. IIT Bhubaneswar Email:cnb@iitbbs. EM Lab Page 5 .N Bhende. Fundamentals by Del Toro 2. Grand Viva and Final Exam: 60 Marks Lab Instructor: Dr.N Bhende Research Scholar: Lab Staff: Mr. Basic Electrical Engineering by Nagrath and Kothari IITBBS. Office# 015 SES. Santosh Ku. Sahoo. Biswal Text Books: 1. Raimohan.Mr.ac. Mr. Routine Viva: 10 Marks. C. INDIAN INSTITUTE OF TECHNOLGY BHUBANESWAR SCHOOL OF ELECTRICAL SCIENCES Electrical Machines Laboratory Course Outline Course Instructors: Dr. Dillip Ku. Electrical Engg. Electric Circuits by JW Nilsson 3. Bikram Ranjan Behera.
inform him/her. IITBBS.  Do not come to class carrying an infection take leave and make up your experiment. No loose garments.  You are required to be familiar with basic safety procedures for electrical shock. INDIAN INSTITUTE OF TECHNOLGY BHUBANESWAR SCHOOL OF ELECTRICAL SCIENCES Electrical Machines Laboratory Instruction to Student  You are required to know the location of the emergency trip switch in the laboratory.  Any other instructions as and when issued by the lab staff or instructor. If you are unable to come class for any reason.  You are required to dress safely.  Reports are due every week at the beginning of the lab class hour as per form decided by your instructor.  During the lab class. EM Lab Page 6 . once the experiment has started. it is required that one student of the group is always at the worktable. nothing that impedes your ability to work.  It is required that you take explicit permission if you have to leave during the class.  See to it that your laboratory partner knows your whereabouts.
B or L 1. Isolating Switch etc. with frequency. Don’t fraction (whenever not required) the Axis when you draw the graph. Resistor & Inductor should be drawn properly.C supply should be clearly indicated with polarity (+ & -). Graph should be pasted at left gutter position. 5. b) D. L 2 L 3) and frequency. Write the specification of machines (wherever required) & other devices (such as Variac. (i. 10. Y. Note down the range & type of meters used in circuit diagram. c) 3 φ AC supply should be clearly indicated with proper phase sequence (R. 8. All the calculation part should be on left side (plane side) of record. Inside two invisible parallel lines should be clear).. INDIAN INSTITUTE OF TECHNOLGY BHUBANESWAR SCHOOL OF ELECTRICAL SCIENCES Electrical Machines Laboratory POINTS FOR MAINTAINING LAB RECORDS 1. 6. Use Pro-circle for drawing all meters & rotating machines. IITBBS. Maintain the contents properly giving experiment date & submission date clearly. 2. 7. Draw the circuit diagram clearly using HB pencil. & N. 3.e. Rheostat. Name different supply & their range clearly as mentioned below- a) A. Load box. 4.C supply should be clearly indicated by Ph. EM Lab Page 7 .) properly. 9.
EM Lab Page 8 .IITBBS.
EM Lab Page 9 .IITBBS.
INDIAN INSTITUTE OF TECHNOLGY BHUBANESWAR SCHOOL OF ELECTRICAL SCIENCES Electrical Machines Laboratory IITBBS. EM Lab Page 10 .
EM Lab Page 11 .IITBBS.
I agree to abide by these rules and procedures at all times while using these facilities. I understand that failure to follow these rules and procedures will result in my immediate dismissal from the laboratory and additional disciplinary action may be taken according to the Institute policies. Student’s Signature Date- Name- RollNo. EM Lab Page 12 . INDIAN INSTITUTE OF TECHNOLGY BHUBANESWAR SCHOOL OF ELECTRICAL SCIENCES Electrical Machines Laboratory Undertaking I have read and understand the rules and procedures set forth for the ELECTRICAL MACHINES LABORATORY.- IITBBS.
4. 5. To measure the Positive and Negative sequence impedance of a Single phase three winding Transformer. 3. Perform Scott connection on two single phase transformers. To determine regulation of 3-Phase alternator by Zero Power Factor (ZPF) method. To study the power factor improvement of a 3-Phase load by capacitor bank. INDIAN INSTITUTE OF TECHNOLGY BHUBANESWAR SCHOOL OF ELECTRICAL SCIENCES Electrical Machines Laboratory List of Experiments Cycle-1 1. To draw the equivalent circuit and phasor diagram per phase of a Single phase Transformer by back to back test. EM Lab Page 13 .Circuit test. To determine regulation of 3 phase alternator by synchronous impedance method using Open -Circuit &Short. To determine Negative sequence & zero sequence impedance of a Three phase Alternator. Cycle-2 1. 4. IITBBS. To perform No load and Block rotor test of a 3- Induction motor and draw Circle diagram. 5. To determine Direct Axis & Quadrature Axis Synchronous Reactance of a 3-Phase Alternator. 2. 2. To perform parallel operation of two single phase Transformer. 3.
EM Lab Page 14 . ➢ The location of the emergency trip switches. ➢ Pen/paper/graph sheet/pencil/calculator. ➢ Graph sheets.2 You should know the following: ➢ The experiment that you are about to conduct. ➢ Hand in all components issued to you for the lab session. ➢ Do not switch on the circuit/experiment until you get it checked once by Technician/ Research Scholar / Instructor. please note that: Your lab group has been formed. INDIAN INSTITUTE OF TECHNOLGY BHUBANESWAR SCHOOL OF ELECTRICAL SCIENCES Electrical Machines Laboratory Familiarization with Lab.1 You should have the following with you: ➢ Report of previous class. ➢ Basis safety procedures as given in the handout to you. ➢ The lab manual. One/two table has been assigned to each experiment. ➢ See that the Instructor/Grad asst/Lab Technician have signed your data sheet of the experiment done on that day. Equipments and Basic Measurements Laboratory Works: In the first class. ➢ Ensure that along with your report. IITBBS. Get your table checked by the technician before you leave. so check which table is meant for what experiment.3 At the end of the class hour: ➢ Clean up your table. 0. ➢ Switch of all equipment. you have rough lab note which contains the data original signed by the instructor or the Lab technician in the previous class. 0. ➢ The location of the experiment table. 0.
24 A .C. 5A 1 No 2 Rheostat Tubular 500.8 pf Excitation.C. Shunt Motor :-6 HP . mm As required Machines Required: Sl.220 V/4 A IITBBS. 3A 1 No 3 Ammeter MC (0-5) A 1 No 4 Ammeter MC (0-10) A 1 No 5 Voltmeter MC (0-300)V 1 No 6 Voltmeter MI (0-300 / 600)V 1 No 7 Ammeter MI (0-10)A 1 No 8 Tachometer Digital (0-2000)rpm 1 9 Connecting Wires Cu 1. b) Measure the resistance of the stator winding of alternator. D.No Machine Specification Quantity 1. 1500 RPM 1 Set Cylindrical Alternator 220 V .1500 RPM . Motor coupled with 3-Φ D.circuit test on a 3-Φ alternator. EM Lab Page 15 .0.5 sq.220 V/ 2 A 3-Φ Alternator :-5 kVA .50 Hz 7 A . Excitation.No Instrument/Equipment Type Specification Quantity 1 Rheostat Tubular 70.1 REGULATION OF 3 Φ ALTERNATOR BY SYNCHRONOUS IMPEDANCE METHOD AIM OF THE EXPERIMENT: a) Perform no-load and short. 415 V. APPARATUS REQUIRED: Instruments/Equipments: Sl. Indian Institute of Technology Bhubaneswar School of Electrical Sciences Electrical Machines Laboratory Experiment No. c) Find out regulation of alternator by synchronous impedance method.
synchronous impedance per phase (Zs) is given by- IITBBS. Since Zs is varying with excitation. The open -circuit characteristic (the O.The leakage reactance and the armature reaction reactance combined together is called the synchronous reactance of the machine. If the generator is short circuited the whole of the voltage E is absorbed in the synchronous impedance of the machine. for laboratory purposes Zs is chosen corresponding to the field current for the rated value of open circuit voltage.THEORY: The regulation of Alternator is defined as “the rise in terminal voltage” when full-load is removed divided by rated terminal voltage with speed and excitation of alternator remaining unchanged. open circuit voltage. Then.e XS = X1 + Xar The corresponding per phase impedance Zs=Ra + jXs is called the synchronous impedance of the machine where Re represents the effective resistance per phase. i. The short-circuit characteristic (the S. E= Isc*Zs. However. The determination of the synchronous impedance requires the knowledge of open circuit and short circuit characteristics.Inthis method the effect of armature reaction is expressed as a voltage drop. EM Lab Page 16 . From the nature of open-circuit and short-circuit characteristics. (E0) and short circuit current (Isc.) corresponding to a particular value of field current is obtained. for proper application the value of Zs is chosen corresponding to the rated value of field current.C. The synchronous impedance method of determining regulation is based on the simple equivalent circuit and phasor diagram given in Fig-1. 3. the ratio of the open circuit armature voltage to the short circuit current gives the synchronous impedance of the machine.C). The experiment involves the determination of the following characteristics and parameters: 1.C. To find out the synchronous impedance from these characteristics. that is. Thus for a given field current. 2. The effective resistance of the armature winding (Ra). IaXar (Xar is commonly called the armature reaction reactance). V OCC Eo SC current SCC Voltage Isc Field current The open circuit and short circuit characteristics of a 3-Φalternator is plotted on per phase basis.C). it is obvious that the value of synchronous reactance is not constant but decreases as the saturation sets in.
