eee lab manual part i

8/13/2019 Eee Lab Manual Part i

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EE 186 ELECTRICAL ENGINEERING LABORATORY MANUAL

BY

R.RAMYAASSISTANT PROFESSOR

DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERINGBS ABDUR RAHMAN UNIVERSITY

VANDALUR, CHENNAI


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Cycle - I

1. Verification of Kirchoffs laws 2. Study of RLC series circuits3. Load test on DC motors4. Speed control of D.C. shunt motor5. Load test on three phase induction motor6. Transfer function of separately excited D.C. generator

Cycle II

7. Transfer function of armature and field controlled D.C. motor8. OCC of DC generator9. Load test on DC generator10. Load characteristics of single phase transformer11. Transfer function of AC servomotor12. OC and SC test on single phase transformer


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FORMAL LABORATORY DISCIPLINE :

Listed below are the (operating) procedures that you are expected to follow in thelaboratory.

1. Every student is required to wear their respective lab uniforms, and ssoes. Girls areexpected to tuck in their hairs inside their coats.

2. Please be regular with your lab reports submission, failure of which will be viewed veryseriously.

3. Please treat the instruments with care, as they are very expensive.4. Read the laboratory documentation prior to each lab meeting.5. Read the viva question section before coming to the lab so that you attend the viva

questions at each lab session.6. Return the components to the Lab-attender when you are finished with them.7. Before leaving the lab, place the stools under the lab bench.8. Before leaving the lab, turn off the power to all instruments including the printer.9. Before leaving the lab, turn off the main power switch to the lab bench.

FORMAL LABORATORY REPORTS

1. Laboratory observation reports will be due at each lab meeting. Work that was performedthe previous lab meeting is to be documented and it has to be attested by the respectivestaff within 2 days of the completion of the experiment and the lab record has to beturned in the following week at the beginning of the lab period.

2. Late reports will have points deducted.3. All labs must be performed and all lab reports (both observations and records) must be

turned in to pass the course. Reports which are so late will be counted as an automaticzero.

4. While laboratory exercises are performed in groups, lab reports are to be written on anindividual basis.

RECORD:

It is required of the students to write a formal report describing the procedure and results.

In this laboratory problems will be posed and each student team will be required to plan and solve

it. Then eachindividual student

will write a formal report describing the laboratory measurements andconclusions. The reports should contain the following sections:I. Aim of the experiment

This section will contain a description of theobjective. It will clearly define the questions to beanswered by the laboratory experiment.

II. Description and theory of the experiment -This section will contain a description of the theory upon which the experiment is based.

III. Procedure :


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A detailed experimental procedure and a clear description of the data taken.

III. Description of data reduction -This section will present sample calculations showing how the theory is applied to the observeddata (as tabulation) to answer the questions posed by the laboratory problem.

IV. Presentation and discussion of the result -

Generally, the result will be a statement along with based on the observations made, withsupporting graph.

OSERVATION:

1. There will be sections of the pre-lab calculations, these will have to be done before coming to thelab session.

2. There will be steps to follow in carrying out the pre-lab calculations, these theoretical values willhave to be cross checked with the observed values in the lab.

3. If a graph is required, it should be associated with the section/step/sub-step in which it is required.Each graph should have a figure number and caption in addition to a title on the graph: Enter and

place the scale ion the graph. So does a circuit diagram.NOTE:

Attendance will be checked in each laboratory. If absence is unavoidable, students should contactthe lab-in-charge to another time to perform the experiment.

GENERAL SAFETY PRECAUTIONS:

1. Conduct yourself in a responsible manner at all times in the laboratory.2. Follow all written and verbal instructions carefully. If you do not understand a direction or part of a

procedure, ASK YOUR TEACHER BEFORE PROCEEDING WITH THE ACTIVITY.3. Avoid bulky, loose or trailing clothes. Avoid long loose hair. Remove metal bracelets, rings or

watchstraps when working in the laboratories4. Discard damaged cords, cords that become hot, or cords with exposed wiring.5. Before equipment is energized ensure, (1) circuit connections and layout have been checked by a

Teaching Assistant (TA) and (2) all colleagues in your group give their assent. 6. Never make any changes to circuits or mechanical layout without first isolating the circuit by switching

off and removing connections to power supplies. 7. Even low voltage DC supplies can be dangerous. This is especially true if your skin is wet or if probes

or wires penetrate your skin. Your body is protected by the high resistance of dry skin. But if theprotection is bypassed then lethal currents may flow through your body on contact with a low voltagesupply. Make sure your skin is dry and avoid skin punctures with probes or component leads


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1. VERIFICATION OF KIRCHOFFS LAWS

INTRODUCTION:Network equations are formulated from two simple laws that were first expressed

by Kirchoff in 1845. These laws concern the algebraic sum of voltages around a loopand currents leaving or entering a node. It is interesting to note that Kirchoff was a 23year old student at the time of the first publication of these laws.

