ee 101all experiments

PEE 101: Electrical Science Laboratory Spring Semester 2009 10

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FOR EXPERIMENTS IN ELECTRICAL SCIENCE (EE 101) The safety precautions are of utmost Importance: 1. While coming to laboratory make sure to be in proper shoes and no loose cloth. 2. Make sure while making the connections, no connecting wire is too long or too short. The

connections must be got checked by a supervising staff before a circuit is energized. 3. Before changing any connections the circuit must be de-energized (switched off mains). 4. The ratings of all components of electrical circuit including the leads used should be such that they

can withstand the maximum current/ voltage during the experiments. 5. The rating of measuring instruments should be chosen such that most of the readings are between

25 - 27% of the range of the Instrument. Also make sure that the polarity of the instruments is correct.

6. In circuits which carry heavy starting current, a short circuiting switch should be connected across the current coils of the Instruments.

7. In certain experiments, some conditions should be satisfied before the machine can be started or the circuit can be energized e. g. in starting shunt motor, the external resistance in the shunt field circuit must be set to a minimum.

Report Writing: 1. You are provided with the format for submitting the report of each experiment to be performed

except experiment No. A 1 which is descriptive one. 2. Students should prepare one separate lab. note book for record in the laboratory. 3. The students should come prepared for the experiment to be done. They must clear any doubts

they have by discussing with the staff. Any special precaution will be explained to them by the laboratory staff.

4. The students must read the background theory of the experiment to be performed before coming to perform the experiment. They should note the object, equipments used in the format provided, circuit diagram, brief theory before coming to laboratory for performing the experiment in the lab. note book. Any student without prior preparation will not be allowed to perform experiment.

5. The students must record the observations in the lab. note book neatly in a tabular form taking care that adequate number of observation are recorded for plotting graphs etc. A minimum seven observations (and often more) are needed to plot a graph. They are advised to repeat at least two observations after taking a series of observations to improve the accuracy. The method of least squares should be adopted for plotting the curves. The students must get one or two observations checked and initialed by the staff.

6. Complete all the entries in the format along with answers for the report questions given and submit it for evaluation on the next time when you come to laboratory after performing experiment. Any late submission will not be evaluated and for that experiment zero marks will be awarded.

7. The students are expected to go through the Indian Standards IS:12032 available on http://192.168.125.8/ and use the standard symbols given there while drawing the circuit diagram.


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Date: Name : Batch :

Experiment No. A 1: Familiarization of the laboratory and apparatus.

Objectives: In this experiment the students are expected to familiarize him/ her with the laboratory, layout, devices, power supplies, various types of meters and auxiliary apparatus. Report: The report should contain the general information and the circuit diagram where necessary about the following:

1. The types of electrical power supplies in the laboratory their voltages and frequency. 2. The function of circuit breaker, fuse and various types of switches used in the laboratory. 3. The types of connecting wires used in the laboratory. 4. The function and connections of a rheostat. 5. The function and connections of a lamp load. 6. The function and connections of a voltmeter, ammeter and wattmeter. 7. The types of DC machines available in the laboratory. 8. The types of AC machines available in the laboratory. 9. The function of auto transformer and transformer. 10. The meaning of the rating of an electrical machine or a component. 11. The function of a tachometer.


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Experiment No. A 2: Study of speed reversal and speed control of a dc shunt motor

Objectives:

1. To study the speed reversal of a dc shunt motor. 2. To study the speed control of a dc shunt motor by armature resistance control. 3. To study the speed control of a dc shunt motor by field resistance control.

Apparatus and Equipments used:

Sr. No. Equipment Range/ rating Make

220 VDC

F1

F2

A1

A2

AL F

A

V

+

-

0-2 A

0-250 V

R2750 ohm/5 A

R1300 ohm/

3 A

Figure 1: Circuit Diagram for speed control of dc shunt motor

Theory: The speed of a dc motor is directly proportional to the back e. m. f. Eb and inversely proportional to the net flux per pole . If brush contact drop is neglected, the speed of a dc motor can be represented as

aatab

RIVK

IRRVK

EKN 111

)(

Where, N = speed of the motor, V = Voltage applied across the armature circuit, Ra = Armature resistance, R1 = external resistance, Ia = Armature current, K1 = a constant


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Thus the speed of a dc motor may be varied by either of the following adjustments: 1. Changing the flux per pole , by varying the field current. 2. Changing R1, external resistance in the armature circuit. 3. Changing the applied voltage V.

