LABORATORY MANUAL
ELECTRICAL MACHINE LAB
4TH SEMESTER
E&TC ENGINEERING
S.K.D.A.V GOVT. POLYTECHNIC
ROURKELA
CONTENTS
EXPERIMENT NO.1 – To study different parts of DC Generator.
EXPERIMENT NO. 2 –To Run a dc shunt generator.
EXPERIMENT NO. 3 –Toconnect and run Dc motor (series, shunt and
compound motor with suitable stator connection and measure speed).
EXPERIMENT NO. 4 –To Study 3-Point and 4-Point starter
EXPERIMENT NO. 5 –To study speed control of DC Shunt Motor by Field
control method.
EXPERIMENT NO. 6 – To study speed control of DC Shunt Motor by
armature control method.
EXPERIMENT NO. 7 –To Perform parallel operation of DC generator
EXPERIMENT NO. 8 –To Connect and run 3 phase I.M with help of DOL &
Star-delta starter.
EXPERIMENT NO. 9 –To perform Short circuit & open circuit Test of a single
phase transformer find losses and efficiency.
EXPERIMENT NO. 10 –ToIdentification of terminals of a single-phase
transformer.
EXPERIMENT NO. 11–To construct switch board & series board using cutout, switches, plug, holder, &Two-way switch.
EXPERIMENT NO-1
AIM OF THE EXPERIMENT: To study different parts of DC Generator.
EQUIPMENT REQUIRED: SL.
EQUIPMENT
SPECIFICATION
NO
01
DC generator
220V,5.1A,1500rpm,1HP
02
Screw driver
Taparia,flat,pinch
03
Hammer
500gm,wooden handle
04
Combinational plier
insulated
05
Adjustable spanner
insulated
THEORY: -
QTY
01
01
01
01
01
An electrical machine is a mechanical device which converts mechanical energy
into electrical energy. The energy conversion based on the principle of
production of dynamically induced emf. There are 2 basic essential parts of
electrical DC generator
1. A magnetic field
2. Armature conductor
This can so move as to cut the flux in particular generator these are the
essential parts as discussed below.
PARTS OF A DC MACHINE
i.
ii.
iii.
iv.
v.
vi.
vii.
Magnetic frame or yoke
Pole core of Pole shoe.
Pole coils or field coils.
Armature core.
Armature winding or conductor.
Commutator.
Brushes & Bearings.
MAGNETIC FRAME OR YOKE:
The outer frame of a dc machine is known as yoke. It acts as a protective cover
for the D.C machine as well as it Provides machine supports for the poles. It
also carries magnetic flux produced by the poles. Yokes are made of Cast iron,
but for large machine usually cast steel or rolled steel is employed. The
modern process of forming yoke consisting of rolling a steel slab.
POLE CORE OR POLE SHOE
For the purpose in a machine either permanent poles or electro magnet poles
are attached or welded The field magnet consists of pole core and pole shoe
Pole shoe serves for two purpose:
i They spread out the flux in the air
ii They support the field coil or field winding
POLE COILS OR FIELD.COILS
The pole coils consist of copper wire or strips. When current is passed through
these coils, the electromagnet the pole which produce the necessary flux that
cut by revolving armature conductor.
ARMATURE CORE
It causes the armature conductor to rotate. The important function of the
armature core is to provide a path of very low reluctance to the flux through
the armature. It is cylindrical is made of circular sheet steel dies Lamination
ARMATURE WINDING OR CONDUCTOR
Within the slot of armature core copper windings are provide and known as
armature winding. It consists of large number of insulated coils, each coil
having one or more number of turns. The coils are usually former wound
These are placed in slot Depending upon the type of winding required. These
are basically two types of winding (1) Lap winding (2) Wave winding
COMMUTATOR
It is of cylindrical structure. It is built of wedge shaped segment of high
conductivity hard drawn copper to reduce Its
were and tear segments are insulated from each
other by 0mm thick mica sheet. The segments
are assembly in such a way that results in
circular shape The commutators in DC machine
are used to come Acto DC
BRUSHES & BEARINGS
Brushes are based in box type brush holder attach to the stator or stator yoke.
A small spring keeps the brushes passed on to the commutator surface Brushes
are made of carbon for small DC machine, electrographite for all DC machine
and copper graphite for low voltage high current DC machine.
CONCLUSIONWe have performed the experiment successfully and studied the different
parts of a DC generator.