STATEMENTS: Kirchoffs Voltage Law:

Kirchoffs voltage law states that the algebraic sum of all branch voltagesaround any closed loop of a network is zero at all instants of time.

Kirchoffs current law: Kirchoffs current law states that the algebraic sum of all branch currents

leaving a node is zero at all instants of time. (The law is a consequence of conservation

of charge. Charge which enters a node should leave the node because it cant be storedthere.)

OBJECTIVE:To verify Kirchof fs current and voltage Laws for a given circuit.

APPARATUS REQUIRED:

S.N

o

Name of the

component

Range Quantity

1. Regulated power supply (0-30) 2 2. Resistors 220 2

330 1 47 1 68 1

3. Ammeter (0-10)mA 1 4. Digital Multimeter 1


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CIRCUIT DIAGRAM:

Fig. 1.1

TABULATION:

1

220 [ohm]

(0-100) mA (0-100) mA

330[ohm] 10 V

47[ohm]

220 [ohm]

(0-100) mA 15 v

68 [ohm]

B

F

C

DE

A A

A A

+ -

(0-30)

(0-30) V

(0-30) V

(0-100) mA

(0-30) V

BRANCH THEORETICALCALCULATION

OBSERVED VALUES

CURRENT(mA)

VOLTAGE(V) CURRENT(mA)

VOLTAGE(V)

AB

BE

BD

BC

ED

CD


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PROCEDURE FOR VERIFICATION OF KVL:

1. Give connections as per circuit diagram.2. Switch on the supply voltage.3. Note the voltage across the voltage source, and the voltage (drops) across the

resistors (using a multi-meter) in the closed loop.4. Check whether the sum of voltage rises in the closed loop is equal to the sum of

voltage drops.5. Check these observed values with the theoretical values calculated using the

algebraic equations formulated based on the KVL law.

PROCEDURE FOR VERIFICATION OF KCL:

1. Give connections as per circuit diagram.2. Switch on the supply voltage.3. Check whether the sum of the incoming currents to a node is equal to the sum of the

out going currents from that node.4. Check these observed values with the theoretical values calculated using the

algebraic equations formulated based on the KCL law.

RESULT:Kirchoffs current and voltage laws have been verified for the given circuit.

VIVA QUESTIONS(No need to write these questions in record):1. State Ohms law. 2. State Kirchoffs current law. 3. State Kirchoffs voltage law. 4. What do you mean by a node?

5. What do you mean by a junction?6. What do you mean by a branch?


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2. STUDY OF RLC SERIES CIRCUITS(FREQUENCY RESPONSE OF SERIES RESONANCE CIRCUITS)

AIM:To study the phenomenon of resonance in electrical circuits.

APPARATUS REQUIRED:

S.No Name of thecomponent

Range Quantity

1. Signal generator 1 2. Inductor 400 mH,

300 mH 1 1

3. Resistor 100 1 5. Capacitor 0.5 F 1 4. Ammeter (0-10)mA 1

FORMULA:1. RLC Series circuit,

CIRCUIT DIAGRAMS:

RLC SERIES CIRCUIT

MODEL GRAPH:RLC SERIES CIRCUIT

100 0.5 F 300 mH

VS (0 -10) mA

I (mA)

f (Hz)


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PROCEDURE:

1. The required circuit is constructed by using circuit components.2. The frequency of the input sinusoidal signal is varied step by step and the

corresponding readings in ammeter are noted.3. Graph is plotted between current and frequency.4. From the graph, resonant frequency is determined and compared with that of

theoretical value.

OBSERVATION:TABLE: RLC SERIES CIRCUIT

S.No. Frequency (Hz) Current(mA)

RESULT:

Thus the frequency response of RL, RC, and RLC circuits are studied.


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3. (i) LOAD CHARACTERISTICS OF DC SHUNT MOTOR

AIMTo conduct the load test and determine the performance (load) characteristics of DC

shunt motorNAME PLATE DETAILS

Name plate Details S.No

1.2.3.4.5.

