15EE204L ELECTRICAL MACHINES LABORATORY-I ACADEMIC...

15EE204L

ELECTRICAL MACHINES

LABORATORY-I

ACADEMIC YEAR: 2017-18 NAME :

REG.NO. :

DEPARTMENT OF ELECTRICAL & ELECTRONICS ENGINEERING

FACULTY OF ENGINEERING & TECHNOLOGY

SRM UNIVERSITY

(Under section 3 of UGC Act, 1956)

S.R.M. NAGAR, KATTANKULATHUR – 603 203

KANCHEEPURAM DISTRICT

SRM UNIVERSITY

(under Section 3 of UGC Act, 1956)

S.R.M. NAGAR, KATTANKULATHUR -603 203

KANCHEEPURAM DISTRICT

BONAFIDE CERTIFICATE

Register No__________________

Certified to be the bonafide record of work done by

________________________ of EEE , B.Tech Degree course in the Practical

15EE204L Electrical machines Lab - I in SRM UNIVERSITY,

Kattankulathur during the academic year 2017-2018

Lab Incharge

Date: Year co-ordinator

Submitted for University Examination held in

Electrical machines Lab, SRM UNIVERSITY, Kattankulathur.

Date: Examiner-1 Examiner-2

INDEX SHEET

C

Y

C

L

E

I

Exp

.

No.

Date

of

Exp.

Title of Exp.

Pre and

Post Lab

(05)

Conduction of

Experiment

(15)

Calucation

and Result

(15)

Viva

(5)

Total

(40)

Faculty

Sign

1 Load Test on DC

Shunt Motor Using

Open Lab Sys

2 Load Test on DC

Series Motor

3 Load Test on DC

Compound Generator

4 OC & LC of Self &

Separately Excited DC

Generator

5 Swinburne’s Test

Using Open Lab Sys

6 Hopkinson’s Test

C

Y

C

L

E

I

I

7 Speed Control of DC

Shunt Motor Using

MATLAB

8 Load Test on Single

Phase Transformer

9 Load Test on Three

Phase Transformer

10 Sumpner’s Test

11 Transfer Function of

DC Machine

12 Three Phase to Two

Phase Conversion of

Transformer and Three

Phase Transformer

Connections

TOTAL

AVERAGE

COMPLETED SIGNATURE OF THE FACULTY WITH DATE

1. LOAD TEST ON DC SHUNT MOTOR USING OPEN LAB SYS

Pre-lab questions

1. State the working principle of a DC Motor

2. DC Shunt motor is called as constant flux motor. Justify.

3. What is the need of a three point starter?

4. Brief about significance of back emf?

5. At what condition a dc motor will develop maximum power?

LOAD TEST ON DC SHUNT MOTOR USING OPEN LAB SYS

Aim:

To conduct load test on DC motor with shunt excitation and plot the typical

characteristics using open lab systems.

Apparatus required:

Sl.

No.

Components Module Specification Qty

1 DC Shunt motor Open lab sys 42V/4A DC 1

2 Supply module DL10281 Fixed DC 32V/14A 1

3 Measurements module DC10282 DC Voltmeter (0-75)V 2

DC Ammeter (0-15)A 2

Speed sensor 1

4 Loads & Rheostats DC10283 - 1

5 Electromagnetic brake DC103004 G=3.5N, G=1.5N 1

Formulae:

Absorbed power : Pin – u I Watts

Output power : Pout = 0.1047 n M watts

Torque : M = G.b Nm

Efficiency : %𝜂 = 𝑃𝑜𝑢𝑡

𝑃𝑖𝑛

Where,

u = Supply voltage in volts

n = Load current in volts

I = Speed on shunt motor in RPM

M = Torque in Nm

G = Measuring weight

b = Distance of the arm in metres

Precautions:

1. In the supply module DL10281, select the selector switch “I” to position “a” for fixed

direct voltage 32V/14A and switch L+/L- to position “0”.

2. In the supply module DL01281, select the selector switch “IV” to position “c” for

variable direct voltage 40V/5A and control knob to 0%.

3. In the supply module DL10283, set the armature resistance (RA) to maximum value

(Control knob in position “b”) and switch R to position “0”.

4. In the supply module DL10283 set the field excitation Rheostat Rf = minium value

(Control knob in position “a”).

5. In the measurement module 10282 ensure the Ammeters and Voltmeters for DC

measurements and observe the polarities.

Procedure:

1. Activate the supply module by setting the L+/ L- switch from position “0” to “1”

2. Observe whether the motor runs in clockwise direction.

3. If not move the switch L+ . L- from “1” to “0” and interchange the field terminals F1 &

F6.

4. Repeat step (1) & (2)

5. In Rheostat module, to cut down the Ra (2) to minimum value, move the control knob

to position “a” and the switch “R” to position “1” (1)

6. Adjust the field excitation Rheostat RF in such a way that the field Ammeter reads If =

0.7A.

7. Balance the brake by moving the balance weight “g” until the water level shows

horizontal position and the speed measurements reads rated speed.

8. Now note down the No load measurements (u, I, G, b, n)

9. The motor is therefore loaded in steps by means of brake.

(The load is increased by moving the weight “g” to a distance “b” from the no load initial

position. Adjust the selector “IV” to balance the system again.

10. Perform the measurements as per previous step and repeat the procedure until rated

current condition.

11. Stop the system by setting the load voltage switch L+ / L- to position “0” to deenergize.

12. Bring back the RF to minimum and Ra to maximum and selector “II” to position “0”.

Tabular Column:

Sl.No. U(V) I

(A)

Pin

(W)

G

(N)

B

(m)

M

Nm

N

RPM

Pout

W

%

Model Graph:

Result:

The load test on DC shunt motor was carried out to determine the efficiency and plot the

typical characteristics.

