Government Girls’ Polytechnic, Bilaspur
Name of the Lab:Electrical&Electronic
Measurement Lab
Practical: Fundamentals of Electrical Engg. Lab
Class : 2nd Semester ( ET&T )
Teachers Assessment:40
End Semester Examination:100
EXPERIMENT NO 1
1. OBJECTIVE : Follow Electrical engineering laboratory practices
i. Supply system & safety. - Introduction to various measuring instruments.
2.MATERIALS REQUIRED :supply system, CRO, ammeter, voltmeter.
3.THEORY :All electrical experiments should be carried out safely. Some of the safety practices
are:
1. Turn off and unplug equipment (instead of relying on interlocks that can fail) before removing
the protective cover to clear a jam, replace a part, adjust or troubleshoot. Ask a qualified person
to do the work if it involves opening equipment and creating an exposure to energized parts
operating at 50 volts or more.
2. Don't use an electrical outlet or switch if the protective cover is ajar, cracked or missing. Call
FIXIT (x3-4948) and report this.
3. Only use DRY hands and tools and stand on a DRY surface when using electrical equipment,
plugging in an electric cord, etc.
4. Never put conductive metal objects into energized equipment.
5. Always pick up and carry portable equipment by the handle and/or base. Carrying equipment
by the cord damages the cord's insulation.
6. Unplug cords from electrical outlets by pulling on the plug instead of pulling on the cord.
7. Use extension cords temporarily. The cord should be appropriately rated for the job.
8. Use extension cords with 3 prong plugs to ensure that equipment is grounded.
9. Never remove the grounding post from a 3 prong plug so you can plug it into a 2 prong, wall
outlet or extension cord.
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10. Re-route electrical cords or extension cords so they aren't run across the floor, under rugs or
through doorways, etc. Stepping on, pinching or rolling over a cord will break down the insulation
and will create shock and fire hazards.
11. Don't overload extension cords, multi-outlet strips and wall outlets.
12. Heed the warning signs, barricades and/or guards that are posted when equipment or wiring
is being repaired or installed or if electrical components are e
(ii)CRO :The CRO is a useful and versatile laboratory equipment used for display, measurement,
and analysis of waveforms and other phenomenon and other electrical and electronic circuits.
AMMETER : Ammeter is an electrical measuring device, which is used to measure electric
current through the circuit. It is the modified form of galvanometer
An ammeter is always
connected in series to a circuit.
VOLTMETER : Voltmeter is an electrical measuring device, which is used to measure potential
difference between two points in a circuit.Voltmeter is always connected in parallel to a circuit.
4.CONNECTION DIAGRAM/BLOCK DIAGRAM/CIRCUIT DIAGRAM
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5.RESULT : The laboratory kit and supply system should be handled safely and carefully.
6.PRECAUTIONS :
1.Never hurry. Work deliberately and carefully.
2.Connect to the power source last
3.If you are working with a lab kit that has internal power supplies, turn the main power switch
OFF before you begin work on the circuits. Wait a few seconds for power supply capacitors to
discharge. 4.These steps will also help prevent damage to circuits.
If you are working with a circuit that will be connected to an external power supply, turn the power
switch of the external supply OFF before you begin work on the circuit.
5.Check circuit power supply voltages for proper value and for type (DC, AC, frequency) before
energizing the circuit.
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EXPERIMENT NO 2
1. OBJECTIVE : Verify ohms law
2.MATERIAL REQUIRED: - Accumulator or battery eliminator, ammeter, voltmeter, rheostat,
coil, connecting wires and key (if necessary).
3.THEORY: - Ohm's Law deals with the relationship between voltage and current in an ideal
conductor. This relationship states that:
The potential difference (voltage) across an ideal conductor is proportional to the current through
it. The constant of proportionality is called the "resistance", R. Ohm's Law is given by:
V=IR
Where V is the potential difference between two points which include a resistance R. I is the
current flowing through the resistance.
Or
Ohm’s law states that the current through a conductor between two points is directly proportional
to the voltage
across the two points, and inversely proportional to the resistance between them. V, I, and R, the
parameters of Ohm's law.
I=V/R
Ohm's law is among the most fundamental relationships in electrical engineering. It relates the
current, voltage, and resistance for a circuit element so that if we know two of the three quantities
we can determine the third. Thus, if we measure the current flowing in a resistor of known value,
we can deduce the voltage across the resistance according to V = IR. Similarly, if we measure
the voltage across a resistor and the current through it, we calculate the resistance of the element
to be R = V/I. Not only does this reduce the number of measurements that must be made, it also
provides a way to check the results of several different measurement methods.
