Final Year MAIN PDF EE- 4207

8/10/2019 Final Year MAIN PDF EE- 4207

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Department of Electrical Engineering, SGSITS, Indore

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SGSITS-Machines Lab

Electrical Machines-III (EE-4201)

SHRI G.S. INSTITUTE OF TECHNOLOGY AND SCIENCE, INDORE

DEPARTMENT OF ELECTRICAL ENGINEERING

ELECTRICAL MACHINE LABORATORY

Expt. No. .. Date: .

Remarks(If any) ... Signature of the staff member

OBJECT:To determine the transfer function of D.C. machine.

SPECIFICATIONS OF THE D.C. MACHINE:

REQURIMENT/EQUIPMENTS:

THEORY:

Most of the D.C. motors in servo applications are of separately excited

type. The output of D.C. amplifier can be connected to either field terminals or to the

armature terminals of the motor. When the field is energized by the amplifier signal,the motor is said to be field controlled and if the armature is supplied by the

amplifier, it is said to be armature controlled.

A

AA

Z

ZZ

MD.C.

Amplifier

Error

Signal

Ia(constant)

LaLf af

Figure 2.1- Field controlled DC motor


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A

AA

Z

ZZ

MD.C.

Amplifier

LaLf af

If (constant)

Error

Signal

Figure 2.2- Armature controlled DC motor

Transfer function of any system in general is a ration of Laplace

transform of the output to the input with all initial conditions zero. It can be a pure

numeric having no units or may be real or complex and may have unit depending upon

the choice of input and output quantities. In the most simplified form, an open loop

system can be described as shown in figure below:

G(s)R(s) C(s)

1 2

Figure 2.3- Block Diagram of control system

Where the number 1 and 2 represent the input and output nodes, R(s) - input and C(s)

-output. (The arrow represents the direction of signal flow.)

The transfer function of such a system is G(s), defined by following relation:

G(s) =C(s)

R(s)

In more complicated closed loop systems, there will be one or more than on

nodes in addition to the input and output nodes as well as feedback loops. The

solution of overall transfer function can be found out by applying basic signal flow

algebra or Massions Gain formula. The signal flow technique forms an essential part

of a feedback system and therefore necessitates the determinations of the transfer

function.

In this experiment we shall determine the transfer function of an armature

controlled D.C. motor. (See figure 2.2)


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We wish to determine the transfer function

G(s) =(s)

Va (s)

We have, Ia(s) = (Va sEb s)Ra (1+sRa ) ..(1)

Where Ta= La/Ra

Eb= K.If where K = ZP/2A

Taking Laplace transform, Eb(s) = sK.If(s).m(s) ..(2)

Also the developed torque, Tm(s) is given by

Tm(s) = K.Ia(s).If(s) ..(3)

But

Tm(s) = TL(s) + Jm.s2.m(s) + sFm.m(s)

Or Tm(s) = TL(s) + sFm(1+sT)m(s) ..(4)

Where T = Jm/Fm= motor time constant

If the machine is running at no load, TL(s) = 0

Hence from equation (2) and (3)

m(s) = K.IfsFm .s(1+sT)Ia(s)

From equation (1), (2), (3) and (4), a block diagram can be draw as shown below:

+- )a1(

1

sTRa K If(s)

Ia(s)

)'1(

1

sTsPm

Tm(s)

sK If(s)

Va(s) m(s)

Eb(s)

Figure 2.4- Closed loop block diagram of DC motor


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From the block diagram, the overall transfer function, G(s) of the motor can be

determined as:

G(s) =m (s)

Va (s)=

K If(s)

s.K2If2+ s Fm Ra (1+sTa )(1+sT

)

Thus the experiment consists of the determination of K, Fm, Jm, Raand La.

PRE EXPERIMENTAL QUESTIONS:

1. What is the moment of inertia? On what physical parameters does it depend?

2. What do you understand by polar moment of inertia?

3. Can the retardation test be conducted under load condition, comment?

4. In retardation test will the time required for the speed to drop increase or

decrease when fly wheel is removed from the motor shaft?

1. Determination of K:

From equation (1), K is defined as

K =induced emf /field current

speed of the machine

Make the connection as shown in figure 2.8, run the machine as a generator at

constant speed and note down the voltage induced voltage for the different values of

the field current. Plot these values of voltage against the field current which will give

the magnetization characteristics of the machine (figure 2.5). From this, determine the

value of K.

=constant

E

If

k=(E/If)/

Figure 2.5-Magnetization characteristics of DC machine


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2. Determination of Fmand Jm:

Perform the retardation test on the D.C. machine. Run the machine at a little

over the rated speed and cut the supply, not down the fall of speed with time. Repeat

the same test with armature circuit connected to a known resistance. Two speed time

curves will have two time constants T1and T2respectively (see figure 2.9). These time

constants bear the following relations with Fmand Jm.

T1=Jm

Fm

And

T2=Jm

Fm +K 2I

f2

Rext .

Where Rext is known resistance connected across the armature in the latter

part. Determine Fm and Jm from these relations. For retardation test, make the

connections as shown below:

A

L1

L2

A

AA

Z

ZZ

Rext

AVM

K

Figure 2.6

3. Determination of Raand La:

Laof armature circuit is usually very small and hence can be neglected. Measurethe resistance of the armature by ammeter voltmeter method (Figure 2.8).


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A

L1

L2

A

AA

Z

ZZ

AVM V

L1

L2

Figure 2.7

Figure 2.8- Measurement of armature resistance

T1 T2

Speed

N

Time

t Figure 2.9- Speed time curve of DC machine


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OBSERVATION:

1. Magnetization Characteristics:

Speed of machine = . RPM, K =

If(A)

E (V)

2. Retardation test:

Field current = .. A

(i)

Rext.= .

Time

(sec)

Speed

(RPM)

(ii)Rext. = ..

Time(sec)

Speed

(RPM)

(iii)

Determination of Ra by ammeter voltmeter method

Va(V)

Ia(A)

Ra()


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REPORT:

1. Find out the transfer function(s)

Va (s)?

2. Find out the time response of the system, if the input is a unit step voltage?

3.