Post-lab questions for load Test on Shunt Motor

1. How to reverse the direction of rotation of DC shunt Motor?

2. What are uses of DC Shunt motor?

3. What happens if the field circuit of a DC shunt motor is opened?

2. LOAD TEST ON DC SERIES MOTOR

Pre-lab questions

1. What will be the condition for attaining maximum efficiency in a DC motor?

2. Why does the DC series motor run dangerously at high speed under no load condition?

3. State Fleming’s Left Hand Rule.

4. Which type of starter is used to start a DC series motor?

LOAD TEST ON DC SERIES MOTOR

Aim:

To perform the load test on a given DC series motor and plot its performance

characteristics

Apparatus Required:

S.No. Apparatus Range Type Quantity

1 Ammeter (0-20)A MC 1

2 Voltmeter (0-300)V MC 1

3 Tachometer (0-10000)

rpm Digital 1

4 Connecting Wires 2.5sq.mm. Copper Few

Precautions:

1. The motor should be started and stopped under loaded condition.

2. Brake drum should be cooled with water when it is under loaded condition only.

Procedure:

1. Connections are to be made as per the circuit diagram.

2. Initially, the motor is loaded with 20 to 30% of the load. By closing DPST switch, the

supply is given to the motor and the motor is started using a two point starter.

3. For various load intervals, voltmeter, ammeter, speed and spring balance readings are

noted down.

4. After bringing the load to its initial position, DPST switch is opened.

Formulae Used

1. Input power = V × I Watts

2. Torque ,T= (9.81) × (S1 ~ S2) × R, N-m, where R is the radius of the brake drum,

Find the circumference of the brake drum. Using 2πR, R is obtained.

3. Output power =2

60

NTWatts

4. % efficiency = 100%Output power

Input power

Tabular Column:

Sl

No.

V

Volts

I

Amp

N

RPM

Spring

Balance

Torque

N-m

Input

Watts

Output

Watts

Efficiency

%

S1

Kg

S2

Kg

S1-

S2

Kg

Model Graph:

Result:

Thus the load test was conducted on DC series motor and its characteristic curves are

drawn.

Torq

ue,

T (

Nm

)

Spee

d, N

(rp

m)

Eff

icie

ncy

,

%

y3 y2 y1

Output Power (Watts)

N

T

Post-lab questions for load Test on DC Series Motor

1. What are applications of a DC Series Motor?

2. Define speed regulation in a DC Motor

3. Series motor has high starting torque. Justify.

4. Why series field winding is made thicker and has lesser number of turns?

3. LOAD TEST ON DC COMPOUND GENERATOR

Pre – lab Questions

1. What is compound generator?

2. Classify compound generator.

3. Mention the losses in compound generator

4. What is the difference between cumulative and differential compound generator?

5. Write down the applications of compound generator.

LOAD TEST ON DC COMPOUND GENERATOR

Aim:

To conduct a load test and to draw the external (or) load characteristics of the given compound generator when it is,

(i) Cumulatively compounded (ii) Differentially compounded




3 Rheostats 1200Ω, 0.8A Wire Wound 2

4 Loading Rheostat 5KW, 230V - 1

5 Tachometer (0-1500)rpm Digital 1

6 Connecting Wires 2.5sq.mm Copper Few

.

Precautions:

1. The field rheostat of motor should be at minimum position.

2. The field rheostat of generator should be at maximum position.

3. No load should be connected to generator at the time of starting and stopping.

Procedure

1. The generator is unloaded and the field rheostat of DC shunt generator is brought to

maximum position and the field rheostat of DC shunt motor to minimum position,

DPST switch is opened.

2. The connections of series field windings are reversed the above steps are

repeated.

3. The values of voltage for the particular currents are compared and then the

differential and cumulative compounded DC generator is concluded accordingly.

Cummulative Compound

VL (Volts) IL (Amps)

Differential Compound

VL (Volts) IL (Amps)

Result:

Thus load characteristics of DC compound generator under cumulative and differential

mode condition are obtained.

Post Lab questions:

1. What is the indication of an over loaded generator?

.

2. What are the causes of an overloaded generator?

3. What are the causes for the failure of generator to build up?

4. OPEN CIRCUIT AND LOAD CHARACTERISTICS OF SELF EXCITED

DC SHUNT GENERATOR

Pre-lab questions

1. State the working principle of a DC generator?

2. Why field winding of shunt generator is made thinner and has more number of turns?

3. List out the conditions to be satisfied for voltage build up process in a generator.

4. Define critical resistance of a generator

5. Define critical speed of a generator

OPEN CIRCUIT AND LOAD CHARACTERISTICS OF SELF EXCITED DC

SHUNT GENERATOR

Aim:

To perform a test on the given self excited DC shunt generator and to plot its open

circuit characteristics and load characteristics curves.

Apparatus Required:



(0-10)A MC 1


3 Rheostats 300Ω/1.5A Wire Wound 1

600Ω/1A Wire Wound 1

4 SPST Switch - - 1

5 DPST Switch - - 1



7 Rheostatic or

lamp Load 5KW, 230V - 1

Formulate Used for Load Characteristics

1. Ia = IF + IL

2. Eg = Ia Ra + VL

Ia Armature current in ampere

If Field current in ampere

IL Load current in ampere

Eg Generated emf in volts

VL Load Voltage in Volts

Ra Armature resistance in ohms (Disconnect all the

connections and measure Ra using multimeter)

Precautions:

1. The motor field should be kept at minimum resistance position at the time of starting

and stopping of the machine.