4.CIRCUIT DIAGRAM:-
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PROCEDURE:- 1) Connect the battery eliminator, ammeter, the given coil, rheostat
and key (if necessary) in series.
2) The voltmeter is connected in parallel connection across the given coil. The circuit is
closed.
3) Now the rheostat is adjusted so that a constant current flows through the coil. Note
down the ammeter reading I and the corresponding potential difference across the coil in
the voltmeter as V. Use the formula to calculate the resistance of the coil.
4) The experiment is repeated for different values of current and the corresponding
potential difference is noted. Calculate the value in each trial. These values will be found
to be a constant. Thus verifying Ohm's law.
5.OBSERVATION TABLE:-
Trail
no.
Ammeter reading
I (ampere)
Voltmeter
reading V(volt)
Resistance of coil
R= V/ I (ohm)
1
2
3
4
5
6.RESULT:- By observing the observation table, it is proved that the ratio of potential difference
and current is constant
.Thus, potential difference at the ends of the conductor is directly
proportional to the current flowing through it. Thus, ohm’s law is verified by this experiment.
7.PRECAUTIONS: - 1) All the connection should be tight.
2) Ammeter is always connected in series in the circuit while voltmeter is parallel to the conductor.
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3) The electrical current should not flow the circuit for long time, Otherwise its
temperature will
increase and the result will be affected.
4) Maximum reading of voltmeter should be greater than the electromotive force of the
cell.
5) It should be care that the values of the components of the circuit is does not exceed
to their
ratings (maximum value).
6) Before the circuit connection it should be check out working condition of all the
Component.
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EXPERIMENT NO 3
1.OBJECTIVE: - Verification of Kirchoff’s law.
2.EQUIPMENT REQUIRED: - Batteries, Resistors, Multimeter,Battery Holders,Connecting
Leads,
Alligator clips..
3.THEORY:- KCL:- This law is also called Kirchhoff's point rule, Kirchhoff's junction rule (or
nodal rule), and Kirchhoff's first rule. Kirchoff's first law states that: ―the sum of the currents
flowing through a node must be zero‖. This law is particularly useful when applied at a position
where the current is split into pieces by several wires. The point in the circuit where the current
splits is known as a node. Or
―The algebraic sum of current at any node of a circuit is zero‖. The
direction of incoming currents to a node being positive the outgoing current should be taken
negative.
n is the total number of branches with currents flowing towards or away from the node.
KVL:- This law is also called Kirchhoff's second law, Kirchhoff's loop (or mesh) rule, and
Kirchhoff's second rule Kirchhoff's Voltage Law describes the distribution of voltage within a loop,
or closed conducting path, of an electrical circuit. Specifically, Kirchhoff's Voltage Law states that:
―The algebraic sum of the voltage (potential) differences in any loop must equal zero.‖
Or
―The algebraic sum of the products of the resistances of the conductors and the
currents in them in a closed loop is equal to the total emf available in that loop.
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Here, n is the total number of voltages measured
Kirchoff's second law, which is similar to his first law, states that the sum of all
voltage drops across each electrical element (such as resistors, capacitors, batteries, etc.) in a
circuit loop must be zero. For a battery, the polarity is usually indicated on the battery with a ―+‖ or
―-― near one of the terminals. On a circuit diagram, the different terminals are represented by the
size of the plate. The larger plate indicates a positive terminal, while a smaller plate indicates a
negative terminal. When going around a loop, the sign we end up on as we go across the battery
is the polarity of the battery in the loop.
The direction of current flow through resistor determines the polarity of resistors
in a circuit. For these types of problems, current is thought to be the flow of positive charges.In
actuality negatively charged electrons flow, but this was not known when Kirchoff’s made his
discovery. If we consider the current to be made up of positive charges flowing through the wires,
then the charges will move from higher, ―+", potential to lower, ―-", potential.Just as in batteries,
the sign we end up on as we go around the loop will determine the polarity of the resistor.
4.CIRCUIT DIAGRAM: -
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PROCEDURE:- For Current/Node Law:-
1. Using the multimeter, measure the value of the resistance of each of the three resistors
provided by setting the scale of the multimeter on the 200K scale.
2. Use the multimeter to measure the voltage from the battery(s) in the single D battery holders
and the two D battery holder.
3. Set up the circuit shown in Figure . In this circuit, use one of the single D battery holder for
VB1a and the two D battery holder for VB2. For the resistors in the circuit, use the resistors
closest to the following values: R1 = 50 k ohm, R2 = 20k ohm, and R3 = 10 k ohm
4. Set the multimeter on 200 u on the current scale (i.e. `the `A" scale). Attach a black lead to the
COM terminal and a red lead to the mA terminal. With these settings, the multimeter is set to
read the current in the circuit in micro Amperes (i.e. ¹A).