In this experiment only first two methods are used to control the speed. Reversal of the speed may be achieved either by changing the F1 and F2 or by changing the A1 and A2. Procedure: Speed reversal of dc shunt motor

1. Connect the circuit as shown in figure 1. Set R1 and R2 at zero resistance value. 2. Start the motor and observe the direction of speed. 3. Switch off the motor and change the F1 and F2 terminals or change the A1 and A2 terminals. 4. Again start the motor and observe the direction of speed.

Speed control of dc shunt motor 1. Connect the circuit as shown in figure 1. Set R1 and R2 at zero resistance value. 2. Start the motor. When motor speed becomes steady, record speed, field current and voltage across

the armature. 3. Change the field resistance R1 in small steps and record field current and speed in observation table

1. (Normally the run should be continued up to about 120% of the rated speed) 4. Again reduce field resistance R1 to zero and check speed and voltage across the armature. 5. Gradually increase the external armature resistance R2 and record speed and voltage across the

armature in table 2, for different R2 values. 6. Stop the motor and switch off the mains.

Observations:

Table 1: Speed and field current record for Field resistance control

Sl. No Field Current (If) Speed in rpm

1

2

3

4

5

6

7

Table 2: Speed and Armature voltage record for external armature resistance control

Sl. No Armature Voltage (V) Speed in rpm

1

2

3

4

5

6

7

Results

Observe the speed reversal either by changing the F1 and F2 or by changing the A1 and A2.

Plot speed as a function of field current from the observation table 1.

Plot speed vs. armature voltage from the observation table 2.


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Report Questions:

1. An increase in field resistance R1 increases the motor speed above rated while an increase in armature resistance R2 decreases the speed below rated, Explain.

2. What is the need of a starter? 3. The field control of speed of a dc shunt motor gives a constant power drive, whereas armature

voltage control gives a constant torque drive, explain.


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Experiment No. A 3: Study the performance of RLC circuits and series resonance

Objectives: 1. To study the behavior of a resistor, capacitor and inductor in a series ac circuit and draw the phasor

diagram of the circuit. 2. To study resonance in RLC series circuit.

Apparatus and Equipments used:


50 Hz

N

A

VV V

V

230V AC

L

( 0 - 300V)( 0 - 600V)( 0 - 500V)( 0 - 150V)

M L

C V

R L C

P

N

( 0 - 5A)

5A, 300VUPF

Circuit Diagram for RLC series circuit

Theory: For a series RLC circuit, Kirchhoffs rules demand that the current be same throughout. Furthermore, the voltages across each element must combine to equal the source voltage. However, each element also has a unique phase relation between the voltage and the current, so the voltages must add according to the rules for combining phasors for the circuit. If we look at each element in turn we can investigate the individual behavior and then the collective behavior of the elements in the circuit. For example, the capacitors potential difference is determined by the charge on it, while the current is the rate of change of charge. This fact leads to a phase difference between current and voltage of 90o with the potential difference lagging the current by that phase angle. The effective potential difference across the capacitor VC equals the effective current I times the capacitive reactance XC.


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Procedure: Make connections as shown in Figure. Make sure that series connections are done first and then parallel connections. Gradually increase the output of auto transformer to 230 V. Make sure that the readings of the measuring instruments are not exceeding their ranges. Record the observations as shown in Table. In table, VR is the voltage across resistance, VL is the voltage across the inductor and VC is the voltage across the capacitor. Two sets of readings must be taken without changing the inductance. For resonance, reduce the source voltage to a range 80- 100V, and vary the inductance and capacitance to make the voltages across them equal. At resonance, the current I in the circuit will be maximum.

Sr. No.

Supply Voltage VS

(V)

Current I (A)

Power P (W)

VR (V)

VL (V)

VC (V)

R ()

C (F)

1

2

3

4

5

6

7

Analysis: 1. Determine the current in the circuit by calculating the current in the resistor.

______ ARV

IR

2. Determine the inductance of the circuit from its reactance, the current calculated above, and the frequency of the supply voltage.

______L LV

XI

and __________ H2

LXLf

3. Determine the phase between the supply voltage and the current and also determine power

factor cos .

4. Draw phasor diagrams for two sets of readings. 5. Write discussions on your results. Report Questions: 1. For the variable inductor used in the laboratory, how are we getting the variable inductance? 2. At resonance, the voltage across the resistor must be equal to the supply voltage. Are you getting the

same in your experiment? If not explain the reason. 3. What is the effect of value of resistance in the resonance experiment?