2. The generator field rheostat should be kept at maximum resistance position at the time

of starting and stopping of the machine.

3. SPST switch has to be kept open while starting and stopping of the machine.

Procedure: Open Circuit Test

1. Connections to be done as per the circuit diagram.

2. By closing DPST switch 1, the supply is given to the motor. Using the three point

starter, the motor is started.

3. By varying the motor field rheostat, the motor has to be brought to its rated speed.

4. Voltmeter and ammeter readings are noted down when the SPST switch is kept open.

5. Now, the SPST switch is closed. The generator field rheostat is varied and its

corresponding voltmeter and ammeter readings are noted down.

6. The above procedure is repeated until 120% of the rated voltage of the generator has

reached.

Procedure: Load Test

1. The generator field rheostat is brought back to its initial position (i,e) maximum.

2. Now, the DPST switch 2 is closed.

3. By varying the generator field rheostat, the generator has to be brought to its rated

voltage. Corresponding reading of voltmeter and ammeter are noted down.

4. By varying the load gradually, the corresponding reading of voltmeter and ammeter

are noted down at regular intervals.

5. The above procedure is repeated until the rated current of generator has reached.

Open Circuit Characteristics:

S.No. If (Amp) Eg (Volts)

Model Graph for Open Circuit Characteristics:

Eo

If

Critical Resistance = Eo / If Ohms Eo (

Volt

s)

If (Amps)

Load Characteristics:

S.No. VL (Volts) If (Amps) IL (Amps) Ia (Amps) Eg (Volts)

Model Graph for Load Characteristics:

Result:

Open circuit and load test on the given self excited DC shunt generator was conducted

and its curves were drawn.

Internal (Eg Vs Ia)

External (VL Vs IL)

V (

Volt

s)

I (Amps)

Post-lab questions

1. What is the role of SPST Switch in this experiment?

2. List out the methods available to give mechanical input for the DC generator

3. Why the shunt generator has drooping external characteristics?

4. Why the magnitude of field current in dc shunt generator is lesser as compared to

armature current?

4. OPEN CIRCUIT AND LOAD CHARACTERISTICS OF SEPERATELY

EXCITED DC GENERATOR

Pre-lab questions

1. State the Fleming’s Right Hand Rule

2. What is the difference between self and separately excited DC Generator?

3. What is the function of the commutators?

4. Define critical resistance and speed of generator

5. Define armature reaction

OPEN CIRCUIT AND LOAD CHARACTERISTICS OF SEPERATELY EXCITED

DC GENERATOR

Aim:

To perform a test on the given separately excited DC generator and to plot its open

circuit characteristics and load characteristics curves.

Apparatus Required:



(0-10)A MC 1


3 Rheostats 300Ω/ 1.5A

Wire Wound 1

600Ω/ 1A 1

4 SPST Switch - - 1

5 DPST Switch - - 1



7 Rheostatic Load

or lamp load 5KW, 230V - 1

Formulae

1. Ia = IL= If

2. Eg = Ia Ra + VL

Ia Armature current in ampere

If Field current in ampere

IL Load current in ampere

Eg Generated emf in volts

VL Load Voltage in Volts

Ra Armature resistance in ohms (Disconnect all the

connections and measure Ra using multimeter)

Precautions:

1. The motor field should be kept at minimum resistance position at the time of starting

and stopping of the machine.

2. The generator field rheostat should be kept at maximum resistance position at the time

of starting and stopping of the machine.

Procedure: Open Circuit Test

1. Connections to be done as per the circuit diagram.

2. By closing DPST switch 1, the supply is given to the motor. Using the three point

starter, the motor is started.

3. By varying the motor field rheostat, the motor has to be brought to its rated speed.

4. Voltmeter and ammeter readings are noted down when the SPST switch is kept open.

5. Now, the SPST switch is closed. The generator field rheostat is varied and its

corresponding voltmeter and ammeter readings are noted down.

6. The above procedure is repeated until 120% of the rated voltage of the generator has

reached.

Procedure: Load Test

1. The generator field rheostat is brought back to its initial position (i,e) maximum.

2. Now, the DPST switch 2 is closed.

3. By varying the generator field rheostat, the generator has to be brought to its rated

voltage. Corresponding reading of voltmeter and ammeter are noted down.

4. By varying the load gradually, the corresponding reading of voltmeter and ammeter

are noted down at regular intervals.

5. The above procedure is repeated until the rated current of generator has reached.

Circuit Diagram

Open Circuit Characteristics:

S.No. If (Amp) Eg (Volts)

Model Graph for Open Circuit Characteristics:

Load Characteristics:

S.No. VL (Volts) If (Amps) IL (Amps) Ia (Amps) Eg (Volts)

Model Graph for Load Characteristics:

Internal (Eg Vs Ia)

External (VL Vs IL)

V (

Volt

s)

I (Amps)

Eo

If

Critical Resistance = Eo / If Ohms Eo (

Volt

s)

If (Amps)

Result:

Open circuit and load test on the given seperately excited DC shunt generator was

conducted and its curves were drawn.

Post-lab questions

1. What are causes of overloading of generators?

2. Why saturation curve for the DC Generator does not start from zero?

3. Will the voltage of a shunt generator drop if load is applied to its terminal. Justify

5. SWINBURNE’S TEST USING OPNE LAB SYS

Pre-lab questions

1. What is the other name for Swinburne’s Test?

2. Mention the uses of Swinburne’s Test.

SWINBURNE’S TEST USING OPNE LAB SYS

Aim:

To conduct No load test on DC motor with shunt excitation and predetermine the

efficiency of DC machine when running as motor and generator.