DISCUSSION QUESTION: 1. Principle of a DC generator
2. Flemings Right hand rule?
3. Explain the emf equation of a generator?
4. Write the function of a commutator?
5. What is the function of brushes?
6. Give layout diagram of classification of d.c generator?
EXPERIMENT NO -2
AIM OF THE EXPERIMENT:To Run a Dc shunt generator.
EQUIPMENT REQUIRED:SL. NO EQUIPMENT
SPECIFICATION
01
DC shunt
generator
02
Neon tester
500v
03
Screw driver
Taparia
04
Combinational
Insulated
plier
05
Insulation tape PVC type, insulated
QUANTITY REMARK
01
01
01
01
THEORY:It is a type of self-excited generator that has its field winding arranged in
parallel with the armature winding. This type gives the constant voltage output
and used for the charging of batteries. Since the field winding is connected in
parallel with the armature it receives less current across it as it is wound with
more turns and thin wire. Due to this, it is capable of producing fewer losses
and it cannot be loaded eventually.
Working Principle
It also works on the principle of electromagnetic induction just like a normal
motor. The field winding is connected shunt to the armature. When an input is
given by the prime mover, the conductor is rotated in the permanent magnetic
field. Due to this, the current gets induced in the conductors placed under the
influence of the magnetic field. According to Faraday’s law of electromagnetic,
an emf will be induced in the conductors when a conductor is rotated in the
magnetic field. This induced emf is used to generate energy that is used by
other mechanical devices. The current induced flow through the armature
winding which is alternating. The output from the armature winding is always
alternating and because of the commutator, the alternating current is
converted to the direct current.
Applications


Used in charging batteries
for constant voltage applications
In a dc shunt generator, the shunt field (c1, c2) is connected in parallel with
armature (A, AA).
The shunt generator is coupled to a dc motor of constant speed& the output
collected in the dc generator.
PROCEDURE:1. The shunt generator coupled to a dc motor was excited by supplying dc
220volt & emf was collected in the output side.
2. During running the motor proper starter was selected.
CONCLUSION:We have performed this experiment successfully and run a DC shunt generator.
DISCUSSION QUESTION: 1.
2.
3.
4.
Write application of a dc shunt generator?
State principle of dc generator?
Is dc shunt generator is self-excited or not?
Advantage of using dc shunt generator?
EXPERIMENT NO. 3
Aim of the experiment:
To connect and run Dc motor (series, shunt and compound motor with suitable
stator connection and measure speed).
EQUIPMENT REQUIRED
SL. NO
1
2
3
4
5
6
7
8
Name of
Specification
equipment
Dc series motor
Dc shunt motor
Dc compound
motor
3-point starter
4-point starter
Drum control
starter
Connecting wires
Tester, screwdriver,
combination plier,
insulation tape
Quantity
Remarks
THEORY
A) DC series motor
In dc motor field winding is connected in series with armature winding.
Drum control is being used to start dc series motor.
Characteristics of dc series motor
In general, for this motor, there are 3-characteristic curves are considered
significant like Torque Vs. armature current, Speed Vs. armature current, &
Speed Vs. torque. These three characteristics are determined by using the
following two relations.
A) Ta ∝ ɸ*I*a
N ∝Eb/ɸ
The above two equations can be calculated at the equations of emf as well as
torque. For this motor, the back emf’s magnitude can be given with the similar
DC generator e. m. f equation like Eb= P ɸ NZ / 60A. For a mechanism, A, P,
and Z are stable, thus, N ∝Eb/ɸ.
The DC series motor torque equation is,
Torque= Flux* Armature current
B) T = If * Ia
Here If= Ia, then the equation will become
C) T= Ia^2
The DC series motor torque (T) can be proportional to the Ia^2 (square of the
armature current). In load test on dc series motor, the motor should be
activated on load condition because if the motor can be activated on no load,
then it will achieve an extremely high speed.
B) Dc shunt motor
In field winding is connected in parallel with armature winding.
3-point starter is being used to start dc sunt motor.
Characteristic of shunt motor
In case of the shunt wound DC motor, this current supply will divide into two
ways like Ia&Ish, where ‘Ia’ will supply throughout the ‘Ra’ resistance armature
winding. In the same way, ‘Ish’ will supply through the ‘Rsh’ resistance field
winding
Therefore I = Ia + Ish
Generally, when the DC motor is in running state & the voltage supply voltage
is stable and the shunt field current given by
Ish = E/Rsh
But we know that the armature current is proportional to the field flux (Ishα
Φ). Thus the Φ remains more otherwise less stable, due to this reason; a shunt
wound DC motor can be named as a constant flux motor.
