ET Lab Manual

Department of Electrical and Electronics Engineering II Year B. Tech. II Sem Electrical Technology Lab Manual Sl. No.

Name of the Experiment Section – Section – A A ( Networks Lab )

1

Verification of Kirchhoff ’s Voltage and Kirchhoff’s Current Law

2

Verification of Thevenin’s and Norton’s Theorems

3

Verification of Maximum Power Transfer Theorem

4

Verification of Superposition and Reciprocity Theorems

5

Determination of two-port network parameters (Z & Y)

6

Determination of two-port network parameters (ABCD & H) Section – Section – B B ( Electrical Machines Lab )

7

Magnetization characteristics of D.C. Shunt generator. Determination of critical field resistance.

Swinburne’s Test on DC shunt machine (Predetermination of 8

9

10

efficiency of a given DC Shunt machine working as motor and generator). Brake test on DC shunt motor. Determination of performance characteristics OC & SC tests on Single-phase transformer (Predetermination of efficiency and regulation at given power factors and determination of equivalent circuit)

BEYOND THE SYLLABUS 11

Series and Parallel Resonance

12

Load Test on a Single Phase Transformer

1. Verification of Kirchhoff ’s Voltage and Kirchhoff’s Current Law AIM: To verify the Kirchhoff’s Voltage Law and

Kirchhoff’s Current Law for a given circuit.

APPARATUS REQUIRED:Sl.

Name of the Component

Specifications

Quantity

1

Resistors

1.1KΩ, 2.2KΩ & 3.3KΩ

1 each

2

Bread Board

-

1

3

D.R.P.S.

(0-30) V

1

4

Ammeters

(0-200)mA

3

5

Voltmeters

(0-30)V

3

6

Connecting wires

Single strand

Required

No.

CIRCUIT DIAGRAM:

1. Verification of Kirchhoff ’s Voltage and Kirchhoff’s Current Law AIM: To verify the Kirchhoff’s Voltage Law and

Kirchhoff’s Current Law for a given circuit.

APPARATUS REQUIRED:Sl.


Specifications

Quantity

1

Resistors

1.1KΩ, 2.2KΩ & 3.3KΩ

1 each

2

Bread Board

-

1

3

D.R.P.S.

(0-30) V

1

4

Ammeters

(0-200)mA

3

5

Voltmeters

(0-30)V

3

6

Connecting wires

Single strand

Required

No.

CIRCUIT DIAGRAM:

PROCEDURE FOR KCL:-

1. Connect the circuit as per the figure shown above. 2. Adjust the input voltage as 10 volts, and switch on the supply. 3. Measure the current flowing through R1, R2, R3 resistors using Ammeters i.e., IT, I1 & I2. 4. Tabulate the readings in the tabular column. 5. Verify that the IT = I1 + I2. 6. Repeat the procedure for different voltage values, and then switch off the off the supply. 7. Compare the values Practical to Theoretical. Th eoretical. PROCEDURE FOR KVL:-

1. Connect the circuit as per the figure shown above. 2. Adjust the input voltage as 10 volts, and switch on the supply. 3. Note the reading of ammeter am meter & voltmeters, i.e., I, V1, V2 &V3 from the voltmeters. 4. Tabulate the readings in the tabular column. 5. Verify that the V1 = V2 + V3.

6. Repeat the procedure for different voltage values, and then switch off the off the supply. 7. Compare the values Practical to Theoretical. Th eoretical.

THEORETICAL CALCULATIONS:For KCL:

R eq eq = (R 2 ║ R 3) + R 1 Ieq = V1 / R eq eq I1 = Ieq * R 3/ (R 2+R 3) I2 = Ieq * R 2/ (R 2+R 3)

For KVL:

For measuring Voltage V2 across R1 R eq eq = (R1+R2) Ieq = V / Req V2 = V * R 1 / (R1 + R2) or V 1=I*R 1 V3 = V * R2 / (R1 + R2) or V2=I*R 2 TABULAR COLUMNS: For KCL: S.No

V1(volts)

IT(mA)

IT(mA)

I1(mA)

I1(mA)

I2(mA)

I2(mA)

theoretical

practical

theoretical

practical

theoretical

practical

V1(volts)

V1(volts)

V2(volts)

V2(volts)

V3(volts)

V3(volts)

theoretical

Practical

theoretical

practical

theoretical

practical

For KVL: S.No

I(mA)

SAFETY PRECAUTIONS:

1. Reading must be taken without parallax error. 2. Measuring instruments must be connected properly & should be free from errors. 3. All connections should be free from loose contacts. 4. The direction of currents should be identified correctly.

RESULT:

VIVA VOCE QUESTIONS:

1. What is KCL? Define with respect to node. 2. What is KVL? Define with respect to loop. 3. On which principle KCL works? 4. On which principle KVL works? 5. What is equivalent resistance when three resistors are connected in series? 6. What is equivalent resistance when three resistors are connected in parallel? 7. Explain voltage division principle? 8. Explain current division principle? 9. What is equivalent resistance when converted from star to d elta network? 10. What is equivalent resistance when converted from delta to star network?