Apparatus required:

Sl.

No.

Components Module Specification Qty

1 DC Shunt motor Open laysys 42V/4A DC 1

2 Supply module DL10281 Fixed DC 32V/14A 1

3 Measurements module DC10282 DC Voltmeter (0-75)V 2

DC Ammeter (0-15)A 2

Speed sensor 1

4 Loads & Rheostats DC10283 - 1

Precautions:

1. In the supply module DL10281, select the selector switch “I” to position “a” for fixed

direct voltage 32V/14A and switch L+ / L- to position “0”

2. In the supply module DL10283, set the armature resistance (RA) to maximum value

(Control knob in position “b”).

3. In the supply module DL10283 set the field excitation Rheostat Rf = minimum value

(Control knob in position “a”).

4. In the measurement module 10282 ensure the Ammeters and Voltmeters for DC

measurements and observe the polarities.

Procedure:

1. Activate the supply module by setting the L+ / L- switch from position “0” to “1” .

2. Observe whether the motor runs in clockwise direction.

3. If not move the switch L= / L- from “1” to “0” and interchange the field terminals F1

& F6.

4. Repeat step (1) & (2).

5. In the supply module DL10283 vary the field excitation Rheostat RF till the rated

speed of the motor.

6. Now note down the No load measurements (Vo, Io, If)

7. Bring back the RF to minimum and the switch L+ / L- to position “0”

Tabular Column:

Sl.

No.

Vo(V) Io(A) If(A) IA = Io+If

Efficiency when running as motor:

IL

(A)

Assume

IA=IL-IF

(A)

IA2RA

(W)

Wc

(W)

WT=Wc+IA2RA

(W)

I/P Power

= Vo IL

(W)

O/P Power =

I/P – Total

Losses (W)

%

motor

Efficiency when running as a generator:

IL

(A)

Assume

IA=IL-IF

(A)

IA2RA

(W)

Wc

(W)

WT=Wc+IA2RA

(W)

O/P

Power =

Vs IL (W)

I/P Power =

O/P power+

Total Losses

(W)

% g

Formulae:

Constant loss Wc = Input power – Armature copper loss

= Vo X Io – (Io – IF)2 X RA

For Motor

1. IA = IL – IF

2. IA2 RA / RA = 1.3 / phase

3. Total loss WT = Wc + IA2 RA

4. Input power Vo IL

5. Efficiency m (%) =𝐼𝑛𝑝𝑢𝑡 𝑝𝑜𝑤𝑒𝑟−𝑇𝑜𝑡𝑎𝑙 𝑙𝑜𝑠𝑠

𝐼𝑛𝑝𝑢𝑡 𝑝𝑜𝑤𝑒𝑟 × 100

For Generator

1. IA = IL + IF

2. IA2 RA / RA = 1.3 / phase

3. Total loss WT = Wc + IA2 RA

4. Output power Vo IL

5. Efficiency G (%) =𝑂𝑢𝑡𝑝𝑢𝑡 𝑝𝑜𝑤𝑒𝑟

𝑂𝑢𝑡𝑝𝑢𝑡 𝑝𝑜𝑤𝑒𝑟+𝑇𝑜𝑡𝑎𝑙 𝑙𝑜𝑠𝑠 × 100

Where,

Io = No load Input current in Amps

If = No load field current in Amps

IA = No load calculated armature current in Amps

IL = Assumed load current in Amps

Vo = No load input voltage in volts

RA = Armature resistance in (measured)

Model Graph:

Result:

Thus Swineburne’s test was conducted on a DC shunt machine using open lab

systems and efficiency of motor and generator were predetermined.

Post-lab questions

1. State the disadvantages of Swinburne’s Test.

2. Is it possible to conduct Swinburne’s test on DC series motor? Justify.

6. HOPKINSON’S TEST ON DC MACHINES

Pre-lab questions

1. What is the other name for Hopkinson’s Test.

2. Mention the uses of Hopkinson’s Test.

HOPKINSON’S TEST ON DC MACHINES

Aim:

To perform Hopkinson’s test on the given pair of DC machines and to obtain the

performance characteristics.

Apparatus Required:


1 Ammeter (0-10)A

(0-2) A

MC

MC

2

2

2 Voltmeter (0-300) V

(0-600)V

MC

MC

1

1

3 Rheostats 300, 1.5A

600, 1A

Wire

Wound 2

4 Tachometer (0-3000) rpm Digital 1

Precautions:

1. The motor field rheostat should be kept at the minimum position at the time of

starting and stopping the machine.

2. The generator field rheostat should be kept at 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 of the

machine.

Procedure:


2. Now, by closing the DPST switch, supply is given to the motor and motor is

started using 3-point starter.

3. The motor has to be brought to its rated speed by varying the motor field rheostat.

4. By varying generator field rheostat, the voltmeter 1 is made to read as zero and

SPST switch is closed (If the reading of voltmeter 1 reads higher voltage, the

terminals of armature winding of generator or motor is interchanged such that the

voltmeter 1 reads zero).

5. Various Ammeter readings, voltmeter readings are noted.

6. The rheostats and SPST switch are brought to their original positions and then

DPST switch is opened.