in dc shunt motor is given by
EB = PΦZN/60A
Here P, A, Z are constant thus
N α Eb/Φ
In dc shunt motor torque equation is
T=Ia (since flux is constant)
C) Dc compound motor
Dc compound motor consist of both series and shunt winding
Compound motor are of two types
1. Cumulative-compound motors
2. Differential-compound motors
4-point starter is being used to start dc compound motor
Characteristics of compound motor
These motors have both series and shunt windings. if series excitation helps
the shunt excitation i.e. series flux is in the same direction then the motor is
said to be commutatively compound. If in other hand, series field opposes the
shunt field, then the motor is said to be the differential compounded.
a) Cumulative-compound motors
Such machines are used where series characteristics are required and
when, in addition, the load is likely to be removed totally such as in
some types of coal cutting machines or for heavy machine tools which
have to take sudden cuts quite often. Due to shunt windings, aped will
not become excessively high but due to series winding, it will be able to
take heavy loads.
Compound motors have a greatest application with loads that
require high stating torques or pulsating loads (because such motors
smooth out the energy demand required of a pulsating load). They are
used to drive electric shovels, metal-stamping machines, reciprocating
pumps etc.
b) Differential-compound motors
Since series field opposes the shunt field, the flux is decreased as the
load is applied to the motor (because, NαEb/Φ). Due to this reason,
there is a decrease in the rate at which the motor torques increases with
load. Such motors are not in common use. But because they can be
designed to give an accurately constant speed under all conditions, they
find limited application for experimental and research work.
One of the biggest drawbacks of such motor is due to weakening
of flux with the increases in tendency towards speed inability and motor
running away unless designed properly.
CONCLUSION;
We have performed this experiment successfully and run a DC motor with
suitable starters connection and measured the speed.
DISCUSSION QUESTION:
1.State type of Dc compound motor?
2.state characteristic of Dc series motor?
Experiment No. 04
AIM OF THE EXPERIMENT:
To Study 3-Point and 4-Point starter
EQUIPMENT REQUIRED: SL. NO Name of
equipment
1
3 Point starter
2
4 Point starter
3
Combination plier
4
Screw driver
5
spanner
6
N-tester
Specification
Quantity
2.2KW,220V,12AMP
2.2KW,220V,12AMP
150mm
300mm
1
1
1
1
1
1
0-500v
Remarks
THEORY:
The current drawn by a motor armature is given bythe relation
Ia=(V-Eb)/RaWhere V is the supply voltage. E the back emf and. the armature
resistance. When the motor is at rest there is as yet, obviously no back emf
developed in the armature. Il now, full supply voltage is applied across the
stationary armature, it will draw a very large current because armature
resistance is very small This excessive current will blow out the fuses and prior
to that current it will damage the commutator and brushes etc to avoid this
happening a resistance is introduced in series with the armature (for the
duration of starting period only say 5-10 second) gradually cut out as the
motor gains speed which limit the starting current to a safe value. The starting
resistance is and develops the back emf which then regulates its speed
3POINT STARTER:
The three terminal of the starting box are marked A, B and C.one line is directly
connected to one armature terminal and one field terminal which are tied
together. The other line is connected to point A which is further connected to
the starting arm through the overcurrent (or overload) release M.To start the
motor, the main switch is the arm make contact with stud No. 1, the field
circuit is directly connected across the line and at the same time full starting
resistance R is placed in series with the armature. The starting current drawn
by the armature=V/(R+R) where Is the starting resistance. As the arm is further
movrd, the starting resistance is further moved the starting resistance is
gradually cut out till, when the move over the various studs againts a stronge
spring which tends to restore it to OFF position. There is a soft iron piece S
attached to the arm which in the full ON or running position is attracted and
held by an electromagnet E energised by the shunt current. It is variously
known as "HOLD-ON coil LOW VOLTAGE (or NO VOLTAGE) release. first closed
and then the starting arm is slowly moved to the right. As soon as It will be
seen that as the arm is moved from stud No. 1 to the last stud, the field current
has to travel back through that portion of the of the starting resistance
decrease of shunt current. But as the value of starting resistance is very small
as compared to shunt field resistance, this slight decrease in tsh is negligible.
