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CHENNAI INSTITUTE OF TECHNOLOGY

Kundrathur to Sriperumbudur Highway, Kundrathur,Nandhambakkam Post, Pudupedu,

Chennai– 600 069.

DEPARTMENTOF ELECTRONICS AND COMMUNICATION

ENGINEERING

LABORATORY MANUAL

EE 6461Electrical Engineering and Control System Laboratory

2

LIST OF EXPERIMENTS

1. Open circuit and load characteristics of separately excited and self excited

D.C.Generator.

2. Load test on DC shunt motor.

3. Swinburne’s test and speed control of DC shunt motor.

4. Load test on single phase transformer and open circuit and short circuit test on single phase

transformer

5. Regulation of three phase alternator by EMF and MMF methods.

6. Load test on three phase induction motor.

7. No load and blocked rotor tests on three phase induction motor (Determination of equivalent

circuit parameters and predetermination of performance characteristics at various loads)

8. Study of D.C. motor and induction motor starters.

9. Digital simulation of linear systems.

10. Stability analysis of linear system using MATLAB.

11. Study the effect of P, PI, PID controllers using MATLAB.

12. Design of lead and lag compensator.

13. Transfer function of separately excited D.C. generator.

14. Transfer function of armature and field controlled DC motor

3

Ex. No: 1A

Date:

OCC AND LOAD CHARACTERISTICS OF SEPARATELY EXCITED D.C GENERATOR

Aim:

To conduct no load and load test on separately excited generators and to obtain the

characteristics

Exercise

1. Obtain the open circuit characteristics (OCC) of a separately excited D.C generator and

determine critical resistance.

2. Draw the external and internal characteristics of a separately excited D.C generator and compute

full load regulation.

Apparatus Required:

Sl.no Name of the component Specification Quantity

Name plate details:

Motor Generator

Fuse rating calculation for field and armature:

No load test

10 % of rated current (full load current)

Load test


Precautions

1. Motor side field rheostat should be kept at minimum resistance position.

2. Generator side field rheostat should be kept at maximum resistance position.

3. Starter should be in off position before switching on the supply.

4. The DPST switch must be kept open.

4

CIRCUIT DIAGRAM FOR OPEN CIRCUIT ON SEPARATELY EXCITED DC

GENERATOR

Procedure for open circuit test

1. Connections are given as per the circuit diagram.

2. The motor is started with the help of THREE POINT starter.

3. Adjust the motor speed to rated speed by adjusting motor field rheostat when the generator is

disconnected from the load by DPST switch 2.

4. By varying the generator field rheostat gradually, the open circuit voltage [Eo] and

corresponding field current (If) are tabulated up to 125 % of rated voltage of generator.

5. The motor is switched off by using DPST switch 1 after bringing all the rheostats to initial

position.

Tabulation for Open Circuit Test on Separately Excited D.C Generator:

Sl.no Open circuit

voltage in

Volts [Eo]

Field

current in

Amps [If]

CIRCUIT DIAGRAM FOR LOAD TEST ON SEPARATELY EXCITED DC SHUNT

GENERATOR

5

Procedure for Load test:

1. Connections are given as per the circuit diagram

2. The prime mover is started with the help of three point starter and it is made to run at rated speed

when the generator is disconnected from the load by DPST switch 2.

3. By varying the generator field rheostat gradually, the rated voltage [Eg] is obtained.

4. The ammeter and voltmeter readings are observed at no load condition.

5. The ammeter and voltmeter readings are observed for different loads up to the rated current by

closing the DPST switch 2.

6. After tabulating all the readings the load is brought to its initial position.


position.

Tabulation for Load Test:

Sl.no

Armature

current

[Ia] in

Amps

Load

voltage

[VL] in

Volts

Load

current

[IL] in

Amps

Armature

drop Ia Ra

In volts

Generated

emf

[Eg =

VL+IaRa]

In volts

6

Circuit diagram for find the generator armature resistance [Ra]

Procedure for find armature resistance Ra:

1. Connections arte given as per circuit diagram

2. Check loading rheostat must be at maximum resistance position.

3. Close the DPST switch and vary the loading rheostat for various values in steps and noted

the corresponding voltmeter and ammeter reading.

4. Open the DPST switch after loading rheostat begins its initial position.

Tabulation for Finding Armature Resistance:

Sl.no Armature voltage

Va

Armature current

I Ra = Va/ Ia

Model graph

Open circuit characteristics Internal (Eg Vs Ia) and External (VL Vs IL)

characteristics

Result:

If

Field current

[If] in amps

Open

cir

cuit

volt

age

in

Volt

s [E

o]

Eo Vs If

Load current [IL] in amps

Armature current [Ia] in amps

Load

volt

age

in V

olt

s [V

L]

Gen

erat

ed e

mf

in V

olt

s [E

g]

Eg Vs Ia

VL Vs IL

7

Ex. No: 1B

Date:

OCC AND LOAD CHARACTERISTICS OF SELF EXCITED D.C SHUNT GENERATOR

Aim:

To conduct no load and load test on self excited generators and obtain the characteristics

Exercise

1. Obtain the open circuit characteristics (OCC) of a self excited D.C generator

and determine critical resistance.

2. Draw the external and internal characteristics of a self excited D.C generator

and compute full load regulation.

Apparatus Required:

Sl.no Name of the component Specification Quantity

Name plate details:

Motor Generator


No load test


Load test


Formula used:

Generated voltage Eg = VL + Ia Ra

Precautions 1. Motor side field rheostat should be kept at minimum resistance position.

2. Generator side field rheostat should be kept at maximum resistance position.

3. Starter should be in off position before switching on the supply.

4. The DPST switch must be kept open.

8

CIRCUIT DIAGRAM FOR OPEN CIRCUIT TEST ON SELF EXCITED DC SHUNT

GENERATOR

Procedure for open circuit test


2. The motor is started with the help of THREE POINT starter.

3. Adjust the motor speed to rated speed by adjusting motor field rheostat when the generator is

disconnected from the load by DPST switch 2.

4. By varying the generator field rheostat gradually, the open circuit voltage [Eo] and

corresponding field current (If) are tabulated up to 125 % of rated voltage of generator.


position.

CIRCUIT DIAGRAM FOR LOAD TEST ON SELF EXCITED DC SHUNT GENERATOR

Procedure for Load test:

1. Connections are given as per the circuit diagram

2 The prime mover is started with the help of three point starter and it is made to run at rated

speed when the generator is disconnected from the load by DPST switch 2.

3. By varying the generator field rheostat gradually, the rated voltage [Eg] is obtained.

4. The ammeter and voltmeter readings are observed at no load condition.

5. The ammeter and voltmeter readings are observed for different loads up to the rated

current by closing the DPST switch 2.

9

6. After tabulating all the readings the load is brought to its initial position.

7. The motor is switched off by using DPST switch 1 after bringing all the rheostats to

initial position.

Tabulation for Open Circuit Test on Separately Excited D.C Shunt Generator:

Sl.no Open circuit

voltage in

Volts [Eo]

Field

current in

Amps [If]

Tabulation for Load Test:

Sl.no

Armature

current

[Ia] in

Amps

Load

voltage

[VL] in

Volts

Load

current

[IL] in

Amps

Armature

drop Ia

Ra

In volts

Generated

emf [Eg

=

VL+IaRa]

In volts

Circuit diagram for find the generator armature resistance [Ra]

Procedure for find armature resistance Ra:

1. Connections are given as per circuit diagram

2. Check loading rheostat must be at maximum resistance position.

3. Close the DPST switch and vary the loading rheostat for various values in steps and noted

the corresponding voltmeter and ammeter reading.

4. Open the DPST switch after loading rheostat begins its initial position.

10

Tabulation for Finding Armature Resistance:

Sl.no Armature voltage

Va

Armature current

I Ra = Va/ Ia

Model graph

Open circuit characteristics

Internal (Eg Vs Ia) and External (VL Vs IL) characteristics

Result:

Load current [IL] in amps

Armature current [Ia] in amps

Load

volt

age

in V

olt

s [V

L]

Gen

erat

ed e

mf

in V

olt

s [E

g]

Eg Vs Ia

VL Vs IL

If

Field current

[If] in amps

Open

cir

cuit

volt

age

in

Volt

s [E

o]

Eo Vs If

11

Ex. No: 2

Date:

LOAD CHARACTERISTICS OF DC SHUNT MOTOR

Aim:

To conduct load test on DC shunt motor and compound motor and draw the characteristic

curves

Exercise

Draw the following characteristic curves for DC shunt motor

i. Output Vs η%

ii. Output Vs T

iii. Output Vs N

iv. Output Vs IL

v. Torque Vs N

Apparatus Required:

Sl.no Name of the component type Range Quantity

-

Name plate details:

MOTOR


Load test

125 % of rated current

Formulae Used:

(i) Torque = )2

(81.9)~( 21

tRSS in N-M

S1, S2 – spring balance readings in Kg

R- Break drum radius in m

(ii) Input power = V x I in Watts

(iii) Output power = 2NT / 60 in Watts

N – Speed of the motor in RPM

(iv) Percentage of efficiency = (Output power /Input power) x 100.

CIRCUIT DIAGRAM FOR LOAD TEST ON DC SHUNT MOTOR

12

Precautions

Starter should be in off position before switching on the supply.

The DPST switch must be kept open.

The motor field rheostat must be kept at minimum resistance position

There should be no load on the motor at the time of starting.

Before connecting the meters check the polarity and zero error.

Procedure for DC shunt motor

Connections are given as per the circuit diagram.

Observe the precaution and using three-point starter the motor is started to run at the

rated speed by adjusting the field rheostat if necessary.

The meter readings are noted at no load condition.

By using break drum with spring balance arrangement the motor is loaded and the

corresponding readings are noted up to the rated current.

After observation of all the readings the load is released gradually

The motor is switched off by using DPST switch.