At higher values of field current. 0 – 300 V 220 Volt. The value of ‘Zs’ calculated for the unsaturated region of the O. 0–5A - DPST SWITCH Fig. 5 A FUSE + A DC SUPPLY 220 Volt. F2 DPST A2 SWITCH F1 F2 + 70  . B N . 0–5A - DPST SWITCH Fig. the synchronous reactance ‘Xs’ is given by- If ‘V’ is the magnitude of the rated voltage of the machine whose regulation is to be calculated for a load current‘I’ at a power factor angle (Φ) then the corresponding magnitude of the open circuit voltage ‘E0’ is given by- E0= V + IZs CIRCUIT DIAGRAM: 3 point starter L F A A1 + F1 R V FUSE 500  .C Test on alternator 3 point starter L F A A A1 R + F1 0 – 10 A Y FUSE 500  . 5 A FUSE + A DC SUPPLY 220 Volt.C is called the unsaturated value of the synchronousimpedance.1 Circuit Diagram for O. N . 3 A Y DC SUPPLY M ALT. If ‘Ra’ is the effective resistance of the armature per phase.2 Circuit Diagram for S. B 220 Volt. saturation occurs and the synchronous Impedance of the machine decreases.C. EM Lab Page 17 .C Test on alternator IITBBS. 3 A DC SUPPLY M ALT. F2 DPST A2 SWITCH F1 F2 + 70  .
The speed of the alternator is adjusted to rated speed by varying field resistance of DC shunt motor. 3. Adjust the speed of alternator to rated speed with No-load for each setting of the field current of alternator and record the alternator terminal voltage. Open-Circuit characteristic: 1. 2. Connect circuit diagram as in Fig-2. Short-Circuit characteristic: 1. Connect the circuit as in Fig-3. 2. 4. B 0 – 300 V N .e –ve supply end). 3. + A + 0 – 10 A R F1 70  . Do not touch any non-insulated part of any instrument or equipment.3 Circuit Diagram for armature resistance measurement of alternator PRECAUTION: 1. IITBBS. The prime mover in this experiment is a D. The current range of the instrument should be about 25-50 % more than the full load current of the alternator. shunt motor coupled with alternator. 220 Volt. the field rheostat of the motor is kept in minimum position. Check the circuit connection thoroughly before switching on the supply. 3. Record readings [field current (If ) verses terminal voltage (Voc) of alternator] still open circuit voltage reaches 120% of the rated voltage of the machine in the observation table. 4. Before starting the dc shunt motor ensure that. Also field rheostat of alternator should be at minimum position (i. Armature resistance measurement: 1. EM Lab Page 18 . 7.C. Switch OFF the power supply. 5. 6. 3. 2. 2. Instruments should be connected in proper polarity and range. Connect the alternator as shown in Fig-1. 5 A FUSE + Y DC SUPPLY V ALT. Note down the readings ammeter (I) and voltmeter (V) correctly in the observation table for different supply voltages. but short-circuit the armature terminals through an ammeter. Avoid parallax error. 3. Starting with zero field current. 4. increase the field current gradually and cautiously till rated current flows in the armature and note down the readings( If versus Isc) in observation table 4. 2. Be ensured the zero setting of instrument is on right position. The speed of the set in this test also is to be maintained at the rated speed of the alternator. Switch ON the power supply. PROCEDURE: 1. Connection should be right and tight. F2 DPST SWITCH Fig.
circuit current. Calculate the corresponding values of the synchronous reactance (Xs). 3. Plot on the same graph sheet. Mean Ra= If Voc If Isc V I Radc Radc 1. EM Lab Page 19 . corresponding to rated armature short.8 power factor leading. the O. CALCULATIONS: Phasor diagram of an alternator at lagging power factor is as follows: Regulation is found by the following expression. c) Full -load current at 0. Calculate the unsaturated value of the synchronous impedance (Zs). b) Full load current at 0.C (open circuit terminal voltage per phase versus the field current).OBSERVATION: Open Circuit Test Short Circuit Test Armature Resistance Sl.2*Radc Data Processing and Analysis: 1. 2. IITBBS.C. where V is the terminal voltage and E0 is the induced voltage.8 power factor lagging. IRa and IXS. E0 is estimated by the following methods.For any load current I and phase angle Ф E0is the vector sum of V. No. and the short-circuit characteristic (short-circuit armature current versus the field current). Calculate regulation of the alternator under the following conditions: a) Full load current at unity power factor.
Why the synchronous reactance of Alternator is different at different values of field current? 6. EM Lab Page 20 . Why is the short circuit characteristic of the alternator is a straight line? Up to what range of Short Circuit current. What is the power factor of alternator on Short Circuited condition? 3. What is the effect of power factor on armature reaction? 5. the linearity of the characteristic is maintained? 4.For lagging power factor For unity power factor For leading power factor CONCLUSION: DISCUSSION: 1. Why it is necessary to separate the effect of armature reaction and leakage reactance of the Alternator? 7. Why does the terminal voltage of an alternator change with load current? How does the load power factor effect this voltage change? IITBBS. What do you understand by effective resistance of Alternator and how can it measured in laboratory? 8. What are the preconditions necessary for performing the Open Circuit characteristics test? 2.
0. Shunt Motor :-6 HP .50 Hz 7 A . mm As required Machines Required: Sl.220 V/ 2 A 3-Φ Alternator :-5 kVA .220 V/4 A IITBBS.02 DIRECT AND QUADRATURE AXIS SYNCHRONOUS REACTANCE OF ALTERNATOR AIM OF THE EXPERIMENT: Determination of the direct and quadrature axis synchronous reactance by slip test of synchronous machine. EM Lab Page 21 . Indian Institute of Technology Bhubaneswar School of Electrical Sciences Electrical Machines Laboratory Experiment No. Machine Specification Quantity 1. Excitation.C. 3A 1 4 3-Variac Iron core 415 V.8 pf Excitation. 24 A .1500 RPM .No Instruments/Equipments Type Specification Quantity 1 Voltmeter MI 0-400V 1 2 Ammeter MI 0-10A 1 3 Rheostat Tubular 500Ω.C. 415 V. No.5 sq. D. 1500 RPM 1 Set 3-Φ Alternator 220 V . Motor coupled with D. 10 A 1 No 5 Tachometer Digital 0-2000rpm 1 6 Phase Sequence Indicator Analog 1 7 Connecting wires Cu 1. EQUIPMENTS REQUIRED: Instruments/Equipments: Sl.
The field winding is left open and positive sequence balanced voltage of reduced magnitude (around 25% of rated value) and rated frequency is impressed across the armature terminals. The synchronous machine is driven by a separate prime-mover (in this case dc motor) at a speed slightly different from synchronous speed. At one instant when the peak of armature mm wave is in line with field pole or direct axis. the reluctance offered by the small air gap is minimum. Under these conditions the relative velocity between the field poles and the rotating armature mmf wave is equal to the difference between synchronous speed and the rotor speed. After one quarter of slip cycle the peak of armature mmf wave acts on the inter polar or q-axis of the magnetic circuit.e. If field poles revolve in a direction opposite to the rotating mmf wave negative sequence reactance would be measured. the slip speed. i. At this instant the ratio of armature terminal voltage per phase to the corresponding armature current per phase gives q-axis synchronous reactance Xq. EM Lab Page 22 . A small ac voltage across the open field winding indicates that the field poles and rotating mmf wave are revolving in the same direction and this is required in slip test. At this instant the impressed terminal voltage per phase divided by the corresponding armature current per phase gives d-axis synchronous reactance Xd. and the reluctance offered by long air gap is maximum.THEORY: From slip test the value of direct and quadrature axis synchronous reactance can be determined. FORMULAE USED: IITBBS.