This defect can, however, be remedied by using a brass are which is connected
to stud no 1. The field circuit is completed through the starting resistance as it
did..The normal function of the HOLD ON coil is to hold on the arm in the full
running positive when the motor is in normal operation. But in case of failure
or disconnection of the supply or a break in the field circuit, it is de energised,
there by releasing the arm which is pulled back by the spring to the OFF
position. This prevents the stationary armature from being This would have
happened if the arm were left in the full ON position. One great advantage of
connecting the HOLD ON coil in series with the shunt field is that should the
field circuit become open, the starting arm Immediately spring back to the OFF
position thereby preventing the metro from running away across the lines
again when the supply is restored after temporary shutdown. put The over
current release consist of an electromagnet connected in supply line. If the
motor heroine overloaded beyond released and returns to off position and
short circuits the electromagnet. Hence, the arm is arm reaches the running
position, the resistance is all cut out. The arm that has been cut out of the
armature circuitIf It Is desired to control the speed of the motor in addition,
then a field rheostat is connected in the field motor speed can be increased by
weakening the flux (Nal/0). Obviously, there is a limit to this way, although
speed ranges of three to four are possible. But there is one difficulty with such
s unable to create enough electromagnetic pull to overcome the spring tension.
Hence The ar for speed control If too much resistance is cut in by the field
rheostat, than field current is reduced ve e arm to off position. It is this
undesirable feature of a three-point starter whích makes it unsuitable for ute
speed motors
4 POINT STARTER:
Such a starter with its internal wiring is shown. connected to a long-shunt
compound motor. When coR three-point starter, It will be noticed that one
Important change has been made i.e, the HOLD-ON c taken out of the shunt
field circuit and has been connected directly across the line through a protectie
as shown. When the arm touches student no.1, then the line current divided in
to 3 parts. One part na e Rs series field and motor armature. Second parts
passes through the shunt field rheostat Rh. Third part passes through the hold
on coil and current protecting resistance Rfrom arrangement any change in the
shunt field circuit does not at all affect the current passing through the
because the two circuits are independent of each other.It means that the
electromagnetic pull exerted by the hold on coil will always be sufficient and
prevents from restoring the staging arm to off position no matter how the field
rheostat or regulator is adjusted
FUNCTION OF NO LOAD RELESE COIL
The function of hold on coil is to hold on the arm in the full running position
then the motorist operation. In case of failure or disconnection of the supply to
the off position. This prevents the stationary armature from be input across
the line again when the supply in after temporary shutdown. Advantage of
connecting the hold on coil is in series with the shunt held is that when the
field becomes open the starting arm immediately spring back to the off
position the motor from away
FUNCTION OVERLOAD RELESE COIL
Overload release coil consist of an electromagnet connected in the supply line.
If the motor boat Add beyond a certain predetermined value than the iron
piece (0) is lifted and short electromagnet. Hence the arm is released and
returns to all
CONCLUSION:
We have successfully performed this experiment and we are able to know
about the 3-point starter and 4-point starter both is similar to construction.
DISCUSSION QUESTION:
1. What is the necessity of a starter in DC machine?
2. What are the advantages of 4-point starter over 3-point starter?
3. Write the function of no volt coil?
4. Write the function of over load release coil?
5. Difference between 3-point & 4. point Starter?
EXPERIMENT NO. – 5
AIM OF THE EXPERIMENT:
To study speed control of DC Shunt Motor by Field control method.
EQUIPMENT REQUIRED:
Sl no.
1
2
3
Equipment Name Specification
DC Shunt Motor
Field Rheostat
Ammeter
Quantity
THEORY:
SPEED CONTROL OF SHUNT MOTOR:
VARIATION OF FLUX OR FLUX CONTROL METHOD:
𝟏
It is seen from above that Nα .By decreasing theflux. The speed can be
𝜱
increased and vice-versa. Hence,the name flux or field controls method. The
flux of a dc motor can be changed by the changing shunt current IShwith help of
a shunt field rheostat. Shunt current Ish is relatively small, shunt field rheostat
has to carry only a small current, which means I2R loss is small, so that rheostat
size is small in size. This method is therefore very efficient. Innon-polar
machine the speed can be increased by this method in ratio 2:1.any further
wreaking of flux Φ adversely affect the communication and hence puts a limit
to the maximum speed obtained with this method. In machine fitted with
interpoles a ratio is maximum to minimum speed 6:1 is fairly common.
PROCEDURE:
1.
2.
3.
4.
All the connection were carefully discontinued from the mains
Connected the rheostat in series with the field winding
Before the switch ON we should check all the connection thoroughly
Then, the external supply was fed to Shunt Motor.
CONCLUSION:
We concluded that the conductor by the field of the resistance and filed of the
machine by the help of DC shunt motor in speed control method.
DISCUSSION QUESTION:
1.
2.
3.
4.
5.
What is the different method to control speed of dc shunt motor?
A dc shunt motor also called as?
Explain the method of speed control by field control method?