Discuss the effect of various time constants on the response of the system and

comment on its stability?

4. Derive the transfer function of a field controlled motor and give the block

diagram representation?

5. What are the assumptions made in this experiment?


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AIM:To draw the torque-slip characteristics of a 3-phase induction motor

APPARATUS: Watt meter-2, ammeter-1, voltmeter-1, tachometer-1, resistance bank-

1, Variable rotor resistance,

SPECIFCATIONS OF THE MOTOR:

CIRCUIT DIAGRAM:

DC

GENERATOR

TWO SPEED

MOTOR

SLIP RING

INDUCTION

MOTOR

A

V

L

O

A

D

A BC

D E F

Ra RbRc

EXTERNAL ROTOR

RESISTANCE

LM

M L

CV

C V

LINE AMPS

LINE

VOLTS


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THEORY:

Induction motors, as they are widely used on account of their low cost, reduced

maintenance and robust construction or a very important class of electrical machines.

Mechanical characteristics of the motors fully define their use to various types of

loads. The load torque variation and the developed torque variation define the point

of operation.

The torque in an induction machine can be formulated in different ways as shown

below

Torque

=222/22+222 =

22/2

2+22 =

Rotor input or air gap power

synchronous speed in rad /sec =

32

The above equation defines the torque slip characteristics.

The torque as it is proportional to the rotor input is calculated from the rotor input

less than stator losses, speed being measured at each load. The load on the induction

motor is put indirectly by putting n electrical load on the d-c generator coupled to it.

The difference between the synchronous speed and rotor speed can be expressed as a

percentage of synchronous speed, known as the slip.

=

s = slip, Ns = synchronous speed (rpm), Nr = rotor speed (rpm)

At no-load, the slip is nearly zero (


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Power flow in induction machine:

Complete Torque slip characteristics of an induction motor


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MODEL GRAPHS:

Torque slips characteristics of IM at different rotor resistances


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PROCEDURE:

Connect the electrical circuit as shown in the circuit diagram.

Start the motor after inserting the full rotor resistance in the circuit.

Note down the power input, current and speed at various loads measure the

stator resistance per phase. (0.81 per phase).

Open circuit the rotor and switch the supply on to the stator. The power gives

approximately the core losses in rotor and stator both (like the open circuit Test

of transformer). Assuming it to be equally divided, find the stator iron loss.

Calculate the torque from power input to the motor that is the copper and

stator loss in the stator, and also slip from the observer values of the

corresponding speed.

OBSERVATIONS:

A)Full load rotor resistance in the circuit

I W1 W2 Win 32R STATORIRON

LOSS

ROTOR

INPUT

WATT

TORQUE SPEED SLIP


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B) Intermediate rotor resistance in the circuit


LOSS

ROTOR

INPUT

WATT

TORQUE SPEED SLIP

C) All rotor resistance out


LOSS

ROTOR

INPUT

WATT

TORQUE SPEED SLIP

d) D-C resistance (stator) per phase _____________ ohm.

e)Total iron loss with rotor open circuited ____________watt.

REPORTS:

Plot the torque slip characteristics and the current speed characteristics of the given

induction machine.


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OBJECT: To study the operation of an induction motor on unbalanced three phase

supply.

SPECIFICATIONS OF THE MACHINE:

REQUIREMENTS/EQUIPENTS:

THORY:

Three phase induction motors are most widely used in the industries .Very frequentlythese motor are called upon to operate in the unbalanced voltage supply under

certain fault conditions. the unbalanced voltages can be resolved into their

symmetrical components i.e. , two set of balanced voltage , one in forward direction

and one in backward direction .if rotor slip relative to the forward field be s , it will be

(2-s) with respect to backward field .This will give rise to two torques opposing each

other i.e.

And TF = I2

R2/S

Tb =I2b R2/ (2-S)

The worst condition of unbalance is when the supply is out of from one of the phase if

this happen when the motor is in operation it will continue to run but with reduced

efficiency and power factor.


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PRE-EXPERIMENTAL QUIZ:

1. What do you mean by unbalancing & single phasing?

2. With the reduction in supply voltage stator current increased why?

3. What is the effect of unbalancing over the net electromagnetic torque?

CIRCUIT DIAGRAM:


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PROCEDURE:

Make the connection as per the circuit diagram keep the variable terminal of the auto

transformer (single phase) to the maximum position. Adjust the auto transformer to

give a balanced three phase voltage and start the induction motor on no load with thehelp of star delta starter. Take the precaution of short circuiting the ammeter and

current coil of the wattmeter when starting the motor.

Give the full 400 volt balanced supply across the lines to the motor and perform the

load test. Record the three line currents, voltage, power speed etc. in the observation

table.

Reduced the load to zero and then reduced the voltage one phase by single phase

autotransformer near to about 150 volt. Load the motor gradually and take the

observations.

Remove the load again.

Now disconnect one phase to give single phase operation. Take the observations.

Again load the machine slightly under this condition & take the observations.

OBSERVATION

a)

Balanced supply voltages:

V1n= V2n= V3n= VL-L=

Parameters At No Load At Load

Current

W1

W2

Power

Speed

Torque

Efficiency

Power Factor

Slip


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b)

Unbalanced Operation:



V1nV2n

V3n

I1

I2

I3

W1

W2

Input

Output

EfficiencyTorque

Speed

Slip

c)

Single Phasing:



V1n

V2n

V3n

I1

I2

I3

W1

W2

Input

OutputEfficiency

Torque

Speed

Slip


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REPORT:

1) For balanced operation plot the curve between-

a) Efficiency and output

b) Power factor and output

c) Slip and output

2) Explain the effect of single phasing over the machine performance.

Derive the equivalent circuit of induction motor under unbalance and balanced supply

voltage.


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OBJECT:No load speed characteristics of Schrage motor

SPECIFICATIONS OF THE MACHINE:

REQUIREMENTS/EQUIPENTS

THEROY AND PROCEDURE:

Schrage motor is a 3-phase induction machine where speed control and

improvement of power factor are possible by voltage injection; this emf is obtained

from the brushes on the commutator which collect the emf at slip frequency from

commutator winding

Open out the slip ring side and commutator side covers of the machine and study

the construction details of the machine and various arrangements provided

The speed of a Schrage motor depends upon the magnitude of the injected emf,

which can be increased by increasing the brush separation.

