DEPARTMENT OF ELECTRICAL & ELECTRONICS ENGINEERING VI SEMESTER (NEW SCHEME)

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1 DEPARTMENT OF ELECTRICAL & ELECTRONICS ENGINEERING VI SEMESTER (NEW SCHEME) 10EEL67 DC AND SYNCHRONOUS MACHINES LAB LABORATORY MANUAL NAM E OF THE STUDENT : BRANCH : UNIVERSITY SEAT NO. : SEMESTER & SECTION : BATCH : 1

2 Vision of the Department To emerge as one of the finest Electrical & Electronics Engineering Departments facilitating the development of competent professionals, contributing to the betterment of society. Mission of the Department Create a motivating environment for learning Electrical Sciences through teaching, research, effective use of state of the art facilities and outreach activities. Graduates of the program will, Have successful professional careers in Electrical Sciences, and IT enabled areas PEO1 and be able to pursue higher education. PEO2 Demonstrate ability to work in multidisciplinary teams and engage in lifelong learning. PEO3 Exhibit concern for environment and sustainable development. After the successful completion of the course, the graduate will be able to, PO1 Apply knowledge of mathematics, science and engineering principles to the solution of engineering problems in electrical and IT enabled areas. PO2 Identify and solve complex engineering problems using first principles of mathematics and engineering sciences. PO3 Design system components and solve complex engineering problems that meet specific societal and environmental needs. PO4 Conduct experiments, analyse, and interpret data to provide valid conclusion PO5 Apply appropriate modern engineering tools to complex engineering activities with an understanding of the limitations. PO6 Demonstrate understanding of societal health, safety, legal and consequent responsibilities relevant to the professional engineering practice. PO7 Understand the impact of engineering solutions in a societal context and demonstrate the knowledge of and need for sustainable development. PO8 Understand social issues and ethical principles of electrical engineering practice. PO9 Function effectively as an individual and as a member or leader in diverse teams to accomplish a common goal. PO10 Communicate effectively with diverse audiences and be able to prepare effective reports and design documentation. Demonstrate knowledge and understanding of engineering and management PO11 principles and apply these as a member and leader in a team to manage projects in multi-disciplinary environments. PO12 Recognize the need to engage in independent and lifelong learning in the context of technological change. 2

3 SI. 1. EXPERIMENTS Department of Electrical & Electronics Engg. Load characteristics of a D.C. shunt and compound generator. Compound generator i) Short shunt-cumulative and Differential (ii) Long shunt-cumulative and Differential. PAGE NO Load test on a DC motor- determination of speed-torque and HPefficiency characteristics. 15 Swinburne s Test. 18 Hopkinson s Test. 20 Load test on series motors. 24 Retardation test- electrical braking method Speed control of DC motor by armature voltage control and flux control Ward Leonard method of speed control of D.C. motor. 32 Voltage regulation of an alternator by EMF and MMF method. 34 & 38 Voltage regulation of an alternator by ZPF method. 41 Slip test and determination of regulation Performance of synchronous generator connected to infinite bus, under constant power and variable excitation & vice - versa V and Inverted V curves of a synchronous motor Measurement of X1, X2 and Xo of a synchronous generator and calculation of currents for an LG, LL or LLG fault. 57 * Viva Questions CONTENTS Overview of Electrical machines 3

4 The world abounds in umpteen forms of energies. From time immemorial human beings have been striving hard in harnessing these energies for improving their living standards. Energy thus serves as the life blood for the perpetual growth and progress of human civilization. In the energy hierarchy electrical energy holds the top rank. It is because electrical energy is easily adaptable for all human needs and interests in an economic and efficient manner. At the same time, electrical energy can be easily controlled and is pollution free at the consumer premises. It is truly said that per capita energy consumption in any country is an index of the living standard of the people in that country. The increase use of electrical energy in different fields of daily life has been primarily due to the availability of a vast variety of electrical machinery for the purpose of generation and utilization. Electrical machinery can be mainly classified as dc machines and ac machines. DC machines can operate as generators and motors same is true for ac machines Introduction to DC MACHINES DC machine is actually an alternating current machine, but furnished with a special device, called the commutator, which under certain conditions converts ac into dc and vice-versa. Inspite of the fact that the commutator has made the operating conditions of a dc machine complicated; it is a highly versatile energy converting device. By means of various combinations of shunt, series and separately excited field windings they can be designed to give a wide variety of voltage-current or speed-torque characteristics for both dynamic and steady state operation. Because of the ease with which they can be controlled, dc motors are often used in applications requiring a wide range of motor speeds or precise control of motor output- rolling mills, overhead cranes and traction; drives for process industry, battery driven vehicles etc. small dc motors are widely used in control application. Small dc generators are used for power supply in ships, air crafts, automobiles and other vehicles isolated from inland ac network system. Both induced emfs and mechanical forces are developed in a machine whether it is a generator or motor. As such a dc generator and motor have identical construction. The term generator denotes that it generates electrical energy but actually it does not. It simply converts mechanical energy supplied to it into electrical energy. The curves or graphs giving the relationship between various quantities such as excitation (or field current), generated emf, terminal voltage and the load current etc are known as generator characteristics. The performance and therefore suitability of a dc motor is determined from its characteristics known as performance characteristics. Introduction to SYNCHRONOUS MACHINES A synchronous machine is an ac machine in which the rotor moves at a speed which bears a constant relationship to the frequency of currents in the armature winding,. A synchronous machine is one of the important types of electrical machines. Large ac networks operating at constant frequency of 50 Hz rely almost on exclusively on synchronous generators also called the alternators for the supply pf electrical energy and may have synchronous compensators at key points for control of reactive power. Private, stand-by and peak load plants with diesel or gas turbine prime movers also have synchronous generators. Synchronous motors provide constant speed industrial drives with the possibility of power factor correction. Synchronous machines are generally constructed in larger sizes. Small size alternators are not economical. The modern trend is to build alternator of very large sizes capable of generating 500 4