Explain the characteristics of dc shunt motor?
What is critical resistance?
EXPERIMENT NO – 6
AIM OF THE EXPERIMENT
To study speed control of DC Shunt Motor by Armature control method.
EQUIPMENT REQUIRED
Sl No.
1
2
3
Equipment name
DC Shunt motor
Rheostat
Ammeter
Specification
Quantity
THEORY
This method is used when speeds below the no loads speed are required. As
the supply voltage is normally constant, the voltage across the armature is
varied by inserting a variable rheostat or resistance in series with the armature
circuit. As controller resistance is increased,p.d. across the armature is
decreased, thereby decreasing the armature speed. From the speed/armature
current characteristic, it is seen that greater the resistance in the armature
circuit , greater is the fall in the speed.
Let, Ia1 = armature current in the first case
Ia2 = armature current in the second case
(If Ia1 = Ia2 then load is of constant torque)
N1,N2 = corresponding speed , V = supply voltage
Then N1αV – Ia1RaαEb1
Let some controller resistance of value R be added to the armature circuit
resistance so that its value become (R+Ra) = Rr.
The N2αV – Ia2RtαEb2, Therefore, N2/N1 = Eb2/Eb1.
(In fact, it is a simplified form of relation given. Because here ◌1 =◌2)
Considering no load speed, we have N/NO = V – IaRt/V-Ia0Ra
Neglecting Ia○Ra with respect to V, we get
N = N○ (1-IaRt/V)
It is seen that for a given resistance Rt the speed is a linear function of
armature current Ia.The load current for which the speed would be zero is
found by putting N=0 above relation. Therefore, 0 = NO(1- IaRt/V) or Ia = V/Rt
This is the max. current and is known as stalling current.
As will be shown in the diagram this method is very wasteful, expensive &
unsuitable for rapidly changing load because for a given value of Rt, speed will
change with load. A more stable operation can be obtained by using a diverted
across the armature in addition to armature control resistance. Now the
changes in armature current will not be so effective in changing the p.d. across
the armature.
PROCEDURE:
1.
2.
3.
4.
All the connection wire disconnected from the mains.
Connect the rheostat in series with the armature control method.
Before the switch is ON we should check all the connection thoroughly.
Then the external supply was fed to DC shunt motor.
CONLUSION:
We can perform the experiment successfully and studied the speed control
of DC shunt motor by armature control method.
DISCUSSION QUESTION:
1. State application of dc shunt motor?
2. State different type of control method for dc shunt motor?
EXPERIMENT NO: - 7
AIM OF THE EXPERIMENT:
To Perform parallel operation of DC generator
EQUIPMENT REQUIRED:
SL.NO.
1.
2.
3.
4.
Name of the
equipment
D.C. Generator
Ammeter
Voltmeter
Rheostat
Specification
Quantity
THEORY:
Whenever generators are in parallel, their positive & negative terminals are
resp. connected to the positive or negative side of the bus bar. These bus bars
are heavy thick copper bars & they act positive or negative terminals for the
whole power stations, if polarity of the incoming generator is not the same as
the line polarity, serious short circuit will occur when S1 is closed.
Moreover, paralleling a generator with reverse polarity effectively short
circuits it damages commutator & blocked out
generator that have been
tripped of the bus because of a heavy fault current should always be checked
for reversed polarity before paralleling shunt generator no1 connected across
bus bar B3 & supplying some of the load. For putting generator in parallel with
it, the following procedure is applied.
PROCEDURE:
1. The armature of generator no2 is speeded by the prime mover up to its
rated value & then switch S2 is closed & circuit is completed by putting a
voltmeter ‘V’ across the open switch S1.
2. The excitation of the incoming generator no2 is changed till ‘V’ reads
zero, then it means that its terminal voltage is same as that of generator
no1 or bus bar voltage.
3. After this, switch S1 is closed & so the incoming machine is parallel to
the system, under this condition however generator no2 is not taking
any load, because its induced emf is the same bus bar voltage & there
can be flow of current between two points at the same potential. The
generator is said to be floating on the bus bar.
4. If generation no2 is to deliver any current, then its induced emf ‘E’
should be greater than the bus bar voltage V0. In that case current
supplied by it is I=(E-V)/Ra, where Ra is the resistance of the armature
circuit.
5. The induced emf of the incoming generator is increased by
strengthening its field till it takes its proper share of load. At the same
time, it may be found necessary to weaken the field of generator no1 to
maintain the bus bar voltage ‘V’ constant.
CONCLUSION:
We have successfully performed the parallel operation of DC generator
1.