3. EM Lab Page 23 . Do not touch any non-insulated part of any instrument or equipment.Set the speed of the alternator slightly less than the synchronous speed (1480 to 1490 rpm) by dc motor. Avoid parallax error. 2. III. Y R . II. Connection should be right and tight. 4. PROCEDURE: I. Note down the maximum and minimum readings of the ammeter and voltmeter deflections. F2 DPST A2 SWITCH 3 phase Variac r FUSE A R 0 – 10 A 3 phase Supply y Y V B 0 – 300/600 V b TPST SWITCH PRECAUTION: 1. Before switching on the supply. 6.CIRCUIT DIAGRAM: 3 point starter L F A F1 F2 A1 N + F1 B FUSE 500  . Check the circuit connection thoroughly before switching on the supply. 3 A DC SUPPLY M ALT. Apply reduced voltage (around 25% of rated value) to the armature terminals by the 3-phase autotransformer. Instruments should be connected in proper polarity and range. 5. Be ensured the zero setting of instrument is on right position. be sure that variable point of Variac should be at zero. Make the field circuit open. IV. IITBBS. 220 Volt.
EM Lab Page 24 . OBSERVATIONS:- Sl. 2. Vph maximum/minimum I maximum/minimun Xd Xq CONCLUSION: DISCUSSION: 1.What is the difference between synchronous reactance.What is the salience factor of an alternator? IITBBS.Will you get Xd and Xq in case of cylindrical rotor type alternator? If not why? Discuss. No. leakage reactance and armature reactance? Do they have any relation among themselves? 3.
3 PERFORMANCE CURVE OF 3 PHASE INDUCTION MOTOR AIM OF THE EXPERIMENT: a.0. Using the data obtained above. c. max torque. Delta connection. 3-ΦInduction Motor 3. Perform no load and block rotor test on 3-Φ induction motor. draw the circle diagram complete in all respect.8 A.5 sq. Indian Institute of Technology Bhubaneswar School of Electrical Sciences Electrical Machines Laboratory Experiment No.No Machine Specification Quantity 1.No Instruments/Equipments Type Specification Quantity 1 3-Variac Iron core 10 A. 600 V. EM Lab Page 25 . 1430 RPM 1 No 415 V. b.2PF 2 Nos 3 Voltmeter MI (0-600) V 1 No 4 Ammeter MI (0-5/10) A 1 No 5 Voltmeter MI (0-150) V 1 No 6 Wattmeter UPF 10 A. 125V 2 Nos 7 Connecting Wires Cu 1. 415V 1 No 2 Wattmeter LPF 5 A.7 kW / 5 HP . APPARATUS REQUIRED: Instruments/Equipments: Sl. 7. Compute max power. IITBBS. mm As required Machines Required: Sl. starting torque and best power factor using the circle diagram.
Power consumed by the Induction motor at no load I0 – No-load current drawn by the Induction motor V0 – Line voltage supplied to Induction motor I1 R10 X10 R2' V1 R0 X0 I1 Equivalent Circuit diagram of Induction Motor Block rotor Test: The locked rotor test of Induction machine. Low voltage is applied to stator windings to circulate rated current in stator winding of the motor by keeping rotor at standstill using brake drum arrangement. The test is performed by applying balanced rated voltage at rated frequency on the stator windings. like short circuit test on a transformer. Since there is no rotation slip. The small power provided to the machine is due to core losses. No-Load Test: The no-load test of Induction machine. like the open circuit test on a transformer. which makes slip nearly zero. friction and winding loses. we do both No-load Test and Block rotor test. To find out the Induction motor parameters which affect the performance of the Motor. Block rotor tests. The circle diagram is drawn using the data obtained from No-Load Test and short circuit Tests or. EM Lab Page 26 . gives information about exciting current and rotational losses. provides the information about leakage impedances and rotor resistance. The machine will rotate at almost synchronous speed. The No-load power factor (cos0) = P0/ ( *V0*I0) Where. Measure the voltage and power per phase.THEORY: Thecircle diagram is the graphical representation of the performance of the electrical machines (such as Induction Motor. P0 . Alternator etc). in case of Induction motor. The short circuit power factor (cossc) =Psc/ ( *Vsc*Isc) IITBBS. s=1.
phase Supply 3.600V 3. 4.Phase Variac Induction PULLEY Y Motor B TPST Switch C V M L 10A .phase Supply 3. UPF WATTMETER Fig-1 Circuit diagram for block rotor test PRECAUTION: 1. Instruments should be connected in proper polarity and range. EM Lab Page 27 .phase ~ 415V . 125V . 600V. 2. 600V .CIRCUIT DIAGRAM: 10A . 50Hz 3. Do not touch any non-insulated part of any instrument or equipment. 125V.150V 3. Check the circuit connection thoroughly before switching on the supply. 3.phase ~ 415V . UPF WATTMETER M L A ~ S1 S2 0 – 10A C V FUSE R V 0. IITBBS.Phase Variac Induction Y Motor B TPST Switch C V M L 10A . 50Hz 3. LPF WATTMETER M L A ~ 0 – 10A C V FUSE R V 0. Connection should be right and tight. LPF WATTMETER Fig-1 Circuit diagram for No load test 10A .
7. Construction of Circle Diagram Conduct No load test and blocked rotor test on the induction motor and find out the per phase values of no load current I0.c. 6. For a given operating point P. 3. supply to stop the motor. Avoid parallax error. Be ensured the zero setting of instrument is on right position. 5. be sure that variable point of Variac should be at zero. Readjust the 3- Variac at zero position. Before switching on the supply. No-load Test: 1. the circle diagram can be drawn as follows. With this data. From point S. With C as centre. Switch off the a. PROCEDURE: 1. Also find short circuit current ISN corresponding to normal supply voltage. 4. The points at which these tangents touch the circle are respectively the maximum power point and maximum torque point. 2. draw tangents to the circle diagram parallel to the output line and torque line respectively. IITBBS. Divide SL at point K so that SK : KL = rotor resistance : stator resistance. Ensure that the motor is unloaded and the 3- Variac is set at zero position.c. Connect the circuit as shown in Fig-1. 3. With suitable scale.c. Block Rotor Test: 1. Note down the readings of all the meters in observation table. Switch on the supply and increase the voltage gradually till the rated voltage of the motor. To find the operating points corresponding to maximum power and maximum torque. 7. FG = stator copper loss. 6. Block the rotor by tightening the belt. 5. draw a vertical line PEFGD as shown. This forms the circle diagram which is the locus of the input current. 3. draw a portion of circle passing through A and S. 5. Draw a horizontal line AB. Switch on the a. Note down the readings of all the meters in observation table. 6. 1. then PE = output power. EM Lab Page 28 . 2. Connect the circuit as shown in Fig-2. Draw the perpendicular bisector to AS to meet the horizontal line AB at C. 4. Draw OS equal to ISN at an angle ΦSC and join AS. 2. Measure the resistance per phase of the stator winding. 3. draw a vertical line SL to meet the line AB. GD = constant loss (iron loss + mechanical loss) 8. 2. supply. supply and apply reduced voltage. 4. Switch off the a. so that the input current drawn by the motor under blocked rotor condition is equal to the full load current of the motor. EF = rotor copper loss. short circuit current ISC and the corresponding phase angles Φ0 and ΦSC. raw vector OA with length corresponding to I0 at an angle Φ0 from the vertical axis. 5.