TABULATION FOR LOAD TEST ON DC SHUNT MOTOR

Radius of the brake drum (R) = in m Thickness of the belt (t) = in m

Sl

No

Load

Voltage

in

Volts

Load

current

I

Amps

speed

in

rpm

Spring balance

Reading

In kg

Input

Power

in

Watts

Torque

in NM

Output

Power

in

Watts

Efficiency

in %

S1 S2 S1S2

13

MODEL GRAPH

(A) Electrical characteristics

(B) Mechanical characteristics

(C) Torque, Speed Vs Load current

in %

T in N-m

Speed in rpm

IL in Amps

N IL T %

Output power in watts

T Vs N

Sp

eed

(N

) in

rpm

Torque ( T ) in N-m

14

Model calculation:

Graph:

Output Vs η%

Output Vs T

Output Vs N

Output Vs IL

Torque Vs N

Result:

Ex. No: 3

Date:

SWINBURNE’S TEST AND SPEED CONTROL OF DC SHUNT MOTOR

Aim

To conduct Swinburne’s test and predetermine the performance characteristics of DC

machine and speed control of DC motor

Exercise

1. Predetermine efficiency at various load current while operating as a motor and generator and

plot a graph output Vs η%

2. Draw the following curves for

a. If Vs N at Va = 0.8 Va and 1Va

b. Va Vs N at 0.8 If and If

Apparatus Required:


To

rqu

e (T

) i

n N

-m

Sp

eed

(N

) i

n r

pm

IL Vs N

Load current (IL) in Amps

IL Vs T

15

Name plate details:

Motor

Speed

Type

Field Armature

Fuse rating calculation:

CIRCUIT DIAGRAM TO FIND THE CONSTANT LOSS

Precaution:

16

Starter should be in off position before switching on the supply.

The DPST switch must be kept open.

The motor field rheostat must be kept at minimum resistance position

The motor armature rheostat must be kept at maximum resistance position.

Before connecting the meters check the polarity and zero error.

Procedure


Observe the precaution and switch ON the supply.

By adjusting the field rheostat get the motor speed to rated speed

A. Armature Control Method

Keep the Field Current Constant

By adjusting armature rheostat the speed and armature voltage are noted.

Repeat the same procedure for various positions.

B. Field Control Method

Keep the armature voltage constant.

By adjusting the field rheostat various field currents and voltage are noted.

Repeat the same procedure for various positions

Tabulation for Armature Control Method

Field current I1 Field current I2

Armature

voltage Va Speed N in RPM

Armature

voltage Va

Speed N in

RPM

Tabulation for Field Control Method

Armature Voltage V1 Armature Voltage V2

Field Current If

In AMPS Speed N in RPM

Field Current

If In AMPS

Speed N in

RPM

17

Result:

Ex. No: 4

Date:

OC AND SC TESTS ON SINGLE PHASE TRANSFORMER

Aim:

To conduct open circuit and short circuit test and to predetermine the efficiency of the

transformer at desired load and power factor and to calculate the regulation at different power factor

Exercise

1. Determine the equivalent circuit of the transformer.

2. Predetermine the efficiency at different load at UPF and 0.8 Power factor lagging.

3. Predetermine the full load regulation at different power factor.

4. Draw the following curves

a. Output Vs η%

b. Power factor Vs %Regulation

Apparatus Required:


-

Name plate details:

Transformer

18

Fuse calculation for transformer (O.C and S.C test):

Primary current IP = KVA rating of the transformer /primary voltage.

Secondary current IS =KVA rating of transformer / secondary voltage.

O.C test

10 % of rated primary current

S.C test

125 % of rated secondary current

Formulae Used:

Open circuit test:

1. No load power factor ococ

oc

IV

W

)(cos 0

WOC = open circuit power in watts

VOC = open circuit voltage in volts

IOC = open circuit current in amps

2. No load working component resistance (RO); oOC

OC

OCosI

VR

in ohms

3. No load magnetizing component (XO); oOC

OC

OSinI

VX

in ohms

Short circuit test:

4. Equivalent impedance referred to HV side (Z02); SC

SC

OI

VZ 2 in ohms.

5. Equivalent resistance referred to HV side (R02); 22

SC

SCO

I

WR in ohms

6. Equivalent reactance referred to HV side (X02); 2

2

2

22 OOO RZX in ohms

7. Transformation ratio (K); 1

2

V

VK

8. Equivalent resistance referred to LV side (R01); 2

2

1K

RR O

O in ohms

9. Equivalent reactance referred to LV side (X01); 2

2

1K

XX O

O in ohms

Efficiency and regulation

10. Output power = )( CosKVAX in watts

11. Chopper loss = )( 2

SCWX in watts

12. Total loss WT = )( lossIronlossCu in watts

13. Efficiency = 100 lossTotalpowerOutput

powerOutputin %

14. Regulation = 100[

2

22

O

OOSC

V

SinXCosRIX in %

19

Precautions:

1. Auto transformer should be kept at zero volt position.

2. At the time of starting the experiment DPST switch kept open and transformer should be no

load.

3. High voltage and low voltage sides of the transformer should be properly used as primary or

secondary respective to experiments.

Procedure (for Open circuit Test)


Ensuring the precautions the supply is switched on by closing DPST switch.

Auto transformer is adjusted to energize the transformer with primary voltage on LV side.

Voltmeter, ammeter and wattmeter readings are noted at no load condition.

Auto transformer is gradually decreased to its initial position.

Switch off the supply by DPST.

Procedure (for Short CKT Test)


Ensuring the precautions the supply is switched on by closing DPST switch.

Auto transformer is adjusted to energize the transformer with primary current on the HV

side.

Voltmeter, ammeter and wattmeter readings are noted at no load condition.

Auto transformer is gradually decreased to its initial position.

Switch off the supply by DPST.

Circuit diagram for open circuit test of 1 transformer

Circuit diagram for short circuit test of 1 transformer

20

Tabulation for OC Test multiplication factor:

Sl.

no

Open circuit

primary current

(IOC)

In Amps

Open circuit

primary voltage

(VOC) in Volts

Open circuit power

(Woc) in Watts Open circuit

Secondary

voltage in volts Observed Actual

Tabulation for SC Test multiplication factor:

Sl.

No

Short circuit

primary current

(ISC)

In Amps

Short circuit

primary voltage

(VSC) in Volts

Short circuit power

(Wsc) in Watts Short circuit

Secondary

Current in Amps Observed Actual

Predetermination of efficiency:

Core (or) Iron loss (Wi) = Watts, KVA rating of Transformer = .

Rated Short circuit current = Amps Short Circuit power (WSC) = .

Fraction

of load/

Load

factor

(X)

Short

circuit

current

(ISC X)

in Amps

Output

power )( CosKVAX in

watts

Copper

loss

)( 2

SCWX

in watts

Total loss

SCiT WWW

in watts

Efficiency

TWpo

po

/

/ X 100

in % 0.2 0.4 0.6 0.8 1

21

¼

½

¾

1

Tabulation to predetermine % Voltage regulation:

ISC = RO2= XO2= V2O=

Fractio

n of

load

(X)

Value of Cos Value of Sin

% of Regulation

100[

2

22

O

OOSC

V

SinXCosRIX

1 0.

8

0.

6

0.

4

0.

2 1

0.

8

0.

6 0.4 0.2 1

0.8 0.6 0.4 0.2

Lag Lead Lag Lead Lag Lead Lag Lead

¼

½

¾

1

Model graph

1) Efficiency 2) Regulation

22

Result:

EXPT NO: 4.b

Date :

LOAD TEST ON A SINGLE PHASE TRANSFORMER

AIM:

To conduct a direct load test on the given single phase transformer and to determine the

efficiency and regulation at different load conditions.

NAME PLATE DETAILS:

KVA rating =

Rated H.V side Voltage =

Rated L.V side Voltage =

INSTRUMENTS AND EQUIPMENTS REQUIRED:

S.No Equipment Type Range Quantity

1.

2.

3.

4.

5.

THEORY:

Direct load test is conducted to determine the efficiency characteristics and regulation

characteristics of the given transformer.

An ideal transformer is supposed to give constant secondary voltage irrespective of the load

current. But, practically the secondary voltage decreases as the transformer is loaded due to primary

23

and secondary impedance drops. Since these drops are dependent on load current, this variation in

terminal voltage is found using direct loading.

PRECAUTIONS:

1. Remove the fuse carriers before wiring and start wiring as per the circuit diagram.

2. Fuse Calculations: This being a load test, the required fuse ratings are 120% of rated current on

L.V side.

PROCEDURE:

1. The circuit connections are made as per the circuit diagram as shown in figure.

2. Keeping the autotransformer in its minimum position and the DPST switch in open position, the

main supply is switched ON.

3. By slowly and carefully operating the Auto transformer the rated voltage (115V) is applied to the

L.V side of the transformer.

4. Under this no-load condition one set of readings namely VH.V, IH.V, WH.Vs, VL.V, WL.V, are

recorded in the tabular column.

5. The DPST switch on the load side is now closed and the load is increased in gradual steps and at

each step all meter readings are noted down in the tabular column.

CIRCUIT DIAGRAM:

6. The procedure is continued until the current on the H.V side is equal to its full load value.

7. After the experiment is completed, the load is decreased to its minimum, the auto transformer is

brought back to its original position and then the main supply is switched OFF.

CALCULATIONS:-

24

I. EFFICIENCY CALCULATION:

i . The efficiency of the transformer for each set of reading is calculated and tabulated

using the expression,

100% XInput

Output

where,

The output of the transformer = VH.V * IH.V on the H.V side

The input of the transformer = WL.V = Wattmeter reading on the L.V side

ii . A Graph is plotted between the percentage efficiency and the output, taking %

efficiency on Y-axis and the output on X-axis, as shown in figure.

II . REGULATION CALCULATIONS: -

i . The regulation is calculated and tabulated for each set of readings using the

expression ,

100Re%

)(.

)(.)(.X

V

VVgulation

NoloadVH

loadVHNolaadVH

where,

VH.V(No-load) - is the no-load voltage on the H.V side .

VH.V(Load) - is the actual voltage on the H.V side under load condition .

ii . A Graph is plotted b=ween the percentage regulation and the output taking % regulation on

Y-axis and the output on X- axis as shown in figure.