5. Measure the current flowing into the top node of the circuit from each of the three branch wires.
To measure the current you will have to break the circuit to insert the multimeter. You must \
also measure the polarity of the current in a consistent manner. If the current flows into the
node, then the current should be measured from the positive (red/mA) terminal to the negative
(black/COM) terminal. Record these measured currents on your data table.
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6. In the space provided on the data table, add the three currents to check that the sum of the
currents is zero (or close to zero).
For Voltage/Loop Law:-
1. Pull the red lead out of the mA terminal on the multimeter and place it in the V - terminal. Set \
the multimeter to the 20 volt scale.
2. Using the circuit shown in Figure, measure the voltage drops across each element in each
loop. The polarity of the voltage must be measured in a consistent manner. In order to
measure the voltage in a consistent manner, always place the positive lead (i.e. the red or V lead) in front of the element, relative to the arrow while the negative lead (i.e. the black or COM
lead) is behind the element, relative to the arrow. Record the voltage drop across each
element, for each loop.
3. For each loop, add the voltage drops across each element to verify that the voltage adds to
zero (or close to zero).
5.OBSERVATION: - For Current/Node Law:(a) Current across individual resistor R1, R2 & R3 (I= V/R):
I1 = ------I2 = -----I3 = -----(b) Verifying KCL using measured values: I1 + I2 + I3 = -------For Voltage/Loop Law:- Loop 1
(a)
Applied Voltage(VB1a): ------------------
(b)
Voltage drop across individual resistors R1 & R3 (V = IR):
V1 = ------V3 = -----(c)
Verifying KVL using measured values: VB1a +V1 + V3 = ---------
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For Voltage/Loop Law:- Loop 2
(d)
Applied Voltage(VB2): ------------------
(e)
Voltage drop across individual resistors R2 & R3(V = IR):
V2 = ------V3 = -----(c) Verifying KVL using measured values: VB2+V2 + V3 = ---------
6.RESULT:- Verify KCL by summing the currents flowing in and out of node. Verify KVL by
summing the
voltages around the two loops. Thus, KCL and KVL is verified .
7.PRECAUTIONS: - 1) All the connection should be tight.
2) Ammeter is always connected in series in the circuit while voltmeter is parallel to the
conductor.
3) The electrical current should not flow the circuit for long time, Otherwise its
temperature will increase and the result will be affected.
4) It should be care that the values of the components of the circuit is does not exceed
to their ratings (maximum value).
5) Before the circuit connection it should be check out working condition of all the
Component.
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EXPERIMENT NO 4
1.OBJECTIVE :Measure voltage & current in RLC series circuit, Calculate
impedance,inductance, capacitance, & power factor, Draw vector diagram.
2.MATERIAL REQUIRED : 1 Phase Auto transformer. (0—270 v), 10 A.
2.Purely Resistance or Rheostat. 90Ω, 2 A.
3.Purely inductive coil or chock. 2A, 1 No.
4.Purely capacitor. (10 µF, 230 V) 1 No.
5.MI type voltmeter (0—250 V)—4 Nos.
6.MI type ammeter (0—5 A)—1 No.
7.Connecting leads.
3.THEORY : ( A ) For R-L Series Circuit A circuit that contains a pure resistance R
ohmconnected in series with a coil having pure inductance of L henry is known as seires circuit.
In R-L series circuit VR = IR and VL = IXL And angle between voltage current is called phase
angle. In R-L series circuit the current lags behind the voltage by an angle Φ which depends
upon the value of Resistance and Inductive Reeactance.
( B ) For R-C Series Circuit
A circuit that contains a pure resistance R ohms connected in
series with a pure capacitor of capacitance C farad is known asR-C series circuit.In R-C Series
Circuit VR = IR and VC = IXC Where Z is same as before i.e., inductance. XC is the Capacitive
Reactance which depends upon the value of capacitance of capacitor.
In R-C series circuit the current leads the voltage by an angle Φ which depends upon the value
of Resistance R and Capacitor C of the circuit.