Divide OCm into 100 equal parts. draw a line from A to the slip line through P to meet the slip line at R1. CALCULATIONS: W01  W02 tan0 = 3 W01  W02 Wsc1  Wsc2 tansc = 3 Wsc1  Wsc2 IITBBS. To find the slip corresponding to any operating point P. draw a line from O′ to the efficiency line through P to meet the efficiency line at T1. From any convenient point on the extended output line. 3. Now QT1 is the efficiency. Draw a horizontal line C′C1 to meet the vertical axis at C1. draw the circle diagram complete in all respect. To find the efficiency corresponding to any operating point P. Divide RQ into 100 equal parts. 2. Divide the line QT into 100 equal parts. 2. OBSERVATION: No-load test Block rotor test V0 I0 W01 W02 Vsc Isc Wsc1 Wsc2 Data Processing and Analysis: 1.Efficiency line: 1. The output line AS is extended backwards to meet the X-axis at O′. Slip Line: 1. To find power factor corresponding to P. Draw a quadrant of a circle with O as centre and any convenient radius. EM Lab Page 29 . extend the line OP to meet the power factor curve at C′. 2. Using the data obtained. 2. meeting the vertical through A at R. utilizing the circle diagram. Draw line QR parallel to the torque line. draw a horizontal line QT so as to meet the vertical from O′. Now OC1 represents power factor. Compute (a) Max Power (b) Max Torque (c) Starting torque and best power factor. Now RR1 is the slip Power Factor Curve: 1.
C and A. Why should there be a difference between D. 3.CONCLUSION: DISCUSSION: 1. What are the possible errors due to the approximate equivalent circuit? 6. What will happen if one line of the supply is cut off (a) When the motor is supplying full load (b) When the motor is at stand still. Does the no-load current steadily decrease as the supply voltage is reduced? If not. 5. Did the blocked rotor loss vary exactly proportional to square of the current? Explain the deviations if any.Why the no load power factor is quite small in case of 3- induction motor.C resistance? 2. 7. using the circle diagram. EM Lab Page 30 . IITBBS. How does core losses vary with voltage and why? 4. 10. Mark clearly the stable and unstable region on the circle diagram. explain why? 8. 11. Find out various losses occurring under full load condition. 12. Why one wattmeter gives negative reading for No-load Test and Block rotor Test but.Discuss the fact that the input power factor of the motor increases with increase in load. positive reading for rated load condition? 9. Are the core losses and mechanical losses constant for all operating conditions? Comments your view.
415 V 1 No 9 Connecting Wires Cu 1.No Machine Specification Quantity 1. Two single-phase transformers of identical rating with suitable tapping provided on both. The common type of connection which can achieve the above conversion is normally called Scott-connection. Indian Institute of Technology Bhubaneswar School of Electrical Sciences Electrical Machines Laboratory Experiment No. (ii) To supply power to two phase apparatus from a 3- source. EM Lab Page 31 . are required for the Scott connection.300 V 2 Nos 7 Load Box Resistive 4 kW.86.6 percent tapping and is called the teasure transformer.No Instruments/Equipments Type Specification Quantity 4 Ammeter MI 0–5 A 5 Nos 5 Voltmeter MI 0 – 600 V 1 No 6 Voltmeter MI 0 . 1. (i) To supply power to two phase electric furnaces. THEORY: Three phase to two-phase conversion or vice-versa is essential under the following circumstances. 220/110 V 2 Nos & 86. IITBBS. mm As required Machines Required: Sl. Transformer A – 50 percent tapping and is called the main transformer.6% tapping.5 sq. (iv) To supply power to three phase apparatus from a two-phase source. Transformer B.Φ Transformer having 50% 3 kVA. (iii) To interlink three phase system and two phase systems. The two transformers used for this conversion must have the following tappings on their primary windings.04 SCOTT CONNECTION OF SINGLE PHASE TRANSFORMERS AIM OF THE EXPERIMENT: Perform Scott connection on two single phase transformers. 250 V 2 Nos 8 3-Φ variac Iron core 10 A. APPARATUS REQUIRED: Instruments/Equipments: Sl.
PROCEDURE: 1. 5. 2. Do not touch any non-insulated part of any instrument or equipment. Before switching on the supply set the 3-Φ variac at its minimum position and all load switches in off position. Apply load on the teasure transformer and note down the readings. Check the circuit connection thoroughly before switching on the supply. 7. 3. Avoid parallax error. IITBBS. 6. 3. Instruments should be connected in proper polarity and range. 4.6 % 0 – 300 V FUSE R 4 kW Three 110 V RESISTIVE Phase LOAD BOX 415 V 3-phase Y 220 V Supply variac B COM A TPST COM A SWITCH 0–5A 0–5A V V 50 % 0 – 300 V 0 – 600 V 4 kW A RESISTIVE 110 V LOAD BOX 220 V 0–5A Fig. Repeat step-9 for various equal loading condition on the two secondaries. Repeat step-6 for various load condition. 6. EM Lab Page 32 . Record the readings of all the meters. 5. CIRCUIT DIAGRAM: A COM COM A 0–5A 0–5A V 86. 2. Connect the circuit as per the circuit diagram. 9. Apply load on both secondaries adjust equal loading for both secondaries. Adjust the 3- Variac for minimum voltage in output circuit. 8.Circuit Diagram for Scott connection PRECAUTION: 1. 4. Close the TPST switch and apply rated voltage across the primaries of the transformers. Similarly apply load and take reading for various load condition on the main transformers. Be ensured the zero setting of instrument is on right position. Connection should be right and tight. Note down the no-load readings with I2T = I2M = 0.
No IR IY IB I2M I2T V2M V2T No load condition When load on main transformer When load on teasure transformer When equal load on main & teasure transformer When unequal load on main & treasure transformer Table-2 V2T V2M VR (Measured) VR calculated i. Repeat step-9 for various unequal loading conditions on the two secondaries. 11. 10. EM Lab Page 33 . With load circuit removed.e. Switch off the load from both the secondaries and switch off the main supply. connect the two secondary windings in series and observe the resultant voltage V R = 2 V2T = = 2 V2M OBSERVATION: Table-1 Sl. % Error VR = 2 V2T = = 2 V2M IITBBS. 12.
EM Lab Page 34 . Draw the phasor diagrams at equal & unequal load conditions. What is the advantages and disadvantages of Scott connection over Open-Delta connection? IITBBS. Why is it essential that 86.6% tapping must be there in teasure transformer? 2.Data Processing and Analysis: 1. What tapping should be available on the main transformer and why? 3. CALCULATIONS: DISCUSSION: 1.
NO. Volt meter MI (0-300)V 1 2. 1-φ autotransformer Iron Core 1 5 Connecting wires Cu 1.5kVA Primary:-415V.6.0-300V 1 4. Wattmeter UPF 5A. 3. Single phase three winding transformer 1.6A Secondary:-230V.5 sq.5A Tertiary:-110V. EQUIPMENTS REQUIRED: Instruments/Equipments: Sl. Indian Institute of Technology Bhubaneswar School of Electrical Sciences Electrical Machines Laboratory Experiment-05 SEQUENCE IMPEDANCE OF A SINGLE PHASE THREE WINDING TRANSFORMER AIM OF THE EXPERIMENT: To measure the positive and negative sequence impedance of a single phase three winding transformer. mm As required Machines Required: SL.13.No Instruments/Equipments Type Specification Quantity 1. NAME OF THE MACHINE SPECIFICATION 1. EM Lab Page 35 . Ammeter MI (0-5)A 1 (0-10)A 1 (0-15)A 1 3.64A IITBBS.
02% of rated current.u. Xl2 =Leakage reactance of secondary winding R1 =Resistance of tertiary winding. the three winding transformer behaves as two winding transformer and standard short circuit tests can be used to evaluate per unit leakage impedances which are defined as follows: Zps = per unit leakage impedance measured from primary with secondary shorted and tertiary open. (It is 0. While both the primary and secondary winding of a two winding transformer have the same KVA rating. so the supply is given to primary. Now the three winding transformer behave as two winding transformer with primary and secondary. large power transformers have three windings. Let consider measurement of Zps. The p. EM Lab Page 36 . Xl3 =Leakage reactance of tertiary winding I0= magnetizing current. all the three windings of a three winding transformer may have different KVA ratings. To provide for the excitation of a regulating transformer. 2. 3. When one winding is left open. Zst = per unit leakage impedance measured from secondary with tertiary shorted and primary open. so it can be neglected when finding equivalent circuit) IITBBS. such a third harmonic currents. To supply a load at a voltage different from the secondary voltage. The third winding is known as a tertiary winding which may be used for the following purposes: 1. The equivalent circuit is like R1 =Resistance of primary winding. THEORY: Generally. impedance in the impedance diagram should therefore be expressed on a common KVA basis. Xl1 =Leakage reactance of primary winding R2 =Resistance of secondary winding.Circuit Diagram for measurement of leakage impedance (Zps) Similarly circuit can be connected for Zpt and Zst. To provide a low impedance for the flow of certain abnormal currents.CIRCUIT DIAGRAM: (0-5)A AC M L A C V Tertiary Winding (0-300)V V Single ph AC 50Hz supply 230V Secondary Winding (0-10)A A AC Figure 1:. Zpt = per unit leakage impedance measured from primary with tertiary shorted and secondary open. secondary is short circuited and tertiary is open.