TABULAR COLUMN:

Input Out put

(%)

%REG VL.V

IL.V

WL.V

(W)

VH.V

(V)

IH.V

(A)

WH.V

(watts)

25

MODEL CALCULATION:

MODEL GRAPH:

RESULT: -

26

Ex. No: 5

Date:

Predetermination of Regulation of Three Phase Alternator by EMF and MMF Methods

AIM:

To predetermine the regulation of three phase alternator by EMF and MMF method and also

to draw the vector diagrams.

Name plate details:

3 Alternator DC Shunt Motor

Fuse rating:

125 % of current (Full load current)

For dc shunt motor.

For alternator

Apparatus required:

s. no Name of the apparatus Type Range Quantity

Formulae used:

Emf method:

Armature resistance Ra = 1.6 Rdc where - Rdc is the resistance in DC supply.

Synchronous impedance Zs = Open circuit voltage (E1 (ph))/short circuit current (Isc)

Synchronous impedance Xs = (Zs2-Ra

2)

Open circuit voltage Eo = ((Vrated cos + Ia Ra) 2

+ (Vrated sin +IaXs)2)(For lagging power

factor)

Open circuit voltage Eo = ((Vrated cos + Ia Ra)2+(Vrated sin - IaXs)

2) (For leading power

factor)

Open circuit voltage Eo = ((Vrated cos + Ia Ra)2+( IaXs)

2) (For unity power factor)

Percentage regulation = (Eo-Vrated /Vrated)*100(For both EMF and MMF methods)

Precaution:

27

i. The motor field rheostat should be kept in the minimum resistance position.

ii. The alternator field potential divider should be in the maximum voltage position.

iii. Initially all switches are in open position.

Procedure for both emf and MMF method:

1. Note down the nameplate details of motor and alternator.

2. Connections are made as per the circuit diagram.

3. Give the supply by closing the dust switch.

4. Using the three point starter, start the motor to run at the synchronous speed by varying the

motor filed rheostat.

5. Conduct an open circuit test by varying the potential divider for various values of field

current and tabulate the corresponding open circuit voltage readings.

6. Conduct a short circuit test by closing the TPST switch and adjust the potential divider to set

the rated armature current, tabulate the corresponding field current.

7. Conduct a stator resistance test by giving connection as per the circuit diagram and tabulate

the voltage and current readings for various resistive loads.

Procedure to draw the graph for EMF method:

1. Draw the open circuit characteristics curve (generator voltage per phase Vs field current)

2. Draw the short circuit characteristics curve (short circuit current Vs field current)

3. From the graph find the open circuit voltage per phase (E1 (ph)) for the rated short circuit

current (Isc).

4. By using respective formulae find the Zs, Xs, Eo and percentage regulation.

Open circuit test:

S.NO Field current(If) Open circuit line

voltage (VOL)

Open circuit phase

voltage (Vo(ph))

Amps Volts Volts

29

Short circuit test:

Tabulation to find out the armature resistance (ra):

Procedure to draw the graph for MMF method:

1. Draw the open circuit characteristics curve (generator voltage per phase Vs field current)

2. Draw the short circuit characteristics curve (short circuit current Vs field current)

3. Draw the line OL to represent If’ which gives the rated generated voltage (V).

4. Draw the line LA at an angle (90Φ) to represent If” which gives the rated full load

current.(Isc) on short circuit [(90Φ) for lagging power factor and (90- Φ) for leading

power factor].

5. Join the points O and A and find the field current (If) measuring the distance OA that

gives the open circuit voltage (E0) from the open circuit characteristics.

6. Find the percentage regulation by using suitable formula.

Procedure to draw the vector diagram:

1. Draw the line OA that represents the rated voltage V.

2. Draw the line OB to represent the rated current Ia, which makes an angle Φ (it may

lags/leads in phase) with the voltage.

3. Draw the line AC to represent IRa drop, which is parallel to current axis (OB)

4. Draw the perpendicular line CD with the line AC (IRa drop) to represent IXs drop.

5. Join the points D and A to represent the IZs drop.

6. Join the points O and D and measure the length OD by voltage scale to find open circuit

voltage Eo.

7. Find the percentage regulation by using suitable using formulae.

RESULTANT TABULATION FOR REGULATION OF THREE PHASE ALTERNATOR BY EMF AND

MMF METHODS

S.No Field current(If)

Short Circuit Current

(120 to 150 % of rated

current ) (Isc)

Amps Amps

S.No Armature current

(I)

Armature voltage

(V)

Armature Resistance

Ra=V/I

Amps Volts Ohms

30

MODEL CALCULATION:

RESULT

Ex. No:6

Date:

Load Test on Three - Phase Induction Motor(Squirrel cage) Aim:

To conduct the load test on three phase squirrel cage induction motor and to draw the

performance characteristics curves.

Name plate details:

3 Induction Motor Auto Transformer

Fuse rating:

S.N

o Power

factor

EMF method MMF method

Lagging Leading unity Lagging Leading unity

1. 0.2

2. 0.4

3. 0.6

4. 0.8

5. 1.0

31

125% of rated current (Full load current)

Apparatus required:

Formulae used:

1. Torque = (S1S2) (R+t/2) x 9, 81 N-m.

S1, S2 – spring balance readings in Kg.

R – Radius of the brake d5rum in m.

T – Thickness of the belt in m.

2. Output power = 2NT/60 Watts

N – Rotor speed in rpm.

T – Torque in N-m.

3. Input power = (W1+W2) Watts

W1, W2 – Wattmeter readings in watts.

4. Percentage of efficiency = (Output power/Input power) x 100%

5. Percentage of slip = (Ns – N)/Ns x 100%

Ns – Synchronous speed in rpm.

N – Speed of the motor in rpm.

6. Power factor (cos ) = (W1+W2)/3 VLIL.

Circuit diagram

i. The motor should be started without any load

PROCEDURE:

S.No Name of the Apparatus Type Range qty

1.

2.

3

4

32

1. Note down the name plate details of motor.

2. Connections are made as per the circuit diagram.

3. The TPSTS is closed and the motor is started using On Line starter to run at rated speed.

4. At no load the speed, current, voltage and power are noted.

5. By applying the load, for various values of current the above-mentioned readings are noted.

6. The load is later released and the motor is switched off and the graph is drawn.

OBSERVATION:

Circumference of the brake drum =

Thickness of the belt =

MODELGRAPH:

The graph drawn for

Output power Vs speed

Output power Vs line current

Output power vs. Torque

Output power Vs power factor

Output power Vs Efficiency

Output power Vs %slip.

Mechanical Characteristics

Electrical Characteristics

Torque Vs Speed

Torque in N-m

Sp

eed

in r

pm

33

TABULATION FOR LOAD TEST ON THREE PHASE SQUIRREL CAGE INDUCTION

MOTOR

Multiplication factor: …………..

MODEL CALCULATION:

S. no

Load current

(IL)

Load voltage

(VL)

Input power (W1)

Input power (W2)

Speed of the

motor

(N)

Spring balance

reading

Torqu

e (T)

(s1~s

2) (R) (9.81)

Output

power

2NT/60

Efficienc

y () o/p

/ i/p x 100

Slip (S)

(Ns-N) / Ns x 100

Power

factor

(cos) i/p / VLIL

Observed Actual Observe

d Actual

S

1

S

2

S1

~S2

Amps Volts Watts Watts Watts Watts rpm K

g Kg Kg N-m Watts % %

Out put Power in Watts

%

%

Cos

Cos

N in

rpm

N i

n r

pm

T in N-

m

T i

n N

-m Sli

p

S

I L

34

RESULT:

Ex. No: 7

Date:

NO LOAD TEST AND BLOCKED ROTOR TEST ON THREE PHASE SQUIRREL

CAGE INDUCTION MOTOR

Aim:

To conduct the No Load test and Blocked rotor on three phase squirrel cage induction Motor

and to predetermine the performance characteristics at various loaded conditions.

Name plate details:

3 INDUTION MOTOR AUTO TRANSFORMERS

Fuse Rating calculation:

No Load: 10% of rated current (Full load current)

Load: 125% of rated current (Full load current)

Apparatus required:

S .No Name of the

Apparatus

Type Range Qty

1

2

3

35

4.

5.

Formulae used:

Open circuit test:

No load power factor ( Cos o) = Po / Vo Io

Working component current (IW) = Io(ph) x Cos o

Magnetizing current (Im) = Io (ph) x Sin o

No Load resistance (Ro) = Vo / Io (ph) Cos o in

No load reactance (Xo) = Vo / Io (ph) Sin o in

Where:

Vo – No load voltage per phase in volts

Io – no load current per phase in amps

Po – no load power per phase in watts

Short circuit test:

Motor equivalent impedance referred to stator (Zsc (ph)) = Vsc(ph) / Isc (ph) in

Motor equivalent resistance referred to stator (Rsc(ph)) = Psc(ph) / I2sc (ph) in

Motor equivalent reactance referred to stator (Xsc(ph)) = (Zsc(ph)2 / Rsc (ph)

2 )in

ROTOR resistance referred to stator (R2’ (ph)) = Rsc(ph) – R1 in

Rotor reactance referred to stator (X2’ (ph)) = Xsc(ph) / 2 = X1 in

Equivalent load resistance (RL’) = R2’ (1/s – 1) in

Where:

R1 – stator resistance per phase

X1 – stator reactance per phase

R1= R (ac) = 1.6 x R (dc) = R2’ (1/s-1) in

Slip (S) = (Ns-N) / Ns

Ns – Synchronous speed in rpm

N- Speed of the motor in rpm

Circuit diagram of No load test of 3 induction motor

36

Circuit diagram of Blocked Rotor test of 3 induction motor

Procedure:

Note down the name plate details of motor

1. For no-load or open circuit test by adjusting autotransformer, apply rated voltage and

note down the ammeter and wattmeter readings .In this test rotor is free to rotate.

2. For short circuit or blocked rotor test by adjusting autotransformer, apply rated current

and note down the voltmeter and wattmeter readings. In this test rotor is blocked.

3. After that make the connection to measure the stator resistance as per the circuit

Diagram

4. By adding the load through the loading rheostat note down the ammeter, voltmeter

reading for various values of load

Tabulation for No load test on three phase squirrel cage induction

Speed of the induction motor: …………..

Type of the stator connection: ……………

Multiplication factor: ………..

.