APPARATUS REQUIRED

S.No Apparatus Type and Range Quantity1. Rheostat 400 ohm/1.5A 12. Ammeter (0-10)A, MC 13. Voltmeter (0-250)V,MC 1

FUSE RATING CALCULATIONFuse rating=120% of the rated current

CIRCUIT DIAGRAM

THEORYIn a DC Shunt motor, the field winding is connected across the supply and hence is

almost constant. Hence the shunt motor has almost constant speed characteristics. Also Ta isdirectly proportional to armature current. Hence, the torque Vs armature current ) Output)


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characteristic will be a straight line. From the expression Eb= V-IaRa, It is evident that as loadincreases, armature current increases, IaRa Drop increases thus reducing Eb.

Speed N = V-IaRa/K = Eb/K.Where K is a constant. From the relation it is clear that as load increases, speed decreases.Hence the speed characteristics will be drooping in nature.

The efficiency of a DC Shunt motor is given by the ratio of output to input . Output canbe ca lculated as 2 NT/60. Input is calculated as the product of input voltage and input current.

As load increases, efficiency increases and at a particular load, maximum efficiency is reached.DC shunt motors are used is situation where the speed has to be maintained

approximately constant between no load and full load. It is also used in situation where avariable load is to be driven at different speed but at each load, the speed is to be kept constant.Since the power is wasted to do this test, it is suitable only for small capacity motors.MODEL GRAPH

PRECAUTIONS

Keep the Field rheostat in the minimum resistance position before starting. Keep the starter in OFF position. Do not start the motor under loaded condition and release the load before stopping. Pour water in brake drum to prevent it from overheating. Make sure that all the meters connected are moving coil type.

PROCEDURE

Make the connection as shown in the circuit diagram. Observing all the precautions, start the motor with the help of the three point starter. With the help of field rheostat, adjust the speed of the motor circuit. Apply the load gradually, in steps, till the motor draws 120% of the rated current from the

supply and at each step note the meter readings, speed and the spring balancereadings.

Release the load and bring back the motor filed rheostat to minimum position andswitch off the motor


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OBSERVATION TABLEVoltagein Volts

Currentinamps

Speedin rpm

Springbalancereadings

Torquein Nm

Input Output % Speedregulation

S 1 S 2

FORMULAE USEDInput= Input voltage X Input Current = VI WattsOutput = 2 NT/60 Watts Torque = ( S 1~ S 2) X 9.81 X R N-m

Where S 1 and S 2 are spring balance readings in KgR is the radius of the brake drum in meter

% Efficiency= Output/ Input *100% Speed Regulation = N no load - N full load / N no load

RESULTThe load test is conducted on DC shunt motor and its characteristic curves are drawn


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3 (ii) LOAD CHARACTERISTICS OF DC SERIES MOTOR

AIMTo conduct the load test on the given dc series motor and draw the performance curves

NAME PLATE DETAILSName plate Details

S.No 4.5.6.7.8.

APPARATUS REQUIRED

S.No Apparatus Type andRange

Quantity

1. Voltmeter (0-250)V 12. Ammeter (0-10)A 1

FUSE RATING CALCULATIONFuse rating=120% of the rated current

CIRCUIT DIAGRAM(Note:Leave space for this circuit diagram on the left side of yourrecord)


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THEORYFor a series motor the flux is proportional to armature current. The expression for speed

of a dc series motor is given as N = V- IaRa/k where k is a constant. If the input voltage isconstant, then speed is inversely proportional to armature current. Hence speed of the seriesmotor will be decreasing as load is increasing. If the series motor is allowed to run at light loador at no load, its speed will become much higher than the normal speed, which may causedamage to the motor. For this reason, series motors are never started on no load and not usedin applications where there Is a chance of the load being completely removed when the motorremains connected to the supply.

The relat ion for torque is given as Ta = kIa or Ta = kIa2, since flux is directlyproportional to armature current. Hence,the torque Vs armature current (output) characteristicswill be in the form of a parabola with increase in armature current the flux also increases linearlyupto the saturation of the magnetic core. Beyond saturation, increase in flux with armaturecurrent is negligible. Thus, beyond saturation, point torque also varies linearly with change inarmature current. Series motor has got very high starting torque and hence it is used in electrictrains, hoists, trolleys, etc.

As the load increases efficiency increases and at a particular load, maximum efficiencyis reached.

MODEL GRAPH

T, ,N %

T (Nm)

N (rpm)

Output(watts)

PROCEDURE

Make the connection as shown in the circuit diagram. Observing all the precautions, start the motor with the help of the two point starter.