Formulae Used

1. Power drawn from supply: VI2

2. Armature copper loss of generator= (I1+I3)2Ra

3. Shunt copper loss of generator=VI3

4. Armature copper loss of motor= (I1+I2-I4)2Ra

5. Shunt copper loss of motor=VI4

6. Total stray loss of both machines,

Ws=VI2 – [ (I1+I3)2Ra + VI3+ (I1+I2-I4)

2Ra + VI4]

7. Stray loss of each machine(generator (or) motor) = 2

sW

Generator:

1. Total loss of generator= WTg = 2

sW+ (I1+I3)

2Ra + VI3

2. Output of generator=VI1

3. g = 100 of generator+Total Loss

Output of generator

Output

Motor:

1. Total loss of motor= WTm = 2

sW+ (I1+I2-I4)

2Ra + VI4

2. Input of motor=V (I1+I2)

3. m = Loss

100Input of generator

Input of motor Total

Readings obtained from Measurement

Applied

Voltage

V

(Volts)

Current taken

from supply

I2

(Amp)

Motor Field

Current

I4

(Amp)

Output current

of Generator I1

(Amp)

Generator

Field Current

I3

(Amp)

Predetermination of efficiency for Generator for various I1

I1*

(Amperes

)

Generator

Armature

Copper

Loss

(I1+I2-I4)2Ra

(Watts)

Genera

tor

Shunt

Copper

Loss

VI4

(Watts)

Stray

Loss

Ws

(Watts)

WT

(Total

Loss)

(Watts)

Output

VI1

(Watts)

Input=

Output+Tota

l Loss

(Watts)

%

20%

40%

60%

80%

100%

Table 3: Predetermination of efficiency for Motor

I1*

(Amperes)

Motor

Armature

Copper

Loss

(I1+I2-

I4)2Ra +

(Watts)

Motor

Shunt

Copper

Loss

VI4

(Watts)

Stray

Loss

Ws

(Watts)

WT

(Total

Loss)

(Watts)

Input

V (I1+I2)

(Watts)

Output=

Input-

Total

Loss

(Watts)

%

20%

40%

60%

80%

100%

*I1=% of rated current of the machine (either generator or motor)

Model Graph:

Result:

Thus Hopkinson’s test on the given pair of DC machines was conducted and the

performance characteristics were drawn.

OUTPUT POWER P0 ()

% η

As a Motor

As a Generator

Post-lab questions

1. What are the advantages of Hopkinson’s Test?

2. What are the disadvantages of Hopkinson’s Test?

7. SPEED CONTROL OF DC SHUNT MOTOR

Pre-lab questions

1. Write the speed relation equations of DC shunt motor

2. What are the factors that control the speed of a DC motor?

3. State Fleming’s Left Hand Rule.

4. Which type of starter is used to start a DC series motor?

5. Define Stalling Current

SPEED CONTROL OF DC SHUNT MOTOR

Aim:

To control the speed of a given DC shunt motor using

a. Field control method

b. Armature control method

c. MATLAB

Apparatus Required:


1 Ammeter (0-2) A MC 1

2 Voltmeter (0-300) V MC 1

3 Rheostats 300, 1.5A Wire

Wound

1

100, 2.8A 1

4 Tachometer (0-10000) rpm Digital 1


Precautions:

1. Motor field Rheostat should be kept at the minimum resistance position at the time of

starting and stopping the motor.

2. Motor armature Rheostat should be kept in the maximum resistance position at the

time of starting and stopping the motor.

Procedure:

1. Connections are made as per the circuit diagram.

2. Now, DPST switch is closed.

(i) Armature Control:

1. The field current is kept constant and the armature voltage is varied in steps with the

help of motor armature rheostat and the corresponding speeds are noted down,

2. The above procedure is repeated for different values of field current.

3. The motor field rheostat and motor armature rheostat are brought to the initial

position.

(ii) Field Control:

1. The armature voltage is kept constant and the field current is varied in steps and the

corresponding speeds are noted.

2. The above procedure is repeated for different values of armature voltage.

3. The motor field rheostat and motor armature rheostat are brought to the initial

position.

4. The DPST Switch is opened.

Armature Control Method

If1 = If2 =

Sl.No. V

Volts

N

Rpm

V

Volts

N

RPM

Field Control Method

Va1= Va2=

Sl.No. If

A

N

RPM

If

A

N

RPM

Model Graphs:

Armature Control Field Control

Result:

The speed control of a given DC shunt motor using field control and armature control

method and using MATLAB were performed.

Spee

d N

(rp

m)

Sp

eed

N (

rpm

)

If (Amps) Va (Volts)

If1

If3

If2

Va3

Va1

Va2

Post-lab questions

1. Why the armature control method is not employed above the rated speed in DC shunt

motors?

2. Why the field control method is not employed below the rated speed in DC shunt

motors?

3. Why the field control method is superior as compared to armature control method for

DC shunt motors?

8. LOAD TEST ON SINGLE PHASE TRANSFORMER

Pre-lab questions

1. What is the working principle of transformer?

2. State principle of mutual induction

3. Write down the EMF equation of a transformer

LOAD TEST ON SINGLE PHASE TRANSFORMER

Aim:

To perform load test on the given single phase transformer and to draw its

performance characteristics.

Apparatus Required:


1 Ammeter (0-10)A MI 1

(0-5) A MI 1

2 Voltmeter (0-150)V MI 1

(0-300) V MI 1

3 Wattmeter (300V, 5A) UPF 1

(150V, 10A) UPF 1

4 Auto Transformer 1, (0-260)V - 1

5 Resistive Load or

lamp load 5KW, 230V - 1


Precautions:

1. Auto Transformer should be kept at minimum position.

2. The transformer should be kept under no load condition.

3. The ‘M’ and ‘C’ terminal of primary and secondary side watt meters should be

shorted.

4. The AC supply is applied and removed from the transformer under no load condition.

Procedure:


2. DPST switch is closed.

3. Under no load condition, ammeter, voltmeter and wattmeter readings on both primary

side and secondary side are noted down.

4. The load is gradually increased and for each load intervals, corresponding reading of

voltmeter, ammeter and wattmeter on both primary and secondary sides are noted

down.