5 MVA or even more. The synchronous motor is rarely built in small sizes owing to superior performance characteristics and economic construction of induction motors. Synchronous machines according to their applications may be synchronous generators, synchronous motors or synchronous compensators. A synchronous generator is synchronous machine which receives mechanical energy from prime mover to which it is mechanically coupled and delivers electrical energy. A synchronous motor receives electrical energy from ac supply main and drives mechanical load. Synchronous compensator is a synchronous machine designed operate on no load with its shaft connected neither to a prime mover nor to a mechanical load and is used to control reactive power in power supply networks. Experiment No. 1 Date: 5

6 Load characteristics of a D.C. shunt generator. Aim: - To draw the external and internal characteristics of the given D.C.Shunt Generator Apparatus Required: - Sl.No. Particular Range Type Quantity 01 voltmeter 0-300v MC v MC Ammeter 0-1/2A MC Rheostats 0-38Ω Ω tachometer Loading Rheostat connecting wires Theory: Generators work on a principle of dynamically induced e.m.f. this principle is nothing but the Faraday s law of electromagnetic induction. It states that whenever the flux linking with a conductor or a coil changes an emf is set up in that conductor. So a voltage gets generated in a conductor as long as there exists a relative motion between conductor and the flux. So a generating action requires following basic components to exist i) the conductor or a coil ii) the flux iii) the relative motion between conductor and flux. In a practical generator the conductors are rotated to cut the magnetic flux keeping flux stationary. To have a large voltage as the out put, the no of conductors are connected together in a specific manner, to form a winding. This winding is called armature winding of a DC machine the part on which this winding is kept is called armature of a DC machine. The necessary magnetic flux is Produced by current carrying winding which is called field winding. DC Generators basically divided into two categories depending on way of deriving the field current or exciting current as i)separately excited generator ii)separately excited generator. When the field winding supply from the armature of the generator itself then it is said to be self excited generator. Based on how field windings are connected to the armature to derive its excitation this type is further divided into the following three types i)shunt generator ii)series generator iii)compound generator. When the field winding is connected in parallel with the armature, and the combination across the load then the generator is called shunt generator. The load characteristics of a DC shunt generator are further divided into two types. i) External characteristics which is the graph of the terminal voltage against load current. ii) Internal characteristics which is the graph of generated induced emf against the armature current. While plotting both the characteristics, the speed of the generator is maintained constant. Procedure: 6

7 1. Connections are made as shown in the circuit diagram. 2. Keeping the rheostat R1 in the motor field circuit in cut-out position and R2 in the generator field circuit, in cut-in Position and the SPST switch in open position, DC motor is started with the help of a 3 point starter. 3. The motor is brought to its rated speed by cutting out R1 if necessary. 4. The terminal voltage across the armature of the generator is noted 5. The generator voltage is built up to its rated value by gradually cutting out the rheostat R2 the load switch is closed and the generator is loaded in steps at each step the corresponding values of the terminal voltage (V L ), the load current(i L )and field current are noted. 6. To stop the motor, the load on the generator is gradually removed, load switch is opened, all the rheostats are brought back to their respective initial positions and the supply switch is closed. 7. A graph of V L v/s I L is drawn which represents the external characteristics curve Determination of armature resistance Ra and shunt field resistance Rsh by ammetervoltmeter 1. Connections are made as shown in the circuit diagram. 2. Keeping the rheostat in cut-in position, the supply switch is closed and the readings of ammeter and voltmeter are noted down. 3. The supply switch is opened. Circuit diagram Figure 1 Internal characteristics: 1. Graphical method: Shunt field resistance line op and armature resistance line OQ are drawn as shown in the external characteristics curve. A point F is selected on the external characteristic curve. 7

8 Conclusion and remarks: 8

9 Load characteristics of a D.C. compound generator. Aim: - To draw the external and internal characteristics of the given D.C.Compound Generator I LONG SHUNT CUMULATIVE COMPOUND GENERATOR Apparatus Required: - Sl.No. Particular Range Type Quantity 01 voltmeter 0-300v MC v MC Ammeter 0-1/2A MC Rheostats 0-38Ω Ω tachometer Loading Rheostat connecting wires Theory: In compound generator, part of the field winding is connected in parallel with armature and part in series with the armature. Both series and shunt field windings are mounted on the same poles. Depending upon the connection of shunt &series winding compound generator is further classified as i) Long shunt compound generator ii) Short shunt compound generator. In long shunt cumulative compound generator, shunt field winding is connected across the series combination armature & series field winding. The two fluxes produced by shunt &series field help each other. As load current increases armature current increases and hence series current also increases producing more flux. Thus the induced emf increases and terminal voltage also increases but due to Armature reaction, there is a drop in the terminal voltage. Procedure: 1. Connections are made as shown in the circuit diagram. 2. Keeping the rheostat R1 in the motor field circuit in cut-out position and R2 in the generator circuit, in cut-in Position and the SPST switch in open position, DC motor is started with the help of a 4 point starter. 3. The motor is brought to its rated speed by cutting in R1 if necessary. The terminal voltage across the armature of the generator is noted. The generator voltage is built up to its rated value by gradually cutting out the rheostat R2. 4. The load switch is closed and the generator is loaded in steps at each step the corresponding values of the terminal voltage (V L ) the load current(i L )and field current are noted. To stop the motor, the load on the generator is gradually removed, load switch is opened, all the rheostats are brought back to their respective initial positions and the supply switch is open. 5. A graph of V L v/s I L is drawn which represents the external characteristics curve 9