..............................tan 1

R

CL

V

VV ...........cos


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Experiment No. B 1:To Study the operation of Single phase transformer and to find out its equivalent

circuit parameters & obtain performance there from. Objectives: 1. To perform open circuit and short circuit tests on a single-phase power transformer in order to

determine its parameters of the approximate equivalent circuit. 2. To perform load test at rated KVA and unity power factor. Apparatus and Equipments used:


S

A

V

230 V AC

supply

50 Hz

P

N

0-270V

15A

(0-300V)

(0-2.5A)

230V:110V

2.5A

300V

LPFM L

VC

P

Figure 1: Circuit diagram for Open Circuit Test of transformer (Secondary open circuited)

S

A

V

230 V AC

supply

50 Hz

P

N

0-270V

15A

(0-30V)

(0-5A)

230V:110V

5A

75V

UPFM L

VC

P

L

N

Figure 2: Circuit diagram for Short Circuit Test of transformer (Secondary short circuited)


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S

A

V

230 V AC

supply

50 Hz

P

N

0-270V

15A

(0-300V)

(0-5A)

230V:110VM L

VC

P

L

N

A

V(0-150V)

(0-10A)

Lamp

Load

10A

230V

Figure 3: Circuit diagram for Load Test of transformer

Thick Connecting wires

Thin Connecting wires

Figure 4: Approximate equivalent circuit of single phase transformer

Theory: Transformer is a device, which transfers electrical energy from one circuit to another circuit without any conductive coupling between them. The two circuits are magnetically coupled to each other. Therefore, it consists of two types of circuits one magnetic and other electrical. Magnetic circuit (core) is made up of ferromagnetic material, which is generally electrical steel (iron). In this core flux circulates and links with the two electrical circuits placed on it. The electrical circuits are made up of copper windings. Although now a days anodized aluminum is also used. Both the circuits do have some losses. The losses in the magnetic circuits are called iron loss and the in the windings of transformer are called copper loss. Since the value of flux in the core is function of V/f ratio, and is independent of the load on the transformer, hence these are constant. These losses are very small as compared to the copper loss at rated load. On the other hand the copper losses are dependent on the amount of current in the two windings or load on transformer. Therefore, from open circuit test shunt parameters of the equivalent circuit can be estimated and that from the short circuit test series parameters can be estimated. These parameters can be used to calculate the efficiency and voltage regulation of transformer at any load condition. The voltage regulation and efficiency at unity power factor can be calculated from the following expressions:

% Voltage Regulation (%VR) = %100,2

,2,2X

V

VV

FL

NLFL = %100])(

2

1[ 2

1

1

1

1X

V

XI

V

RI eqeq

% efficiency = pperLossFullLoadCoIronlossVArating

VARating

Req Xeq

RC Xm


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Where, NL stands for no load and Fl stands for full load Procedure: (a) Open Circuit Test:

Connect the ammeter, voltmeter and wattmeter in the primary winding of the transformer as shown in figure 1. Keep the secondary winding of the transformer open. Energize the primary winding through an auto transformer such that rated voltage is applied to this winding. Note the readings of voltmeter, ammeter and low power factor wattmeter.

OC

OC

I

VZ 0

mmCROC XIRIV

OCOC

OC

IV

PCos 0

0CosII OCR

0SinII OCm

R

oc

I

V

CR

m

oc

I

V

mX Where, POC is wattmeter reading at rated voltage and secondary side open circuit. VOC is applied rated voltage IOC is ammeter reading for open circuit test Cos 0 is no load power factor (b) Short Circuit Test:

Connect the ammeter, voltmeter and wattmeter in the primary winding of the transformer as shown in figure 2. Short the two terminals of the secondary winding with a shorting link. Energize the primary winding through an auto transformer such that rated current circulates in this winding. Note the readings of voltmeter, ammeter and wattmeter.

SC

SC

I

V

eqZ

2

SC

SCeq

I

PR

22

eqeqeq RZX

Where, PSC is wattmeter reading at rated current and secondary side short circuited. VSC is applied primary voltage for rated current in primary winding ISC is ammeter reading for short circuit test

(c) Load Test:

Make connections as shown in figure 3. Set the input voltage equal to the rated voltage. Gradually increase the load by switching on the lamp load switches till it reaches the rated current. Adjust the input voltage such that it always remains equal to the rated voltage. For every increase in load note applied voltage, current and power in primary circuit and secondary voltage and load current.