Measure the no load speed of the Schrage motor the brush separation .Also measure

the value of E, The injected emf .perform the experiment with the two possible

arrangement of secondary connection Namely three poles parallel when D1 ,DS etc.


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connected together &Six poles in parallel (When D1 D4&d2 d5etc. are connected

together ) . Measure the max value of injected voltage Emax& also the secondary stand

still emf per phase (E20). The approximate speed of motor can be given by:

Nr =Ns(1-(EMAX/ E20) sin/2)

PRE-EXPERIMEMENTAL QUIZE

1 What are the other methods of speed control of induction motor?

2 can Schrage motor run at synchronous speed?

3 How is the desired frequency of the injected voltage achieved at all speed?

4 what are the other methods of generating Ej for controlling the speed of induction

motor?

OBSERVATION FOR THREE POLES IN PARALLEL

S .NO Injected voltage Brush separation () Observed speed Calculated

speed


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FOR SIX POLES IN PARALLES

S.NO Injected voltage Brush separation () Observed speed Calculated

speed

REPORT:

1

Give the report about the connection of primary, secondary and tertiarywinding of the machine and also arrangement of the brushes on the

commutator.

2 Draw the speed VS brushes separation characteristics of motor in the two

arrangements of secondary connection

(1) From the observation.

(2) By calculation


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CIRCUIT DIAGRAM:


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Equivalent circuit is the representation of the actual motor by fictitious elements forming a

simple electrical network. Equivalent circuit so obtained is capable of giving the performance

characteristics of the motor under various operating conditions obtained.

The equivalent circuit can be determined by performing (a) Light running test (b) Blockedrotor test (c) DC measurement of stator resistance.

PRE-EXPERIMENTAL QUIZ:

1. Why single phase motors are not self-starting?

2. What are the different methods of starting single phase Induction motor?

3. Why is the resultant forward flux stronger than the backward flux in a single phase

induction motor at all speeds?

4. What is centrifugal switch?

5. What are the theories used for the analysis of single phase motors? Indicate basic

differences?

CIRCUIT DIAGRAM:

PROCEDURE:

Connect up the circuit as shown. Perform light running test at rated voltage. Note down the

current and the power input.

Perform the blocked rotor test on the motor applying a reduced voltage to the main

winding so that rated current flow through it, for this test insulate the starting winding at the

centrifugal switch s by a piece of paper (Note the ammeter and wattmeter readings).


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OBSERVATIONS:

Test Voltage Current Power

Light Running Test

Blocked Rotor Test

DC resistance of the stator winding ..

REPORT:

1. Draw the equivalent circuit referred to stator for

(a)Light running test

(b)

Blocked rotor test

2. Compute the values of various parameters from the test results and indicate them on the

equivalent circuit for slip s.

3. Determine for slip, s=0.05

(a)Input current

(b)Forward and backward components of rotor current referred to stator.

(c)Forward and backward torques and gross motor torque in synchronous watts.

(d)Combines Iron, friction and windage loss, and net output in watts.

(e)

Efficiency of the motor.4. Draw the torque-slip curve for a single phase induction motor with its forward and

backward components.

5. What are the approximations made while evaluating the equivalent circuit parameters?

How are these approximations justified?

6. How does the Efficiency of test motor compare with that of the three phase motor of

same rating?

While evaluating the performance from the equivalent circuit for different values of

slip, the backward impedance need only be found for one value of slip & the same can

be assumed constant for other normal operating values of slip. Why?


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OBJECTIVES:-

To determine the performance characteristics of a 3-phase induction generator as

a) Grid connected induction generator

b)

Isolated(self-excited) induction generatorConduct power generation test on grid connected induction generator and for self-

excited induction generator and draw

1) Efficiency vs. power

2) Power factor vs. power

3) Stator current vs. power

4) The speed vs. power curves at rated voltage and frequency

MOTIVATION:-Over the past few decades, there has been an increasing use of squirrel cage type

induction generators, particularly in wind energy conversion systems and micro-hydro

power systems. The grid provides frequency and voltage regulation, as well as the

reactive power required by the generator. Their advantages in these applications are

that they are rugged, require less maintenance, high power/weight ratio and self short

circuit protection and cheap. It is not essential to operate precisely at synchronous

speed.

THEORY:-

The set up mainly consists of an I.M coupled with D.C.M. The three phase supply is

given to the starter of the I.M it will start working as a motor as it is coupled with the


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D.C.M it starts working as generator. Now with the help of a voltmeter, measure the

voltage and check the polarity of the generated emf. Its value is made equal to the dc

supply available.

Now the D.C.M is connected with the supply and it starts running as a motor. At an

instant the induction machine and the D.C.M will run as motors. They drive each other

now the I.M crosses its synchronous speed and starts generating power to the grid and

it draws reactive power from the grid.

Induction machine in both of its motoring mode and generating mode draws reactive

power for the shunt branch. Now if we remove the grid from the machine it will stop

generating the power. As the machine is not having the reactive power supply. So by

removing the grid and giving the external reactive power to I.M will make machine to

generate power and this mode of operation is termed as self excited mode of

operation and machine is called self excited machine.

EQUIPMENTS AND COMPONENTS:-

(a) A three phase squirrel cage induction motor coupled with separately excited dc

motor

(b) One AC Ammeter (0-5/10A)

(c) One AC Voltmeter (0-500V)

(d)

Two Low pf wattmeter (600V,10A)

(e) Two unity pf wattmeter (600V,10A)

(f) Suitable dc loads (440V, 10A)

(g) Tachometer

DATA SHEET

Note down the name plate details of the both machines and identify the terminals.

Observe the constructional features. Note the type of rotor used and the winding

connections.