2. THEVENIN’S & NORTON’S THEOREMS Aim:

To verify Thevenin’s and Norton’s theorems.

Apparatus required:

S. No.


1

Resistors

2

Decade Resistance Box

10-1M

1

3

Multimeter

DMM

1

4

Dual Regulated Power Supply

(0-30) V

1

5

Ammeter

(0-20) mA

1

6

Voltmeter

(0-20)V

1

7

Bread board

8

Connecting Wires

Circuit diagrams: Thevenin’s Theorem:

R 1=

Specifications

Quantity

, R 2=

3

, R 3=

1 Single strand

As required

THEORITICAL CALUCLATIONS:

For the given circuits the resistors values are as follows For 10v supply: Finding Rth Rth=((R 1*R 2)/(R 1+R 2))+R 3=……….kΩ Finding Vth=Vapp*(R 2)/(R 1+R 2)=……….V Finding LOAD current ITH=VTH/(R TH+R L) Procedure:

1. Apply a DC voltage of 10 V from voltage source to be input terminals of the network and measure the output voltage Voc without load. 2. Connect the load at the output of the network and measure the current through the load. 3. Disconnect the voltage source and load, short the input terminals of the network and

4.

measure the Thevenin’s equivalent impedance at output terminals. Adjust the input voltage of the voltage source that is equal to Thevenin’s and a voltage and apply to the input terminals of the equivalent circuit.

5. Measure the load current IL and compare it to the theoretical value V1 and tabulate. Observations:

S. No.

1 2 3

I L

V th V I N V th (theo)

V th (prac)

I L (theo)

I L (prac)

Norton’s Theorem :

Procedure:

1. Apply the DC voltage of 10V from the voltage source to the input terminal of the network and measure the load current at the output of the network. 2. Apply the DC voltage of 10V and measure short circuit current I sc by short circuiting the load terminals. 3. Find Zth by disconnecting the voltage source and the load, short the input terminals of the

4. 5.

network and measure the Thevenin’s equivalent impedance at the output terminal. Draw the Norton’s equivalent circuits by connecting Zth in parallel with Isc Convert the Norton’s equivalent to the Thevenin’s equivalent circuit and measure load current with connecting load at output terminals and compare with I.

Theoretical calculations:

Finding R N R N= =((R 1*R 2)/(R 1+R 2))+R 3=……….kΩ Finding Total current=Vapp/R 1+((R 2*R 3)/(R 2+R 3)) =…………mA Finding Norton’s current= IT* (R 2*(R 2+R 3)) =…………mA Finding Load current= IT*(R N/(R N+R L)) =…………mA

Tabular Column:

I L

I N S. No.

V I N I N (theo)

1 2 3

Result:

VI VA QUE STI ONS: 1.

State Thevenin’s Theorem.

I N (prac)

I L (theo)

I L (prac)

the

2. What is the condition for reciprocity for a network? 3. What is an independent voltage source? 4. What is an independent current source? 5. Draw the symbols of all the dependent current and voltage sources. 6. 7. 8.

What is Thevenin’s voltage? What is Norton’s current? Write Ohm’s law.

9. Write the expression for the voltage and current through an inductor. 10. Write the expression for the voltage and current through the capacitor.

3. Maximum Power Transfer Theorem Aim :- To verify the power transferred to be maximum across the load using Maximum Power Transfer Theorem. Apparatus required :

S. No.


1

Resistors

2


10-1M

1

3

Multimeter

DMM

1

4


(0-30) V

1

5

Ammeter

(0-20) mA

1

6

Voltmeter

(0-20)V

1

7

Bread board

8

Connecting Wires

Circuit Diagram:

R 1=

Specifications

Quantity

, R 2=

3

, R 3=

1 Single strand

As required

Procedure :

1. Connect the circuit as shown in figure 2. Varying the load resistance in steps and note the ammeter readings and calculate power 3. Plot the graph by taking resistance on X – axis and power on Y – axis 4. Connect the circuit as in figure (b) 5. Varying V note the corresponding values of I 6. Rs = V / I 7. Rs should be equal to R L for maximum power transfer. Theoritical calculations:

For the given circuits the resistors values are as follows R1,R2, R3&RL=1K Ω For 10v supply: Finding Rth Rth=((R 1*R 2)/(R 1+R 2))+R 3=……….kΩ Finding Vth=Vapp*(R 2)/(R 1+R 2)=……….V Finding LOAD current ITH=VTH/(R TH+R L)

S.No

V I N V ( volts)

Load Resistance

Load Current I L

Load Power

R L ( )

(mA )

P L = I 2 R L watts

EXPECTED GRAPH:

Result :


1. State Maximum Power Transfer Theorem. 2. What is power? 3. What is the relationship between power and energy? 4. What is the difference between a DC and a AC voltage source? 5. What is current? 6. What is voltage or potential difference? 7. In what form energy is stored in an inductor and a capacitor? 8. Under what condition the source transfers maximum energy to th e load? 9. What do you mean by network analysis? 10. What do you mean by network synthesis?