5. The experiment is repeated until the rated current of the transformer (take the

minimum rated current of the transformer side) has reached.

6. The transformer is brought to the no load condition. The auto-transformer is brought

to its minimum position and then the DPST switch is opened.

Formulae:

1. % Efficiency, = 100Ws

Wp

2. % Regulation = 100No load Load

No Load

V V

V

Tabular Column

Vp

(Volts)

Ip

(Amps)

Wp (Watts) Vs

(Volts)

Is

(Amps)

Ws (Watts) % %

Regulation OBS *ACT OBS *ACT

*ACT=OBS × Multiplication Factor,

Where,

factorFull Scale Deflection used

wattmeter wattmeterV I Power factorMultiplication

Model Graphs:

Result:

Thus load test on the single phase transformer was carried out and efficiency was

determined.

Eff

icie

ncy

%

Reg

ula

tion R

%

R


Post-lab questions

1. What are the disadvantages of Load Test?

2. Transformer is rated in KVA. Justify.

9. LOAD TEST ON THREE PHASE TRANSFORMER

Pre-lab questions

1. List out various three phase transformer connections

2. What are the advantages of open delta connections?

3. What is other name for Scott connection and state its applications?

LOAD TEST ON THREE PHASE TRANSFORMER

Aim:

To connect the primary and secondary of the given 3 phase transformer in star-delta

and to perform the load test on the same & to plot its performance characteristics.

Apparatus Required:

S. No. Name of the Apparatus Range Type Quantity

1 Ammeter (0-10A)

MI 1

(0-15A) 1

2 Voltmeter (0-600V)

MI 1

(0-300V) 1

3 Wattmeter 600V, 10A

300V, 15A UPF

2

2

4 Three Auto Transformer 3, (0-440)V - 1

5 Three phase Resistive Load or

lamp load 3KW, 415V - 1


Precaution:

1. 3 phase auto transformer should be kept at minimum position.

2. The transformer should be kept under no load condition.

3. The ‘M’ and ‘C’ terminal of primary and secondary side watt meters should be

shorted.

4. The AC supply is applied and removed from the transformer under no load condition.

Procedure


2. TPST 1 switch is closed.

3. Under no load condition, ammeter, voltmeter and wattmeter readings on both

primary side and secondary side are noted down.

4. The load is connected to the transformer through TPST switch 2. Then the load is

gradually increased and for each load intervals, corresponding reading of

voltmeter, ammeter and wattmeter on both primary and secondary sides are noted

down.

5. The experiment is repeated until the rated current of the transformer (take the

minimum rated current of the transformer side) has reached.

6. The transformer is brought to the no load condition. The three phase auto-

transformer is brought to its minimum position and then the TPST switch is

opened.

Formulae Used

1. Input = Wp = Wp1 + Wp2 (watts)

2. Output power = Ws = Ws1 + Ws2 (watts)

3. % Efficiency = Ws / Wp × 100 %

Tabular Column 1

Wp1 (Watts) Wp2 (Watts) Wp=

Wp1+ Wp2

(Watts)

Ws1 (Watts) Ws2 (Watts) Ws=

Ws1+ Ws2

(Watts) OBS *ACT OBS *ACT OBS *ACT OBS *ACT


Where,



Tabular Column 2

Vp

(Volts)

Ip

(Amps)

Wp (Watts) Vs

(Volts)

Is

(Amps)

Ws (Watts) % %

Regulation

Model Graphs:

Result:

Load test was conducted on three phase transformer and regulation efficiency were

determined.

Eff

icie

ncy

%

Reg

ula

tion R

%

R


Post-lab questions

1. List out the difference between single phase and three phase transformer.

2. What are the disadvantages of load test?

10. SUMPNER’S TEST ON SINGLE PHASE TRANSFORMER

Pre-lab questions

1. What is the other name for Sumpner’s test?

2. Define all day efficiency of transformer?

SUMPNER’S TEST ON SINGLE PHASE TRANSFORMER

Aim:

To perform Sumpner’s test on the given single phase transformers and

1. To draw its equivalent circuit

2. To predetermine its efficiency and regulation

Apparatus Required:

S. No. Name of the Apparatus Range Type Quantity

1 Wattmeter 150 V, 2A LPF 1

75 V, 5 A UPF 1

2 Ammeter (0-2) A

MI 1

(0-5)A 1

3 Voltmeter

(0-150) V MI

1

(0-75) V 1

(0-600)V 1


5 DPST Switch - - 1

Precautions:

1. Both the autotransformers should be kept at its minimum potential position.

2. SPST switch should be kept open, at the time of starting.

Procedure:

1. Connections are to be made as shown in the circuit diagram.

2. DPST switch 1 is closed. Rated voltage of 110V is varied to get in voltmeter by

adjusting the Auto Transformer 1.

3. The readings of voltmeter 1, ammeter 1 and wattmeter 1 are noted on the primary side

(LV Side).

4. The voltmeter 3 reading connected across the SPST switch is noted down.

5. If the reading of voltmeter 3 reads higher voltage, the terminals of any one of

secondary coils (HV side) is interchanged such that the voltmeter 3 reads zero.