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Name Plate Details of the Machine

Name of the manufacturer:

Rated output:

Rated voltage:

Supply Frequency:

Rated speed:

No. of poles:

Rated current:

Type of rotor:

Type of starting method:

Ic Ic Ic

A

V

STAR

DELTA

STARTER

AFrequency

meter

R

Y

B

3 PHASE

AC

SUPPLY

MAIN

SWITCH

N

L1

L2

L3

STATOR ROTOR

INDUCTION MACHINE

A

AA

Z

ZZ

DC MACHINE as prime

mover

GRID CONNECTED

INDUCTION

GENERATOR

LOAD II

MCB

LOAD I

MCBML

C

V

VC

M

MCB

L1

L2

L3

SELF EXCITED

INDUCTION

GENERATOR

L M

V C

ML

CV

A

Capacitor bank delta

connected

L

A

B

C

Grid connection and self excitation of an induction machine


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PROCEDURE

Power Generation Test

Make the connections as shown in Fig above

Switch on the field winding DC supply and set field current to its rated value.

Start the dc motor using starter and set the field current up to its rated current.

Record the speed of motor/generator set.

Now adjust the field current and increase the speed up to synchronous speed.

Now switch on the induction machine supply using autotransformer gradually.

Monitor carefully the ammeter and Wattmeters readings.

Use field voltage control for further speed increment of DC motor and tabulate

the observations in Table. Take care about the ratings of both machines.

OBSERVATIONS

Winding connections for stator/rotor:

(b) Average stator winding resistance/phase=_____ohm

(c) Average rotor winding resistance/phase=______ohm

Data Processing and Analysis

a) Grid connection

S. No V IL W1 W2 F N Vdc Idc If


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b) Self excited below rated speed

S. No V IC IL W1 W2 f N Vdc Idc If

c) At rated speed


d) At above rated speed



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REPORT:-

a) Plot using measured data efficiency vs. output Power

b) Plot using measured data power factor vs. output Power

c) Plot using measured data stator current vs. output Power

d) Plot using measured data Efficiency vs. output Power

e) Plot using measured data speed vs. output Power

f) What are the advantages and disadvantage of induction machine as a

generator?

g)

Draw and explain torque speed characteristics of induction generator.

h)

How the voltage and frequency control takes place in grid connected

induction generator? Explain.

i)

Critically comment on the characteristics you obtained? j) Induction generator draws leading VAR? Justify.

PRECAUTIONS:

Check the direction of rotation of both machines before conducting the power

generation test. It must be same.


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OBJECT:To determine the equivalent circuit parameters and also perform the routine

test and type test for three phase induction motors as per ISS i.e. IS 325:1996

APPRATUS REQUIRED:

SPECIFICATIONS:

THEORY:-

To know the performance of an induction motor the motor is translated in terms of an

electrical/circuit where the power output etc are represented by the dissipation in

some fictitious element in the circuit which is called the equivalent circuit.

The equivalent circuit can be determined by performing:-

(a) Light running (No load) test

(b) Blocked rotor test and

(c) d-c measurement of the stator resistance.

LIGHT RUN TEST

The no load test on an induction motor gives information with respect to

exciting current and no-load losses. The test is performed at rated frequency andbalanced poly-phase voltages applied to the stator terminals. Readings are taken at

the rated voltage, after the motor runs long enough for bearings to be properly

lubricated.


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At no load, the rotor current is only the very small value needed to produce sufficient

torque to overcome the friction and windage losses associated with rotation. The no-

load rotor I2R loss is, therefore, negligibly small. Unlike the continuous magnetic core

in a transformer, the magnetizing path in an induction motor includes an air gap which

significantly increases the required exciting current. Thus, in contrast to the case of a

transformer, whose no-load primary I2R loss is negligible, the no-load stator I

2R loss

of an induction motor may be appreciable because of this larger exciting current.

Neglecting rotor I2R losses, the rotational loss Prot for normal running conditions can be

found by subtracting the statorI2R losses from the no-load input power.

P = constant losses + cu losses

Constant losses=mech. Losses + core loss

Cu losses =..

Mechanical losses can be separated by graphical method as given below

Core loss


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BLOCKED ROTOR TEST:-

Like the short-circuit test on a transformer, the Blocked-Rotor test on an induction

motor gives information with respect to the leakage impedances. The rotor is blocked

so that it cannot rotate (hence the slip is equal to unity), and balanced polyphasevoltages are applied to the stator terminals.

In some cases, the blocked-rotor torque also is measured. The equivalent circuit

for blocked-rotor conditions is identical to that of a short circuited transformer. An

induction motor is more complicated than a transformer, however, because its

leakage impedance may be affected by magnetic saturation of the leakage-flux paths

and by rotor frequency.

The blocked-rotor impedance may also be affected by rotor position, although this

effect generally is small with squirrel-cage rotors. The guiding principle is that the

blocked-rotor test should be performed under conditions for which the current and

rotor frequency are approximately the same as those in the machine at the operating

condition for which the performance is later to be calculated. For example, if one is

interested in the characteristics at slips near unity, as in starting, the blocked-rotor

test should be taken at normal frequency and with currents near the values


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encountered in starting. If, however, one is interested in normal running

characteristics, the blocked-rotor test should be taken at a reduced voltage which

results in approximately rated current; the frequency also should be reduced, since

the values of rotor effective resistance and leakage inductance at the low rotor

frequencies corresponding to small slips may differ appreciably from their values at

normal frequency, particularly with double-cage or deep-bar rotors. The total leakage

reactance at normal frequency can be obtained from this test value by considering the

reactance to be proportional to frequency. The effects of frequency often are

negligible for normal motors of less than 25-hp rating, and the blocked impedance can

then be measured directly at normal frequency. The importance of maintaining test

currents near their rated value stems from the fact that these leakage reactances are

significantly affected by saturation. Based upon blocked-rotor measurements, the

blocked-rotor reactance can be found from the blocked-rotor reactive power

PRECAUTION:-

In Blocked rotor test we must apply reduced voltage (10-12% of v rated) so that the

rated current could flow.

PROCEDURE:-

Connect up the circuit as shown. Perform light running test at the rated voltage. Note

down the power input and the current.

Apply a reduced voltage across the motor so that approximately the rated current

flows through the circuit.

Measure the dc value of the resistance.