10 Determination of armature resistance Ra and shunt field resistance Rsh by ammetervoltmeter 1. Connections are made as shown in the circuit diagram. 2. Keeping the rheostat in cut-in position, the supply switch is closed and the readings of ammeter and voltmeter are noted down. 3. The supply switch is opened. CIRCUIT DIAGRAM: Conclusion and remarks: II) LONG SHUNT DIFFERENTIAL COMPOUND GENERATOR Aim: - To draw the external and internal characteristics of the given D.C.Shunt Generator Apparatus Required: - Sl.No. Particular Range Type Quantity 01 voltmeter 0-300v MC v MC Ammeter 0-1/2A MC Rheostats 0-38Ω Ω tachometer Loading Rheostat connecting wires Theory: In compound generator, part of the field winding is connected in parallel with armature and part in series with the armature. Both series and shunt field windings are mounted on the same poles. Depending upon the connection of shunt &series winding compound generator is further classified 10

11 as i) Long shunt compound generator ii) Short shunt compound generator. In long shunt cumulative compound generator, shunt field winding is connected across the series combination armature & series field winding. The two fluxes produced by shunt &series field oppose each other. The net flux is difference between the two. As load current increases shunt flux almost constant but series flux increases rapidly. Hence the resultant flux reduces. Thus the induced emf and terminal voltage also decreases drastically. There is drop due to armature resistance, series field resistance armature reaction due to which terminal voltage drops further. CIRCUIT DIAGRAM: Interchange the field terminals of generator(say Y to A of armature) and repeat the procedure. III) SHORT SHUNT CUMULATIVE COMPOUND GENERATOR Aim: - To draw the external and internal characteristics of the given Short Shunt Cumulative Compound Generator Apparatus Required: - Sl.No. Particular Range Type Quantity 01 voltmeter 0-300v MC v MC Ammeter 0-1/2A MC Rheostats 0-38Ω Ω tachometer Loading Rheostat connecting wires Procedure: 1. Connections are made as shown in the circuit diagram. 2. Keeping the rheostat R1 in the motor field circuit in cut-out position and R2 in the generator circuit, in cut-in Position and the SPST switch in open position, DC motor is started with the help of a 4point starter. 3. The motor is brought to its rated speed by cutting in R1 if necessary. The terminal voltage across the armature of the generator is noted. The generator voltage is built up to its rated value by gradually cutting out the rheostat R2. 4. The load switch is closed and the generator is loaded in steps at each step the corresponding values of the terminal voltage (V L ) the load current(i L )and field current are noted. To stop the motor, the load on the generator is gradually removed, load switch is opened, all the rheostats are brought back to their respective initial positions and the supply switch is open. 5. A graph of V L v/s I L is drawn which represents the external characteristics curve Determination of armature resistance Ra and shunt field resistance Rsh by ammetervoltmeter 1. Connections are made as shown in the circuit diagram. 11

12 2. Keeping the rheostat in cut-in position, the supply switch is closed and the readings of ammeter and voltmeter are noted down. 3. The supply switch is opened. Circuit Diagram: Interchange the field terminals of generator(say Y to A of armature) and repeat the procedure. VI) SHORT SHUNT DIFFERENTIAL COMPOUND GENERATOR Aim: - To draw the external and internal characteristics of the given D.C.Shunt Generator Apparatus Required: - Sl.No. Particular Range Type Quantity 01 voltmeter 0-300v MC v MC Ammeter 0-1/2A MC Rheostats 0-38Ω Ω tachometer Loading Rheostat connecting wires Procedure: 1. Connections are made as shown in the circuit diagram. 2. Keeping the rheostat R1 in the motor field circuit in cut-out position and R2 in the generator circuit, in cut-in Position and the SPST switch in open position, DC motor is started with the help of 4 point starter. 3. The motor is brought to its rated speed by cutting in R1 if necessary. The terminal voltage across the armature of the generator is noted. The generator voltage is built up to its rated value by gradually cutting out the rheostat R2. 12

13 4. The load switch is closed and the generator is loaded in steps at each step the corresponding values of the terminal voltage (V L ) the load current(i L )and field current are noted. To stop the motor, the load on the generator is gradually removed, load switch is opened, all the rheostats are brought back to their respective initial positions and the supply switch is open. 5. A graph of V L v/s I L is drawn which represents the external characteristics curve Determination of armature resistance Ra and shunt field resistance Rsh by ammetervoltmeter 1. Connections are made as shown in the circuit diagram. 2. Keeping the rheostat in cut-in position, the supply switch is closed and the readings of ammeter and voltmeter are noted down. 3. The supply switch is opened. CIRCUIT DIAGRAM: Interchange the field terminals of generator(say Y to A of armature) and repeat the procedure. TABULAR COLUMN: S L N o. Cumulatively Compounded Differentially Compounded Long Shunt Short Shunt Long Shunt Short Shunt V (Volts) I L (Amps) V Volts I L I L I L (Amps) V (Volts) (Amps V Volts (Amps) ) 13

14 Conclusion and remarks: 14

15 Experiment No. 2 Department of Electrical & Electronics Engg. Date: LOAD TEST AND PERFORMANCE CHARACTERISTICS OF D.C SHUNT MOTOR Aim: To plot the performance characteristics of a D.C. shunt motor after conducting load test. Apparatus required:. S.l No Apparatus Range Quantity 1 Ammeter 2 Voltmeter 3 Rheostats 4 Tachometer Theory: In a shunt motor we have E = ØZNP and Ø α Ish 60A Therefore E b α N Also E b = V - I a R a As the motor is loaded Ia increases and Eb decreases. Hence speed also decreases. The torque is directly proportional to Ia and therefore varies linearly. At low loads, copper loss is less but iron loss is more. At higher loads copper loss increases. At a particular load (around 80%) the two losses are equal and the efficiency becomes maximum. Beyond this region, the copper losses exceed the iron losses thus increasing the net losses. Hence the efficiency droops. Circuit diagram: 15