6. Then DPST switch 2 is closed after ensuring zero reading in the voltmeter 3.

7. The auto-transformer 2 is varied so that full load rated secondary current flows.

8. Corresponding readings of wattmeter 2, ammeter 2 and voltmeter 2 are noted down.

Tabular Column

Vo

(Volts)

Io

(amp)

Wo

(Watts)

Vsc

(Volts)

Isc

(Amp)

Wsc (Watts)

OBS *ACT OBS *ACT


Where,



Formulae Used:

Vo = V1

Io = I1/2

Wo = W1/2

Vsc = V2/2

Isc = I2

Wsc = W2/2

1. Cos 0 = oo

o

IV

W

2. Sin 0 = oCos 21 or 0 = Cos-1

o

o o

W

V I

Open Circuit parameters referred to LV side (test conducted on LV side):

3. RoLV = oo

o

CosI

V

where Io cos 0 = Iw = working component

4. XoLV = oo

o

SinI

V

where Io sin 0 = I = magnetising compent

Short Circuit Parameters referred to HV side (test conducted on HV side):

5. Z1eHV = SC

SC

I

V

6. R1eHV = 2

SC

SC

I

W

7. X1eHV = 2 2

1 1e eZ R

1. Equivalent circuit referred to LV side

Note: The OC test is conducted on LV side. The SC test is conducted on HV side. Hence the

obtained open circuit parameters are referred to LV side and the obtained short circuit

parameters are referred to HV side. To obtain the complete equivalent referred to LV side, it

is necessary to transform short circuit parameters referred to LV side. This can be carried out

using the transformation ratio KLV. The open circuit parameters are retained as such.

1. KLV = Voltage(115)

High Voltage(230)

Low

2. R2eLV = K2

LV ×R1eHV

3. X2eLV = K2

LV ×X1eHV

R1eHV

RoHV XoHV

Vo’

Io’

I1’

P

N

Equivalent Circuit referred to LV Side:

2. Equivalent circuit referred to HV side

Note: To obtain the complete equivalent referred to LV side, it is necessary to transform open

circuit parameters referred to HV side. This can be carried out using the transformation ratio

KHV. The short circuit parameters are retained as such.

1. KHV = High Voltage(230)

Low Voltage(115)

2. RoHV = K2

HV ×RoLV

3. XoHV = K2

HV ×XoLV

Equivalent Circuit referred to HV Side:

X2eLV R2eLV

RoLV XoLV

Vo

Io

I1 P

N

L

O

A

D

X1eHV

L

O

A

D

3. Predetermination of efficiency for various load conditions at any given power factor

1. From OC test, Core loss = Wo

2. From SC Test, Copper loss = Wsc (copper loss at full load) % Efficiency at any load

for the given power factor can be calculated using the formula,

3. % Efficiency at any load = 2 2

2

2 2

cos

cos ( )

rated rated

rated rated o sc

n V I

n V I W n W

(or)

4. % Efficiency at any load = 2

(rating)cos

(rating)cos ( )o sc

n VA

n VA W n W

Where n is the fraction of load

4. Predetermination of Regulation for various power factors at any given load

For Lagging PF,

2 2 2 2

2

( cos ) ( sin )% 100rated eLV rated eLV

R

rated

n I R n I XV

V

For Leading PF,

= 2 2 2 2

2

( cos ) ( sin )% 100rated eLV rated eLV

R

rated

n I R n I XV

V

Predetermination of Efficiency:

Sl

No.

Fraction of Load (n) %

p.f=1 p.f=0.8

1 1

2 3/4

3 1/2

4 1/4

Predetermination of Voltage regulation:

Cos % Regulation for load fraction

n=1

% Regulation for load fraction

n=0.5

Lag+ Lead

- Lag

+ Lead

-

0

0.2

0.4

0.6

0.8

1

Model Graphs:

Eff

icie

ncy

%

Output power (Watts)

Drawn

for

p.f=0.8

Result:

Thus sumpner’s test was conducted to determined efficiency and regulation and the

equivalent circuit were also drawn.

Power factor

%VR for lagging

% VR for

leading

Drawn for Rated Full

Load Current

Post-lab questions

1. State the merits of Sumpner’s test

2. State the demerits of Sumpner’s test

11. TRANSFER FUNCTION OF ARMATURE CONTROLLED DC MOTOR

Pre-Lab Questions

1. State DC motor principle

2. Define poles and zeros

3. What is the significance of deriving the transfer function

TRANSFER FUNCTION OF ARMATURE CONTROLLED DC MOTOR

Aim

To obtain the transfer function of armature controlled DC motor

Apparatus Required

Sl. No. Apparatus Type & Range Quantity

1 Rheostat 50 / 5A

300 / 1.2A

1

1

2 Ammeter (0-10A) MC

(0-200mA) MI

1

1

3 Voltmeter (0300V) MC

(0-30V) MI

2

1

4 1-phase Variac -- 1

Formula

Transfer function = ])1)(1[()(

)(

bama

a

a KKSTST

K

sV

s

BR

KK

a

t

a

where Kt is the slope of T – Ia curve (motor gain constant)

radKgm

dt

dNN

PJ

tt

tPP /

0106.0

.'

' 2

21 loglog

12

N

e

N

e

m

m

ttT

T

JB

b

a

a

a KR

LT = back emf constant volt / rpm from no load test curve

Procedure

Load Test

1. The supply is switched on and the motor is started with a 3-point starter

2. Motor field rheostat is adjusted and the motor is brought to rated speed

3. Speed, Ammeter, Voltmeter and spring balance readings are noted down

4. Motor is loaded gradually till rated current and corresponding readings are

noted down.

Circuit diagram: Load Test

Tabulations: Load Test

Sl.

No.

V

(volts)

I

(A)

Spring balance readings Speed

(rpm)

T

(N-m) S1

(Kg)

S2

(Kg)

S1 ~ S2

(Kg)

II Procedure: Retardation Test

1. Motor is started on noload using 3-point starter

2. Adjust motor field rheostat and run motor at speed slightly greater than

rated speed.