2.
3.
4.
5.
DISCUSSION QUESTION:
Why parallel operation is required?
Write condition for operating two generations in parallel.
If two generators are directly connected without checking their
conditions what will happen?
What are copper bars?
If the terminals aren’t same & parallel operation are done, what will
happen?
EXPERIMENT NO: - 8
To Connect and run 3 phase I.M with help of DOL & Star-delta starter.
AIM OF THE EXPERIMENT:
Apparatus Required
Sl.
No.
1
2
3
4
5
6
7
8
9
10
Name of the
Item
Induction
Motor
D.O.L Starter
Voltmeter
Ammeter
Tachometer
C. Pliers
Screwdriver
E-Knife
N-tester
Connecting wire
Specification
Quantity
3 phi, Squirrel Cage, 5 H.P,
400v, 50Hz
3 phi, 5 H.P, 440v, (6-10) Amp
M.I Type (0-500)v, 50 Hz
M.I Type (0-10) Amp. 50 Hz
Digital Type, (0-9999) RPM
Insulated , 15 cm
Insulated , 15 cm
Insulated , 15 cm
(0-500)v
2.5mm2, Flexible Cu. Conductor
1
1
1
1
1
1
1
1
1
10 Mts.
Theory:
The 3 phase induction motor having capacity up to 5 H.P is started by direct on
line starter. In D.O.L starter method the motor is connected directly to rated
supply voltage. With full voltage applied across the stator terminals, the
starting current will be that may be 10 times the full load current. Such a large
starting current produces excessive voltage drop in the line supplying the
motor. The current gradually decreases as the motor picks up speed. Duration
of pick up the normal speed is very less. D.O.L starter may be manual or
electrically operated type. The motor gets connected across the supply mains
through the main contacts of the contractor. There are provisions to protect
the motor from over loading and single phasing. In the circuit in addition to
fuses, the thermal over load relay (O.L.R) has been used to protect the motor
winding against over load. Fuses are provided for short circuit protection of
Induction motor. The method is very simple & cheap for starting squirrel cage
motor.
Different parts of DOL Starter
The main constituents of DOL starter are –
-
Start button/switch(Normally open type)
Stop button/switch(Normally close type)
Main contacts
Contactor coil
Auxiliary contact
Thermal over load relay unit
Kit Kat fuse
Incoming terminals(Connecting to supply terminal)
Outgoing terminals(Connecting to the motor terminal)
Working function of Different Parts :
3 phase supply i.e. R, Y, and B first connected to kit – Kat fuses, through main
switch which provides for short circuit protection. The terminals come out
from fuse are connected to starter incoming terminals. The motor is connected
to the outgoing terminal of starter. There is also controlling circuit for start,
stop, over load protection (through relay) to the motor.
When ‘Start’ push button switch (which is normally open) is pressed, the
contactor coil ‘A’ becomes energized and its open contacts are closed.
Consequently the main contact of contactor becomes connected. So the motor
gets connected across the main supply through main contact. The motor
continues to get supply even when the pressure in ‘Start’ push button is
released. Because the contractor coil ‘A’ will get supply through hold on
contact ‘a’ (which is already closed during starting.) When Stop push button
switch (Which normally is close) is pressed then the supply through the
contactor coil ‘A’ is disconnected. Since the contactor coil gets de-energized,
the main contacts and auxiliary contact ‘a’ are opened. The supply to the
motor is disconnected, and the motor stops.
UNDER VOLTAGE PROTECTION
When the voltage falls below certain value, single phasing, or failure of supply
during motor operation, the contactor coil ‘A’ is de-energized. The motor is
disconnected from supply.
OVERLOAD PROTECTION
In case of overload in the motor then over load relay (OLR) coils are energized.
So contact point ‘v’ which remains closed of overload relay will open which deenergized the contact coil ‘A’ subsequently the supply to the motor is
disconnected, and the motor stops.
CIRCUIT DIAGRAM
PROCEDURE:
The 3 phase squirrel cage inductor motor, starter, and equipments are
connected to the main switch with main supply voltage as per the circuit
diagram. Put on the main switch & press the (green push button switch) ON
switch of starter to start the induction motor. Note the starting current, No
load running current, Supply voltage, Speed of motor by the help of Ammeter,
Voltmeter & Tachometer respectively, stop the motor by pressing the (Road
push button switch) OFF switch of inductor motor.
Observation Table
NO.
Starting Current in
Amp.
Running current in
Amp.
Supply
voltage in
volt.
Speed in
RPM.