16 Procedure: 1. Make connections as per circuit diagram. 2. Keeping Motor Field circuit resistance at minimum position close the supply switch S1. 3. Gradually increase the motor field circuit resistance such that the motor runs at rated speed. 4. Note down all the meter readings including the speed. 5. Apply load using brake drum arrangement and increase the load in steps and note down the corresponding readings of all the meters including the speed. 6. This is repeated till the full load (rated current) is reached. 7. Reduce the load, bring motor field circuit resistance to minimum position and open supply switch S1. TABULAR COLUMN: I Amps V Volts Speed rpm Force Kgs F1 F2 Motor output Watts Motor output BHP % =Output *100 input Torque T Kgm Calculations: Radius R = Torque T = (F 1 F 2 ) x R x 9.81 Nm Input Power P i = VI Watts 16

17 % = BHP = GRAPH: Conclusions and remarks: Experiment No. 3 Date: SWINBURNE S TEST Aim: To determine the constant losses and hence to find efficiency of a given D.C.Machine at any desired load. Apparatus: Sl.No particular Range Type Quantity 01 Voltmeter 0-300v M.C Ammeter 0-10/20A M.C Rheostat 0-38 Ω Tachometer Connecting wires Procedure: 17

18 1. Connections are made as shown in the circuit diagram. 2. Keeping the rheostat R1 in the field circuit of the motor in cut-out position,the supply switch is closed. 3. The motor is brought to its rated speed by cutting in the rheostat R1 if necessary. 4. Readings of all the meters and speed are noted down. 5. To stop the motor the rheostat is brought back to their respective initial position and the supply switch is opened 6. Determination Of Armature Resistance Ra by Ammeter-Voltmeter method i) Connections are made as shown in the circuit diagram. ii) Keeping the rheostat in cut-in position, the supply switch is closed and the readings of ammeter and voltmeter are noted down. iii) The supply switch is opened. Calculation: I L = No load motor current, Amp I FL = Full load motor current, Amp I f = Field Current, Amp V L =No load Motor terminal voltage,volt(as per the name plate details) i)no load input power = V L X I L watts. ii)armature copper loss=(i L -I f ) 2 X Ra iii) Constant losses, Wc= No load input power- Armature copper loss watt = (V L X I L )_- (I L -I f ) 2 X Ra watt I) Efficiency when Working as motor at full load: a)i a = (I FL - I f ) Amp b) Armature copper loss= I a 2 X R a Watt =( I FL -I f ) 2 x Ra Watt c) Total losses = Wc + armature copper loss Watt = Wc + [ (I FL -I f ) 2 x Ra] watt d) Input to the motor = V L X I FL watt e) Output of motor = Input Total losses Watt= (V L x I L )- [W C + (I FL -I f ) 2 x Ra] Watt f) %ήm = II) Efficiency when Working as motor at full load: a) Iag =( I FL + I f ) Amp b) Armature copper loss = Iag 2 x Ra Watt c) Total losses = Wc+ Armature copper loss Watt = Wc+ (I FL -I f ) 2 x Ra] Watt d) Out put of generator = VL x IFL Watt e) Input to generator = output + Total losses Watt= (V L x I L )+ [WC+ (I FL -I f ) 2 x Ra] Watt Circuit Diagram: 18

19 Conclusion and Remarks: Experiment No. 4 Date: HOPKINSON S TEST Aim: - To conduct Hopkinson s test on (regenerative or back to back test) a given similar pair of DC shunt machines and to determine their efficiencies (or heat run test). 19

20 Apparatus Required: - Sl Apparat No us 1 Ammet er 2 Voltmet er 3 Rheosta ts 4 Tachom eter Range Quanti ty PRECATUIONS: 1.The field rheostat of the motor should be in the minimum position at the time of starting and stopping the machine. 2.The field rheostat of the generator should be in the maximum position at the time of starting and stopping the machine. 3.SPST switch should be kept open at the time of starting and stopping the machine. Theory: In this test a D.C motor is mechanically coupled to D.C Generator in turn the generator is electrically coupled to the motor. The power taken by the supply is mainly used to supply the losses in the two machines. The combination is loaded by weakening the flux of the motor or strengthening the flux of the generator. By this method, full load test can be carried out on two similar shunt machines with out wasting their outputs. Circuit for Measurement of R a: 20

21 Circuit Diagram: Procedure: For Hopkinson s Test: 1. Make the connections as shown in the figure (a). 2. Keep the field circuit resistance of the motor kept at minimum position (Cut-in)and the field circuit resistance of the generator at the maximum position(cut-out). Keep the SPST switch S1 open. 3. Close the supply switch, gradually increase the motor field circuit resistance such that the motor runs at rated speed. 4. Build up the generator voltage to supply voltage by decreasing its field circuit resistance. Check the voltmeter connected across the switch S 1, it should read zero if not change the polarity of the voltmeter. Repeat the above steps. 5. The combination is loaded by either decreasing the generator field circuit resistance(over excitation) or increasing motor field circuit resistance(under excitation) in steps So that the required load current is adjusted, (like 50%, 75% of full load etc). 21

22 6. Each time note down the readings of all the meters. 7. Reduce the motor field circuit resistance and increase the generator field circuit resistance to original positions of Rheostats by observing the voltmeter, open the supply switch. Measurement of R a : 1. Make the connection as in fig (b). 2. Close the supply switch and note the readings of all meters by switching lamps one by one. Take three readings within 2 A. For Hopkinson s Test. V 1 volts I 1 amps I 2 amps I 3 amps I 4 amps For measurement of R a I amps V volts R a = 1.5*V/I Volts Tabular Column:- Calculations:- 22 Let R a be the armature resistance of each machine. (As both machines are identical, same R a for each machine). Supply voltage = V 1 volts. Generator output current = I 2 amps. Generator output = V 1 I 2 watts. Motor input current = (I 1 + I 2 ) amps. Motor input = V 1 *(I 1 + I 2 ) watts. Generator armature current = (I 2 + I 4 ) amps. Motor armature current = (I 1 + I 2 I 3 ) amps. Field current of generator = I 4 amps. Field current of motor = I 3 amps.