C ) For R-C-L Series Circuit A circuit that contains a pure Resistance R ohm, a pure Inductance
of L henry and a pure capacitor of capacitance C farad all connected in series is known as R-L-C
series circuit. In R-L-C series circuit the current will be leading to the voltage if ( X L < XL ) and
lagging if ( XC > XL)
An RLC circuit (or LCR circuit) is an electrical circuit consisting of aresistor, an inductor, and
a capacitor, connected in series or in parallel. The RLC part of the name is due to those letters
being the usual electrical symbols for resistance, inductance and capacitance respectively. The
circuit forms a harmonic oscillator for current and will resonate in just the same way as an LC
circuit will. The difference that the presence of the resistor makes is that any oscillation induced in
the circuit will die away over time if it not kept going by a source. This effect of the resistor is
calleddamping. Some resistance is unavoidable in real circuits, even if a resistor is not specifically
included as a component. A pure LC circuit is an ideal which really only exists in theory.
There are many applications for this circuit. They are used in many different types of oscillator
circuit. Another important application is fortuning, such as in radio receivers or television sets,
where they are used to select a narrow range of frequencies from the ambient radio waves. In
this role the circuit is often referred to as a tuned circuit. An RLC circuit can be used as a bandpass filter or a band-stop filter. The tuning application, for instance, is an example of band-pass
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filtering. The RLC filter is described as a second-order circuit, meaning that any voltage or current
in the circuit can be described by a second-order differential equation in circuit analysis.
The three circuit elements can be combined in a number of different topologies. All three
elements in series or all three elements in parallel are the simplest in concept and the most
straightforward to analyse. There are, however, other arrangements, some with practical
importance in real circuits. One issue often encountered is the need to take into account inductor
resistance. Inductors are typically constructed from coils of wire, the resistance of which is not
usually desirable, but it often has a significant effect on the circuit.
4.CIRCUIT DIAGRAM :
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Procedure : ( 1 ) Connect the circuit for Resistance and Induction and set the Auto transformer
to zero position and switch on on supply.
( 2 ) Adjust the Auto transformer till a suitable voltage is applied. Record voltage of supply ( V ),
current ( I ), voltage across resister (VR ), voltage across inductor ( VL ).
( 3 ) Repeat step step( 2 ) by varying the supply voltage and record the reading in observation
table.
( 4 ) Connect the circuit for resistance and capacitor and repeat the experiment.
( 5 ) Now connect all three components : Resistance, Inducting and Capacitor and repeat the
experiment.
5.OBSERVATION TABLE :
SR
NO
VOLTMETER
READING
VL
VR
AMMETER
READING
Z=V/I
R=VR/I
XL = VL/I
XC=VC/I
PF
VC
1
2
3
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6.RESULT ::
( ii ) Compare the value of Impedance Z asdetermined from experiment with ( V/I ).
( iii ) Draw a phasor diagram.
6.PRECAUTIONS :
1.Never hurry. Work deliberately and carefully.
2.Connect to the power source last
3.If you are working with a lab kit that has internal power supplies, turn the main power switch
OFF before you begin work on the circuits. Wait a few seconds for power supply capacitors to
discharge. 4.These steps will also help prevent damage to circuits.
If you are working with a circuit that will be connected to an external power supply, turn the power
switch of the external supply OFF before you begin work on the circuit.
5.Check circuit power supply voltages for proper value and for type (DC, AC, frequency) before
energizing the circuit

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EXPERIMENT NO 5
1.OBJECTIVE : Measure voltage & current in RLC parallel circuit, Calculate impedance,
inductance, capacitance, & power factor, Draw vector diagram.
2.MATERIAL REQUIRED : : 1 Phase Auto transformer. (0—270 v), 10 A.
2.Purely Resistance or Rheostat. 90Ω, 2 A.
3.Purely inductive coil or chock. 2A, 1 No.
4.Purely capacitor. (10 µF, 230 V) 1 No.
5.MI type voltmeter (0—250 V)—4 Nos.
6.MI type ammeter (0—5 A)—1 No.
7.Connecting leads.
3.THEORY : The ac circuits in which no of branches are connected in such a manner so that
voltage across each branch is same but current flowing through them is different are called
parallel circuits. The properties of the parallel RLC circuit can be obtained from the duality
relationship of electrical circuits and considering that the parallel RLC is the dual impedance of a
series RLC. From this consideration is immediately obtained the result that the differential
equations describing this circuit will be identical to the general form of those describing a series
RLC.
For the parallel circuit, the attenuation α is given by
and the damping factor is consequently
This is the inverse of the expression for ζ in the series circuit. Likewise, the other scaled
parameters, fractional bandwidth and Q are also the inverse of each other. This means that a
wide band, low Q circuit in one topology will become a narrow band, high Q circuit in the other
topology when constructed from components with identical values. The Q and fractional
bandwidth of the parallel circuit are given by
and
Frequency domain
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Figure 6. Sinusoidal steady-state analysiss
normalised to R = 1 ohm, C = 1 farad, L = 1 henry, and V = 1.0 volt
The complex admittance of this circuit is given by adding up the admittances of the components:
The change from a series arrangement to a parallel arrangement results in the circuit having a
peak in impedance at resonance rather than a minimum, so the circuit is an antiresonator.