Observations:

VOC Rc

IOC

IR Im

Xm


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(a) Open Circuit Test: Multiplication factor of wattmeter = POC = VOC = IOC =

(b) Short Circuit Test: Multiplication factor of wattmeter = PSC = VSC = ISC =

(c) Load Test: Multiplication factor of wattmeter =

Sr. No. Primary Side Readings Secondary Side Readings

Voltage (V) Current (I) Power (W) Voltage (V) Current (I)

1.

2.

3.

4.

5.

6.

7.

8.

9.

10.

Results:

1. From the open circuit and short circuit tests calculate the parameters of the equivalent circuit of transformer.

2. Calculate percentage regulation at unity power factor and rated KVA from OC and SC test parameters.

3. Calculate the efficiency and voltage regulation at UPF and rated KVA from load test. Report Questions:

1. Why generally open circuit test is done by connecting voltage to low voltage side and short circuit test by shorting on low voltage side?

2. Why low power factor (LPF) wattmeter is connected for open circuit test? 3. What is the significance of voltage regulation? Should it be low or high? 4. Why Xm is far greater than Xeq?


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Experiment No. B 2(i): Squirrel Cage Induction Motor

Objectives: a. To study three phase star delta starter of three phase squirrel cage induction motor.

b. To determine performance characteristics of a three phase squirrel cage induction motor by load

test. Apparatus and Equipment Used:


3-p

has

e M

ain

s4

00

V/5

0H

z

V

A

SPDT0-600 V

0-10 A10 A, 600 V, UPF

Star/ Delta Starter

W1 W2

L1

L2

L3

M L

C V

I1

T1 T2

Brake Drum(Load)

IM

A1

A1

A2

A2

B1

B1

B2

B2

C2

C2

C1

C1

Figure 1: Starting and Load Test of Squirrel Cage Induction Motor using start Delta Starter

Procedure: Following steps should be followed:

1. Make connections as shown in figure 1. 2. Remove load i.e. T1 = T2 = 0. 3. Put on 3- Phase mains.


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4. Move the handle of Star- Delta starter to Star position and hold it in that position; the motor starts and picks up speed; move the handle in Delta position. Now leave the handle, it stays in Delta position.

5. The motor is now running normally under no-load. 6. Load the motor gradually and note the readings

Observations: (a) Name Plate Data of Motor (Power, Voltage, Current, Speed): (b) Multiplying factor of Wattmeter : (c) Supply voltage (L-L) V1 : (d) Radius of Brake Drum in meters (r) :

Table of Observations:

Sr. No.

I1 W1 W2 W= W1+ W2 T1 (kg) T2(kg) Speed (rpm)

1

2

3

4

5

6

7

Calculations:

Sr. No.

I1 (A) Wtotal=W*M.F. (Watts)

Speed(N) (rpm)

Torque*(T) (N-m)

Power Factor

Output Power*(Po)

(Watts)

Efficiency

1

2

3

4

5

6

7

*T = (T1 T2)*r*9.81 Nm Po = (2**N*T)/60 Wtts Report: Draw the following characteristics:

1) Speed v/s Power output 2) Power factor v/s Power output 3) Efficiency v/s Power output 4) Input current v/s Power output


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Experiment No. B 2(ii): Slip Ring Induction Motor

Objectives: a. To study three phase Rotor resistance starter of three phase Slip Ring Induction Motor. b. To determine performance characteristics of a three phase slip ring induction motor by load test.

Apparatus and Equipment Used:


Rotor Resistance Starter

3-p

has

e M

ain

s4

00

V/5

0H

z

V

A

SPDT0-600 V

0-10 A10 A, 600 V, UPF

W1 W2

L1L2L3

M L

C V

I1

T1 T2

Brake Drum(Load)

Slip Ring IM

Rotor(Slip Rings)

Stator

To Slip Rings

To Stator

Figure 2: Starting and Load Test of Slip Ring (or wound rotor) type Induction Motor using Rotor

Resistance Starter Procedure: Following steps should be followed:

1. Make connections as shown in figure 2. 2. Remove load i.e. T1 = T2 = 0. 3. Put on 3- Phase mains. 4. Move the handle of Rotor Resistance starter gradually to cut the resistance; the motor starts and

picks up speed; Now leave the handle. 5. The motor is now running normally under no-load.