4. Super position and Reciprocity Theorems Aim :- To verify Superposition and Reciprocity Theorem. Apparatus required :

S. No.


1

Resistors

2

Multimeter

DMM

1

3


(0-30) V

1

4

Ammeter

(0-20) mA

1

5

Voltmeter

(0-20)V

1

6

Bread board

7

Connecting Wires

Circuit Diagram :-

R 1=

Specifications

Quantity

, R 2=

3

, R 3=

1 Single strand

As required

Procedure : Superposition Theorem : 1.

Connect V1, V2 as shown in figure 1(a).

2.

For different V1 and V2 values

3.

4.

5.

note the ammeter reading as “IT” Replace ‘V1’ with a short circuit as shown in figure 1(b) and read the ammeter reading as “I2” for corresponding values of V2. Replace “V2” with a short circuit as shown in figure 1(c) and connect “V1” in the circuit and read ammeter reading as ‘I1’ for corresponding values of V1. IT = I1 + Ic

Observations Superposition Theorem :

S. No.

V 1 (Volts) Theo Prac


I T (mA) Theo Prac

1 2

S. No.


I 2 (mA) Theo Prac

S.No.

1

1

2

2


I 1 (mA) Theo Prac

THEORITICAL CALUCLATIONS FOR SUPERPOSITION THEOREM: Case-1 Form fig-1: Apply mesh analysis Total current(Through R 2) I= ………mA Case-2 Form fig=2: V1= 0, V2=20V Calculate Req=(R 1*R 2)/(R 1+R 2)+R 3=………KΩ

Total current I=V/R eq=………..mA Current(Through R 2)

I1=I*(R1/(R1+R2) )= …….mA

Case-3 Form fig-3 V1= 20V, V2=0V Calculate Req=(R 3*R 2)/(R 3+R 2)+R 1=………KΩ

Total current I=V/R eq=………..mA Current(Through R 2) I2=I*(R 3/(R 3+R 2) )= …….mA As per Super position Theorem, I=I1+I2 Circuit Diagram : Reciprocity Theorem

Procedure: 1. Connect the circuit as shown in figure 1(a).

2. Apply some voltage V. 3. Note down the ammeter ( 0 – 50 mA) reading as “I1” 4. Inter change ammeter and voltage source as shown in figure 1(b). and take the ammeter

reading as “I2” 5. Repeat the above procedure for different values or V and tabulate the values. 6.

I1 should be equal to I2.

THEORETICAL CALCULATION: For the given circuits the resistors values are as follows R1=1K Ω,2.2K Ω,1K Ω,RL=1K Ω Case-1 From fig-1: Calculate Req=(R 3*R 2)/(R 3+R 2)+R 1=………KΩ Total current I=V/R eq=………..mA Current (Through R 3) I2=I*(R 2/(R 3+R 2) )= …….mA Case-2

From fig-2 : Calculate Req=(R 1*R 2)/(R 1+R 2)+R 3=………KΩ Total current I=V/R eq=………..mA Current (Through R 1) I1=I*(R 2/(R 1+R 2) )= …….mA Result: VIVA VOCE QUESTIONS:

S. No.

V

I1

V

I2

1 2

S. No.

1 2

1. What is linear element? 2. What is a bilateral element? 3. What is KCL? 4. What is KVL? 5. What is the difference between a circuit and a network? 6. State Superposition Theorem. 7. State Reciprocity Theorem. 8.

What do you mean by equivalent resistance of a network?

9. What is the action performed by a short circuited vo ltage source in SPT verification? 10. If the network contains an independent current source how would you deactivate it while verifying the SPT?

5. Z and Y Parameters of a Two Port Network Aim:

To measure “ Z” and “Y” parameters of a given two port passive network

Apparatus required:-

S. No.


1

Resistors

2


10-1M

1

3

Multimeter

DMM

1

4


(0-30) V

1

5

Ammeter

(0-20) mA

1

6

Voltmeter

(0-20)V

1

7

Bread board

8

Connecting Wires

R 1=

Specifications

Quantity

, R 2=

3

, R 3=

1 Single strand

As required

Procedure : 1. Connect the circuit as shown in figure (1)

2. Keep port 2 open : I2 = 0 3. Set different voltages on V1. 4. Measure V2 and I1 and tabulate V1 , V2 and I1 5. Connect the variable voltage to port 2 and keep the port 1 open circuit i.e. I1 = 0 As shown in figure (2) . Measure V2, V1, I2 . Set different voltages at V 2 and measure I2 and V1 for each setting and tabulate. Circuit Diagrams:

Observations: When I2 = 0

V1

V2

I1

Z11

When I1 = 0

Z21

V2

30

30

25

25

When I2 = 0.

V1

I2

Z22

Z12

When I1 = 0

Z11 = V1 / I1

Z22 = V2 / I2

Z21 = V2 / I1

Z12 = V1 / I2

For Y- Parameters:

Procedure:

1. Connect the circuit as shown in figure (3) conne ct the variable voltage at port 1. Short circuit the port 2. By varying the V1 , note down the I1 , I2 and tabulate 2. Connect the variable voltage at port 2 short circuit the port 1 as shown in figure (4)

3.

By varying the V2 , note down the I1 , I2 and tabulate.