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CIRCUIT DIAGRAM

THREE PHASE

AUTO

TRANSFORMER

Star/delta

startor

Three

phase

induction

motorv

A

c v

LM

M L

C V

R

Y

B

L1

L2

L3

OBSERVATIONS:

S. NO TEST VOLTAGE CURRENT POWER INPUT

D-C resistance of the winding per phase =ohms

Equivalent A-C resistance per phase =..ohms

REPORT:

1. Draw the equivalent circuit of the induction motor and put the values for

various elements in the circuits.

2. Calculate x and plot for the rated voltage line current power factor,

efficiency, torque speed vs power output on the same graph.

3. Draw the equivalent circuit for all load operation.

4. Draw torque slip characteristics.


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ROUTINE TEST AND TYPE TEST

22.2 Test certificates

22.2.1 Unless otherwise specified when

inviting tenders, the purchaser, if so

desired by manufacturer, shall accept

manufacturers certificate as evidence

of the compliance of the motor with

the requirements(see 10,11,12,13 and

17) of this standard together with a

type test(see 22.3.1) certificate on a

motor identical in essential details withthe one purchased, together with

routine test certificate on each

individual motor is supplied on one

order, type tests, as specified, shall be

made on one of these motors, in

addition to the other certificates if the

purchaser so requires.

22.2.2 Certificates of routine tests (see

22.3.2) shall show that the motor

purchased has been run and has been

found to be electrically and

mechanically sound and in working

order in all particulars.

22.3 Classification of test

22.3.1 Type tests

The following shall constitute type

tests:

a) Dimensions (for motors covered

by IS 1231:1974 and IS2223:1983 only) (see 10).

b) Measurement of resistance of

windings of stator and wound

rotor.

c)

No load test at rated voltage to

determine input current, power

and speed (see 23.1).

d) Open circuit voltage ratio of

wound rotor motors (slip ring

motors)(see 23.3).

e) Reduced voltage running up test

at no load( for squirrel cage

motors up to 37KW only)(see

23.2)

f) Locked rotor readings of voltage,

current and power input at a

suitable reducedvoltage(see23.2)

g) Full load test to determine

efficiency, power factor and

slip.(see 23.5)

h) Temperature rise test (see14).

i) Momentary overload test

(see13.1).

j)

Insulation resistance test(see25)k) High voltage test(see 24)

l) Test for vibration severity of

motor(see15)

m)Test for noise levels of

motor(see16)


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n) Test for degree of protection by

enclosure(see5)

o) Temperature rise test at limiting

values of voltage and frequency

variation.

p) Over speed test(see26)

q) Test on insulation system( see 27

These are optional tests subject to

mutual agreement between purchaser

and the manufacturer.

22.3.1.1 It is recommended that the

reports of type tests be made in theform recommended in Annex C.

22.3.2 Routine tests

The following shall constitute the

routine tests:

a) Insulation resistance test(see25)

b) Measurement of resistance of

winding of stator and woundrotor.

c) No load test(see23.1)

d) Locked rotor readings of voltage,

current and power input at a

suitable reduced voltage(see

23.4)

e) Reduced voltage running up test

(see23.2) (for squirrel cagemotors).

f)

High voltage test(see23.4)

23 PERFORMANCE TESTS

23.1 No load test

The motor shall run at rated voltage

and frequency given on the rating

plate. The motor shall run to its normal

speed and shall not show abnormal

electrical or mechanical noise. The

input power, current and speed shall be

measured and used in the

determination of no load losses and

efficiency at full load.

NOTE- in case proper facilities for

conducting this test at rated voltage are

not available, the method of testing

shall be mutually agreed between the

manufacturer and the purchaser.

23.2 Reduced voltage running up test

The test is applied to squirrel cage

motors. The test is made to check the

ability of motor to run up to its rated

speed at no load. The motor up to

37KW shall be supplied with reduced

voltage 1/of rated value for each

direction rotation. For motors above

37KW, the voltage shall be 1/ of rated

value or less but motor shall run only in

the specified direction of rotation.

23.3 Open circuit voltage ratio test for

wound rotor (slip ring) motors

The stator of the motor is supplied with

rated voltage and open circuit voltage

at the slip rings shall be determined (by

lifting the slip ring brushes). The voltage


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shall comply with the declared values of

the manufacturer.

23.4 Locked rotor test

The tests shall be carried out in

accordance with provision of IS

4029:1967. The test may be carried out

at reduced voltage. The readings of the

input current, power and breakaway

torque shall be determined. The values

of breakaway torque shall be not less

than the value given in IS 8789:1996.

23.5 Full load test

The motor shall be supplied with rated

voltage and load on the shaft shall be

adjusted such that it delivers the rated

output.

The value of voltage, input power,

current and speed shall be measured.

The efficiency determined for full load

shall not be less than the values

specified in IS 8789:1996. The detailed

procedure of testing three phase

induction motors shall be in accordance

with IS 4029:1967.

NOTE- In case proper facilities for

conducting this test at rated voltage are

not available; the method of testing

shall be mutually agreed between the

manufacturer and the purchaser.

24 HIGH VOLTAGETEST

24.1 The requirements specified in IS

4029:1967 shall apply.

25 INSULATION RESISTANCE TEST

25.1 The requirements specified in 30.2

of IS 4722:1992 shall apply.

26 OVER SPEED TEST

26.1 All motors shall be designed to

withstand 1.2 times the maximum

rated speed.

26.2 An over speed test is not normally

considered necessary, but may be

performed when this is specified and

has been agreed between the

manufacturer and the purchaser at the

time of the order. An over speed test

shall be considered as satisfactory, if no

permanent abnormal deformation is

apparent subsequently and no other

weakness is detected which may

prevent the motor from operating

normally, and provided the rotor winding

after the test comply with the required

high voltage test. The duration of any over

speed test shall be two minutes.

27 TESTS ON INSULATION SYSTEM

NOTE- Unless otherwise specified when

inviting tenders, the purchaser, if so

desired by the manufacturer, shall accept

manufacturers test certificate as evidence

of the compliance of the motor/ insulation

system with the requirements of the


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following tests together with the tests

certificate as stated in 22.2.

27.1 Tangent delta and delta tangent delta

test

The requirement and method of test shall

be as per IS 13508:1992.