Solving these equations we find Zp = ½ (Zps + Zpt . Be ensured the zero setting of instrument is on right position. be sure that variable point of Variac should be at zero. Check the circuit connection thoroughly before switching on the supply. and Zst are leakage impedance of the primary.. Avoid parallax error. 50Hz supply supply V Let Zps. 5. Zs. Zs.. secondary and tertiary. Do not touch any non-insulated part of any instrument or equipment. (f) These equations can be used to evaluate the per unit series impedances Zp. Instruments should be connected in proper polarity and range. 50Hz Single ph AC. 3. we have - Zps = Zp + Zs …………… (a) Zpt = Zp + Zt ……………… (b) Zst = Zs + Zt ………………(c) Where Zp. EM Lab Page 37 . IITBBS. (d) Zs = ½ (Zps + Zst -Zpt) ………. PRECAUTION: 1. 6. Then from transformer theory. Connection should be right and tight. (e) Zt = ½ (Zpt + Zst – Zps) ………. 2. and Zt : the impedances of primary. Zpt.Zst) ……. 4. Before switching on the supply. R1 Xl1 Xl3 R3 I1 I1' Io Tertiary Winding open circuit Primary Winding Ro Xo Xl2 R2 Single ph.. and Zt of three winding transformer equivalent circuit from the per unit impedances Zps. 50Hz supply I2 230V Secondary Winding Short circuited I1 R1 Xl1 Xl2'=Xl2/K2 R2'=R2/K2 Req Xleq I1'=I2*K2 I Io Primary Winding Primary Winding Ro Xo Single ph. secondary and tertiary windings referred to primary circuit. Zpt and Zst which in turn are determined from short circuit tests.
measured in primary with tertiary short circuited and secondary open. Tertiary Table 2 Sl. • Gradually increase the supply voltage by variac. Then do the following calculation IITBBS. All impedances are referred to same KVA base and to a same voltage base generally referred to primary circuit. NO. so that rated current will flow through the short circuit side (secondary side for Zps). similarly connect for other two cases). Primary 2. No.r. Measurement 1: Obtain leakage impedance Zps in p. Impedance to be Impedance measured Winding short Winding open Impedance(pu) measured w. measured in primary with secondary short circuited and tertiary open. • Give the supply to primary (Zps) through variac. Winding Rated voltage Rated MVA (Line to line KV) (Three phase) 1. • Connect the circuit as shown in figure 1(circuit for calculating Zps. u. • Record the voltmeter and ammeter reading OBSERVATIONS: Table 1 SL. EM Lab Page 38 . Secondary 3.t winding circuited 1 Zps Primary Secondary tertiary 2 Zpt Primary tertiary secondary 3 Zst secondary tertiary primary CALCULATIONS: Z p s = (Reading of voltmeter in primary side)/ (Reading of ammeter in primary side) Z pt = (Reading of voltmeter in primary side)/ (Reading of ammeter in primary side) Z s t = (Reading of voltmeter in secondary side)/ (Reading of ammeter in secondary side) Z s t measured is referred to secondary side so convert it to primary side. u. measured in secondary with tertiary short circuited and primary open. Experimental procedure for the measurement of leakage impedances for a single phase three winding transformer.u. PROCEDURE: Measurement of leakage impedances:- These are obtained experimentally from three independent short circuit measurements. Measurement 2: Obtain leakage impedance Z pt in p. Measurement 3: Obtain leakage impedance Z st in p.
value for the sequence impedances of three phase two winding and three phase three winding transformer ? IITBBS. What is the utility of a three phase three winding transformer? 4. Z p = (Z p s +Z pt. What are the representative p. CONCLUSION: DISCUSSION: 1. What is the importance of sequence impedances? 3. secondary tertiary windings referred to primary circuit.Z s t)/2 Zs = (Z p s +Z s t. 2. EM Lab Page 39 .Z p s)/2 Where Z p. Define symmetrical components.u. Z s and Z t are the leakage impedances of the primary.Z pt)/2 Z t = (Z pt +Z st.
mm As required 9 TPST Switch Knife 16A 1 Machines Required: Sl. 1500 RPM 1 Set Cylindrical Alternator 220 V .C.0. 415 V.220 V/4 A IITBBS. EM Lab Page 40 . Motor coupled with 3-Φ D. 24 A . b) Perform load test on 3-Φ alternator with highly lagging load (Approximately zero power factor) when rated voltage and rated current flowing in the starter winding.No Machine Specification Quantity 1. APPARATUS REQUIRED: Instruments/Equipment: Sl.50 Hz 7 A .5 sq. c) Find out regulation of alternator by using zero power factor method. Excitation. Indian Institute of Technology Bhubaneswar School of Electrical Sciences Electrical Machines Laboratory Experiment-06 REGULATION OF 3 Φ ALTERNATOR BY ZERO POWER FACTOR METHOD AIM OF THE EXPERIMENT: a) Perform open circuit and short circuit test on a 3-Φ alternator.1500 RPM .C. 5A 1 No 2 Rheostat Tubular 500. D. 3A 1 No 3 Ammeter MC (0-5/10) A 1 No 4 Voltmeter MC (0-300)V 1 No 5 Voltmeter MI (0-300 / 600)V 1 No 6 Ammeter MI (0-10)A 1 No 7 Tachometer Digital (0-2000)rpm 1 8 Connecting Wires Cu 1.8 pf Excitation. Shunt Motor :-6 HP .No Instruments/Equipments Type Specification Quantity 1 Rheostat Tubular 70.220 V/ 2 A 3-Φ Alternator :-5 kVA .
3. Ifsc corresponding to full load short circuit current (line OB). Field current corresponding to full load. thus obtaining a point P on the zero power factor. ➢ Join D and P. Now PCD is a triangle. 2. ➢ Draw the field current. zero power factor.e. full load characteristic (line TP).THEORY: Zero power factor saturation curve method is most reliable for determining the regulation of alternators because it properly takes into account of the effect of armature leakage reactance drop and the saturation. which normally called as Potier triangle. ➢ From the point C draw a line CD parallel to air gap line. To plot zero power factor characteristic from the experimental data and to determine the regulation of the Alternator proceed as follows: Plotting of zero power factor characteristic G OCC Air gap line D T P C E V ZPF curve D’ Voltage P’ C’ O B Ifsc Ifzp Field current Fig-1 Zero power factor characteristic of alternator ➢ Draw the open circuit characteristic to proper scale and draw the air gap line as shown in Fig-1. 1. The following experimental data is needed to determine the regulation by this method. 4. PC=OB. Open circuit characteristic at rated speed of the alternator. AC resistance of the stator winding per phase of the alternator. EM Lab Page 41 . ➢ From the point P draw a horizontal line PC representing the field current corresponding to full load short circuit current i. ➢ Draw the field current. Ifzp at rated voltage which corresponding to full load zero power factor. rated voltage. IITBBS. Field current corresponding to full load short circuit current.
➢ Terminal voltage phasor. then line ED represents the leakage reactance drop. Ex is added in quadrature to the current phasor (line BC).Determination of leakage reactance ➢ Drop a perpendicular from the point D. V is drawn at power factor angle Φ with respect to current (line OA). ➢ Potier reactance drop. Determination of Regulation Air gap line OCC G Ifs F H Ifg E D C Ex B A Eg V Voltage Reference vector Ia O Field current Fig-2 Determination of saturation effect ➢ Draw the current phasor. which is also called as Potier reactance drop (Ex). ➢ Add armature resistance drop IaRa (line AB) to the terminal voltage phasor V. EM Lab Page 42 . Ia as shown in Fig-2 horizontally. line OC represents the internally generated emf. ➢ Join O and C. ➢ The portion GH of the intercept FH represents the field current. Ifs which takes into account the effect of saturation. Ifg corresponding to rated no load voltage. IITBBS. Eg. meeting the line PC at the point E. which is a reference phasor. ➢ Phasors OA and OC are projected by arc to vertical line. ➢ Intercept DE shown by dotted horizontal line in Fig-2 represents the field current.