No

No

load

Current

(Io)

No

Load

Voltage

(Vo)

No load power Total No

Load

Power Po

=

(W1+W2)

No load

power /

phase

Po(ph)

=

(Po/3)

No load

Current

/ Phase

Io (ph)

No load

Voltage

/ phase

Vo (ph)

W1 W2

Observed Actual Observed Actual

Amps Volts Watts Watts Watts Watts Watts Watts Amps Volts

37

Tabulation for blocked rotor test on three phase squirrel cage induction

Type of the stator connection: ……………

Multiplication factor: ………..

No

Short

Circuit

Current

(Isc)

Short

Circuit

Voltage

(Vsc)

Short Circuit power Total

Short

Circuit

Power Po

=

(W1+W2)

Short

Circuit

power /

phase

Psc

(ph) =

(Psc/3)

Short

Circuit

Current

/ Phase

Isc (ph)

Short

Circuit

Voltage

/ phase

Vsc (ph)

W1 W2

Observed Actual Observed Actual

Amps Volts Watts Watts Watts Watts Watts Watts Amps Volts

Measurement of armature resistance

Tabulation to find out the stator resistance (r1)

38

S No Stator current (I) Stator Voltage (V)

Stator Resistance Rs

= V/I

Amps Volts Ohms

MODEL CALCULATION:

RESULT:

P R1

N

X1

230 V, 1,

50Hz

AC Supply

Equivalent circuit of 1 induction motor

Ro Xo

I1 R2’ X2’ I2

Io

RL’ = R2’ (1/s-1)

39

Expt. No: 8

Date:

TRANSFER FUNCTION OF SEPERATELY EXCITED DC GENERATOR

AIM:

To determine the transfer function of separately excited dc generator.

INSTRUMENTS & EQUIPMENTS REQUIRED:

S.

No

Name of the

Equipment

Range Type No of

Quantity

1

2.

3.

4.

5.

NAME PLATE DETAILS:

D.C.GENERATOR: D.C.MOTOR:

Rated voltage: Rated voltage:

Rated Current: Rated Current:

Rated Speed: Rated Speed:

Power Rating: Power Rating:

EXCITATION:

Voltage:

Current:

40

CIRCUIT DIAGRAM:

THEORY:

The transfer function for DC generator is defined as ratio of Laplace Transform

Of output V1(t) to Laplace Transform of Input Vf(t).

Transfer function = V1(t) / Vf(t)

The KVL to field circuit is

Vf(t) = If(t)Rf + Lf (dIf(t) /dt) ………………… 1

The armature induced emf Ea(t) is

Ea(t) If(t)

= Kf If(t) ………………… 2

where Kf is proportionality constant

The KVL to armature circuit is given by

41

Ea(t) = Ia(t) (Ra +RL) +La (dIa /dt) ………………… 3

The load voltage

V1(t) = Ia(t) RL ………………… 4

Ia(t) = IL(t)

Taking Laplace transform for equations 1,2,3 & 4 we get

Vf(s) = If(s) Rf + sLf If(s) ………………… 5

Ea(s) = Kf If(s) ………………… 6

Ea(s) = Ia(s) (Ra +RL) + sLa Ia(s) ………………… 7

V1(s) = Ia(s) RL ………………… 8

From the above equations we get

Ea(s) = Kf Vf(s) / (Rf + sLf ) ………………… 9

From 7 & 9

Kf Vf(s) / (Rf + sLf ) = Ia(s) (Ra +RL) + sLa Ia(s) ………………… 10

From equation 10

Ia(s) = Kf Vf(s) / (Rf + sLf ) [(Ra +RL) + sLa ] ………………… 11

V1(s) = Kf Vf(s) R1 / (Rf + sLf ) [(Ra +RL) + sLa ]

V1(s) / Vf(s) = Kf R1 / (Rf + sLf ) [(Ra +RL) + sLa ]

G(s) = V1(s) / Vf(s) = Kf R1 / (Rf + sLf ) [(Ra +RL) + sLa ………………… 12

G(s) = V1(s) / Vf(s) = (Kf RL / Lf La ) / (s + Rf / Lf) (s + (Ra +RL) /La )

Where Lf / Rf = field time constant, La / Ra = armature time constant

La / (Ra +RL) = total time constant

The above equation is known as the load transfer function of separately excited D.C generator.

PRECAUTIONS: (Not to be included in the Record)

42

1. Remove the fuse carriers before wiring and Start wiring as per the circuit diagram.

2. Check the positions of the various rheostats as specified.

3. The SPST switch is kept open at the time of starting the experiments.

4. Fuse calculations: As this is a no-load test the required fuse ratings are 20% of the rated

current.

5. Replace the fuse carriers with appropriate fuse wires after the circuit connections are checked

by the staff-in-charge.

PROCEDURE: (To Find K)

1. The circuit connections are made as per the circuit diagram in the shown figure 4.1.

2. Keeping the motor field rheostat in its minimum position, generator field rheostat in

maximum position and the starter in its OFF position, the main supply is switched ON to the

circuit.

3. The motor is started using the 3-point starter by slowly and carefully moving the starter

handle from its OFF to ON position.

4. The motor is brought to its rated speed by adjusting its rheostat and checked with the help of

a tachometer.

5. With the SPST switch open, the residual voltage is noted.

6. Now the SPST switch is closed and the generator field rheostat is gradually decreased in

steps and at each step the field current (If) and the corresponding induced EMF (Eg) are

recorded in the tabular column. This procedure is continued until the generator voltage

reaches 120% of its rated value.

7. After the experiment is completed the various rheostats are brought back to their original

position in sequence and then main supply is switched OFF.

CIRCUIT DIAGRAM:

43

Procedure: (To Find Ra & La)

1. The circuit connections are made as per the circuit diagram shown in figure 4.2.

2. Keeping autotransformer in minimum position, Main is switched ON.

3. Slowly adjust the variac and apply a small voltage (say 20V) to the armature winding.

4. Note down voltmeter, ammeter and wattmeter readings.

5. Bring the variac to minimum position and switch OFF the main supply.

Procedure: (To Find Rf & Lf)

1. The circuit connections are made as per the circuit diagram shown in figure 4.3.

2. Keeping autotransformer in minimum position, Main is switched ON.

3. Slowly adjust the variac and apply a small voltage (say 60V) to the field winding.

4. Note down voltmeter, ammeter and wattmeter readings.

5. Bring the variac to minimum position and switch OFF the main supply.

CALCULATION:

1. The open circuit characteristic is drawn to scale as shown in model graph.

2. A tangent is drawn to the linear portion of this OCC.

3. The slope of tangent is found using the relation Kf = Ea / If

4. The inductance and resistance of the field winding are calculated as follows:

44

W1=If2Rf

Rf =W1 / If2

Zf=Vf / If

Xf = (Zf2 – Rf

2)1/2

Lf = Xf / 2пf

5. The inductance of the armature winding is calculated using the equation

W2=Ia2Ra

Ra =W2 / Ia2

Za=Va / Ia

Xa = (Za2 – Ra

2)1/2

La = Xa / 2пf

6. The transfer function of the given separately excited D.C shunt generator is then evaluated by

substituting the values Kf, Rf, Lf, Ra & La in the standard equations

For no Load

TABULAR COLUMN :

Tabulation 1: OCC test

S.NO If (A) Eg (V)

45

Tabulation 2: To find Rf and Lf

Sl.No. W1 If Vf

Tabulation 3: To find Ra and La

Sl.No. W2 Ia Va

Model Graph

MODEL CALCULATION:

RESULT:

Thus the Transfer Function of Separately Excited D.C Shunt Generator is determined &

is given by

1. G(s)NL =

2. G(s)L =

Ex. No : 9A

Date:

TRANSFER FUNCTION OF ARMATURE CONTROLLED DC SERVO MOTOR

Aim:

To derive the transfer function of the given DC Servomotor and experimentally determine

the transfer function parameters

Apparatus required:

Sl no Apparatus Name Type/ Range Quantity

46

Name plate details:

Voltage 220 V

Current 19 A

Speed 1500 RPM

H.P 5 hp

Load Brake drum

Fuse calculation:

125 % of full load current

Formula used:

1) Transfer function ]KK)f)(JssLs[(R

K

(s)E

θ(s)G(s)

bToaa

T

a

Where:

KT – Torque constant calculated from graph (T Vs Ia)

Ra – Armature Resistance in

La – Inductance of Armature in H

fo – Viscous friction coefficient In N-M / rad /sec

J – Equivalent moment of inertia of motor and load referred to motor shaft (Kg-m2)

Kb – Is the back EMF constant.

2) Inertia constant: J

21

21

2

2

60

*

*

tt

tt

NN

IVJ

av

avav

In Kg/m

2

47

Where:

T1 – Time for fall of speed from N1 to N2 in no load condition

T2 – Time for fall of speed from N1 to N2 in load condition

2

21 VVVav

,

2

21 IIIav

2

21 NNNav

21 NNN

3) Frictional coefficient of motor and load

2

2

2

2

1

2

**60

2

NNJfo

In N-M / rad /sec

Where:

60

2 avN

4) Back EMF constant Kb

60

2 N

RIVK aa

b

Where:

V- Applied voltage in volts

Ia – Armature current in A

Ra – Armature Resistance in

N – Rated speed in RPM

Theory:

Armature control method is used when speed below the no load speed are required. As

the supplied voltage is normally constant, the voltage across the armature is varied by inserting a

variable rheostat in series with the armature circuit as shown. As controlled resistance is

increased, potential difference across the armature is decreased. For load of constant speed

approximately proportional to the potential difference across the armature.

Derivation of transfer function of armature controlled DC servo motor:

Consider the armature controlled d.c. servo motor shown in fig. below

In this system,

Ra = resistance of armature (Ω).

La = Inductance of the Armature Winding (H).

ia= = Armature Current(A).

if = Field Current (A).

ea = Applied Armature Voltage(V).

eb = Back EMF (volts).

TM = torque developed by armature (Nm).

48

θ = angular displacement of motor shaft (rad).

J = equivalent moment of inertia of motor and load referred to motor shaft

(Kg-m2)

fo = equivalent viscous friction coefficient of motor and load referred to motor

Shaft (N m/( rad/s))

In servo applications, the d.c motors are generally used in the linear range of the magnetization

curve. Therefore, the air gap flux Φ is proportional to field current

Φ= Kfif

where, Kf, is a constant.