27.2 Impulse voltage withstand test

The requirements and method of test

should be as per IS 14222:1995

ANNEX A

(Clause 2.1)

LIST OF REFFERED INDIAN STANDARDS

900:1992- code of practice for installation and

maintenance of induction motors

(revised)

996:1979- Single phase small AC and universal

electric motors (second revision)

1076(in parts) - Preferred numbers

1231:1974- Dimensions of three phase foot

mounted induction motors (third

revision)

1271:1985- Thermal evaluation and

classification of electrical

insulation(first revision)

1885(part 35): 1973/IEC 50(411):1993-

Electro technical vocabulary:

rotating machinery

2223:1983- Dimensions of flange mounted AC

induction motors (second revision)

2254:1985- Dimensions of vertical shift motors

for pumps(second revision)

3043:1987- Code of practice for earthing

(second revision)

3855(in parts) - Rectangular and square

enameled copper conductors

4029:1967- Guide for testing three phase

induction motors

4691:1985- Degrees of protection provided by

enclosures for rotating electrical

machinery (first revision)

4722:1992- Rotating electrical machines (first

revision)

4728:1975- Terminal marketing and direction of

rotation for rotating electrical


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machinery(first revision)

4800(part5):1968- Enameled round winding

wires: Part 5 wires for

elevated temperatures.

4889:1968- Method of determination of

efficiency of rotating electrical

machines.

6362:1995 IEC Pubs: 34-8:1991- Designation of

methods of cooling for rotating

electrical machines

6455:1972- Single row radial ball bearings

6457:1972- Dimensions and output ratings for

foot mounted rotating electrical

machines with frame numbers

355 to 1000

8544(in parts) -Motor starters for voltages not

exceeding 1000V

8789:1996- Values of performance

characteristics for three phase

induction motors

12065:1987- Permissible limits of noise level for

rotating electrical machines

12075:1986- Mechanical vibration of rotating

electrical machines with shaft

heights 56mm and higher

measurement, evaluation and

limits of vibration severity

12360:1988- Voltage bands for electrical

installations including preferred

voltages and frequency

12661(Part1):1988-High voltage motor starter:

Part 1 direct on line (full

voltage) AC starters

12802:1989- Temperature rise

measurement of rotating electrical machines

12824:1989- Type of duty and classes of

Rating assigned (second revision)

13947(Part4/Sec1):

1993/IEC947-4-1(1990) LV Switchgear and

control gear: Part4 contactors and motor

starters, sec1 Electromechanical


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ANNEX C

FORM FORTYPE TEST REPORT OF THREE PHASE INDUCTION MOTOR

(Clause 22.3.1.1)

MANUFACTURER CERTIFICATE NO.

PURCHASER

PURCHASE ORDER NO. ORDER ACCEPTANCE NO.

NAME PLATE DATA

OUTPUT PHASE VOLTAGE CONNECTION FULL LOAD

CURRENT

FREQUENCY FULL

LOAD

SPEED

FRAME DUTY INSULATION EFFICIENCY

NOMINAL

PERCENT

MANUFACTURERS

NUMBER/REFERENCE


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TESTS

LOAD CONNECTION LINE

VOLTAGE

LINE CURRENT POWER SLIP LOAD POWER FACTOR EFFICIENCY

GUARANTEED TEST GUARANTEED TEST

TEMPERATURE RISE TEST RUN

HOURS RUN VOLTAGE CURRENT INPUT

POWER

CALCULATED

OUTPUT POWER

COOLING AIR(C) TEMPERATURE RISE(C)

STATOR ROTOR

Core Winding Core Winding

BREAKAWAY TORQUE AND STARTING CURRENT

VOLTAGE BREAKAWAY STARTING CURRENT TORQUE POWER


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INSULATION RESISTANCE STATOR ROTOR

HIGH VOLTAGE TEST

OPEN CIRCUIT ROTOR VOLTS:

RESISTANCE OF WINDING PER PHASE

1) STATOR- Ohms at C

2) ROTOR- Ohms at C

REDUCED VOLTAGE RUNNING UP TEST:

OVERLOAD

A) MOMENTARY EXCESS TORQUE TEST

B) PULL UP TORQUE

VIBRATION SEVERITY

NOISE LEVEL

DEGREE OF PROTECTION BY ENCLOSURE

TESTED BY APPROVED BY

DATE DATE


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1. INTRODUCTION

The classical way of teaching electrical machinery theory to undergraduates to start

off with the DC machines and finish with the elementary principles of operation of

single phase motors, covering the transformer, the synchronous machine, theinduction machine and the AC commutator motors. Mostly the steady state

operation of these machines is dealt with and the transient operation is either

completely omitted or confined to the synchronous machine. With the result the

student is left with the impression that each type of electrical machine is a class by

itself having nothing in common with other types of electrical machines.

Kron pointed out 32years ago that all electrical machines can be mathematically

reduced to a basic two axis machine. Further work by Gibbs, Adkins, White and

Woodson and others created interest among the academic circles in the generalized

theory of electrical machines as a possible method of teaching electrical machinery

theory. The important requirement in adopting the new method is to provide thephysical meaning for the various mathematical transformations employed and to

physically show that the different types of electrical machines are simply different

terminal conditions of one and the same physical phenomenon pertaining to the

primitive machine of Kron. It is primary function of the generalized

electromechanical energy converter (GEMC) to meet this requirement. After the

advert of the GEMEC more interest is now being shown in India and abroad, in the

teaching of generalized theory of electrical machines to undergraduates.

The GEMEC is as yet a newcomer to them market and these are only a handful of

manufactures in the whole world who make such machines. The PSG industrial

institute, India is one of those few. It is not sufficient for GEMEC to operate only as a

primitive two axis machine. It must also be able to physically simulate the various

mathematical transformations used in the generalized theory and consequently be

able to operate as a primitive two axis machine and as various type of machines as

many types as possible consistent worth the manufacturing possibilities, size, cost,

utility etc. The GEMEC made by PSG industrial institute provides facilities for such

transformations. This manual gives a description of GEMEC manufactured by the PSG

Industrial Institute. Some of the possible modes of operation, erection and

maintenance instructions and connection diagrams and performance characteristics

for certain modes of operation. The modes of operation listed in this manual aresome of the possibilities and many other modes can be devised by the user, taking

care that the current ratings are within limits as specified under technical data. The

machine is so designed as to give maximum accessibility for demonstration and

maintenance purposes.