➢ Join OT and add the field current Ifs (line TU). thus giving a total field current Ifl. 0–5A - DPST SWITCH Fig.4 Circuit Diagram for O. B N . 0 – 300 V 220 Volt. 5 A FUSE + A DC SUPPLY 220 Volt. ➢ No load emf. EM Lab Page 43 . F2 DPST A2 SWITCH F1 F2 + 70  .C Test on alternator IITBBS. 3 A Y DC SUPPLY M ALT. ➢ Add the field current Ifsc (line ST) at power factor angle Φ with the vertical as shown in Fig-3. Eo corresponding to field current Ifl is found out from the open circuit characteristic. U T Ifs Ifl c Ifs O Ifg S Fig-3 Phasor diagram for ZPF method ➢ Draw the field current Ifg horizontally (line OS) as shown in Fig-3. Then ➢ CIRCUIT DIAGRAM: 3 point starter L F A A1 + F1 R V FUSE 500  .
5 A FUSE + A DC SUPPLY 220 Volt.5 A FUSE + A DC SUPPLY 220 Volt. F2 DPST A2 SWITCH F1 F2 + 70  . F2 Load DPST A2 SWITCH F1 F2 + 70  . 5 A FUSE + Y V ALT. full load test on alternator IITBBS. 3 A DC SUPPLY M ALT. B 220 Volt. 3 point starter L F A A A1 R + F1 0 – 10 A Y FUSE 500  . 0–5A - DPST SWITCH Fig-7 Zero power factor. B Highly Inductive . EM Lab Page 44 .6 Circuit Diagram for armature resistance measurement of alternator 3 point starter L F A A 0 – 10 A V A1 R + F1 0 – 300 V N FUSE 500 .3 A DC SUPPLY M ALT.C Test on alternator + A 0 – 10 A R F1 70  . B 0 – 300 V N F2 DPST SWITCH Fig. Y 220 Volt.5 Circuit Diagram for S. N . 0–5A - DPST SWITCH Fig.
The speed of the set in this test also is to be maintained at the rated speed of the alternator. Avoid parallax error. Do not touch any non-insulated part of any instrument or equipment.e –ve supply end). Instruments should be connected in proper polarity and range. 6. Be ensured the zero setting of instrument is on right position. IITBBS. 7. 6. 6. The prime mover in this experiment is a D. 7. 7. 8. Switch on the dc supply and start the dc shunt motor with the help of starter. increase the field current gradually and cautiously till rated current flows in the armature and note down the readings( If versus Isc) in observation table-1 8. 2. shunt motor coupled with alternator. 2. Switch off the dc supply to the field of the alternator and dc motor. For zero power factor test: 1. till full load of the alternator. Set the field rheostat of alternator. 8. Check the circuit connection thoroughly before switching on the supply. 5. 5. Connection should be right and tight. The current range of the instrument should be about 25-50 % more than the full load current of the alternator. 7. Load the alternator gradually in steps and adjust the rated terminal voltage across the load at each step by increasing the field current. 2. The speed of the alternator is adjusted to rated speed by varying field resistance of DC shunt motor. 9. reduce the field current of the alternator. 3. 6. 3. 3. 4. Switch OFF the power supply.C. Open-Circuit characteristic: 5. Vary the field current of the alternator to obtain rated voltage.PRECAUTION: 1. Short-Circuit characteristic: 5. Adjust the speed of alternator to rated speed with No-load for each setting of the field current of alternator and record the alternator terminal voltage. Connect the alternator as shown in Fig-4. so that the field current of alternator is minimum. Decrease the load on the alternator gradually and side by side. 6. 4. Starting with zero field current. Note down the readings ammeter (I) and voltmeter (V) correctly in the observation table-1 for different supply voltages. Connect the circuit as in Fig-6. Connect the circuit as in Fig-7. 4. Switch ON the power supply. the field rheostat of the motor is kept in minimum position. Also field rheostat of alternator should be at minimum position (i. Record readings [field current (If) verses terminal voltage (Voc) of alternator] still open circuit voltage reaches 120% of the rated voltage of the machine in the observation table-1. Armature resistance measurement: 5. Switch on the dc supply to the field of the alternator. but short-circuit the armature terminals through an ammeter. PROCEDURE: 1. Vary the field current of motor to obtain rated speed. Before starting the dc shunt motor ensure that. 8. Connect circuit diagram as in Fig-5. EM Lab Page 45 . 7.
By which other methods can you load the alternator for watt less current? 6.C. the O. What is the power factor of alternator on Short Circuited condition? 3. No. Stator Current Terminal voltage Field current Data Processing and Analysis: 1. e) Full load current at 0. 2.8 power factor leading. and the short-circuit characteristic (short-circuit armature current versus the field current).OBSERVATION: Table – 1 (OC & SC Test and Ra Measurement) Open Circuit Test Short Circuit Test Armature Resistance Sl. What are the preconditions necessary for performing the Open Circuit characteristics test? 2. CALCULATIONS: CONCLUSION: DISCUSSION: 1. Write in brief construction of the Potier triangle. Discuss how it enables to separate the armature reaction drop from the leakage reactance drop. Also calculate the corresponding values of the synchronous reactance. Plot on the same graph sheet. Why do you think ZPF method is more accurate method as compared to synchronous impedance method? 5. 3.8 power factor lagging. Why is the Short Circuit characteristic a straight line? Up to what range of Short Circuit current the linearity is maintained? 4. 7. IITBBS. EM Lab Page 46 . Calculate regulation of the alternator under the following conditions: d) Full load current at unity power factor. Mean Ra= If Voc If Isc V I Radc Radc 1.2*Radc Table – 1 (ZPF Test) Sl. f) Full -load current at 0. and the value corresponding to rated current at short circuit. Calculate the unsaturated value of the synchronous impedance.C (open circuit terminal voltage per phase versus the field current). No.
APPARATUS REQUIRED: Instruments/Equipments: Sl. No Machine Specification Quantity 1. Indian Institute of Technology Bhubaneswar School of Electrical Sciences Electrical Machines Laboratory Experiment No. 1500 RPM 1 Set Alternator 220 V .50 Hz 7 A .0. 415 V. To determine zero sequence impedance Z0 of a 3-Φ alternator.8 pf Excitation. 3A 1 No 70.1500 RPM . D.7 SEQUENCE IMPEDANCE OF 3 Φ ALTERNATOR AIM OF THE EXPERIMENT: a. 3A 1 No 5 1-Variac Iron core 230 V.220 V/4 A IITBBS.5 sq.C.220 V/ 2 A 3-Φ Alternator :-5 kVA . b. mm As required Machines Required: Sl. 10 A 1 No 6 3-Variac Iron core 415 V.C. EM Lab Page 47 . 24 A . Shunt Motor :-6 HP . To determine negative sequence impedance Z2 of a 3-Φ alternator. No Instruments/Equipments Type Specification Quantity 1 Ammeter MI 0 – 5/10 A 2 Nos 2 Voltmeter MI 0 – 15/30/75 V 1 No 3 Voltmeter MI 0 – 150/300/600 V 1 No 4 Rheostat Tubular 500. Motor coupled with 3-Φ D. Excitation. 10 A 1 No 7 Tachometer Digital (0-2000)rpm 1 8 Phase Sequence Indicator Analog 1 9 Connecting Wires Cu 1.
THEORY: Symmetrical components are mainly used for the resolution of unsymmetrical Phase currents or voltages in to a set of components that possess certain symmetry features. The Impedance offered to these sequences components are called Positive. the negative sequences components possess three phase symmetry having the phase sequences R2Y2B2 or A2C2B2. EM Lab Page 48 . The positive sequence components possess –three phase symmetry having the phase sequences R1Y1B1 or A1B1C1. Negative and Zero-sequence Impedances. and the Zero sequences components (R0Y0B0 or A0B0C0) have equal magnitudes and phases. IITBBS.
IITBBS. • The sequence at which the system is working before fault is called as original sequence of network. NEGATIVE SEQUENCE COMPONENT These are the components having equal in magnitude and having 1200 phase displacement. Its phase sequence is same as that of the original phase sequence of network. • Direction of rotation of rotor of synchronous generator is the reference in order to decide the sequence of power system network. EM Lab Page 49 .POSITIVE SEQUENCE COMPONENT These are the components having equal in magnitude and having 1200 phase displacement. Its phase sequence is opposite to that of the original phase sequence of network.
rotates with twice the normal speed with respect to the rotor.
lowest of the synchronous machine reactances.
I0 = current flowing in three phase windings in series.
by the current in each of the phase.
Fig- 2 Circuit Diagram for zero sequence Impedance (Z0).