The graph opposite shows that there is a minimum in the frequency response of the current at the
resonance frequency
when the circuit is driven by a constant voltage. On the
other hand, if driven by a constant current, there would be a maximum in the voltage which would
follow the same curve as the current in the series circuit.
4.CIRCUIT DIAGRAM :
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



Procedure : ( 1 ) Connect the circuit for Resistance and Induction and set the Auto transformer
to zero position and switch on on supply.
( 2 ) Adjust the Auto transformer till a suitable voltage is applied. Record voltage of supply ( V ),
current ( I ), voltage across resister (VR ), voltage across inductor ( VL ).
( 3 ) Repeat step step ( 2 ) by varying the supply voltage and record the reading in observation
table.
( 4 ) Connect the circuit for resistance and capacitor and repeat the experiment.
( 5 ) Now connect all three components : Resistance, Inducting and Capacitor and repeat the
experiment.
5.OBSERVATION TABLE :
SR
NO
VOLTMETER
READING
VL
VR
AMMETER
READING
Z=V/I
R=VR/I
XL = VL/I
XC=VC/I
PF
VC
1
2
3
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6.RESULT :
( ii ) Compare the value of Impedance Z as determined from experiment with ( V/I ).
( iii ) Draw a phasor diagram.
7.PRECAUTIONS :
1.Never hurry. Work deliberately and carefully.
2.Connect to the power source last
3.If you are working with a lab kit that has internal power supplies, turn the main power switch
OFF before you begin work on the circuits. Wait a few seconds for power supply capacitors to
discharge. 4.These steps will also help prevent damage to circuits.
If you are working with a circuit that will be connected to an external power supply, turn the power
switch of the external supply OFF before you begin work on the circuit.
5.Check circuit power supply voltages for proper value and for type (DC, AC, frequency) before
energizing the circuit
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EXPERIMENT NO 6
1.OBJECTIVE : Use rheostat as Regulator and Potential divider.
2.MATERIALS REQUIRED : Rheostat, voltmeter, connecting wire.
3.THEORY : In electronics, a voltage divider (also known as a potential divider) is a simple linear
circuit that produces an output voltage (Vout) that is a fraction of its input voltage (Vin). Voltage
division refers to the partitioning of a voltage among the components of the divider. The formula
governing a voltage divider is similar to that for a current divider, but the ratio describing voltage
division places the selected impedance in the numerator, unlike current division where it is the
unselected components that enter the numerator.
A simple example of a voltage divider consists of two resistors in series or a potentiometer. It is
commonly used to create a reference voltage, and may also be used as a signal attenuator at low
frequencies. The most common way to vary the resistance in a circuit is to use a variable resistor
or a rheostat.A rheostat is a two-terminal variable resistor. Often these are designed to handle
much higher voltage and current. Typically these are constructed as a resistive wire wrapped to
form a toroid coil with the wiper moving over the upper surface of the toroid, sliding from one turn
of the wire to the next. Sometimes a rheostat is made from resistance wire wound on a heatresisting cylinder with the slider made from a number of metal fingers that grip lightly onto a small
portion of the turns of resistance wire. The "fingers" can be moved along the coil of resistance
wire by a sliding knob thus changing the "tapping" point. They are usually used as variable
resistors rather than variable potential dividers.
Any three-terminal potentiometer can be used as a two-terminal variable resistor by not
connecting to the third terminal. It is common practice to connect the wiper terminal to the unused
end of the resistance track to reduce the amount of resistance variation caused by dirt on the
track.
4.CONNECTION DIAGRAM/BLOCK DIAGRAM/CIRCUIT DIAGRAM
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Potential divider
Rheostat
If RL is large compared to the other resistances (like the input to an operational amplifier), the
output voltage can be approximated by the simpler equation:
As an example, assume
,
,
, and
Since the load resistance is large compared to the other resistances, the output voltage VL will be
approximately:
Due to the load resistance, however, it will actually be slightly lower: ≈ 6.623 V.
5.OBSERVATION TABLE :
Sr no
Total voltage
Resistance R1
Resistance R2
Resistance
Rl
Load
voltage
1
2
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6.RESULT : While voltage dividers may be used to produce precise reference voltages (that is,
when no current is drawn from the reference node), they make poor voltage sources (that is,
when current is drawn from the reference node). The reason for poor source behavior is that the
current drawn by the load passes through resistor R1, but not through R2, causing the voltage
drop across R1 to change with the load current, and thereby changing the output voltage.