CONCLUSION:
The Motor and Supply terminals should be connected to the corresponding
terminals of D.O.L. Starter. Starting current is 2 times of Running Current.
DISCUSSION QUESTION:
1. What is DOL starter?
2. State different part of DOL starter?
3. Where DOL starter used?
EXPERIMENT NO. 9
AIM OF THE EPERIMENT
TO Determine voltage regulation of transformer by direct loading.
EQUIPMENT REQUIRED
Sl no
1
2
3
4
5
6
Name of equipment
Variac
Single phase
transformer
Voltmeter(AC)
Single core copper wire
Rheostat load
Ammeter(AC)
Specification
(0-270)v,5Amp
1kva,0-11,5-199230,50Hz
0-300 V
3/22swg
0-2500 watt
0-5 amp
Quantity
1
1
2
As per required
1
1
THEORY
Transformer is an electrical device which transfers electrical power from one
circuit to another circuit without changes in frequency. In other word it is static
piece of apparatus by means of which electrical power of the same frequency
is transfer into another circuit. it accomplishes this by electromagnetic
induction and the two electric circuit are in mutual inductive influence of each
other.
There are two winding in transformer voltage regulation. it is defined as the
change in secondary terminal voltage from no load to full load condition.
Voltage regulation =v02-v2/v02.where v02=no load secondary voltage, v2=full
load secondary voltage. So % of voltage regulation =((v02-v2)/v02) x100.
If the regulation of a transformer is in between 5%-10% then the transformer is
said to be a good transformer.
PROCEDURE
AT first the circuit diagram was studied then connects wire4s .connecting wires
were connected with the variac and the primary of transformer, .secondary
winding of transformer was connected to one part of load .thus connections
are so made. at last voltage reading is taken in no condition. thus the
voltageregulation taken but is in between 5%-10%.then the transformer is said
to be a good condition.
TABULATION
SL NO Load
No load
in watt voltage
1
2
3
4
5
6
Secondary Secondary Regulation((v02- Remark
voltage
current
v2)/v02)x100
CONCLUSION:
DISSCUSSION QUESTION
1. What is the voltage regulation of t/f?
2. Write down types of voltage regulation in t/f?
3. What is need of voltage regulation in t/f?
EXPERIMENT: -9
AIM OF THE EXPERIMENT: To perform Short circuit & open circuit Test of a single phase transformer find
losses and efficiency
EQUIPMENT REQUIRED: Sl.
no
Name of the equipment
Specification
Quantity
1
Single phase transformer
1KVA,0-11,5-199-230,50 HZ
1 no.
2
Variac
0-260volt
1 no.
3
Multimeter
DM.352,10amp,1000v
1 no.
4
Connecting wire
3/22 swg
1 no.
5
Watt meter
(0-15)amp,(250-500)V,50HZ
1 no.
6
A.C ammeter
0-5 amp
1 no.
THEORY:From this experiment we can know that copper loss of a single phase
transformer.
Copper loss W =I2R
Where W = wattmeter reading.
I =current flowing in the winding.
R =resistance of the winding.
It is variable loss which is proportional to current. It happens in winding of the
transformer in the form of heat.
PROCEDURE:I.
Before short circuit test of the transformer the low voltage side is short
circuited.
II.
III.
IV.
(5-10)% of normal primary voltage is applied & the reading of ammeter
is observed , when, ever it reaches.
Ammeter, voltmeter & wattmeter are connected on the high voltage
side.
Since in this test the applied voltage is a small percentage of the normal
voltage the mutual flux produced is also a small percentage of its normal
value. Hence core losses are very small with the result that the watt
meter reading represent the full load copper loss or IR loss for the whole
transformer.
TABULATION: Sl.
no
Primary voltage
Primary
current
Secondary
current
Wattmeter
reading
Copper
loss
PRECAUTION:I.
II.
The connection should be perfect right & tight.
Proper terminal should be chosen for short circuit.
CONCLUSION: Thus form the above experiment we test short circuit and open circuit and
successfully find the losses of efficiency.
DISCUSSION QUESTION:
i.
ii.
iii.
iv.
v.
State different types of test in a transformer?
Transformer rating should measure in?
What Are Power Transformer?
What Is the Purpose of Laminating the Core in A Transformer?
What Are the Properties of Ideal Transformer?
EXPERIMENT NO:10
AIM OF THE EXPERIMENT:
To perform parallel operation of a single phase Transformer.