For Y – Parameters : When V2 = 0

V1

I1

I2

When V1 = 0

Y11

Y21

V2

Y11 = I1 / V1

Y22 = I2 / V2

Y21 = I2 / V1

Y12 = I1 / V2

I1

I2

Y22

Y12

CONCLUSION:

Z 11(Ω)

Z 11(Ω)

Z 12(Ω)

Z 12(Ω)

Z 22(Ω)

theoretical Practical theoretical Practical theoretical

Y 11(Ω)

Y 11(Ω)

Y 12(Ω)

Y 12(Ω)

Y 22(Ω)

Z 22(Ω)

Z 21(Ω)

Practical

Y 22(Ω)

Z 21(Ω)

theoretical Practical

Y 21(Ω)

Y 21(Ω)

theoretical Practical theoretical Practical theoretical Practical theoretical Practical

Result:

VIVA QUESTIONS:

1. What do you mean by a 2-port network? 2. What are impedance, admittance and immittance? 3. What is driving point impedance? 4. What is driving point admittance? 5. What is driving point immittance? 6. Write equations for Z-parameter. 7. Write equations for Y-parameter. 8. What is the relationship between Z- and Y- parameter? 9. What is the condition for reciprocity for a network? 10. What is the condition for symmetry for a network?

6. Transmission & Hybrid Parameters of Two Port Network Aim:

To measure “Hybrid & Transmission parameters of given two port passive network

Apparatus required:-

S. No.


Specifications

Quantity

1

Resistors

, R 2=

3

2


10-1M

1

3

Multimeter

DMM

1

4


(0-30) V

1

5

Ammeter

(0-20) mA

1

6

Voltmeter

(0-20)V

1

7

Bread board

8

Connecting Wires

R 1=

, R 3=

1 Single strand

As required

Circuit Diagram:

Procedure:

1. Connect the circuit as shown in the figure1(a). 2. Short circuit the port -2 & note the readings of V1, I1 & I2. 3. Repeat the above step for different values of V1. 4. Now connect the circuit as shown in fig 1(b). 5. Open circuit port-1 & note the readings of V1. V2 & I2 6. Repeat the above step for different values of V2 & Calculate the hybrid parameters.

Observations:

Equations describing hybrid parameters: V1 = h11 I1 + h12 V2 I2 = h21 I1 + h22V2 To measure h 11 & h21

To measure h 12 & h22

When V2 = 0 S.No

V1

I1

When I1 = 0 I2

h11

h21

S.No

1

1

2

2

h11=V1/I1 h21=I2/I1 Transmission Parameters:

Transmission Parameters:

1. Connect the circuit as shown in figure 2(a)

V1

h12=V1/V2 h22=I2/V2

V2

I2

h12

h22

2. Open circuit port-2 & note down the readings of V1, V2 & I1. 3. Repeat the above step for different values of V1. 4. Now connect the circuit as shown in figure 2(b). 5. Short circuit port-2 & note down the readings of V1, I1 & I2. 6. Repeat the above step for different values of V1 & calculate the A, B, C, D parameters. For A, B, C, D Parameters:

Equation Describing A B C D parameters V1 = AV2 – BI2 I1 = CV2 – DI2 To Calculate A & C

To calculate B & D

When I2 = 0 S.No

V1

I1

V2

When V2 = 0 A

S.No

C

1

1

2

2 A=V1/V2

I1

I2

B

D

C=I1/V2

B=V1/I2 CONCLUSION:

h11

V1

h11

D=I1/I2

h12

h12

h 22

h 22

h 21

h 21


A

A

B

B

C

C

D

D


Result:


1. What do you mean by a 2-port network? 2. What are impedance, admittance and immittance? 3. What is input impedance? 4. What is forward current gain? 5. What is output admittance? 6. What is reverse voltage gain 7. Write equations for h-parameter. 8. Write equations for Transmission-parameter. 9. What is the condition for reciprocity for h-parameter network? 10. What is the condition for reciprocity for ABCD parameter network? 11. What is the condition for symmetry for h-parameter network? 12. What is the condition for symmetry for ABCD parameter network?

7. MAGNETIZATION CHARACTERISTICS OF A D.C. SHUNT GENERATOR AIM: To obtain the Magnetization Characteristics of a D.C. Shunt Generator and to determine

its Critical field resistance & Critical speed. NAME PLATE DETAILS: Type

DC Shunt Motor

DC Shunt Generator

Ratings

3.0HP

2 KW

Volts

220 V DC

220 V DC

Current

12 A

12 A

Exc. Volts

220 V DC

220 V DC

Exc. Current

0.6 A

0.7 A

Duty

S1

S1

B

B

Ins. Class Speed

1500 rpm

1500 rpm

APPARATUS: S.No 01

Apparatus Required Voltmeter

Rating

Type

Qty

(0-300)V

M.C

1

02

Ammeter

(0-1)A

M.C

1

03

Rheostat

360 ohm/1.2A

-

3

04

Rheostat

360 ohm/1.2A

-

05

Tachometer

-

Digital

Circuit Diagram:

1

THEORY: I) Magnetization Characteristics 

The magnetization characteristics shows the relation between the no load generated emf in armature, E0 and the field (or) exciting current, If at a given fixed speed as shown in model graph.