23 Armature copper loss in generator = (I 2 + I 4 ) 2 * R ag.. watts. Armature copper loss in motor = (I 1 + I 2 I 3 ) 2 * Ram watts. Generator field copper loss = V 1 I 4 watts. Motor field copper loss = V 1 I 3..watts. Power drawn from supply = V 1 I 1 watts = Total losses in both the machines together. Total stray losses for the set = V 1 I 1 [(I 2 + I 4 ) 2 R ag + (I 1 + I 2 I 3 ) 2 R a m + V 1 I 3 + V 1 I 4 ] = W s. Stray losses for each machine = W s / 2 watts. % g for generator :- Total losses = (I 2 + I 4 ) 2 R ag + V 1 I 4 + W s / 2 = W g watts. Percentage efficiency = % g = % m for motor :- Total losses in motor = W m =(I 1 + I 2 I 3 ) 2 R a + V 1 I 3 + W s / 2 watts. Motor input = V 1 (I 1 +I 2 ) watts. Percentage efficiency of motor = % m = The efficiencies for motor and generator are calculated for different generator currents or load currents. Graph:- Output V s % efficiency curve is drawn for both motor and generator. CONCLUSION & REMARKS: Experiment No. 5 Date: 23

24 FIELD TEST ON DC SERIES MACHINE Aim: To find the efficiency of both machines by conducting field test. Apparatus required:- Sl Apparat No us 1 Ammet er 2 Voltmet er 3 Rheosta ts 4 Tachom eter Theory: Range Quanti ty This test is applicable to two similar series motor. The two machines are coupled mechanically one machine runs normally as motor and drive the other as generator whose output is wasted in a variable load. Iron and friction losses of the two machines are made equal by joining the series field of the generator in the motor armature circuit so that both machines are equally excited. The load resistance is varied till the motor current reaches its full load value. Circuit Diagram: 24

25 Procedure:- 1. Make circuit connections as per the circuit diagram with few lamp switches of the load kept on. 2. Close the Supply switch and apply load in steps till rated current and note down all the meter readings. 3. Reduce the load by keeping few load switches on so that the load is not made zero. 4. Open the supply switch. Tabular Column: V V 1 I 1 V 2 I 2 Calculations: V = Supply voltage V 2 = Voltage across motor I 2 = Motor current V 1 = Generator voltage I 1 = Generator current Power input to whole set= V I 2 Power output of generator = V 1 I 1 Total losses = W= VI 2 - V 1 I 1 Total Ohmic loss = W c = I 2 2 (r am +r shm +r shg )+I 12 r ag No load rotational loss of both the machines W o = W-W c No load rotational losses of each machine = W o /2 Motor power input = V 2 I 2 a. Motor m = (V 2 I 2 - (W o /2+I 1 2 (r am +r shm )) / (V 2 I 2 ) 25

26 b. Gen g= V 1 I 1 - (W o /2+ I 1 2 r shg + I 12 r ag ) / V 1 I 1 Conclusion & Remarks: Experiment No. 6 Date: RETARDATION TEST Aim: 1. To determine the stray losses 2. To predetermine the efficiency of the D.C. motor at a given load Apparatus Required: 26 Sl Appara No tus 1 Ammete r 2 Voltmete r 3 Rheostat s Range 0-10A,0-2A V 0-200Ω Quanti ty 2 2 2

27 4 Stop watch 5 Tachom eter Department of Electrical & Electronics Engg. Theory: This method is applicable to shunt motors and generators and is used for finding stray losses. Then, knowing the armature and shunt copper losses at a given load current, the efficiency can be calculated. The machine under test is speeded up slightly beyond its normal speed and then supply is cut off from the armature, keeping the field excited. Consequently the armature slows down and its kinetic energy is used to meet the rotational losses (friction, windage and iron losses).in addition a retarding torque by way of no inductive resistance is applied to the armature.the power drawn by this resistance acts as a retarding torque on the armature, there by, making it slow down comparatively quickly. Circuit Diagram: Measurement of field resistance: Fig (a) Measurement of R a : fig.c Procedure: 1. Make the connections as per the circuit diagram of fig (a). 2. Keep the armature resistance at maximum and motor field circuit resistance at minimum position. 27

28 3. Close the supply switch and DPDT on the armature side (position I). Gradually adjust armature circuit resistance to minimum. Then increase the motor field circuit resistance so that the motor runs slightly beyond rated speed (say by 50 rpm). The field current is noted. 4. With the motor running, open the DPDT and note the time taken for a certain amount of fall in speed corresponding to the fall in voltage of 100 v is observed (v2-v1). Let it be t 1 sec. Repeat steps 2, 3, 4 for different fall in voltage like 80 v, 60 v. 5. Repeat steps 2,3 and now open the DPDT switch and close immediately on the load side (position II). Note the time taken for the same fall in voltage (v3 - v4). Let it be t 2 sec. 6. While recording the time t 2, note the ammeter reading while starting as well as at stopping of the stop clock (let that be I a1 and I a2 respectively ). Measurement of R a : 1. Make the connection as in fig (b). 2. Close the supply switch and note the readings of all meters by switching lamps one by one. Take three readings within 2 A. Measurement of Field Resistance: 1 Make the connection as in fig(c). 2 Close the supply switch and note the readings of all meters by switching lamps one by one. Take three readings within 2 A. Tabular Column: I f amps V 1 Volts V 2 Volts Time t 1 sec V 3 Volts V 4 Volts I a1 amps I a2 amps Time t 2 sec Measurement of R a : I a Amps V volts R a =1.5 xv /I a Ohms Measurement of R f : I f Amps V volts R f =V /I f Ohms Calculation: 28 Power taken up by braking load = W = (I a1 + I a2 ). (V 3 + V 4 ) 2 2 =I av. V av