The torque TM developed by the motor is proportional to the product of the armature

current and air gap flux,

TM = K1Kf if ia

where, K1, is a constant.

In the armature controlled d.c motor, the field current is kept constant, so that TM =

kTia

where, KT, is motor torque constant.

The motor back emf being proportional to speed is given as

dt

dθKe bb

where, Kb, is the back emf constant.

The differential equation of the armature circuit is

abaa

a

a eeiRdt

diL

The torque equation is

aTM02

2

iKTdt

dθf

dt

θdJ

Taking the Laplace transform and assuming zero initial conditions, we get

Eb(s) = Kb s θ(s)

(Las+Ra) Ia(s) = Ea(s) - Eb(s)

(Js2+fos) θ(s) = TM(s) = KTIa(s)

+

-

If (costant)

Ra

ea

La

θ ia

TM

49

The transfer function of the system is obtained as

]KK)f)(JssLs[(R

K

(s)E

θ(s)G(s)

bToaa

T

a

Assumptions:

The field current is constant.

The flux which is proportional to the field current is also constant.

The torque generated is proportional to the product of flux and the armature current

Tm ΦIa

T Ia

Tm = KtIa

Where Kt is the motor torque constant

Back EMF of the motor is proportional to the speed and the flux Eb Φ.

Precautions:

1) At the time of starting the motor should be at no load condition

2) Armature rheostat must be kept at maximum resistance position

3) Field rheostat must be kept at minimum resistance position

Procedure:

1) To find inertia constant [J]

Connections are made as per the circuit diagram

The DPST switch is switched ON. It is in the initial position at the time of starting.

After observing the precautions, switch on the DPST.

Adjust the field side rheostat and the armature side rheostat and allow the motor to run at

rated speed N1.

Open the DPST and observe the speed of the motor note the time taken for the speed to

fall down to any three values of the speed N2.

Adjust the rheostat to initial position and switch of the DPST.

Open the DPST and bring 2-2 position and immediately note down the reading

Repeat the steps 2, 3, 4.

Observe that the speed falls rapidly for the same values of speed noted in steps note down

the time taken, voltage and current.

Switch off the dc supply.

Inertia Constant is calculated using formula 21

21

2

2

60

*

*

tt

tt

NN

IVJ

av

avav

2) To Find Torque Constant [KT]


50

2. The DPST is switched on.

3. Adjust the armature side rheostat and keep in fixed position so that the value of Ia is

maintained constant through the experiment.

4. Note down If, Va, Ia in table.

5. Adjust the field rheostat and note down the Va, Ia, If and Speed.

6. Graph is drawn between the torque and If.

KT = T/If

3) To fined Back EMF constant [Kb]

The connections are given as per the circuit diagram

The D.C supply is given by closing the DPST switch

Run the motor at its rated speed by adjusting armature rheostat

At rated speed the readings of applied voltage and armature current were noted down

Back MEF constant is calculated using the formula

60

2 N

RIVK aa

b

4) To find armature resistance [Ra]


The resistive should be in off position at the time of starting.

Adjust the load, for each values of load, note down the ammeter, voltmeter readings.

Armature resistance is calculated by using the formula

5) To find field impedance [Zf]

1. Connections are made as per the circuit diagram

2. Vary the auto transformer and note down the corresponding ammeter and voltmeter

readings.

3. Calculate the value of Zf = Vf /If and find the mean of Zf.

Circuit diagram for calculating inertia constant J

51

Tabulation to find Torque constant [J]

Sl no

Armature

current Ia

in Amps

Field

current If

in Amps

Spring balance reading Torque T =

9.81*

22~1

tRSS

in NM

S1 in

Kg

S2 in

Kg

S1~ S2

in Kg

Circuit diagram for find armature resistance Ra

Circuit diagram for find Impedance Za

52

Tabulation to find Back EMF constant [Kb]

Armature

Voltage Va in

Volts

Armature

current Ia in

Amps

Speed in RPM

Back EMF

Constant

60

2 N

RIVK aa

b

Tabulation to find Armature Resistance [Ra]

Armature

Voltage Va in

Volts

Armature

current Ia in

Amps

Armature

resistance Ra

= V * I in Ω

Tabulation to Find Armature Resistance [Za]

Armature

Voltage Va in

Volts

Armature

Current Ia in

Amps

Armature

Impedance Za

= V / I in Ω

53

Result:

Ex. No : 9B

Date:

TRANSFER FUNCTION OF FIELD CONTROLLED DC SERVO MOTOR

Aim:

To derive the transfer function of the given D.C Servomotor and experimentally determine

the transfer function parameters

Apparatus required:

Sl No. Apparatus Name Type/ Range Quantity

Name plate details:

Voltage

Current

Speed

H.P

Load

Fuse calculation:

125 % of full load current

T

Ia

T in

N-M

Ia in

Amps

Model graph Torque Vs Ia

a

TI

TK

T

54

Formula used:

1) Transfer function 1)s1)(τss(τ

K

(s)E

θ(s)

mef

m

f

Where:

Km = KT’/Rff – Motor Gain Constant

τf = Lf/Rf –Time Constant of Field Circuit

τme = J/f – Mechanical Time Constant.

lf – inductance of field winding in H

Rf – Resistance of field winding in

J – Equivalent of inertia of motor and load referred to motor shaft (kg-m2).

f – Equivalent viscous friction coefficient of motor and load referred to motor shaft rad/s

Nm

2) Inertia constant: J

21

21

2

2

60

*

*

tt

tt

NN

IVJ

av

avav

In Kg/m

2

Where:

T1 – Time for fall of speed from N1 to N2 in no load condition

T2 – Time for fall of speed from N1 to N2 in load condition

2

21 VVVav

,

2

21 IIIav

2

21 NNNav

21 NNN

3) Frictional coefficient of motor and load

2

2

2

2

1

2

**60

2

NNJfo

In N-M / rad /sec

Where:

60

2 avN

Derivations of transfer function of Field Controlled D C motor:

In this system

Rf - Field Winding Resistance (Ω)

Lf -Field Winding Inductance (H).

e- Field control voltage. (V).

if - Field Current(A).

TM - Torque Developed By Motor (Nm).

J- Equivalent of inertia of motor and load referred to motor shaft (kg-m2).

f- Equivalent viscous friction coefficient of motor and load referred to motor shaft rad/s

Nm

55

θ - Angular displacement of motor shaft (rad).

In this field controlled motor, the armature current is fed from a constant current source.

Therefore

TM = K1Kfiaif = KT’ if where KT’ is a constant.

The equation for the field circuit is

ffff

f eiRdt

diL

The torque equation is

(s)I 'KTdt

dθf

dt

θdJ fTM2

2

Taking the Laplace transform and assuming zero initial conditions we get

(Lfs + Rf) If(s) = Ef(s)

(Js2+fs) θ(s) = TM(s) = KT’ If(s)

From the above equations, the transfer function of the motor is obtained as

1)s1)(τss(τ

K

(s)E

θ(s)

mef

m

f

where

Km = KT’/Rff – motor gain constant

τf = lf/Rf –time constant of field circuit

τme = J/f – mechanical time constant.

Theory:

The speed of the dc motor is directly proportional to the armature voltage and inversely

proportional to the flux. In the field controlled dc motor, armature voltage is kept constant and

the speed is varied by varying the flux of the machine.

Precautions:

The DPST is kept open initially.

The field rheostat is kept at maximum position.

Procedure:

Rf

ef Lf

θ If

ia( constant)

TM

J,f

56

1) To find inertia constant [J]


The DPST switch is switched ON. It is in the initial position at the time of starting.

After observing the precautions, switch on the DPST.

Adjust the field side rheostat and the armature side rheostat and allow the motor to run at

rated speed N1.

Open the DPST and observe the speed of the motor note the time taken for the speed to

fall down to any three values of the speed N2.

Adjust the rheostat to initial position and switch of the DPST.

Open the DPST and bring 2-2 position and immediately note down the reading

Repeat the steps 2, 3, 4.

Observe that the speed falls rapidly for the same values of speed noted in steps note down

the time taken, voltage and current.

Switch off the dc supply.

Inertia Constant is calculated using formula 21

21

2

2

60

*

*

tt

tt

NN

IVJ

av

avav

2) To Find Torque Constant [KT]


8. The DPST is switched on.

9. Adjust the armature side rheostat and keep in fixed position so that the value of Ia is

maintained constant through the experiment.

10. Note down If, Va, Ia in table.

11. Adjust the field rheostat and note down the Va, Ia, If and Speed.

12. Graph is drawn between the torque and If.

KT = T/If

3) To find armature resistance [Rf]


The resistive should be in off position at the time of starting.

Adjust the load, for each values of load, note down the ammeter, voltmeter readings.

Armature resistance is calculated by using the formula Rf= V/I

4) To find field impedance [Lf]

1. Connections are made as per the circuit diagram

2. Vary the auto transformer and note down the corresponding ammeter and voltmeter

readings.

3. Calculate the value of Zf = Vf /If and find the mean of Zf.

57


Sl no Armature Field Spring balance reading Torque T =

T

If

T in

N-M

If in

Amps

Model graph Torque Vs If

58

current Ia

in Amps

current If

in Amps S1 in

Kg

S2 in

Kg

S1~ S2

in Kg

9.81*

22~1

tRSS

in NM


Sl

no

Armature

current Ia

in Amps

Field

current If

in Amps

Spring balance reading Torque T =

9.81*

22~1

tRSS

in NM

S1 in

Kg

S2 in

Kg

S1~ S2

in Kg

Tabulation to find out the field resistance (Rf)

S no Field current (I) Voltage (V)

Stator Resistance

Rf= V/I

Amps Volts Ohms

59

Calculation:

Result:

Expt. No: 10

Date

DESIGN AND IMPLEMENTATION OF COMPENSATORS

AIM:

To study the compensation of the second order process by using lead – Lag Compensator

EQUIPMENT REQUIRED:

1. LEAD – Lag network system kit

2. Capacitors – 0.1μF

3. Decade Resistance Box

4. CRO

DESIGN:

Lead – Lag network using operational amplifier:

An electronic lead –lag network using operational Amplifier is shown in Fig. 4.1.