These characteristics are also known as the No load saturation characteristics or Open circuit characteristics. The shape of these characteristics is practically same for all generators whether separately excited or self excited



Due to the residual magnetism in the poles, some emf is generated even when If = 0 represented by OD**. Hence, the curve starts a little way up.



The slight curvature, DE** at the lower end is due to magnetic inertia. It is seen that the first part of the curve, EC** is practically straight. This is due to the fact that at low flux densities, reluctance of iron path being negligible (due to high permeability), total reluctance is given by the air gap reluctance, which is constant. Hence, the flux and consequentially the generated emf are directly proportional to the exciting current.



How ever at high flux densities, where m is small, iron path reluctance becomes appreciable and straight relation, CF** between Eo and If no longer holds good, i.e., saturation of poles start. (** refers to the model graph)

II) Critical resistance 

It is that maximum value of the field resistance, above which the machine fails to excite i.e. there will be no build up of the voltage.



This resistance corresponds to the straight-line position of the magnetization characteristic because the magnetic circuit does not offer any appreciable reluctance to the magnetic flux.

III) Critical speed 

It is that speed for which the given shunt field resistance will represent critical field resistance (OR)It is that minimum value of the speed of the machine below which the machine fails

to excite. PROCEDURE:

1. Connect the circuit as per the circuit diagram. 2. Initially the starter must be in OFF & SPST Switch in open positions. 3. Switch on the D.C. Motor to 220V D.C. Supply by closing the DPST Switch.

4. Start the D.C. motor using the three point starter and thereby adjust the speed of it to the rated speed of the D.C. Generator using field method of speed control. 5. Note down the voltage of the voltmeter which represents the residual voltage of the generator when SPST switch is in open condition. 6. Excite the field winding D.C. Generator in steps by decreasing its external resistance gradually and note down various corresponding readings of ammeter and voltmeter till 1.1 to 1.25 times the rated voltage of the generator is reached, maintaining constant speed . 7. Gradually reduce the field current of generator and make it to zero finally by opening SPST switch. and disconnect the D.C. Motor from the 220V D.C. Supply

OBSERVATION TABLE: At constant speed of 1500r.p.m. S.No

Field Current (  ) A

MODEL GRAPHS:

Armature Voltage ( ) V

CALCULATIONS: TO FIND CRITICAL FIELD RESISTANCE :

1. Plot the magnetization curve. 2. Draw the tangent such that it touches most of the linear part of the curve. This line is the Critical field resistance line. 3. The slope of the above line gives the Critical field resistance. TO FIND CRITICAL SPEED:

1. Draw the constant field resistance line Rf . 2. From point

draw a line on to the Critical field resistance line.

Now the Critical speed, Nc = (AB /AC) ×N, where N is the rated speed of D.C. generator i.e., 1500 r.p.m. PRECAUTIONS:-

1.

The field rheostat of the motor must be kept in minimum & for the generator in maximum positions before switching on the D.C. supply.

2. Ensure that the starter arm is at extreme left position. 3. Avoid loose connections 4. Note down the readings form the meters without any parallax error RESULT: 

Critical field resistance = ________ ohms.



Critical speed = ________ r.p.m.


1. Why the speed maintained constant during the experiment? 2. What is residual magnetism? 3. Define critical resistance? 4. Define critical speed? 5. How do you determine critical resistance with the help of O.C.C.? 6. Explain magnetization curve? 7. How do you determine critical speed graphically? 8. What is residual voltage? 9. How does the speed of a prime mover affect the generator characteristics? 10. How you classify the parts of a D.C generator?

8.SWINBURNE’S TEST OF D.C. SHUNT MACHINE AIM : To Pre-determine the efficiency and performance characteristics of a DC Shunt machine.

(both as a generator & motor). NAME PLATE DETAILS: S.No

Type

DC Shunt Motor

01

Ratings

3.0HP

02

Volts

220 V DC

03

Current

12 A

04

Exc. Volts

220 V DC

05

Exc. Current

0.6 A

06

Duty

S1

07

Ins. Class

08

Speed

B 1500 rpm

APPARATUS: S.No

Apparatus Required

01

Voltmeter

Rating

Type

Qty

(0-300)

M.C

1

02

Ammeter

(0-10)

M.C

1

03

Ammeter

(0-5)

M.C

2

04

Rheostat

360 Ohm / 1.2 A

M.C

1

05

Tachometer

Digital

1

06

Fuse

20

2

THEORY: SWINBURNE’S TEST:

It is a simple method in which losses are measured separately and from their knowledge, efficiency at any load can be pre-determined in advance. The onlyrunning test needed is a no load test.



Swinburne s test is applicable to those machines in which flux is practically constant i.e. Shunt wound and Compound wound machines.



The machine is running as a motor on no-load at its rated voltage and its speed be adjusted to its rated value using Shunt regulator.