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6. Load the motor gradually and note the readings

Observations:

(a) Name Plate Data of Motor (Power, Voltage, Current, Speed): (b) Multiplying factor of Wattmeter : (c) Supply voltage (L-L) V1 : (d) Radius of Brake Drum in meters (r) :

Table of Observations:

Sr. No I1 W1 W2 W= W1+ W2 T1 (kg) T2(kg) Speed (rpm)

1

2

3

4

5

6

7

Calculations:

Sr. No I1 (A) Wtotal=W*M.F. (Watts)

Speed (N) (rpm)

Torque* (T) (N-m

Power Factor

Output Power* (Po)

(Watts)

Efficiency

1

2

3

4

5

6

7

*T = (T1 T2)*r*9.81 Nm Po = (2**N*T)/60 Wtts

Report: 1) Draw the following characteristics: 2) Speed v/s Power output 3) Power factor v/s Power output 4) Efficiency v/s Power output 5) Input current v/s Power output


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Experiment No. B 3: To Study the load test on D.C. shunt generator and to draw following

characteristics: Objectives:

1. To perform the load test on D.C. shunt generator in order to determine efficiency of the motor generator set (MG set) V/s output power.

2. Motor current V/s output power. 3. Input current V/s output current. Apparatus and Equipment Used:


A

V

+

_

L F A

(0300 V)

22

0 V

DC

Su

pp

ly

(030 A)

(300 Ohm/ 3 A)

RFMF1

F1

F2F2 A2 A2

A1A1

(0300 V)

RFG

(300 Ohm/ 3 A) (020 A)

A

Lam

p L

oad

20

A/2

30

V

V

Figure 1: Circuit diagram for load test on D.C. shunt Generator Theory: The self-excited D.C. shunt generator is coupled to a DC motor, which acts as prime mover. Voltage and current relationships for D.C. shunt generator are as follows:


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brushaat

sh

tsh

shLa

VRIVE

R

VI

III

Where

load noat emf Generated

drop ageBrush volt

resistance ArmatureR

resistance fieldShunt R

voltageTerminal

current fieldshunt

current Load

current Armature

a

sh

E

V

V

I

I

I

brush

t

sh

L

a

Two characteristics are more important. The internal or total characteristic that gives the relation between the emf actually induced in the armature and the armature current. This is of interest mainly to the designer. The external characteristics called performance characteristics (also voltage regulating curve) which give the relation between the terminal voltage and load current. This curve lies below the internal characteristics due to armature drop. This is important in judging the suitability of a generator for a particular purpose. These characteristics can be obtained by a load test with total field resistance remaining fixed as the speed is to be kept constant. Procedure: Circuit diagram for load test on D.C. shunt Generator is shown in Figure 1.

1. Before starting the motor ensure that: (a) There is no external resistance in the motor field circuit i.e. resistance RFM is zero. (b) The external resistance in the generator field circuit i.e. resistance RFM is a maximum. (c) There is no load on the generator i.e. all the switches of lamp load are in off position.

2. Start the motor and bring it to the rated speed of the generator by adjusting the rheostat RFM and checking the speed with the help of the tachometer.

3. Adjust the rheostat RFG to obtain the rated voltage of the generator. Check this with the help of the voltmeter connected to generator terminals.

4. Load the generator by switching on one switch of the lamp at a time. 5. Maintain the speed constant. 6. Note the reading of voltmeters and ammeters. 7. Report steps (4) to 6 till full load current of the generator is obtained.

If the current drawn by the motor reaches its rated value before the generator rated current is obtained, terminate the experiment then and there only. Do not exceed the load current of motor or generation.


Page 18 of 18

Observations:

Sr. No.

Input Output Speed (r.p.m)

Current (IM) Voltage (VM) Current (IG) Voltage (VG)

1.

2.

3.

4.

5.

6.

7.

8.

9.

10.

Results:

From the load- test on D.C. shunt generator obtain the followings

1. Input Power = MM IV Watts

2. Output Power= GG IV Watts

3. Calculate the percentage efficiency of the D.C. shunt generator. Report Questions:

1. What is difference between a generator and a motor? 2. Which part of D.C. machine is laminated? Why? 3. Explain the necessity of starters for starting of D.C. shunt motors. Describe the principle of

functioning starters. 4. Plot the following curves

i. Efficiency of MG set Vs output power. ii. Motor current Vs output power

iii. Voltage Vs current Explain the nature of characteristics obtained.

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