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2. DESCRIPTION OF THE MACHINE

The stator of the machine has 48slots accommodating 4coils of 12 slot pitch. All the

coil ends are brought out to terminals arranged in four concentric circles on a

terminal board for easy connection. The terminals are numbered and coils indicated.This enables the stator to be connected for different number of poles and phases.

Single search conductors are provided in six suitably chosen stator slots so that

search coils are provided in six suitable chosen stator slots so that search coils of

various pitches can be arranged.

The rotor has 36 slots accommodating a double layer closed lap winding with a coil

pitch of 8 slots. The winding is provided with a 144 segment commutator on one side

and slip ring tapings on the other side. There are two sets of slip rings tappings:

One set of six symmetrical tappings and another of four.

Two of the tapping being common to the two set. All the eight tappings are brought

to the slip rings. A rotor search coil whose terminals are brought to two more slip

rings is also provided.

The commutator is equipped with a set of rocking brushed and a set of rotating

brushes. The rocking brush set is arranged on two rings, each ring carrying 6brushes,

equally spaced along the periphery.

The rings can be rocked opposite to one another by bevel gear and the whole set can

be rocked relative to the stator winding. Locking arrangement is provided for each of

the movements. Graduated scales indicate the position of the set as a whole and the

angular displacement between the two rings. The rotating brush set consists of four

brushes arranged in quadrature and can be driven round the commutator in eitherdirection by an external drive. The shaft extension for coupling this external drive is

arranged to be co-axial with the main shaft of the PSG GEMEC but independent of

the same. The rotating brush set can also be locked in any desired position.

Diagrammatic representation of the rocking brush set and the rotating brush set

with terminals is provided on the panel board. Connections from the rotating brush

set are brought through slip rings terminals on the panel board. Leads from the

rocking brushes are brought to terminals on the brush carriage and these could be

connected, when required, to the corresponding terminals. Diagrammatic

representation by flexible leads provided.

A short circuiting ring, which can be easily fitted on to the commutator, is provided.When so short circuited, the rotor behaves like a semi cage winding, responding to

the various pole numbers that can be produced by the stator winding.


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The nominal rating of the PSG GEMEC as a #-phase, 50 Hz, 4 pole, slip ring induction

motor is 5.5KW at 230V per phase. The machine will however withstand appreciable

overloads.

A DC work machine coupled to the main shaft and a variable speed drive motor for

rotating brushes would be required for normal use of PSG GEMEC. It is preferable tomount the DC work machine on trunnion bearings so that it could be used also as a

swinging frame dynamometer. If desired, a shaft torque meter, a tachometer. And

an accelerometer may also be added which would increase the versatility of the

machine as a research unit.

3. TECHNICAL DATA

Nominal rotoring a 3-Phase, 4 pole, slip ring induction motor:

Line voltage : 400V

Frequency : 50Hz

Output : 5.5KW

Speed : 1440 RPM

Line current : 12.5A

Stator:

Outer diameter : 344mm

Inner diameter : 230mm

Core length : 102mm

Number of slots : 48

Number of coils : 48

Conductor size : 16SWG

Coil pitch : 12Slots

Conductor current : 7.5A

Rotor:

Number of slots : 36

Number of commutator : 144Segments

Winding : double layer

Lap coil pitch : 8 slots

Conductor current : 11A


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Rotating and rocking brushes:

Carbon brushes : 6mm*20mm*35mm

Current per brush : 10A

Maximum operating speeds

Rotor : 3000RPM

Rotating brushes : 2000RPM

4. INSULATION AND MAINTENANCE

Normally PSG GEMEC is supplied separately as shown in the cover photograph and in

a sectional view. Because of improvements made from time to time the actual

machine supplied may vary to some extent from these illustrations and descriptions.For the use of the machine it must be coupled to a drive motor of about 6.5KW

rating and a brush drive motor of 1KW rating with speed control as desired. Care

must be taken in coupling the three machines as any misalignment can damage the

bearings of PSG GEMEC. All the commutator brushes are locked in position before

dispatching. The rotating brushes can be released by unscrewing two radial screws

on the outer cover. The rocking brushes can be released by unscrewing the knurled

head screw follow the operating instructions and in any case. Do not exceed any of

the ratings of the machine. The commutator and slip rings should be cleaned

periodically. The bearings must be cleaned and lubricated with lithium soap based

grease.

Trade names: Shell Alvania grease, Shell Multipurpose Grease or Mobilux Grease)


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OPERATION

GENERAL

Some of the modes in which the machine can be operated and the corresponding

ratings are listed in appendix 1 and the connection diagrams and some of the

operating characteristics in the form of graphs are given in appendix2. Other modes

of operation like the induction generator, synchronous converter etc are possible

and many more modes can be devised by the user. In all cases the following points

may be noted:

1. Any of the ratings specified should not be exceeded.

2. Commuatator brushes when not in use must be lifted and the carriage locked in

position

INDUCTION MACHINES

Since the entire stator coil terminals are brought out, the stator can be connected

for various numbers of poles and 2 or 3 phase operation, the rotor may either be

short circuited through the slip rings or the commutator may be short circuited.

When the stator is connected for other pole numbers, the commutator has to be

short circuited. The machine can also be operated as 2 or 4 pole, or 2 or 3-phase

rotor fed induction machine.

The stator can also be connected for various types of single phase operation.

SYNCHRONOUS MACHINES

It can be operated either as rotating armature or rotating field synchronous machine

of different pole and phase combinations. However, it is not possible to introducethe effects of saliency, but by introducing symmetry in the field circuit, it is possible

to introduce a difference in the reactance of the tow axes. It can be operated as a


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synchronous converter by supplying the machine through a suitable transformer

bank and by making use of the commutator.