29 Stray losses = W s = W ( t 2 ) watts ( t 1 -t 2 ) To find the efficiency of D.C. motor at a given load: Let I L be the full load current (From name plate) Input = V (.I L ) watts Armature current = [I L ) - I f ] = I a 2 Armature copper loss = I a R a Field copper loss = I 2 f R f Total loss = stray loss + Armature copper loss + Shunt field copper loss Output = Input Total Loss %Efficiency = ( Output x100)/input Conclusion and Remarks: Experiment No. 7 Date: SPEED CONTROL OF D.C.SHUNT MOTOR AIM: To control the speed of D.C.Shunt motor by 1) Armature control method 2) Flux control method Apparatus: Sl.No particular Range Type Quantity 1 Voltmeter 0-300v M.C Ammeter 0-10/20A M.C Rheostat 0-38 Ω Tachometer connecting wires CIRCUIT DIAGRAM : 29

30 Theory: In a D.C shunt motor, the speed is governed by the following relations E b = ØZNP / 60A Therefore N α E b / Ø (1) Also E b = V - IaRa Therefore N α (V IaRa) / Ø (2) Ø α I sh (3) I sh = V / R sh (4) The above may be combined as V - Ia (Ra+R) N α (5) V / (Rsh+R) Speed is controlled by two methods a.) Flux control keeping armature voltage constant. b ) Armature control keeping flux constant. In the flux control method we keep the numerator of eq(5) constant and vary R in denominator of (5).We start with minimum value of R and gradually increase it to increase the speed. In the armature control method we keep the denominator of (5) constant and vary R in the numerator of (5). We start with maximum value of R and gradually reduce it to increase speed. In this experiment we conduct speed control by armature method first followed by flux method. Procedure: ARMATURE CONTROL METHOD 30

31 1. Connections are made as shown in the circuit diagram. 2. Keeping the rheostat R 1 in the field circuit of the motor in cut-out position, the rheostat R 2 In the armature circuit of the motor in cut-in position, the supply switch is closed. 3. Field current is adjusted to a constant value by adjusting the rheostat R1 and the rheostat R2 is gradually cut-out in steps and each step the readings of voltmeter and speed are noted down. 4. The above procedure is repeated for another value of field current FLUX CONTROL METHOD 1. Keeping the rheostat R1 in the field circuit of the motor in cut-out position, the rheostat R2 in the Armature circuit of the motor in cut-in position, the supply switch is closed. 2. The rheostat r2 is adjusted to get the required voltage across the armature. 3. the rheostat r1 is gradually cut-in steps and at each step the readings of ammeter and speed are noted down( Note: The rheostat r1 is cut-in till the speed is little above the rated speed of motor) 4. The experiment is repeated for another value of armature voltage. 5. To stop the motor, all the rheostats are brought back to their respective initial position and supply switch is closed. Tabular Column: If = Amp V = Volts Sl.No. Armature Voltage(volts) Speed (rpm) Sl.No. Field Current Amps Speed (rpm) 31

32 N rpm N rpm Armature voltage, volt I f Amp CONCLUSION & REMARKS: 32

33 Experiment No. 8 Department of Electrical & Electronics Engg. Date: SPEED CONTROL OF DC SHUNT MOTOR BY WARD LEONARD METHOD Aim: To control the speed of DC Shunt motor by Ward Leonard method. Apparatus: Sl.No particular Range Type Quantity 01 Voltmeter 0-300v M.C Ammeter 0-10/20A M.C Rheostat 0-38 Ω Tachometer Connecting wires 06 DPDT switch 01 CIRCUIT DIAGRAM Procedure: 1. Connections are made as shown in the circuit diagram. 2. Keeping the rheostat R1 in the field circuit of the motor in cut-out position, potential divider R2 in cut in position, keeping switch S2 in open position, switches S1& S3are closed. 3. The motor M1 is brought to its rated speed with the help of 3-point starter & cutting out the rheostat R2 if necessary. 33

34 4. Switch S2 is closed & by using potential divider, voltage across the field circuit of the generator is gradually increased in steps up to the rated speed of the motor M2.At each step the readings of voltmeter M2 are noted down. 5. Potential divider is brought to its original position & switch S2 is open. 6. Know keeping the potential divider in minimum position the direction of rotation of motor M2 is changed by reversing the polarities of the generator by throwing DPDT switch on to the other side. 7. Step no 4 is repeated. 8. To stop the motor, the potential divider, all the rheostats are brought back to their respective initial position, switches S2,S3,& S1 are opened. 9. Graph of speed of motor M2 v/s voltage is plotted. Tabular Column: Forward rotation Sl No Voltage, volts Speed of M2 rpm Sl No Reverse rotation Voltage, volts Speed of M2 rpm CONCLUSION & REMARKS: 34

35 Experiment No. 9(i) Date: PRE-DETERMINATION OF PERCENT REGULATION OF A 3 Ф ALTERNATOR BY EMF METHOD. Aim: To find the percent voltage regulation of 3 Ф alternator by EMF method Apparatus required: Theory: Sl Appara No tus 1 Ammet er 2 Voltmet er 3 Rheosta ts 4 Tachom eter Range Quant ity In this method the synchronous impedance is obtained from the SC and O C tests. This method is applicable to cylindrical rotor alternator. In this method the magnitude of regulation obtained is very large. Hence it is usually called the pessimistic method. The vector diagram is as shown below: E Ф Ia δ V IaXs IaRa 35

36 The vector diagram is drawn for lagging p.f. From the vector diagram, we have E δ = V 0 + Ia ±Ф * Zs θ Where Ф is the p.f angle, δ is the load angle, θ is the impedance angle θ = tan -1 (Xs / Ra) Use + for leading p.f and for lagging p.f for the angle Ф CIRCUIT DIAGRAM: PROCEDURE: (a) For O.C. test: - 1. Make connections as shown in the circuit diagram. Keep TPST switch open and motor field resistance in minimum position and alternator field resistance in maximum position, S1 open. 2. Close the D.C. supply switch. Bring Motor speed to its rated value by increasing its field resistance. 3. Note down the Voltmeter reading. 4. Now close S1.Gradually decrease the alternator field resistance in steps and at each step, note down voltmeter reading and ammeter reading (If) till 125% of rated voltage is reached. Tabulate under OC test. 36