1. Connection should be right and tight.
2. Check the circuit connection thoroughly before switching on the supply.
3. Instruments should be connected in proper polarity and range.
4. Do not touch any non-insulated part of any instrument or equipment.
5. Be ensured the zero setting of instrument is on right position. Avoid parallax error.
6. While applying voltage the armature current should not exceed 7 A.
7. The short circuit current should be kept low in order to avoid undue heating of the field winding.
1. Connect the circuit as shown in Fig-1.
2. Rotate the rotor at synchronous speed with field winding unexcited & short circuited.
3. Apply the balanced 3-ɸ voltage.
4. Note down the instrument readings in observation table-1.
5. Switch off the 3-ɸ supply & stop the machine.
Switch off the1-ɸ supply & stop the machine. For Zero Sequence Synchronous Impedance (Z0) 1. 5. No V I If Z2 Table-2 for Z0 Sl. Explain how double frequency current are produced in the rotor field when negative sequence currents are impressed on armature. OBSERVATION: Table-1 for Z2 Sl. 2. Apply the 1-ɸ voltage. Connect the circuit as shown in Fig-2. 5. IITBBS. negative and zero sequence components for unbalanced power system. 3.2. 4. No V I If Z0 CALCULATIONS: Z2 = V 3I Z0 = 3V I CONCLUSION: DISCUSSION: 1. Can zero sequence currents produce rotating field? Justify your answer. Rotate the rotor at synchronous speed with field winding unexcited & short circuited. 3. Explain why X1& X2 are different in synchronous machine whereas they are equal in Transformer. EM Lab Page 53 . 4. Note down the instrument readings in observation table-2. Define positive. 2. Explain how X2 is arithmetic sum of “Xd” and “Xq”.
125V 2 Nos 7 Connecting Wires Cu 1. 1430 RPM 1 No 415 V. IITBBS.7 kW / 5 HP .No Machine Specification Quantity 1.No Instruments/Equipments Type Specification Quantity 1 3-Variac Iron core 10 A. 415V 1 No 2 Wattmeter LPF 5 A. 7. mm As required Machines Required: Sl. 3-ΦInduction Motor 3. Delta connection.F 2 Nos 3 Voltmeter MI (0-600) V 1 No 4 Ammeter MI (0-5/10) A 1 No 5 Voltmeter MI (0-150) V 1 No 6 Wattmeter UPF 10 A. 600 V.5 sq.2 P. Indian Institute of Technology Bhubaneswar School of Electrical Sciences Electrical Machines Laboratory Experiment No.0. EM Lab Page 54 .8 A.08 POWER FACTOR IMPROVEMENT OF 3 PHASE INDUCTION MOTOR AIM OF THE EXPERIMENT: APPARATUS REQUIRED: Instruments/Equipments: Sl.
the power triangle would look like a horizontal line.phase Supply 3-Phase Variac Induction PULLEY Y Motor B TPST Switch . 600V. 50 Hz 3. KVA is the apparent power and KVAR (not included in the equation) is the reactive power.CIRCUIT DIAGRAM: 10A. Like all ratio True Power (KW) measurements it is a unit-less quantity and can be represented mathematically as P.1 C V M L 10A. UPF WATTMETER Circuit diagram for power factor improvement of 3-Ph Induction Motor THEORY: In power systems.phase 415 V . active power performs the work and reactive power creates the electromagnetic field. such as a motor. because the opposite (reactive power) side would have zero length. because the adjacent (true power) side would have zero length. IITBBS. the power factor is 1 (Perfect). safety problems and higher energy costs. For the purely inductive circuit. EM Lab Page 55 . is often overlooked. 600V. In an inductive load. Here the power triangle would look like a vertical line. PF is power factor. the power factor is 0.F. The lower your power factor. Apparent Power (KVA) Where. because true power equals zero. = . UPF WATTMETER M L A A ~ S1 S2 0 – 10 A 0 – 10 A C V FUSE V R 0-600V 3. the less economically your system operates. because the reactive power equals to zero. Power factor is the ratio between the real power and the apparent power drawn by an electrical load. kW is the real power that actually does the work. wasted energy capacity. For the purely resistive circuit. Here. It can result in poor reliability. also known as poor power factor.
If there are no dissipative (resistive) components in the circuit.) Power factor can be an important aspect to consider in an AC circuit. The effect of these two opposing reactance in parallel is to bring the circuit’s total impedance equal to its total resistance (to make the impedance phase angle equal. making any power in the circuit purely reactive. paradoxically. to zero). where R is the resistance. The poor power factor makes for an inefficient power delivery system. A power factor of 1 will result in the most efficient loading of the supply’ a load with a power factor of 0. Poor power factor can be corrected. or at least closer. more electrical current is required to provide the same amount of real power. so we have to add a capacitor in parallel to our example circuit as the additional load. The same could be said for a purely capacitive circuit. by adding another load to the circuit drawing an equal and opposite amount of reactive power. The power triangle for a purely capacitive circuit would again be a vertical line (pointing down instead of up as it was for the purely inductive circuit. EM Lab Page 56 .5 will result in higher losses in the distribution system. Inductive reactance can only be canceled by capacitive reactance. because any power factor less than 1 means that the circuit’s wiring has to carry more current than what would be necessary with zero reactance in the circuit to deliver the same amount of (true) power to the resistive load. Reactive Power (VAR) IC Apparent Power (VA) (S) V (Q) φ2 φ1 I1 φ IC Active Power or Real Power or True Power (W) I2 (P) [Phasor Diagram for Power factor improvement by Capacitor Bank] [Power Triangle] IITBBS. Power factor measures how efficiently the current is being converted into real work with a low power factor. to cancel out the effects of the load’s inductive reactance. These losses can be modeled as (Loss – I2*R). then the true power must be equal to zero. All current causes dissipation in a distribution system.
P. OBSERVATION: For Full-Load Test Without Capacitor Bank Sl. IITBBS. Compute (a) Max Power (b) Max Torque (c) Starting torque and best power factor.P.No. Do not touch any non-insulated part of any instrument or equipment. 3. Keep both T. Using the data obtained. Before switching on the supply set the 3-Φ variac at its minimum position.PRECAUTION: 1.-1 close to conduct Full-load test without capacitor Bank.S. PROCEDURE: 1.T. Connection should be right and tight. 3.-1 close to conduct Full-load test without capacitor Bank. Avoid parallax error. Increase the load up to rated current with rated voltage for both cases.P. VL I1 I2 W1 W2 PL=W1+W2 Cos1 Data Processing and Analysis: 1.-2 and T. Take the readings of the wattmeter’s in watt (W1 and W2) ammeter in ampere (I) and voltmeter in volt (VL). VL I1 I2 W1 W2 PL=W1+W2 Cos2 For Full-Load Test Without Capacitor Bank Sl. Check the circuit connection thoroughly before switching on the supply. Make the connection as per the circuit diagram. Instruments should be connected in proper polarity and range.S.S.T. 5.P.T. draw the circle diagram complete in all respect. 5. Be ensured the zero setting of instrument is on right position. Keep T.T. utilizing the circle diagram. 2. 4. 4.No. 2. 2. EM Lab Page 57 . 6.S.-2 open and T.
What are the disadvantages of low power factor ? 3. Is there any alternative method to improve power factor? Discuss about it’s advantages and disadvantages oas compared to capacitor method ? 2.How to improve power factor incase it leads ? IITBBS.CALCULATIONS: W01  W02 tan0 = 3 W01  W02 Wsc1  Wsc2 tansc = 3 Wsc1  Wsc2 CONCLUSION: DISCUSSION: 1. EM Lab Page 58 .