EQIPMENT REQUIRED: SL
NO
1
2
EQUIPMENT
VARIAC
1 PHASE
TRANSFORMER
3
VOLTMETER AC
4
1 CORE COPPER
WIRE
5
RHEOSTATIC LOAD
THEORY:
SPECIFICATION
QUANTITY
0-270V,5A
1KVA,,0-220KVA,50HZ
1
1
0-300V
3/22SWG
2
AS PER
REQUIRED
1
0-2500WATT
REMARK
For supplying a load in excess of the rating of an existing transformer, a
second transformer may be connected in parallel. It is seen that primary
windings are connected to the supply bus bars and secondary windings
are connected to the load bus bars. In connecting two or more than two
transformers in parallel, it is essential that their terminals of similar
polarities are secondary which are parallel with incorrect polarities, will
act together in the local secondary circuit even when supplying no load
will hence produce the equivalent of a dead short-circuit. joined to the
same bus bars. If this in not done, the two emf induced in the
There are certain definite conditions which must be satisfied in order to
avoid any local circulating current and to ensure that the transformers
share the common load in proportion to therekva ratings. The conditions
are:
1.Primary winding of transformer should be suitable for the supply
system voltage and frequency.
2. The transformers should be properly connected with regard to polarity.
3. The voltage rating of both primaries and should have the same turn
ratio i.e transformation ratio.
4.The percentage impedance should be equal in magnitude and have
the same X/R ratio in order to avoid circulating current and operation in
different power factor
5. With transformers having different KVA ratings, the equivalent
impedances should be inversely proportional to the individual KVA rating
if circulating currents are to be The percentage impedance should be
equal in magnitude and have the same X/R ratio in order to avoid
PROCEDURE
i) Study the connection diagram first.
ii)Connect the circuit as per circuit diagram.
iii)The transformer should be properly connected with regard polarity.
iv)Connect single phase rheostatic load with the secondary windings of
parallel connections of The transformers should be properly connected
with regard to polarity. transformer.
v)Then give 230V of AC supply to the primary winding of transformers
connected in parallel.
vi) Then take the wattmeter reading connected in the secondary side of
parallel connection of transformer in each of 250watt load switching.
vii)Repeat the above step maximum up to1500-watt load.
SL NO
Load in
watt
Primary
current
Load
current
Primary
volatage
Secondary
voltage
o/p power
wattmeter
reading
1
2
3
4
5
6
PRECAUTION
1. All connection should be proper & tight.
2. The load should be switched off in steps.
3.The switch S2 should be opened only after switching off the full load.
4.The switch S1 on the primary side should be opened onlyafter opening
switch S2 in the othersecondary side.
CONCLUSION:
DISCUSSION QUESTION:
1.What are the conditions of parallel operation of 1phae transformer?
2. What are the advantages and disadvantages of parallel operation?
3. What is load sharing of parallel operation?
EXPERIMENT NO:11
AIM OF THE EXPERIMENT:Construct switch board & series board using cut-out, switches, plugs, holder &
two way switches.
EQIPMENT REQUIRED:SL
NO
1
2
3
4
5
6
7
8
9
EQUIPMENT
SPECIFICATION
QUANTITY
REMARK
Switch Board
Socket
One way switch
Two way switch
Incandescent bulb
Kit Kat fuse
Hacksaw, screw
driver, neon,
tester, hand drill,
hammer
Connecting wire
Miscellaneous
items
THEORY-(Switch Board)
An electric switchboard is a device that directs electricity from one or more
sources of supply to several smaller regions of usage. It is an assembly of one
or more panels, each of which contains switches that allow electricity to
redirect.
A switch board is used to control the ON & OFF position of the different loads
connected.
It is used to extend the connection where required.
Phase
Phase or live wire carry the current from the source to the electrical circuit and
neutral wire carry the current back to source for balancing voltage. So we
connect switch to phase line so that it will cut the source of current to the
circuit.
The phase is always kept to the right side of socket viewed in front of it & the
phases are spitted in the switches.
In a series board the phase is in series with filament & the neutral is drawn
directly to the test side.
SWITCH BOARD
The circuit diagram is as in the figure.
SERIES BOARD
The circuit diagram of a series board is as in figure.
PROCEDURE
1. The given electric board was made slot for the housing of socket, switch,
fuse & holder.
2. The housing was made carefully with the help of series lamp.
3.The circuit was checked with the help of series lamp.
CONCLUSION:
We have performed the experiment successfully and construct the switch
board and series board using cut-out, switches, plugs, holder and two way
switches.
DISCUSSION QUESTION:1.
2.
3.
4.
What are the 4 type of switches?
How does an electrical switch work?
How many types of switch boards are there?
How does a 2 way light switch work?