The no-load armature current Iao is measured using an ammeter, where as shunt field current Ish is given by another ammeter. The no-load input current is given by Io = Iao + Ish



Let the supply voltage be V volts No-load input = V Io watts Power input to armature = V Iao watts Power input to shunt = V Ish watts No-load input supplies Copper losses (Armature & Field), Iron losses (Hysteresis &

Eddy current) & Mechanical losses ( Friction losses & Windage). Constant losses = No load input power - Armature copper losses Wc = V Io – Iao² Ra watts. 

Predetermination of efficiency of a motor at any load

Input = V IL watts.

Rated value IL = 12A

Armature Cu losses = Ia 2 Ra Constant losses = Wc Total losses = Wc + ( I L - Ish)² Ra Efficiency = (Input - Total losses) / (Input) ɳ (Efficiency)x = (x Input - Wc + ( x IL - Ish)² Ra) / x input

X may be ¼, ½, ¾, full load(1) 

Predetermination of efficiency of a generator at any load

Output = V IL watts. Armature Cu losses = Ia 2 Ra Constant losses = Wc Total losses = Wc + ( I L + Ish)² Ra Efficiency = (Output) / (Output + Total losses) ɳ (Efficiency)x = (x Output) / (x output+ Wc + ( x IL + Ish)² Ra)

X may be ¼, ½, ¾, full load (1) 

Maximum Efficiency condition : Variable losses (Ia² Ra) = Constant losses ( Wc)

Procedure:

1. Connect the circuit as per the Circuit diagram. 2. Initially the starter must be in off position. 3. Switch on the D.C. Motor to 220V D.C. Supply by closing the DPST Switch.

4. Start the D.C. motor using the three point starter and thereby adjust the speed to its rated speed using field rheostat.230 5. Note down the readings of Voltmeter & Ammeters in Table 6. Switch off the D.C. Motor from 220V D.C. Supply by opening the DPST Switch.

OBSERVATION TABLES: SWINBURNE’S TEST At Constant speed of 1500r.p.m.

S.No.

Input Voltage V

Armature Current

Field Current

1

Wc = V Io – Iao² Ra Watts = ________ Watts CALCULATION TABLE: SWINBURNE’S TEST: I)

For Motor S.No

Input

Input

Field

Armature

Total

Input

Voltage

Current

Current

Copper

Losses

Power

(V)

(I)

(Ish)

ɳ

Losses

For Generator S.No

Output

Output

Field

Armature

Total

Input

Voltage

Current

Current

Copper

Losses

Power

(V)

(I)

(Ish)

Losses

ɳ

MODEL GRAPHS: SWINBURNE’S TEST

PRECAUTIONS:-

1. The field rheostat of the motor must be kept in minimum before switching on the 220V D.C supply. 2. Ensure that the starter arm is at extreme left position. 3. Avoid loose connections 4. Note down the readings from the meters without any parallax error RESULTS:  

Maximum Efficiency for motor = __ %. Maximum Efficiency for generator = __________ %.

VIVA VOCE QUESTIONS :

1. 2.

What are the advantages of SWINBURN’S test? Why SWINBURN’S test cannot perform on series machines? Explain.

3. How do you obtain accurate measurements in this experiment? 4. Comment on the accuracy of SWINBURN'S test over other methods? 5.

Why the SWINBURN’S test is called as indirect test?

6. What will happen in a motor if armature coil is opened? 7. Why output is not equal to input? 8. 9.

What is the Fleming’s left hand rule? How the direction of torque is determined? Why the magnetic losses calculated by SWINBURN’S test is differant from the actual value?

10. What is the meant by indirect testing?

9.BRAKE TEST ON A D.C. SHUNT MOTOR AIM : To obtain the Performance characteristics curves of a D.C. shunt motor by conducting

brake test on it. NAME PLATE DETAILS: S.No

Type

DC Shunt Motor

01

Ratings

3.0HP

02

Volts

220 V DC

03

Current

12 A

04

Exc. Volts

220 V DC

05

Exc. Current

0.6 A

06

Duty

S1

07

Ins. Class

08

Speed

B 1500 rpm

APPARATUS: S.No 01

Apparatus Required Voltmeter

Rating

Type

Qty

(0-300)V

M.C

1

02

Ammeter

(0-20)A

M.C

2

03

Ammeter

(0-10)A

M.C

1

04

Rheostat

360 ohm/1.2A

-

1

05

Tachometer

-

Digital

1

-

2

06

Fuse

20A

THEORY: 

It is a simple method of testing low rating DC machines and consists of applying a brake to a water-cooled drum mounted on the motor shaft.



The four important characteristics curves of a D.C. Shunt Motor, namely, Torque, Speed, Armature Current & efficiency, each plotted against the useful Power, as shown in the model graph are known as Performance characteristics



A belt is wound round the brake drum and its two ends are attached to two spring balances S1 & S2. The tension of the belt can be adjusted with the help of swivels.



The force acting tangentially on the drum is equal to the difference between the readings of the two spring balances the readings of S pring balances 1& 2 in Kg.f.



Shaft torque, T developed by the motor is 9.81 (S1 S2) R Nm where, R is the radius of the pulley in meters & N is the speed in rpm



Useful Output Power = (2)/60 Watts



Input Power = V IL Watts, where IL = (Ia + Ish)



% Efficiency , = (Output power / Input power) x 100.