Machine Specification Quantity 1.0.5 sq. 10 A 02 08 Connecting wires Cu 1.2PF 07 1 Variac Iron core 230 V. Indian Institute of Technology Bhubaneswar School of Electrical Sciences Electrical Machines Laboratory Experiment-09 BACK TO BACK TEST OF TWO 1-Ø TRANSFORMER AIM OF THE EXPERIMENT: To determine the equivalent circuit parameters. Single phase transformer 1kVA 1 No.F 04 Voltmeter MI 0 – 150V 01 05 Ammeter MI 0 – 20A 01 06 Wattmeter LPF 20A. No. EQUIPMENTS REQUIRED: Instruments/Equipments: Sl.9A IITBBS. 01 350V. mm As Required Machines Required: Sl. Primary:-220V.No Instruments/Equipments Type Specification Quantity 01 Voltmeter MI 0 -300V 01 02 Ammeter MI 0 – 5A 01 03 Wattmeter LPF 5A.2P.0. phasor diagram & efficiency of a given pair of 1-phase Transformers by conducting Back to Back test (Sumpner's test). EM Lab Page 59 . 02 150V.5A Secondary:-110V. 4.
the input and output parameters are directly measured under different loading conditions. To obtain exact equivalent circuit and losses. By connecting so there would be no secondary current flowing around the loop formed by the two secondary. • A large transformer supplying large essential loads has usually a second identical transformer installed in the same location for back-up. On secondary side a low voltage just sufficient to flow the full load current is connected. • This test can simulate the loading conditions on the transformer without using real loads. We can justify that the current is just twice the no load current. However for large transformers. The iron loss of one transformer=1/2Wo The copper loss of one transformer=1/2Wsc The total losses of one transformer=1/2(W0+Wsc) Why Back-to-back test is used in case of large transformers? • The short circuit test is difficult to be applied. since applying a reduced voltage is very difficult and unpractical. By this test. efficiency. The core losses are determined from the open circuit test. IITBBS. These consist in measuring the input voltage. The copper losses are determined from the short circuit test. This test requires two identical transformers. the equivalent Circuit parameters. This is easy for small rating transformers. Primary winding of both the transformer are connected in parallel across same supply and the Wattmeter connected in primaries reads the core losses (Iron losses) of both transformers. A Back to Back Test is used in this case. current. The secondary winding of both the transformers is connected in phase opposition so that their potentials are in opposite to each other. first with the secondary short circuited and then with secondary open circuited. so using back-to-back transformer in this case is very practical. These are fed by rated voltage at rated frequency.THEORY: Two very simple tests are used to determine the equivalent circuit parameters and the power losses in the transformer. and power to the primary. EM Lab Page 60 . it is difficult and expensive to take direct measurements. Stray load loss consists of the losses arising from the non-uniform current distribution in the copper and the additional core losses produced in the iron by distortion of the magnetic flux by the load current. regulation & heating of both the T/F can be determined This test facilitates the collection of data for open and short circuit test simultaneously. Back-to-Back test is also known as Sumpner's test/Heat run test. It is difficult to determine such losses accurately by conventional no-load and short circuit load tests. This means the wattmeter connected on the primary side reads the total iron loses of both the transformers.
3) Note the readings of Ammeter (Isc). the values Vo. If V2 = 0 then polarities of connected transformers are correct i. Avoid parallax error. 6. 2) Switch-ON the supply keeping the polarity switch open and autotransformer 2 at zero position and apply rated voltage to the primary winding by using the auto transformer 1. 5. AC AC AC Input 110V AC S/W Autotransformer 1 Autotransformer 2 TFR-2 PRECAUTION: 1. Short Circuit Test: 1) Keeping the primary supply as it. 4. Check the circuit connection thoroughly before switching on the supply. connections are back to back and emf induced in secondaries are in phase opposition but if V2 = 2xKxV1.5A. 3) Note the readings of Ammeter (Io).5)A LPF WATTMETER UPF WATTMETER (0-20)A AC AC M L TFR-1 L M Io Isc S/W C V V C Input Input W0 WSC 1-φ. 2) Vary the autotransformer 2 till rated full load current flows through transformers. 1-φ. Be ensured the zero setting of instrument is on right position. 75 V. Open Circuit Test: 1) Make connections as per the circuit diagram. 230V. EM Lab Page 61 . Switch-ON the supply and close the polarity switch. Now check the correctness of polarities of the two transformers. Do not touch any non-insulated part of any instrument or equipment. be sure that variable point of Variac should be at zero.e. Vo (0-150)V (0-300)V AC Vsc 230V. Before switching on the supply. Voltmeter (Vsc) & Wattmeter (Wsc) while doing so. Io and Wo should not deviate from their earlier readings. PROCEDURE: 1. Voltmeter (Vo) & Wattmeter (Wo) 2. 20A . then secondary emfs are in phase. 150V. 2. 3. (0-2.CIRCUIT DIAGRAM: 2. Instruments should be connected in proper polarity and range. IITBBS. Connection should be right and tight. in that case change the polarities of any one secondary winding.
What are the advantages of the test ? IITBBS. Why two transformers. and that too identical are needed in this test ? 2. EM Lab Page 62 . current power Current power (Vo) (Vsc) (Io) Iron loss (Wo ) (Isc) Cu.OBSERVATIONS:- SL Primary voltage Primary Primary Secondary voltage Secondary Secondary No. Loss(Wsc ) CALCULATIONS: Iron loss per transformer Wi = Wo / 2 Copper loss per transformer Wcu = Wsc / 2 Equivalent Circuit: Phasor Diagram: CONCLUSION: DISCUSSION: 1.
(0-600) V 1 No 5 Ammeter M.10 PARALLEL OPERATION OF SINGLE-PHASE TRANSFORMERS AIM OF THE EXPERIMENT: To perform polarity test and parallel operation of two single-phase transformers. The relative polarities of the primary and secondary terminals at any instant must be known per connecting windings of the same transformer in parallel or series or for interconnecting two or more transformers in parallel or for connecting single-phase transformers for polyphase transformation of voltages. (0-15) A 1 No 7 Lamp load 3kW 1 No 8 SPST switch 230V. (b) For three phase transformers. IITBBS.I. EM Lab Page 63 . APPARATUS REQUIRED: Instruments/Equipment: Sl. their satisfactory performance requires that the following conditions must be satisfied. Indian Institute of Technology Bhubaneswar School of Electrical Sciences Electrical Machines Laboratory Experiment No. The same voltage ratio.5mm2 As required THEORY: Polarity test is performed to determine the terminals having the same instantaneous polarity. (0-10) A 2 Nos 6 Ammeter M. Parallel operation of transformers is frequently necessary in the power system network.I. 2. When operating two or more transformers in parallel. (0-300) V 2 Nos 4 Voltmeter M.I. 15A 1 No 9 Connecting Wires Cu 1.I. The same polarity. (a) For single phase transformers. substations etc.No Instruments/Equipments Type Specification Quantity 1 1- variac Iron Core 15A. which consist of a number of a number of transformers installed at generating stations. 230V 1 No 2 1- transformer Iron Core 3KVA 2 Nos 3 Voltmeter M. 1.
Do not touch any non-insulated part of any instrument or equipment. 3. Be ensured the zero setting of instrument is on right position. Connection should be right and tight. 2. 2. 4. CIRCUIT DIAGRAM: A T-1 0 . 1. 1. Zero-relative phase displacement. EM Lab Page 64 . 2.15 A M I 1-PHASE 230 V . Same voltage ratio. The same polarity.600 V MI 0 .300 V M I PRECAUTIONS: 1. Two winding of a transformer the two windings are connected in series across a voltmeter while one of the winding is excited from a suitable ac voltage source when the transformer has a subtractive polarity the voltmeter IITBBS. Equal per unit impedances. 4. Same phase sequence. the transformers to the operated in parallel should have the following for better load sharing and operating power factor. 5. 3. Ensure that the two secondaries have been connected properly as per the polarity. In addition to the above essential requirements.10 A MI V 0 . PROCEDURE: 1. Avoid parallax error. Instruments should be connected in proper polarity and range. Equal ratio of resistance to reactance. 6. 50 Hz SPST SWITCH SUPPLY A DPST T-2 LAMP 0 .300 V M I A 0 .10 A M I LOAD SWITCH V 3 KW V 0 . Check the circuit connection thoroughly before switching on the supply.
What is meant by circulating current with regard to parallel operation of transformers? How much percentage of circulating connects can be permitted for satisfactory parallel operation? How can it be minimized? IITBBS.the polarity marking of one of the windings must be interchanged 2. OBSERVATIONS : Sl. Adjust a particular load on the secondaries and note down the readings of all the meters. EM Lab Page 65 . will read the difference of E1 & E2. 3. Plot graph – (1) I1 Vs IL & (2) I2 Vs IL CONCLUSION : DISCUSSION : 1. 5. Switch on the power supply and adjust the rated voltage across the circuit. Repeat step-3 for more readings. If the voltmeter reads E1=E2.No VL IL WL I1 W1 I2 W2 Data Processing and Analysis: 1. 4. If two transformers of the same kVA ratings and transformation ratio but of different equivalent impedances are connected in parallel which transformer will be loaded more? 2. 6. Switch off the supply. Connect the circuit as per the circuit diagram.

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