7.PRECAUTIONS : 1.Never hurry. Work deliberately and carefully.
2.Connect to the power source last
3.If you are working with a lab kit that has internal power supplies, turn the main power switch
OFF before you begin work on the circuits. Wait a few seconds for power supply capacitors to
discharge. 4.These steps will also help prevent damage to circuits.
If you are working with a circuit that will be connected to an external power supply, turn the power
switch of the external supply OFF before you begin work on the circuit.
5.Check circuit power supply voltages for proper value and for type (DC, AC, frequency) before
energizing the circuit
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EXPERIMENT NO 7
1.OBJECTIVE :Identify the different parts of a dismantled motor.
2.MATERIAL REQUIRED : 1. Three phase induction motor. 2.
Autotransformer.3.
Tachometer.
3.THEORY : A 3-phase induction motor consists of two main parts namely stator and rotor.
1. Stator: It is the stationary part of the motor. It has three main parts, namely; (i) Outer frame, (ii)
Stator core and (Hi) Stator winding.
(0 Outer frame : It is the outer body of the motor. Its function is to support the stator core and to
protect the inner parts of the machine. For small machines the frame is casted but for large
machines it is fabricated. To place the motor on the foundation, feet are provided in the outer
frame .
(ii) Stator core : The stator core is to carry the alternating magnetic field which produces
hysteresis and eddy current losses, therefore^ core is built up of high grade silicon steel
stampings. The stampings are assembled under hydraulic pressure and are keyed to the frame.
Each stamping is insulated from the other with a thin varnish layer. The thickness of the stamping
varies usually from 0.3 to 0.5 mm. Slots are punched on the inner periphery of the stampings, as
shown in Fig. (6), to accommodate stator winding.
(Hi) Stator winding: The stator core carries a three-phase winding which is usually supplied from
a three-phase supply system. The six terminals of the winding (two of each phase) are connected
in the terminal box of the machine. The stator of the motor is wound for definite number of poles,
the exact number being determined by the requirement of speed. It will be seen that greater the
number of poles, the lower the speed and vice-versa, since
N =120 f. The three-phase winding may be connected in star or delta externally
through a starter.
2. Rotor : It is the rotating part of the motor. There are two types of rotors, which are employed in
3-phase induction motors :
(i) Squirrel cage rotor (ii) Phase wound rotor.
(i) Squirrel cage rotor : The motors employing this type of rotor are known as squirrel cage
induction motors. Most of the induction motors are of this type because of simple and rugged
construction of rotor. A squirrel cage rotor consists of a laminated cylindrical core having semiclosed circular slots at the outer periphery. Copper or aluminium bar conductors are placed in
these slots and short circuited at each end by copper or aluminium rings, called short circuiting
rings, as shown in Fig. (c). Thus, the rotor winding is permanently short circuited arid it is not
possible to add any external resistance in the rotor circuit.
The rotor slots are usually not parallel to the shaft but are skewed. Skewing of rotor has the
following advantages :
(a) It reduces humming thus ensuring quiet running of a motor,
(6) It results in a smoother torque curves for different positions of the rotor,
(c) It reduces the magnetic locking of the stator and rotor, ;
(d) It increases the rotor resistance due to the increased length of the rotor bar conductors.
(ii) Phase wound rotor. Phase wound rotor is also called slip ring rotor and the motors employing
this type of rotor are known as phase wound or slipring induction motors. Slip ring rotor consists
of a laminated cylindrical core having semi-closed slots at the outer periphery and carries a 3phase insulated winding. The rotor is wound for the same number of poles as that of stator. The
three finish terminals are connected together forming star point and the three start terminals are
connected to three copper sliprings fixed on the shaft [See Fig. (cQl.
Fundamentals of Electrical Engg. Lab Manual:2nd semester(ET&T)
23
In this case, depending upon the requirement any external resistance can be added in the rotor
circuit. In this case also the rotor is skewed.
A mild steel shaft is passed through the centre of the rotor and is fixed to it with key. The purpose
of shaft is to transfer mechanical power.
Procedure:
(i) Study the constructional details of the stator and its winding, rotor and its winding,
slip rings etc. ,
-(ii) Note down the name plate specifications.
(Hi) Start the squirrel cage motor with the help of starter.
(iv) To reverse the direction of rotations interchange any two supply terminals.