Speed Regulation = [ (No Load speed ) - ( Full load speed )] / Full Load. Speed =



The size of the motor that can be tested by this method is limited from the consideration

 − 

of the heat that can be dissipated at the brake drum 

Where the output power exceeds about 2 H.P., or where the test is of long duration, it s necessary to use a water cooled brake drum.

PROCEDURE:

1. Connect the circuit as per the Circuit diagram. 2. Initially the starter must be in off position. 3. Switch on the D.C. Motor to 220V D.C. Supply by closing the DPST Switch. 4. Start the D.C. motor using the three point starter and thereby adjust the speed to its rated speed using field rheostat. 5. Note down the readings of Voltmeter & Ammeters in Table under No Load condition. 6. Apply the Load on the drum gradually in steps by tightening the belt around it. At each step, note down the readings of the Ammeters, Voltmeter, two Spring balances and the Tachometer. 7. Pour water in the pulley and cool it often when the motor is loaded. 8. When the full load is reached, slowly reduce the load and switch off the Motor from 220V D.C. Supply by opening the DPST Switch

FORMULAE:

The induced voltage E b =V-Ia R a and E b= KΦN, Thus, KΦ=E b /N V= applied voltage, Ia =armature current, R a =armature resistance. Total power input to the motor Pin =Field circuit power + Armature power= Vf If + Va Ia

If ‘R’ is the radius of the pulley, then torque at the pulley is given by Tshaft = 9.81* (T1~T2 )*R = 1.5* (T1~T2) N-m

ω

=

2N 60

is the angular velocity of the pulley, in rad/sec.

Radius of pulley R = …….. Motor output power Pout =Tshaft * ω = 1.5* (T1~T2)*

% Efficiency

=

P out P in

2N 60

X 100

OBSERVATION TABLE: S.No

Input

Armature

Field

Voltage (V)

Current

Current

( )

( )

Spring Balances





Speed (N)

CALCULATION TABLE:

Radius of the Brake Drum, R = ______ mts. S.No

Input

Input

Torque,

Output

Input

Voltage

Current

N-m

Power

Power

(V)

()

%

(T)

PRECAUTIONS:

1. The field rheostat of the motor must be kept in minimum before switching ON the motor. 2. Ensure that the starter arm is at extreme left position. 3. Avoid loose connections 4. Note down the readings from the meters without any parallax error 5. Tachometer should be kept horizontal to the shaft while measuring the speed. 6. Before switch OFF the motor make sure that there is nos load connected to motor. MODEL GRAPHS:

RESULTS: At full load:

i) Torque = __________ Nm. ii) Speed = __________ rpm iii) Armature Current = __________ A iv) Efficiency = __________ %. v) Speed Regulation = _________


1. Why the speed falls as load increases for a DC shunt motor? 2. What are the applications of DC shunt motors? 3. When is the efficiency of the motor maximum? 4. What will happen when DC shunt motor is started with load? 5. Give the expressions for various torques in DC motors. 6. What is the effect on speed if part of the field winding is shorted? 7. Where actually the mechanical energy available? 8. What do you mean by the armature drop? 9. Does the yoke carry the same flux as is the flux per pole? 10. How the D.O.R of a DC motor can changed?

10.OC & SC TESTS ON A SINGLE PHASE TRANSFORMER Aim:

(a) To predetermine the efficiency and regulation of Single Phase Transformer by conducting no-load test and short circuit test. (b) To draw the equivalent circuit of single phase transformer referred to LV side as well as HV side. Apparatus: S.N.

Meter

1.

Single phase Variac

2.

Ammeter

3.

Type Range

Quantity

0-250/270V

1

MI

0-2A

1

Ammeter

MI

0-10A

1

4.

Voltmeter

MI

0-150V

1

5.

Voltmeter

MI

0-30V

1

4.

Wattmeter

LPF

0-2.5A/150V

1

5.

Wattmeter

UPF

0-10A/75V

1

Name plate details:

OPEN CIRCUIT TEST Circuit Diagram:

Procedure:

(1)

Connect the circuit for no-load test as per the circuit diagram. Shown in fig(1).

(2)

Keep the variac in minimum output position and switch on the supply.

(3)

Apply the rated voltage to the transformer by properly adjusting the variac.

(4)

Note down the readings of various meters and switch off the supply.

Observations: (O. C. Test) S.N. Vo (V) Io (A) Wo = W x M.F (w)

SHORT CIRCUIT TEST

Fig

–

2 SHORT CIRCUIT TEST

Procedure: 1.Connect the circuit for SC test as per the circuit diagram, shown in fig (2) with appropriate

ranges of meters. 2.Keep the variac in minimum output position and switch on the supply. 3.Apply proper voltage (low voltage) to the transformer by adjusting the variac such that rated

current flows through the transformer. 4. Note down the readings of various meters and switch off the supply. S. C. Test: S.N. VSC (V)

ISC (A)

WSC = W x M.F (w)

Where M. F. = Multiplication factor =

VI cos FSD



FSD = Full scale divisions Model Calculations:

Find the equivalent circuit parameters R 0, X 0, R 01, R 02, X01 and X02 from the O. C. and S. C. test results and draw the equivalent circuit referred to L. V. side as well as H. V. side. Let the transformer be the step-down transformer Primary is H. V. side. Secondary is L. V. side

X 0

V 1 

X 0

1

I m



R0

where Im = I0 sin 0

Z 01

2

R01



2

:

X 02



R0



2

X 01 where

K=

I w

W SC

1

K

V 1 

I sc V 2



V 1

, Z 01

2

where Iw = I0 cos 0



V SC I SC

Transformation ratio.