Note the initial readings of motor including the spring blance readings Load the motor in steps till the motor draws rated current from the supply and in each

step note the meter readings, speed and spring balance readings. Switch off the motor with load


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Voltage(Volts)

Current(amps)

Speed(rpm)

Spring balancereadings

TorqueNm

Inputwatts

Outputwatts

% SpeedRegulation%S 1 S 2

Formula used:Input = input voltage x Input current = VI (watts)Output = 2NT/60 (watts) Torque = (S 1~S 2)x9.81xR (Nm)Where S 1 and S 2 ar spring balance readings in kgR is the radius of the brake drum in meter%Efficiency =( output/input ) x 100

Result:Therefore, the load test was conducted and performance was determined


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4. SPEED CONTROL OF DC SHUNT MOTORAIM

To control the speed of DC shunt motor by(1)armature control method(2)flux controlmethod.NAME PLATE DETAILS


3.4.5.6.7.

APPARATUS REQUIRED

S.No Apparatus Type and range Quantity1. Rheostat 800 ohm/0.8A 1

500 ohm/4.5A 12. Ammeter (0-2)A,MC 13. Voltmeter (0-250)V, MC 1

FUSE RATING CALCULATION120 % of the rated current

CIRCUIT DIAGRAM

PRECAUTIONS Before closing the field rheostat is to be kept in minimum resistance position and

armature circuit series rheostat has to be kept in maximum resistance position. All meters are to be checked before giving connections.

THEORY


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The speed of DC shunt motor is given by relation N=Eb/, where N is the speed ofmotor, Eb is the back emf and is the flux per pole. So speed can be controlled by includingseries resistance in the armature circuit and also by including resistance in the field circuit. Thedifferent types of speed control of shunt motors are1.Variation of flux or flux control method

It is seen above that N` 1/.By decreasing the flux, the speed can be increased andvice versa. Hence, the name flux or f ield control method. The flux of a dc motor can be changedby changing Ish with the help of a shunt field rheostat. Since Ish is relatively small, shunt fieldrheostat has to carry a small current, which means IR loss is small, so that rheostat is small insize. This method is very efficient in interpolar machines, the speed can be increased by thismethod in the ration of 2:1.Any further weakening of flux, adversely affects the commutation andhence puts a limit to the maximum speed obtainable from this method.2. Armature or Rhoestatic control method:

This method is used when speeds below the no load speeds are required. As the supplyvoltage is normally constant, the voltage across the armature is varied by inserting a variablerheostat or resistance in series with the armature circuit. As the controller resistance isincreased, p.d across the armature is decreased thereby decreasing the armature speed. For aload of constant torque, speed is approximately proportional to the p.d across the armature

PROCEDURE Armature conrol method:

Connections are given as per the circuit diagram After connections are checked keeping the R 1 in minimum position R 2 in maximum

position supply switch is closed. Motor is started with the help of three point starter Adjust R 1 such that the ammeter reads some value Now vary R 2 and note down the reading of V, N and tabulate it.

Flux control method: Bring back R 1, R 2 to their original position. Adjust R 2 such that the voltmeter reads some value Vary R 1 and note the values of IF, N at each step, the voltmeter reading must be

maintained constant. A graph of N VS IF is drawn by taking N on y axis and IF on x axis.

TABULATION Armature control method:s.no If If

V(volts) N(rpm) V(volts) N(rpm)

Flux control method:s.no V V

If (amps) N(rpm) If (amps) N(rpm)


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MODEL GRAPH

RESULTThus the speed control of DC shunt motor is controlled by(1)armature control method(2)fluxcontrol method.


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5. LOAD TEST ON THREE PHASE INDUCTION MOTOR

AIM:To conduct the load test on the given three phase induction motor and to draw theperformance curves

NAME PLATE DETAILSName plate Details

S.No 1.2.3.4.5.

APPARATUS REQUIRED

S.No Apparatus Type and range Quantity4. Three phase

autotransformer1

5. Ammeter (0-5)A, MI 16. Voltmeter (0-500)V, MI 17. Wattmeter 500V, 5A 2

FUSE RATING CALCULATIONFuse Rating = 120% of rated current

CIRCUIT DIAGRAM


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THEORYThree phase induction motor is the most popular type of AC motor which runs essentially atconstant speed from no load to full load. It is very commonly used for industrial drives sinceit is cheap, robust, efficient and reliable. It has good speed regulation, high starting torqueand requires maintenance. It has a reasonable overload capacity.

The main parts of induction motor are stator and rotor. The stator carries three phasewinding and it is placed in the slots for defnite number of poles. When the stator is suppliedwith three phase supply, a revolving flux of constant magnitude but rotating withsynchronous epdd given by Ns = 120f/P is obtained. This flux sweeps through the air gapbetween the stator and the rotor and induces an emf in the rotor by mutual induction. Thisemf induces a current in the rotor circuit which opposes the main field and thus the rotorrotates. The rotor may be of squirrel cage or wound type.