4.CIRCUIT DIAGRAM :
FIGURE OF MOTOR
POLE TYPE ROTOR
5.RESULT : The internal construction of motor is studied.
Fundamentals of Electrical Engg. Lab Manual:2nd semester(ET&T)
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6.PRECAUTIONS : 1.Never hurry. Work deliberately and carefully.
2.Connect to the power source last
3.If you are working with a lab kit that has internal power supplies, turn the main power switch
OFF before you begin work on the circuits. Wait a few seconds for power supply capacitors to
discharge. 4.These steps will also help prevent damage to circuits.
If you are working with a circuit that will be connected to an external power supply, turn the power
switch of the external supply OFF before you begin work on the circuit.
5.Check circuit power supply voltages for proper value and for type (DC, AC, frequency) before
energizing the circuit
Fundamentals of Electrical Engg. Lab Manual:2nd semester(ET&T)
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EXPERIMENT NO 8
1.OBJECTIVE :Identify the different parts of 3-point starter and use it for starting single-phase
induction motor.
2.MATERIAL REQUIRED : Disassembled : 1ɸ capacitor start-Run I.M. Disassembled : Saded
pole motor.
3.THEORY :It is also a split phase motor. The starting winding has capacitor in series with it.
This is improved form of above said split phase motor. In these motors, the angular displacement
o
between Is and Im can we made nearly 90 and high starting torques can be obtained since
starting torque is directly proportional to sine of angle θ. The capacitor in the starting winding may
be connected permanently or temporally. Accordingly, capacitor motors may be first
1. capacitor start motor .
2. capacitor run motor .
3. capacitor start and capacitor run motor .
1. Capacitor start motor : In the capacitor or start induction motor capacitor C is of
large value such that the motor will give high starting torque. Capacitor employed is
of short time duty rating. Capacitor is of electrolytic type . Electrolytic capacitor C is
connected in series with the starting winding along with centrifugal switch S as shown
in Fig. (a). When the motor attains the speed of about 75% of synchronous speed
starting win ding is cut-off. The construction of the motor and winding is similar to
usual split speed phase motor. It is used where high starting torque is required like
refrigerators.
Performance and characteristics: Speed is almost constant with in 5% slip. This
type of motor develops high starting torque about 4 to 5 times the full load torque. It
draws low starting current. A typical torque speed curve is shown in fig. (c). The
direction of rotation can be changed by interchanging the connection of either starting
or running winding.
2. Capacitor run motors : In these motors, a paper capacitor is permanently
connected in the starting winding, as shown in Fig. (d). In this case the electrolytic
capacitor cannot be used since these type of capacitor is designed only for short time
rating and hence cannot be permanently connected in the winding. Both main as will
as starting winding is of equal rating.
Performance and characteristics : Starting torque is lower about 50 to 100% of full
load torque. Power factor is improved may be about unity . Efficiency is improved to
about 75%. A typical characteristics have be shown in Fig. (e) is usually used in
fans, room coolers, portable tools and other domestic and commercial electrical
appliances.
3. Capacitor start and capacitor run motor : In these case, two capacitor are used
one for starting purpose and other running purpose as shown in Fig. (f). The
capacitor used for starting purpose Cs is of electrolytic type and is disconnected from
the supply when the motor attains 75% of synchronous speed with the help of
Fundamentals of Electrical Engg. Lab Manual:2nd semester(ET&T)
26
centrifugal switch S. Whereas, the other capacitor CR which remains in the circuit of
starting winding during operation is a paper capacitor. This type of motor gives best
running and starting operation. Starting capacitor Cs which is of higher value then the
value of running capacitor CR.
Performance and characteristics : Such motor operate as to phase motor giving best
performance and noiseless operation. Starting torque is high, starting current is low and
gives better efficiency and higher p.f. The only disadvantage is high cost. A typical
torque speed curve is shown in Fig. (g).
Shaded pole motor is constructed with salient poles in stator. Each pole has its
rd
own exciting coil as shown in Fig.(h). A 1/3 portion of each pole core is surrounded by a
copper strip forming closed loop called the shading band as shown in Figs. (h) and (i).
Rotor is usual squirrel cage type. A single phase supply produces alternating flux . When
the flux is increasing in the pole a portion of the flux attempts to pass through the shaded
portion of the pole.
This flux induces voltage and hence current in the copper ring, and by Lenz’s law the
direction of current is such that it opposes the increase of flux in shaded portion. Hence in
the beginning, the greater portion of flux passes through un shaded side of each pole and
resultant lies on un shaded side of the pole. When the flux reaches its maximum value,
its rate of change Is zero, there by the e.n.f. and hence current in the shading coil
becomes zero. Flux is uniformly distributed over the pole phase the resultant field lies at
the centre of the pole. After that the main flux tends to decrease, the current induct in the
shading coil now tends to increase the flux on the shaded portion of the pole and
resultant lies on the shaded portion of the pole as shown in Fig.(j).