60

The transfer function for this circuit can be obtained as follows:

Let

Z1 = R1 || C1

Z2 = R2 || C2

The second op-amp acts as a sign inverter with a variable gain to compensate for the magnitude.

The transfer function of the entire system is given by G(j).

)1(

)1()(

2213

1124

sCRRR

sCRRRsG

TABULATION:

SI NO AMPLITUDE

(V)

FREQUENCY

(HZ)

PHASE

SHIFT

()

R1

(OHMS)

C1 (F) R2

(OHMS) C2 (F)

61

We have

)1(

)1()(

22

231

22

142

TRR

TRRjG

Where

T1 = R1C1

T2 = R2C2 and

Thus the steady state output is

)tantan()1(

)1()( 2

1

1

1

22

231

22

142

TTtSin

TRR

TRRtYss

for an input Esint.

From this expression, we find that if T1>T2, then 2

1

1

1 tantan TT >0. Thus if T1>T2, then the

network is a lead network. If T1 <T2, the network is a lag network.

Determination of values for angle compensation:

Frequency of sine wave (f)= 20Hz.

Phase angle to be compensated =14.50

sec023.0

)*20*2(tan)1.0*20*2(tan5.14

sec1.0

)2(tan)2(tan

2

2

11

1

2

1

1

1

T

T

TLet

fTfT

Hence the values of T1 and T2 are chosen from which the values of R1, R2, C1, and C2 can be

determined. For Example,

T1 = R1C1 = 0.1; If C1 = 0.1μF, R1=1MΩ

T2 = 0.023sec

If C2 = 0.1 μF, R2 =230KΩ.

These values produce a phase lead of 14.5o, which is the desired compensation angle.

PROCEDURE:

62

1. Switch ON the power to the instrument.

2. Connect the individual blocks using patch chords bypassing the compensating

network and gain as shown in fig. 4.2.

3. Give a sinusoidal input as the set value to the error detector.

4. Measure the amplitude and frequency of the input signal.

5. Measure the amplitude and phase difference of the output signal with respect to the

input signal using DSO.

6. Using the technique explained previously, calculate the values of R1, R2, C2, and C1

to compensate for the phase shift of the output signal.

7. Connects the components at the points provided.

8. Now include the compensation block in the forward path before the process using

patch chords as shown in fig.4.2.

9. Observe the compensated wave form through DSO.

CALCULATION: (frequency = Hz)

CALCUALTION : (frequency = Hz)

RESULT:

Thus the compensator is designed for the given process and the performance of

the compensated system is found to work satisfactorily.

Frequency : Hz R1 = C1 =

R2 = C2 =

Frequency : Hz R1 = C1 =

R2 = C2 =

63

Expt No: 11 Date

STUDY OF D.C MOTOR STARTERS

AIM:

To study the different kinds of D.C motor starters

EQUIPMENT AND APPARATUS REQUIRED :

Sl No. Name of the apparatus Quantity

1 Two Point starter 1

2 Three Point starter 1

3 Four Point starter 1

THEORY :

The value of the armature current in a D.C shunt motor is given by

Ia = ( V – Eb )/ Ra

Where V = applied voltage.

Ra = armature resistance.

E b = Back .e.m.f .

In practice the value of the armature resistance is of the order of 1 ohms and at the instant of

starting the value of the back e.m.f is zero volts. Therefore under starting conditions the value of

the armature current is very high. This high inrush current at the time of starting may damage the

motor. To protect the motor from such dangerous current the D.C motors are always started

using starters.

The types of D.C motor starters are

i) Two point starters

ii) Three point starters

iii) Four point starters.

The functions of the starters are

i) It protects the from dangerous high speed.

ii) It protects the motor from overloads.

i) TWO POINT STARTERS: ( refer fig 1)

It is used for starting D.C. series motors which has the problem of over speeding due to the loss

of load from its shaft. Here for starting the motor the control arm is moved in clock-wise

direction from its OFF position to the ON position against the spring tension. The control arm is

64

held in the ON position by the electromagnet E. The exciting coil of the hold-on electromagnet

E is connected in series with the armature circuit. If the motor loses its load, current decreases

and hence the strength of the electromagnet also decreases. The control arm returns to the OFF

position due to the spring tension, Thus preventing the motor from over speeding. The starter

also returns to the OFF position

65

when the supply voltage decreases appreciably. L and F are the two points of the starter which are connected with the motor terminals.

66

ii) THREE POINT STARTER: ( refer fig 2 )

It is used for starting the shunt or compound motor. The coil of the hold on electromagnet

E is connected in series with the shunt field coil. In the case of disconnection in the field circuit

the control arm will return to its OFF position due to spring tension. This is necessary because

the shunt motor will over speed if it loses excitation. The starter also returns to the OFF position

in case of low voltage supply or complete failure of the supply. This protection is therefore is

called No Volt Release

( NVR).

Over load protection:

When the motor is over loaded it draws a heavy current. This heavy current also flows

through the exciting coil of the over load electromagnet ( OLR). The electromagnet then pulls

an iron piece upwar6.ds which short circuits the coils of the NVR coil. The hold on magnet gets

de-energized and therefore the starter arm returns to the OFF position, thus protecting the motor

against overload. L, A and F are the three terminals of the three point starter.

iii) FOUR POINT STARTER:

The connection diagram of the four point starter is shown in fig 3. In a four point starter

arm touches the starting resistance, the current from the supply is divided into three paths. One

through the starting resistance and the armature, one through the field circuit, and one through

the NVR coil. A protective resistance is connected in series with the NVR coil. Since in a four

point starter the NVR coil is independent of the of the field ckt connection , the d.c motor may

over speed if there is a break in the field circuit. A D.C motor can be stopped by opening the

main switch. The steps of the starting resistance are so designed that the armature current will

remain within the certain limits and will not change the torque developed by the motor to a great

extent.

67

STUDY OF INDUCTION MOTOR STARTERS

AUTO –TRANSFORMER STARTING

68

An auto transformer starter consists of an auto transformer and a switch as shown in the

fig. When the switch S is put on START position, a reduced voltage is applied across the motor

terminals. When the motor picks up speed, say to 80 per cent of its mornal speed, the switch is

put to RUN position. Then the auto-transformer is cut out of the circuit and full rated voltage

gets applied across the motor terminals.

(Ref. To text book for fig)

The circuit dia in the fig is for a manual auto-transformer starter. This can be made push button

operated automatic controlled starter so that the contacts switch over from start to run position as

the motor speed picks up to 80% of its speed. Over-load protection relay has not been shown in

the figure. The switch S is air-break type for small motors and oil break type for large motors.

Auto transformer may have more than one tapping to enable the user select any suitable starting

voltage depending upon the conditions.

Series resistors or reactors can be used to cause voltage drop in them and thereby allow low

voltage to be applied across the motor terminals at starting. These are cut out of the circuit as the

motor picks up speed.

STAR- DELTA METHOD OF STARTING:

The startor phase windings are first connected in star and full voltage is connected across its free

terminals. As the motor picks up speed, the windings are disconnected through a switch and they

are reconnected in delta across the supply terminals. The current drawn by the motor from the

lines is reduced to as compared to the current it would have drawn if connected in delta.The

motor windings, first in star and then in delta the line current drawn by the motor at starting is

reduced to one third as compared to starting current with the windings delta-connected.

In making connections for star-delta starting, care should be taken such that sequence of supply

connections to the winding terminals does not change while changing from star connection to

delta connection. Otherwise the motor will start rotating in the opposite direction, when

connections are changed from star to delta. Star-delta starters are available for manual operation

using push button control. An automatic star – delta starter used time delay relays(T.D.R)

through which star to delta connections take place automatically with some pre-fixed time delay.

The delay time of the T.D.R is fixed keeping in view the starting time of the motor.

(Ref. To text book for fig)

69

FULL VOLTAGE OR DIRECT –ON-LINE STARTING

When full voltage is connected across the stator terminals of an induction motor, large

current is drawn by the windings. This is because, at starting the induction motor

71

behaves as a short circuited transformer with its secondary, i.e. the rotor separated from the

primary, i.e. the stator by a small air-gap.

At starting when the rotor is at standstill, emf is induced in the rotor circuit exactly

similar to the emf induced in the secondary winding of a transformer. This induced emf of the

rotor will circulate a very large current through its windings. The primary will draw very large

current from the supply mains to balance the rotor ampere-turns. To limit the stator and rotor

currents at starting to a safe value, it may be necessary to reduce the stator supply voltage to a

low value. If induction motors are started direct-on-line such a heavy starting current of short

duration may not cause harm to the motor since the construction of induction motors are rugged.

Other motors and equipment connected to the supply lines will receive reduced voltage. In

industrial installations, however, if a number of large motors are started by this method, the

voltage drop will be very high and may be really objectionable for the other types of loads

connected to the system. The amount of voltage drop will not only be dependent on the size of

the motor but also on factors like the capacity of the power supply system, the size and length of

the line leading to the motors etc. Indian Electricity Rule restricts direct on line starting of 3

phase induction motors above 5 hp.

RESULT:

Thus the construction and working of different starters for starting D.C series, shunt,

compound and three phase induction motors are studied.

Ex. No : 12

Date:

Digital Simulation of Linear Systems

72

Aim:

To digitally simulate the time response characteristics of higher-order MIMO linear systems

using state – variable formulation

Equipments required:

PC system with mat lab

Theory: Introduction to MATLAB & SIMULINK

What is MATLAB?

MATLAB® is a high-performance language for technical computing. It integrates computation, visualization, and programming in an easy-to-use environment where problems and solutions are expressed in familiar mathematical notation. Typical uses include

Math and computation

Algorithm development

Data acquisition

Modeling, simulation, and prototyping

Data analysis, exploration, and visualization

Scientific and engineering graphics

Application development, including graphical user interface building

MATLAB is an interactive system whose basic data element is an array that does not

require dimensioning. This allows you to solve many technical computing problems, especially

those with matrix and vector formulations, in a fraction of the time it would take to write a

program in a scalar no interactive language such as C or FORTRAN.