The difference between synchronous speed of stator flux and the actual rotor speed iscalled slip.

The characteristics of induction motor can be studied by conducting load test on the givenmotor. From the figure, it is evident that torque increases linearly and power factor alsoincreases with load. The speed slightly decreases and slip correspondingly increases withthe load.

FORMULAE USEDInput power to the motor = W 1+W 2(watts)Where W 1, W 2 are wattmeter readingsPower factor cos = input power/ 3 (V1*I1)Where V 1 = Line voltage in voltsI1 = Line current in ampsTorque T = (S 1~S 2)*r*9.81 Nm

Where S 1,S 2 = spring balance readings (Kg)R = Radius of the loading drum (m)

Output power = 2NT/60 watts Where N = Speed of the motor (rpm)

T = Torque (Nm)Efficiency , = Output power/Input Power *100 % slip = (Ns N)/Ns * 100%

Where Ns = Synchronous speed (rpm)

PRECAUTIONS1. Ensure that TPST switch is kept in OFF position2. Before starting, the motor should be on no load3. Make sure that all the meters connected are moving iron type


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PROCEDURE

1. Make the connection as shown in figure2. Observing all the precautions, switch ON the supply and start the motorusing a star delta starter3. Note down the no load readings4. at no load, one of the wattmeter will show negative deflection5. Stop the motor and interchange the connections of the terminals M and L.

Again start the motor following the above procedure6. Take the wattmeter reading as negative for which the connections arereversed7. Gradually increase the load in steps and observe the meter readings,speed and spring balance reading, till the current r eaches 120% of its rated value 8. Release all load from the motor and switch off the power supply9. Tabulate the reading and determine the performance in both the cases

MODEL GRAPH

QUESTIONS (Note: No need to write these questions in record)1. Why one of the wattmeter shows negative reading at no load?2. What are the various losses occurring in the induction motor?3. What is the nature of power factor curve with load current?4. what are the different types of starting methods of three phase

induction motor?5. Which types of speed control has the advantage of improving the

starting torque?6. What happens to motor if one of the phases goes off suddenly?

7. What is meant by slip in an induction motor? Why just slip bepresent for motor action?

8. Why does the rotor of an induction motor turn slower than therevolving field?

9. What is the difference between cage and wound rotor?10. If we double the number of poles on the stator of induction motor,

will its synchronous speed also double? 11. What is the normal value of slip of induction motor at full load?12. How will you change the direction of rotation of induction motor?


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RESULT

Thus the load test on three phase induction motor was conducted and thecharacteristics curves were drawn.


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6. TRANSFER FUNCTION OF SEPARATELY EXCITED DC GENERATOR Aim:To obtain the transfer function of separately excited DC generator


1.2.3.4.5.

Apparatus Required:

S.No Apparatus Type & Range Quantity 1. Rheostat 300/1.2A 1 2. Ammeter (0-2A)MC 1

(0-2A)MI 1 3. Voltmeter (0-300V)MC 1

(0-30V)MI 1


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TO FIND LF AND RF

PRECAUTIONS1. Motor field rheostat, should be in minimum position.2. Generator field rheostat should be kept in maximum position

PROCEDURETo find Kg

1. Give the connection as per the circuit diagram2. To perform the OC test bring motor to rated speed3. Vary the potential using the potential divider and note the field current and generated

emf4. Using the formula obtain the value of Kg


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To find Rf1. Give the connection as per the circuit diagram2. The dc supply is given3. Using potential divider assembly vary voltage across the coil and note down the

corresponding values of current

4. Using ohms law find the value of resistance of the coilTo find Lf

1. Give the connections as per the circuit diagram2. Vary the potential divider and note down the corresponding values of current3. The ratio of voltage to current gives the impedance of circuit4. From the value of Zs and Rf, Xf is calculated5. From the value of Lf, Xf is calculated

TABULATIONTo find Kg

S.No If(A) Eg(V) 1.2.3.4.5.

To find RfS.No Vf(Volts) If(Amps) Rf = Vf/If

To find ZfS.No V(Volts) I(mA) Zf = (V/I)

FORMULAETransfer function of a separately excited DC generator

Kg/Rf

Ls1+s

Rf


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Where Kg = Eg (from OCC) If

Rf = field resistance in

Lf = field inductance in HVf

Rf = If

Zf = V

IXf = Zf2 Rf2

Lf = Xf

2f

RESULT

Thus the transfer function of a separately excited DC generator is determined

eee lab manual part i

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