37 5. Plot a graph of OC voltage per phase Vs field current. This gives OCC. 6. Increase the alternator field resistance to maximum position, open S1. (b) For S.C. test:- 1. With machine running at rated speed, close TPST switch. and S1. 2. Decrease the Alternator field resistance gradually in steps, and at each step note down both the ammeter readings.tabulate under SC test. 3. Increase the alternator field resistance to maximum, open TPST and S1, reduce the motor field resistance to minimum position 4. Plot a graph of Isc, vs, I f.this gives SCC. (c) For Measuring Armature Resistance:- 1. Make connections as shown in the circuit diagram. 2. Close the D.C. supply switch.. a) Switch on the lamps one by one and note down the reading of voltmeter and ammeter till the ammeter reads 2 A. b) Tabulate the readings under armature resistance. Tabular column: O.C. Test: Field current I f in amps OC voltage V 0 volts OC voltage per phase V 0 ph=v 0 / 3 Tabular Column for S.C.Test:- Field current I f amps SC current Isc amps For measurement of Ra I amps V volts Ra = (1.5) x V /phase. 37

38 2I Calculations: EMF METHOD OR SYNCHRONOUS IMPEDANCE METHOD OR PESSIMISTIC METHOD O.C.C and S.C.C are drawn as shown below. Graph: Draw a horizontal line corresponding to rated voltage/ ph of the alternator. Let it cut the O.C.C. at A. Drop the perpendicular from A. Let it cut the S.C.C.at B and X-axis at C. Then synchronous impedance Z s in ohms/ph is given by Z s = AC in Volts ohms/ph = O.C voltage per phase (both for the same I f ) BC in Amps S.C. current X s = Z At some assumed power factor cos, and for full load induced voltage/ph is given by +Sign for lagging p.f. and u.p.f. - vesign for leading p.f. V t is the rated terminal voltage per phase I A is the full load current (rated) current of alternator. cos is the p.f. at which regulation is required. R a is the armature resistance per phase X s is the synchronous reactance per phase % regulation = E 0 V t x 100 % V T pf =cos % regulation 0.8 lag upf 0.8 lead 38

39 Date: Experiment No. 9(ii) PRE-DETERMINATION OF PERCENT REGULATION OF A 3 Ф ALTERNATOR BY MMF METHOD OR AMP TURN METHOD. Aim: To find the percent voltage regulation of 3 Ф alternator by MMF method Apparatus required: Sl Appara No tus 1 Ammet er 2 Voltmet er 3 Rheosta t 4 Tachom eter Range Quant ity Theory: This method is based on the ampere-turns. In the alternator on load, ampere-turns are required to generate the induced emf, to account for the armature reaction effect and to account for the armature drop in the machine. From the SC and OC tests, we obtain the ampere-turns to account for the armature drop and the ampere turns to generate the induced emf. These are vectorially added to obtain the total ampere-turns corresponding to the given load and p f (assumed). Corresponding to the total ampere turns us then obtains the induced emf from the OCC. This method gives % regulation whose value is numerically less.hence this method is called optimistic method. The vector diagram is given as below. F1: MMF required to generate induced emf on open circuit. 39

40 F2: MMF required to generate rated current on short circuit. F3: Total MMF F3 = F1 + F2 ( vectorial addition ) Calculations: MMF Method or Amp turn method or optimistic method O.C.C & S.C.C are drawn as below. Graph: (a) MMF method or amp turn method or optimistic method. OCC and SCC are as shown below: For a given pf cos, at full load calculate E = V t + I a R a cos where V t is the rated terminal voltage per phase in volts, I a rated armature current in amps, R a armature resistance in ohms/phase, cos is the pf at which regulation is required. From the OCC, for a voltage of E volts note the field current required. This is I f1 amps. I f2 is the field current required to circulate rated current on short circuit. Read this from SCC. Find I f3, as follows either graphically or analytically, I f3 is the excitation required for the given load conditions. To find I f3 graphically:- choose a scale 1cm= amps. Plot to some convenient scale, I f1 and I f2 for given pf at full load, obtain I f3. Or find I f3 analytically:- I f3 = I f1 2 + I f2 2 2I f1 I f2 Cos(90 ) I f3 = amp = excitation required. From the OCC for a field current of I f3 amps, read the voltage. This is E 0 volts/phase = no load emf/phase. % regulation = (E 0 V t )*100 V t pf =cos % regulation 40

41 0.8 lag upf 0.8 lead Conclusion and remarks: 41

42 Experiment 10 Date: PRE-DETERMINATION OF REGULATION OF A 3 PHASE ALTERNATOR BY POTIER REACTANCE MRTHOD OR ZERO POWER FACTOR (ZPF) METHOD Aim:- 1. To conduct OC test. 2. To conduct SC test. 3. To obtain ZPF lagging saturation curve at full load. 4. To determine the armature resistance for the given 3 synchronous machine and hence predetermine the regulation for full load at any desired power factor. Apparatus Required:- Sl Appara No tus 1 Ammet er 2 Voltmet er 3 Rheosta t 4 Tachom eter Range Quant ity Theory: In this method in addition to the OC and SC test we perform a load test on the alternator with a purely inductive variable load. This method is based on the separation of armature leakage reactance drop and the armature reaction effects. Hence it gives more accurate results. The ZPF characteristic is the curve of terminal volts against excitation when armature is delivering full load current at zero pf. The reduction in voltage due to armature reaction is found from the above and the voltage drop due to armature leakage reactance X L (Also called potier reactance X P ) is found from OCC, SCC and ZPFC. By combining these two the induced emf can be calculated. The vector diagram is shown below. 42