AC COMMUTATOR MACHINES

The machine can be very easily connected as a polyphase 2pole or 4pole shunt

commutator motor. When connecting the 2-phase operation, it will be necessary to

use the rotating brush set, locking it a definite position. An autotransformer may be

used to provide controlled voltage to the brushes. With this arrangement, the

machine can operate also as a frequency converter.

It is possible to operate the machine as a rotor fed synchronous motor as a Schrage

motor at reduced voltage. Taking care not exceed the current rating of the statorconductor the machine can also be operated as a series commutator motor.

Various modes of single phase operation, such as repulsion motor, repulsion start

induction motor can also be arranged.

DC MACHINES

PSG GEMEC can be operated as a shunt, series, compound or separately excited DCmachine of different pole numbers. When operating for poles other than 2 or 4, care

must be taken to carefully set and lock the rocking and rotating brush sets and to

choose the proper brushes. It is also possible to use the machine as a DC

transformer, a Rosenberg Generator etc. however, it is not possible to introduce

saliency.

UNCONVENTIONAL MODES

Operation of the so called DC induction motor can be demonstrated by supplying

direct current to the quadrature brushes and then rotating these by means of the

brush carriage rotor.


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Many other unconventional modes of operation may be devised by the user. One

such mode of operation developed in the PSG laboratory by Charlu results in a

variable speed adjustable PF motors. (Trans A.I.E.E., P.A.S., Vol. 78, 1959, PP 407-

413)

LIMITATIONS

The coil pitch of the stator coils as 12 slots corresponding to the full pitch for 4 pole

operation. This has been chosen so that at least for 1 pole number the winding is full

pitched. This choice makes it impossible for the machine to operate as an 8pole

machine.

Another is the uniform air gap. It is not possible to introduce physical saliencynormally met with the DC machines and in some synchronous machines. As has

already been suggested this effect can be simulated to some extent by the use of

asymmetrical connections in the excitation circuit.

TRANSFORMATION

One important feature of PSG GEMEC as already pointed out, is that it can be used

as a physical model to demonstrate the mathematical transformation of a particular

machine to the generalized machine or of one machine to another. Particular mode

of operation are simulated in PSG GEMEC by connecting same active conductors in

different ways and joining them to terminals via solid leads, slip rings or commutator

and fixed or rotating brushes. Each mode of operation is distinguished by its two

components field patternstator and rotor field. A field pattern can be setup by the

different components arrangements, current and voltage. Therefore currents,

voltages and impedance of 1 type of winding (and hence machine) can be

transformed to those of another taking into account the invariance of power.


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OBJECT: To separate the no load losses of a D.C. shunt machine.

SPECIFICATIONS OF THE D.C. MACHINE:

REQURIMENT/EQUIPMENTS:

THEORY AND PROCEDURE:

The mechanical losses (no load) of a D.C. shunt machine can be separated into

hysteresis, eddy current, friction and windage losses by the method given below:

Wnl = Wcore + Wfrictionand windage

= (Whysterisis +Weddy current) + Wbrushfriction +Wbearingfriction +Wwindage

Now, Wh B1.6

N, and We Be N2

Therefore at constant excitation, the total core losses are

Wc = (KhN + KeN2)


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Also,

Wbrushfriction N , Wbearing friction N, and Wwindage N2

Bearing friction loss is small as compared to the other two losses (i.e. Wbrush friction and

Wwindage) and can be neglected.

The total friction and windage losses are

= (KfN + Kw N2)

Thus the total mechanical loss can expressed as

Wnl = (KhN + KeN2) + (KfN + Kw N

2)

= (Kh+ Kf).N + (Ke+ Kw) ..(1)

Separation of loss therefore requires the determination of four constants K h, Ke, Kfand Kw.

Let C = Kh+ Kf and D = Ke+ Kw ..(2)

So Wnl = C.N + D.N2

Or Wnl/N = C + D.N ..(3)

This is a straight line equation. Hence C and D can be determined by observing Wnl

for different values of N and then plotting (Wnl/N) against N on a graph (with Ifconstant).

Determination of C and D will not be sufficient to calculate all four constant.

Therefore, repeat the above test and perform at some other value of field current. The core

loss constants will change to some other values. Hence

C = Kh+ Kf and D = Ke+ Kw ..(4)

Since hysteresis loss and eddy current loss is proportional to B1.6

and B2respectively, so

(Kh/Kh) = (B/B)1.6

= (E/E)1.6

& (Ke/Ke) = (B/B)2= (E/E)

2 ..(5)

So, C = (E/E)1.6

Kh+ Kf and D = (E/E)2Ke+ Kf ..(6)

Now all four constants can be calculated from the equation excitation constant (2) and (6).

Make the connection as shown in the circuit diagram. Keeping excitation constant,

for all observation, note down the voltage and armature current at different speed of

motor. Speed variation should be obtained by varying the voltage across the armature.

Repeat the same procedure with some other value of excitation. Measure the armature

resistance.


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PRE EXPERIMENTAL QUESTIONS:

1. What are friction, windage and iron loss? Why and where do they occur?

2. What are the effects of excitation, speed and load on the friction & iron losses?

3. How iron losses are related to the input voltage and speed?

4.

Is it necessary to have armature of a D.C. machine laminated?

5. Is it necessary to have field also laminated?

CIRCUIT DIAGRAM:

DC shunt machine


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OBSERVATION:

Armature resistance, Ra = . Field current, If= .

Speed

Va

Ia

I2

a.Ra

Wnl

Wnl/N

E at speed .. RPM = .. Volts

Armature resistance, Ra = . Field current, If= .

Speed

Va

Ia

I2

a.Ra

Wnl

Wnl/N

E at speed .. RPM = .. Volts


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REPORT:

1. Calculate all the four constants. Give all calculations.

2. Calculate the constituents of no load losses at the rated speed.

3. What are the pole face losses? Are these caused by hysteresis and eddy currents or

both?

4. What are alternating and rotational hysteresis losses? Differentiate between them?

Is it possible to separate friction and iron losses by making a single plot of input power with

exciting current at a constant speed? Suggest procedure?

Final Year MAIN PDF EE- 4207

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Transcript of Final Year MAIN PDF EE- 4207