The name MATLAB stands for matrix laboratory. MATLAB was originally written to provide

easy access to matrix software developed by the LINPACK and EISPACK projects. Today,

MATLAB engines incorporate the LAPACK and BLAS libraries, embedding the state of the art

in software for matrix computation.

MATLAB has evolved over a period of years with input from many users. In university

environments, it is the standard instructional tool for introductory and advanced courses in

mathematics, engineering, and science. In industry, MATLAB is the tool of choice for high-

productivity research, development, and analysis.

MATLAB features a family of add-on application-specific solutions called toolboxes. Very

important to most users of MATLAB, toolboxes allow you to learn and apply specialized

technology. Toolboxes are comprehensive collections of MATLAB functions (M-files) that

extend the MATLAB environment to solve particular classes of problems. Areas in which

73

toolboxes are available include signal processing, control systems, neural networks, fuzzy logic,

wavelets, simulation, and many others.

Starting MATLAB

Instructions for starting MATLAB® depend on your platform. For a list of supported

platforms, see the system requirements in the installation documentation, or the Products section

of the MathWorks Web site, http://www.mathworks.com

Starting MATLAB on Windows Platforms To start MATLAB on a Microsoft Windows

platform, select the Start -> Programs -> MATLAB 7.0 -> MATLAB 7.0, or double-click the

MATLAB shortcut icon on your Windows desktop. The shortcut was automatically created by

the installer.

Transfer function of the given 4 systems

Transfer function:

s - 1

-------------

s^2 + s + 6.5

Transfer function:

s + 7.5

-------------

s^2 + s + 6.5

Transfer function:

s + 3.553e-015

--------------

s^2 + s + 6.5

Transfer function:

s^2 + s + 13

-------------

s^2 + s + 6.5

Matlab program:

Open new m file and type the given program % State Space Analysis of MIMO System %-----X^ = Ax+Bu; y =Cx+Du -------%

A=[-1 -1; 6.5 0]; %----State Matrix(nxn)-----% B=[1 1;1 0]; %----Input Mtrix(nxm)------% C=[1 0;0 1]; %----Output Matrix(pxn) ------% D=[0 0;0 1]; %----Transistion Matrix(pxm)---%

74

step(A,B,C,D,1) hold step(A,B,C,D,2) title('Step Response of MIMO System') grid [num1,den1]=ss2tf(A,B,C,D,1) [num2,den2]=ss2tf(A,B,C,D,2) n1=num1(1,:) n2=num1(2,:) n3=num2(1,:) n4=num2(2,:) d1=den1(1,:) d2=den2(1,:) tf1=tf(n1,d1) tf2=tf(n2,d1) tf3=tf(n3,d2) tf4=tf(n4,d2)

For impulse response

response MIMO system % State Space Analysis of MIMO System %-----X^ = Ax+Bu; y =Cx+Du -------% A=[-1 -1; 6.5 0];%----State Matrix(nxn)-----% B=[1 1;1 0];%----Input Mtrix(nxm)------% C=[1 0;0 1];%----Output Matrix(pxn) ------% D=[0 0;0 1];%----Transistion Matrix(pxm)---% impulse(A,B,C,D,1) hold impulse(A,B,C,D,2) title('Impulse Response of MIMO System') grid [num1,den1]=ss2tf(A,B,C,D,1) [num2,den2]=ss2tf(A,B,C,D,2) n1=num1(1,:) n2=num1(2,:) n3=num2(1,:) n4=num2(2,:) d1=den1(1,:) d2=den2(1,:) tf1=tf(n1,d1) tf2=tf(n2,d1) tf3=tf(n3,d2) tf4=tf(n4,d2)

75

Step Response of MIMO System

Time (sec)

Am

plit

ude

0 2 4 6 8 10 12-0.5

0

0.5

1

1.5

2

2.5

3

Current plot held

num1 =

0 1.0000 -1.0000

0 1.0000 7.5000

den1 =

76

1.0000 1.0000 6.5000

num2 =

0 1.0000 0.0000

1.0000 1.0000 13.0000

den2 =

1.0000 1.0000 6.5000

n1 =

0 1.0000 -1.0000

n2 =

0 1.0000 7.5000

n3 =

0 1.0000 0.0000

n4 =

1.0000 1.0000 13.0000

d1 =

1.0000 1.0000 6.5000

d2 =

1.0000 1.0000 6.5000

Transfer function:

s - 1

-------------

s^2 + s + 6.5

Transfer function:

s + 7.5

-------------

s^2 + s + 6.5

Transfer function:

s + 3.553e-015

--------------

s^2 + s + 6.5

Transfer function:

s^2 + s + 13

-------------

s^2 + s + 6.5

Result:

77

Ex. No : 13

Date: Stability Analysis of Linear Systems

Aim

To analyse the stability of linear systems using Bode, Root locus, Nyquist plots

Equipments required:

PC system with mat lab

Program:

STABILITY ANALYSIS Program For Nyquist Plot. %---Given System G(s)=1/(s^2+0.8s+1)-----%

%--------Nyquist plot-----------%

num=[0 0 1];

den=[1 0.8 1];

nyquist(num,den);

axis(v)

grid

title('Nyquist plot of G(s)=1/(s^2+0.8s+1)')

xlabel('Real axis')

ylabel('Imag axis')

hold on Program for Root Locus %---conditionally stable system--%

%---Given System G(s)=k(s^2+2s+4)/[s(s+4)(s+6)(s^2+1.4s+1)-----%

clc;

close all;

78

clear all;

%--------Root Locus----------%

numz=[0 0 0 1 2 4];

denp=[1 11.4 39 43.6 24 0];

r=rlocus(numz,denp);

plot(r,'o');

axis(v)

grid

title('Root locus plot of G(s)=k(s^2+2s+4)/[s(s+4)(s+6)(s^2+1.4s+1)]')

xlabel('real axis')

ylabel('imag axis')

hold

Program for Bode Plot

%---Given System=s^3+2s+3/(s^5+s^4+s^3+s^2+s+1)---%

%--------Bode Plot ----------%

numg=[1 0 2 3];

deng=[1 1 1 1 1 1 ];

'G(s)'

u=tf(numg,deng);

bode(u)

grid

hold

title('Bode plot of G(s)=s^3+2s+3/(s^5+s^4+s^3+s^2+s+1)')

[Gm,Pm,Wcg,Wcp] = margin(u)

Gm_dB = 20*log10(Gm)

Program For Polar Plot

format compact

set(gcf,'Toolbar','none','Name','Polar Plot', ...

'NumberTitle','off','Position',[10,350,350,300]);

theta = 2*pi*linspace(0,1,30);

r = 2*(1 + cos(theta));

Polar(theta,r,'r-')

set(gca,'Position',[0.1 0.1 0.75 0.75]);

title('\bf\itA Polar Plot','Color','k','VerticalAlignment','bottom')

textstr(1)='r = 2(1+cos\theta)';

textstr(2)='\theta = 0 -> 2\pi';

text(5*cos(pi/4),5*sin(pi/4), ...

strcat(textstr))

title('Polar plot ')

hold

Program for Nichols Chart

79

%Plot the Nichols response of the system

num = [-4 48 -18 250 600];

den = [1 30 282 525 60];

H = tf(num,den)

nichols(H); ngrid

Response of various systems

Nyquist plot of )18.0(

1)(

2

sssG

Root locus plot of

)14.1)(6)(4(

42)(

2

2

sssss

ssksG

80

Bode plot of

)1(

32)(

2345

3

sssss

sssG

82

Result:

Ex. No: 14

Date:

STUDY THE EFFECT OF P, PI, PID CONTROLLERS USING MAT LAB

Aim:

To Study the effect of P, PI, PID controllers using Mat lab.

1 Choice of the Controller type

In so far were described proportional, integrative and derivative modes of the controllers

and a rational behind their use was explained. However, excerpt for a few tips, an attention was

not given to a question when to use different types of controllers. The rest of this section will

give some answers on that particular topic.

1.1 On-off Controller

On-off controller is the simplest controller and it has some important advantages. It is

economical, simple to design and it does not require any parameter tuning. If oscillations will

hamper the operation of the system and if controller parameter tuning is to be avoided, on-off

controller is a good solution. In addition, if actuators work in only two modes (on and off), then

it is almost always only controller that can be used with such actuators. That is a reason why on-

off controllers are often used in home appliances (refrigerators, washers etc.) and in process

industry when control quality requirements are not high (temperature control in buildings etc.).

Additional advantage of on-off controllers is that they in general do not require any maintenance.

1.2 P Controller

83

When P controller is used, large gain is needed to improve steady state error. Stable

system do not have a problems when large gain is used. Such systems are systems with one

energy storage (1st order capacitive systems). If constant steady state error can be accepted with

such processes, than P controller can be used. Small steady state errors can be accepted if sensor

will give measured value with error or if importance of measured value is not too great anyway.

Example of such system is liquid level control in tanks when exact approximate level of liquid

suffice for the proper plant operation. Also, in cascade control sometime it is not important if

there is an error inside inner loop, so P controller can a good solution in such cases.

Derivative mode is not required if the process itself is fast or if the control system as

whole does not have to be fast in response. Processes of 1st order react immediately on the

reference signal change, so it is not necessary to predict error (introduce D mode) or compensate

for the steady state error (introduce I mode) if it is possible to achieve satisfactory steady state

error using only P controller.

1.3 PD controller

It is well known that thermal processes with good thermal insulation act almost as

integrators. Since insulation is good and thermal losses are small, the most significant art of the

energy that is led to the system is used temperature rise. Those processes allow 18 for large gains

so that integral mode in the controller is not needed. These processes can be described as

different connections of thermal energy storages. Thermal energy is shifted from one storage into

another. In general, with such processes there is present a process dynamics with large inertia.

Since dynamics is slow, derivative mode is required for control of such processes. Integral mode

would only already slow dynamics make more slowly. The other reason for using PPD

controllers in such systems is that is possible to measure temperature with low level of noise in

the measured signal.

PD controller is often used in control of moving objects such are flying and underwater

vehicles, ships, rockets etc. One of the reason is in stabilizing effect of PD controller on sudden

changes in heading variable y(t). Often a "rate gyro" for velocity measurement is used as sensor

of heading change of moving object.