43 Procedure:- (a) For O.C. test: - 1. Make connections as shown in the circuit diagram. Keep TPST switch open and motor field resistance in minimum position and Alternator field resistance in maximum position, S1 open. 2. Close the D.C. supply switch. Bring Motor speed to its rated value by increasing its field resistance. 3. Note down the Voltmeter reading. 4. Now close S1.Gradually decrease the alternator field resistance in steps and at each step, note down voltmeter reading and ammeter reading (If) till 125% of rated voltage is reached. Tabulate under OC test. 5. Plot a graph of OC voltage per phase Vs field current. This gives OCC. 6. Increase the alternator field resistance to maximum position, open S1. (b) For S.C. test:- 1. With machine running at rated speed, bring alternator field resistance to maximum position and close the TPDT switch to position I. 2. Gradually reduce Alternator field resistance in steps and at each step note down both ammeter readings. Tabulate under SC test. 3. Bring alternator field resistance to maximum position, open TPDT, open S1, motor field resistance to minimum position, motor armature resistance to maximum position and open the DC supply switch. 4. Plot a graph of I sc, VS, I f. This gives SCC. 43

44 For ZPF characteristics:- Department of Electrical & Electronics Engg. 1. With machine running at rated speed, bring alternator field resistance to maximum position and close the TPDT switch to position II. 2. Gradually reduce alternator field resistance in steps and simultaneously increase the load in steps such that rated current flows in the alternator and note down corresponding voltmeter and ammeter reading (I f ) obtain a number of readings keeping alternator load current at rated value. Tabulate under ZPF test. 3. Increase alternator field resistance to maximum position, reduce the load completely, open TPDT switch, open S1, reduce motor field resistance to minimum position, motor armature resistance to maximum position and open the DC supply switch. 4. Plot a graph of V LPH Vs If. For Measurement Of Armature Resistance :- 1. Make connections as shown in the circuit diagram. 2. Close the D.C. supply switch.. 3. Switch on the lamps one by one and note down the reading of voltmeter and ammeter till the ammeter reads 2 A. 4. Tabulate the readings under armature resistance. Tabular column: For OC Test. I f amps 0 V o volts V o / 3 volts 125%rated voltage For SC Test. Sl. No. I F amps I SC amps For ZPF Test. Sl. No. I f amps I a amps V L volts 44

45 For measurement of armature resistance. Sl. No. V volts I amps R a =1.5V/2I ohms R a = Armature resistance per phase in ohms. Calculations:- 1. OCC and SCC are drawn as shown below. OA = field current required to circulate full load current in AC test. Point B corresponds to values from ZPF test (I f, V L / 3). Make PQ =OA. Draw QR parallel to air gap line, MP horizontal line corresponding to rated phase voltage = V t. Measure SR in volt scale. 2. SR in volts = I a X L X L = SR in volts = ohms/phase. I a in amps X L =potier reactance in ohms/phase. 3. Calculate E g from E g = (V t Cos + I a R a ) 2 + (V t Sin I a X L ) 2 Cos is the pf at which % regulation is to be determined. V t is the rated phase voltage. I a is the full load current of alternator. R a is the armature resistance per phase. X L is the potier reactance in ohms/phase. + ve sign for lagging pf and upf. -ve sign for leading pf. E g is the induced voltage per phase. Sin = (1- Cos 2 ) 4. Corresponding to a phase voltage E g, from the OCC, find the field current. Let it be I f1. 5. Find the resultant field current I f3 from the following vector diagrams:- 45

46 Graph: 6. I f2 = SP in amps. 7. Corresponding to a field current of I f3 amps, from the OCC read the no load phase voltage (E o ). This is the no load emf. 8. Percentage regulation is given by: % regulation = (E o V t ) *100% V t Note:-calculate %regulation for 0.8 lag, 0.8 lead, and upf. conclusion and remarks: %Regulation = for 0.8 lagging pf. %Regulation = for 0.8 leading pf. %Regulation = for upf. Experiment No.: 11 Date: SLIP TEST FOR THE DETERMINATION OF DIRECT AXIS AND QUADRATURE AXIS SYNCHRONOUS REACTANCES OF A SALIENT POLE SYNCHRONOUS MACHINE 46

47 Aim: 1. To conduct slip test on the given three phase synchronous machine so as to calculate direct axis (X d ) and quadrature axis (X q ) reactances. 2 To measure stator resistance R a 3. To predetermine the regulation using X d and X q for full load and required power factor Apparatus Required: Sl Appara No tus 1 Ammet er 2 Voltmet er 3 Rheosta ts 4 Tachom eter Range Quant ity Associated Theory: This method is applicable to salient pole alternator. Here we measure the direct axis and quadrature axis reactance on a per phase basis. The direct axis reactance is usually more than the quadrature axis reactance because more flux is established along the direct axis. In the vector diagram shown below the induced emf is found to be established along the quadrature axis. 47

48 Circuit Diagram: Measurement of R a : Procedure: 1. Make connections as shown in the circuit diagram. Keep the field circuit of the alternator open. 2. Keep the motor field resistance at minimum positions. 3. Start the DC motor bring it to rated speed by increasing the field resistance. 4. Apply reduced 3 phase AC voltage to the alternator armature through the three phase auto transformer (say 30 v) 5. Slightly adjust the motor field resistance to obtain maximum oscillation in ammeter and voltmeter. Note down the maximum and minimum readings of oscillation in both the meters. Tabulate the readings. 6. Repeat the steps for different applied voltages of 50V and 70V (Note: Even after adjusting the speed, if there is no oscillation in the meters, then any two of three supply AC terminal to Auto transformer should be interchanged). Tabular Column: Sl. No. I max amp I min amp V max Volt V min Volt X d =V max / ( 3 I min ) X d =V min / ( 3 I max ) 48