Calculations to find efficiency and regulation

For example at ½ full load Cupper losses = Wsc x (1/2)2 watts, where WSC = full – load cupper losses Constant losses = W0 watts Output = ½ KVA x cos  [cos  may be assumed] Input = output + Cu. Loss + constant loss % efficiency

Output 

Input

x 100

Efficiency at different loads and P.fs cos  = ___________ S.N.

Load

Cu.loss (W)

Output (W)

cos  = ___________ Input

%

Xx S.N.

Load

(W)

¼F.L.

¼F.L.

½F.L.

½F.L.

¾F.L.

¾F.L.

F.L.

F.L.

Cu.loss

Output

Input

(W)

(W)

(W)

%

Regulation : From open circuit and Short circuit test % Re gulation 

I 2 R02

cos  I 2 X 02 sin 

V 2

‘+’ for lagging power factors

x 100

‘-‘ for leading power factors Lagging Pf

S.N.

P.F.

Leading Pf

% Reg. S. N.

P. F.

1.

0.2

1.

0.2

2.

0.4

2.

0.4

3.

0.6

3.

0.5

4.

0.8

4.

0.6

5.

Unity

5.

Unity

% Reg.

Graphs: Plots drawn between

(i)

% efficiency Vs output

(ii)

% regulation Vs power factor

Precautions:

(i)

Connections must be made tight

(ii)

Before making or breaking the circuit, supply must b e switched off

Result:

11. Series and Parallel Resonance Aim: - To obtain frequency characteristics of series and parallel resonant circuits, Resonance frequency, Band width and Q – factor for RLC network.

Apparatus required:

S.No.


Specifications Quantity

1

Resistor

1 K 

1

2

Decade Capacitors Box

0.1 F -1F

1

3

Decade Inductance Box(DIB)

ImH-10mH

1

4

Function Generator

5

Ammeters

0-20 mA ac

2

6

CRO

1 MHz

1

Circuit Diagrams :

Procedure:Series Resonance:

1

1. Connect the circuit as shown in figure 1(a). 2. Connect the signal generator (function generator) and keep the voltage constant i.e.,5V, vary source frequency and note down the voltmeter reading (VR ). 3. Plot the graph VR Vs F. 4.

Find “f r” ,3db frequencies and Band Width from the graph.

5. Compare theoretical and practical values of “f r” and Q factor. Parallel Resonance :

1. Connect the circuit as shown in figure 1(b). 2. Keep voltage source constant i.e.,5V, vary source frequency and note voltmeter readings. Calculate I in the circuit using relation VR / R = I 3. Calculate the impedance (Z) of the circuit using Vs / I = Z where I is obtained in the above step. 4.

Plot “Z” Vs “freq” Graph.

5.

Find “f r” , Band Width and Q – factor from graph.

6.

Compare theoretical and practical values of “f r” and Q factor.

Expected graphs

Observations : Series Resonance : S.No.

1

Frequency (kHz) 1

2

Parallel Resonance : Current (mA)

S.No

1

Frequency (Hz) 1

2

2

2

3

3

3

3

4

4

4

4

5

5

5

5

6

6

6

6

7

7

7

7

8

8

8

8

9

9

9

9

10

10

10

10

VR

I=Vs/R

Calculations: B.W = f 2 – f 1 = ………kHz. Q = f 0 / f 2 – f 1 = f 0

= 1 / 2 LC =………. kHz.

Practical:

Frequency

Series resonance

Parallel resonance

Band width

Q – factor

Z=Vs/I

Theoretical:

F requency

Band width

Q – factor

Seri es resonance Parallel r esonance

Result:- Frequency characteristics of series and parallel resonant circuits, Resonance frequency, Band width and Q – factor for RLC network are obtained.

12. LOAD TEST ON A SINGLE PHASE TRANSFORMER

AIM: To find the efficiency and regulation of single phase transformer by using load test. APPARATUS REQUIRED:

Circuit Diagram:

PROCEDURE:

1. Connections are made as per the circuit diagram. 2. After checking the no load condition, minimum position of auto transformer and DPST switch is closed. 3. Ammeter, Voltmeter and Wattmeter readings on both primary side and secondary side are noted. 4. The load is increased and for each load, Voltmeter, Ammeter and Wattmeter readings on both primary and secondary sides are noted. 5. Again no load condition is obtained and DPST switch is opened. FORMULAE:

Output Power = W2 x Multiplication factor Input Power = W1 x Multiplication factor Efficiency  % = Output Power/ Input Power

x 100%

Regulation R % = VNL - VFL (Secondary) / VNL TABULAR COLUMN:

MODEL GRAPHS:

x 100%

ET Lab Manual

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