1.3 PI controller

PI controllers are the most often type used today in industry. A control without D mode is

used when:

a) fast response of the system is not required

b) large disturbances and noise are present during operation of the process

c) there is only one energy storage in process (capacitive or inductive)

d) there are large transport delays in the system

If there are large transport delays present in the controlled process, error prediction is

required. However, D mode cannot be used for prediction because every information is delayed

till the moment when a change in controlled variable is recorded. In such cases it is better to

predict the output signal using mathematical model of the process in broader sense (process +

84

actuator). The controller structures that can be used are, for example, Otto-Smith predictor

(controller), PIP controller or so called Internal Model Controller (IMC).

An interesting feature of IMC is that when the model of the process is precise

(A = AM and B = BM), then a feedback signal eM = y – yM is equal to disturbance:

It follows that a control signal is not influenced by the reference signal and control

systems behaves as open loop. A usual problems with stability that arrise when closed loop

systems are used are then avoided. Control system with IMC controller will be stable and if IMC

and process are stable. With the exact model of process IMC is actually a feedforward controller

and can designed as such, but, unlike feedforward controllers, it can compensate for unmeasured

disturbances because feedback signal is equal to disturbance, which allows suitable tuning of the

reference value of the controller.

If model of the process is not exact5 (AM = B), then feedback signal eM will

contain not only disturbance d but a modeling error, also. Thus, a feedback will

have its usual role, and stability problem can arise. This requires for parameters6 to be tuned

again so the stability is not lost.

86

1.4 PID controller

Derivative mode improves stability of the system and enables increase in gain

K and decrease in integral time constant Ti, which increases speed of the controller

response. PID controller is used when dealing with higher order capacitive processes

(processes with more than one energy storage) when their dynamic is not similar to

the dynamics of an integrator (like in many thermal processes). PID controller is often

used in industry, but also in the control of mobile objects (course and trajectory

following included) when stability and precise reference following are required.

Conventional autopilot are for the most part PID type controllers.

1.5 Topology of PID controllers

Problem of topology (structure) of controller arises when:

There are a number of different PID controller structures. Different

manufacturers design controllers in different manner. However, two topologies are the

most often case:

parallel (non-interactive)

Parallel structure is most often in textbooks, so it is often called "ideal" or

"textbook type". This non-interactive structure because proportional, integral and

derivative mode are independent on each other. Parallel structure is still very rare in

the market. The reason for that is mostly historical. First controllers were pneumatic

and it was very difficult to build parallel structure using pneumatic components. Due

to certain conservatism in process industry most of the controller used there are still in

serial structure, although it is relatively simple to realize parallel structure controller

using electronics. In other areas, where tradition is not so strong, parallel structure can

be found more often.

1.5.1 Parallel PID topology

A parallel connection of proportional, derivative and integral element is called parallel

or non-interactive structure of PID controller. Parallel structure is shown in Fig.

87

It can be seen that P, I and D channels react on the error signal and that they are

unbundled. This is basic structure of PID controller most often found in textbooks.

There are other non-interactive structures.

RESULT:

Thus the effect of P, PI, PID controllers using Mat lab are studied.

VIVA questions for the experiments

88

OPEN CIRCUIT CHARACTERISTICS OF SELF EXCITED

DC SHUNT GENERATOR

VIVA QUESTIONS:

1. Define critical field resistance and critical speed.

2. State the conditions to be satisfied by a DC shunt generator to build-up voltage.

3. What is residual flux and what happens to the generator induces EMF when

residual flux is zero?

4. What is the purpose of SPST switch connected in the field circuit of the

generator?

5. Why the speed must be maintained constant throughout the experiment?

LOAD TEST ON SELF EXCITED DC SHUNT GENERATOR

VIVA QUESTIONS:

1. What is a prime mover?

2. Why the speed of generator should be maintained constant during the experiment?

3. Why does the terminal voltage fall as the load on the generator is increased?

4. What is armature reaction and what are its effects on the performance of DC

generator?

OPEN CIRCUIT CHARACTERISTICS OF A SEPARATELY

EXCITED DC SHUNT GENERATOR

VIVA QUESTIONS:

1. Define critical field resistance and critical speed.

2. State the conditions to be satisfied by a DC shunt generator to build-up voltage.

3. What is residual flux and what happens to the generator induces EMF when

residual flux is zero?

4. What is the purpose of SPST switch connected in the field circuit of the

generator?

5. Why the speed must be maintained constant throughout the experiment?

89

LOAD CHARACTERISTICS ON SEPARATELY EXCITED DC SHUNT

GENERATOR

VIVA QUESTIONS:

1. What is a prime mover?

2. Why the speed of generator should be maintained constant during the experiment?

3. Why does the terminal voltage fall as the load on the generator is increased?

4. What is armature reaction and what are its effects on the performance of DC

generator?

LOAD TEST ON DC SHUNT MOTOR

VIVA QUESTIONS:

1. What is the need for a starter?

2. Name the different types of starters for DC motors.

3. Why a DC shunt motor is called a constant Speed motor?

4. State few applications of DC shunt motor.

5. What is the role of commutator in a DC motor.

6. What is the effect of armature reaction on the performance of DC motor?

7. What happen when the field circuit gets opened when a DC shunt motor is running?

8. How to reverse the direction of rotation of DC shunt motor?

SPEED CONTROL OF DC SHUNT MOTOR

VIVA QUESTIONS:

1. Which method of speed control is used for controlling the speed of the motor above its

rated speed? Give reason.

2. Which method of speed control is used for controlling the speed of the motor below its

rated speed? Give reason.

3. Explain the reasons for the shape of the graphs obtained.

4. State any method to control the speed of a D.C series motor?

SWINBURNE'S TEST

VIVA QUESTIONS:

1. What are the advantages of predetermination techniques?

2. Can the efficiency of a DC series motor be predetermined by Swinburne's test?

3. The efficiency of a generator is always more than the efficiency of motor at all load

conditions - Justify.

4. Enumerate the various losses in a DC machine.

90

LOAD TEST ON A SINGLE PHASE TRANSFORMER

VIVA QUESTIONS:

1. Define Regulation of a Transformer.

2. What is the effect of load p.f on regulation of Transformer?

3. What is the condition for maximum efficiency?

4. Determine the percentage load at which maximum efficiency occurred for the given

single-phase transformer?

5. What is the effect of change in frequency on the efficiency of the transformer?

O.C AND S.C TESTS ON A SINGLE PHASE TRANSFORMER

VIVA QUESTIONS:

1. Why O.C test is conducted on the L.V side and S.C test on the H.V side?

2. Define regulation in a transformer.

3. Why the regulation graph is not passing through the origin?

4. State the condition for maximum efficiency?

5. What is the regulation of an Ideal transformer?

6. At what fraction of full load does the efficiency of the given transformer is maximum?

PREDETERMINATION OF REGULATION BY EMFAND MMF METHOD

VIVA QUESTIONS:

1. Define regulation.

2. What is meant by pessimistic method?

3. Which method is called as optimistic method?

4. What are the advantages of EMF and MMF method?

5. Name some other methods used to predetermine the regulation.

LOAD TEST ON SQUIRREL CAGE INDUCTION MOTOR

VIVA QUESTIONS: 1. What is squirrel cage induction motor?

2. What is Skewing?

3. What is cogging?

4. What is crawling?

5. What is the no load current of an induction motor?

6. Distinguish between rotating transformer and static transformer?

7. Define slip.

NO LOAD AND BLOCKED ROTOR TEST ON THREE PHASE INDUCTION

MOTOR

VIVA QUESTIONS:

1. How will you measure three phase power using two watt meters?

91

2. What is the necessity to have starter for three phase induction motor?

3. How mechanical load is represented in the equivalent circuit of induction motor?

4. Define synchronous speed.

5. Why induction motors cannot run at synchronous speed?

STUDY OF D.C MOTOR STARTERS

VIVA QUESTIONS:

1. Differentiate two point and three point starter

2. What is the need for starter in electrical technology?

3. Differentiate four point and three point starter

4. What are the types of starter?

5. What are the protective devices used in starters?

STUDY OF INDUCTION MOTOR STARTERS

VIVA QUESTIONS:

1. Differentiate star – delta and auto transformer starter

2. What is the need for starter in electrical technology?

3. Differentiate auto transformer and DOL starter

4. What are the types of AC starters?

5. What are the protective devices used in starters?

DIGITAL SIMULATION OF LINEAR SYSTEMS

VIVA QUESTIONS:

1) Define linear system.

2) What is impulse signal?

3) What is MIMO?

4) What is time invariant system?

5) What is step signal?

STABILITY ANALYSIS OF LINEAR SYSTEM

VIVA QUESTIONS:

1) What is root locus?

2) What is bode plot?

3) What is Nyquist plot?

4) What is phase margin?

5) What is gain margin?

DESIGN AND IMPLEMENTATION OF COMPENSATORS

VIVA QUESTIONS:

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1. What is compensation?

2. What is compensator?

3. When lag/lead/lag-lead compensators are employed?

4. What are the types of compensator?

5. Differentiate lag and lead compensators?

TRANSFER FUNCTION OF SEPERATELY EXCITED DC SHUNT

GENERATOR

VIVA QUESTIONS

1. What is the need for transfer function of a system?

2. What are the types of transfer function?

3. Define feedback.

4. Mention few applications of Separately Excited DC generator.

5. What are the basic elements used for modeling mechanical rotational system?

TRANSFER FUNCTION OF ARMATURE CONTROLLED DC SHUNT MOTOR

VIVA QUESTIONS

1. What are the draw backs of transfer function and advantages of transfer function?

2. What are the types of transfer function?

3. Define transfer function.

4. Mention few applications of Separately Excited DC generator.

5. What are the basic elements used for modeling electrical system?

TRANSFER FUNCTION OF FIELD CONTROLLED DC SHUNT MOTOR

VIVA QUESTIONS

1. What is the need for transfer function of a system?

2. Mention few applications of DC motor.

3. Differentiate open loop and closed loop system

4. Write transfer function for field control DC motor

5. Define Mechanical time constant

6. Define Electrical time constant.

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