3. Using DPST switch cut off the supply and allow the motor to retard

4. Various values of speed changes to corresponding time are taken.

5. Motor is started again and brought to the rated speed

6. DPST switch is used to cut off armature supply but a known resistance is

added to armature circuit & motor is allowed to retard.

7. Time for 5% fall on speed & corresponding voltmeter, ammeter readings are

noted down.

Circuit diagram: Retardation Test

Retardation Test:

(Without load R) (With load R)

N (rpm) Time (s) N (rpm) V (volts) I (A) Time, T(s)

No Load Test

Sl. No. Speed (rpm) V (volts) Ia (A) Eb (V)

8. Time for 5% fall in speed without R is noted

Model Graphs

Model Calculation:

Find Kb and Kt from Eb Vs N and TVs Ia graphs

Find La from Ra and Xa measurements

Determine dN / dt, the slope of NVs Time graph

)(2

1)(

2

1' 2

2

2

12211 aa RIRIIVIVP from retardation test values with load

t1 = Time in ‘sec’ for retardation of the machine with resistive load

t = Time in ‘sec’ for retardation of the machine without resistive load

find

dt

dNN

PJ

ttT

NNm

0109.0

,loglog 21

12

wheremT

JB

tt

tPP

''

BR

KK

a

t

a

. Obtain transfer function by substitution of constants.

III To find Ra:

1. The connections are given as per the circuit diagram

2. By varying the rheostat, different values of V and I are noted

3. From these above values, the value of Ra is computed.

To find Ra:

Va(V) Ia (A) Ra = Va / Ia ()

Average

IV To find La

To find La:

1. The connections are given as per the circuit diagram

2. By varying the 1 phase variac, different values of V and I are noted

3. From these values, the values of Z are obtained. From Z and Ra, the value of

Xa (and hence La) are computed.

To find La:

Va(V) Ia (A) Za = Va / Ia () Xa () La (H)

Average

Result

Hence the transfer function of the given armature controlled DC motor was found to

be

TRANSFER FUNCTION OF FIELD CONTROLLED DC MOTOR

Aim

To determine the transfer function of a field controlled DC motor.

Apparatus Required

Sl. No. Apparatus Type & Range Quantity

1 Ammeter (0-10A) MC

(0-2A) MC

(0-2A0 MI

1

1

1

2 Voltmeter (0-300V) MC

(050) MC

1

2

3 Rheostat 300 / 1.2A

100 / 3A

1

1

Formula

The transfer function of a field controlled DC motor is

)1)(1()(

)(

mf

m

f STST

K

E

Tm = Mechanical time constant of rotor = J/B

J = Moment of Inertia of rotor = Kg m2 / rad – sec

Lf = Field inductance (H)

Km = Determined Using Load Test

T = R x 9.8 X (S1 ~ S2) N-M

Tf = Time constant of field circuit Lf / Rf

Procedure

I) To determine motor gain constant – Km (Load test):-

1. Motor field rheostat is kept at minimum position

2. Supply is given and the motor is started

3. Adjust the motor field rheostat and bring the motor to rated speed

4. Voltmeter, ammeter and spring balance readings are noted.

5. Readings are taken for different field event keeping armature current cut.

LOAD TEST

3 Point Starter

Load Test:

Sl.

No.

V

(Volts)

If

Ia kept

emf)

N

(rpm)

Spring balance readings Torque

T=9.81 R X S1 ~ S2 N-

m S1

(Kg)

S2

(Kg)

S1 ~ S2 (Kg)

To find Rf:

To find Rf :

1 Connections are given as per the circuit diagram

2 By varying rheostat different ammeter and voltmeter readings are obtained.

Sl.No. V (volts) I (A) Rf = V/If ()

Average

II) Retardation Test:-

1. Connections are given as per the circuit diagram

2. Motor sis started on no load

3. Motor field rheostat is adjusted to bring the motor slightly above the rated

speed

4. Using DPDT switch supply is cut off and motor is allowed to retard

5. Different values of speed changes to the corresponding time are noted

6. Now motor is started as usual and brought to rated speed

7. DPDT switch is thrown off such that supply to armature is cut off, but a

known resistance R is connected to the armature and the motor is allowed to

retard.

8. Time taken of 5% fall in speed, voltmeter voltmeter and current readings are

noted.

9. Similarly time taken for 5% fall in speed without R is obtained.

To find Lf:

Model Graph:

To find Ra:

To find Ra:

Sl.

No.

Va

(Volts)

Ia

(A)

Ra

(Ω)

Retardation Test:

Retardation Test:

Without load resistance With load resistance

N (rpm) Time (s) I (A) V (volts) N (rpm) t (sec)

To fine Lf:

1 Connections are given as per the circuit diagram

2 The variac is adjusted to obtain different voltages and currents

Sl. No. V (volts) If (mA) Zf (Vf/If () Xf Lf

Average

Model Calculation

Obtain sf

tI

TK

from T – If curve

dT

dNis calculated from N-t curve obtained from Retardation test without R

)(1

1

tt

tPP

where P1

power consumed in the load resistor during retardation test

)(2

1)(

2

1 2

2

2

12211 aa RIRIIVIV

t = Time taken for speed reduction during retardation test without load R

t’ = Time taken for speed reduction during retardation test with load R.

Now, P = 0.0109 JN dt

dN

J can be determined now.

21 loglog

12

NNm

ttT

obtained from speed time curve

Find B = mT

J

BR

KK

f

tm

Substituting the values for different constants in the general formula for TF, we get the

transfer function of the given M/C

Result

Hence the transfer functions of the field controlled DC motor was found to be

15EE204L ELECTRICAL MACHINES LABORATORY-I ACADEMIC...

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