Hence, a revolving field is set up which rotates from un shaded portion of the
pole to the shaded portion of the pole as marked by the arrow head in Fig. (i). Thus, by
electromagnetic induction, a starting torque develops in the rotor and the rotor starts
rotating. After that its rotor picks up the speed.
Performance and characteristics : A typical speed torque characteristics is given
in Fig.(k). Starting torque very small about 50% of full load torque. Efficiency is low
because of countinuous power loss in shading coil. These motors are used for small fans,
electric clocks, gramophone etc.
Its direction of depends open the position of the shading coil, i.e., which half of
the pole is wrapped with shading coil. The direction of rotation cannot be reversed unless
the machine is constructed so that of the shading coil can be shifted to other half of the
pole.
4. CIRCUIT DIAGRAM :
Fundamentals of Electrical Engg. Lab Manual:2nd semester(ET&T)
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Circuit for starting
Single phase induction
5.RESULT : The internal construction of 3 point starter is studied.
6.PRECAUTIONS : 1.Never hurry. Work deliberately and carefully.
2.Connect to the power source last
3.If you are working with a lab kit that has internal power supplies, turn the main power switch
OFF before you begin work on the circuits. Wait a few seconds for power supply capacitors to
discharge. 4.These steps will also help prevent damage to circuits.
If you are working with a circuit that will be connected to an external power supply, turn the power
switch of the external supply OFF before you begin work on the circuit.
5.Check circuit power supply voltages for proper value and for type (DC, AC, frequency) before
energizing the circuit
:
Fundamentals of Electrical Engg. Lab Manual:2nd semester(ET&T)
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EXPERIMENT NO 9 & 10
1.OBJECTIVE :Perform open circuit test on single-phase transformer &Perform short circuit test
on single-phase transformer.
2.MAREIAL REQUIRED : 1. Single phase Autotransformer 1 No. 10 A, 0-270 V
2. Single phase transformer under test.
3. Ammeter MI type 1 No.
4. Voltmeter MI-type 1 No.
5. Wattmeter Dynamometer Type 2 Nos.
6. Connecting leads.
3.THEORY :
This test is carried out to determine the no load loss or iron loss and no load current Io which is
helpful in finding the no-load parameters Ro and Xo of the transformer .this test is helpful carried
out on the low-voltage side of the transformer i.e., a wattmeter W, a voltmeter V and an ammeter
A are connected in low voltage winding (say primary). The primary winding is then connected to
the normal rated voltage V1 and frequency as given on the plate of the transformer . The
secondary side is kept open or connected to a voltmeter V’.Since the secondary (high voltage
winding) is open , the current drawn by the primary is no load current Io measured by the
ammeter A. The value of no-load current Io is very small usually 2 to 10% of the rated full-load
current . Thus , the copper losses in the primary are negligibly small and no copper loss in the
secondary as it is open . Therefore, wattmeter reading Wo only represent the core or iron losses
for all practical purposes . These core losses are constant at all loads. The voltmeter V’ if
connected on the secondary side measures the secondary induced voltage V2.
The ratio of voltmeter readings, V2/V1 gives the transformation ratio of the transformer.
Procedure :
(A)
For open circuit test :
1. connect the circuit as shown in Fig. (c) and set up the autotransformer to zero position .
2. Adjust the supply voltage to the transformer with help of autotransformer to 230V with
secondary winding terminal open.
3. Record the ammeter, voltmeter and wattmeter reading.
4. Vary the supply voltage with the help of the autotransformer and enter the reading in the
observation table.
5. Switch off the supply.
(B) For short circuit test :
1. Connect the circuit as shown in Fig. (d) and set up the Auto-transformer to zero position.
2. Switch on the supply and apply the voltage gradually with the secondary winding terminals
short circuited. Keep in mind that only 10-12 percent of the rated voltage is sufficient to
circulate full rated current in the short circuited winding.
3. Adjust the input voltage to obtain 50%, 75%, 125% rated full load current in secondary.
Record the instrument reading in the observation table.
4.CIRCUIT DIAGRAM :
Fundamentals of Electrical Engg. Lab Manual:2nd semester(ET&T)
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:
Wiring diagram for open circuit test
Wiring diagram for closed circuit test
5.OBSERVATION TABLE :(A)for open circuit test :
Ammeter readings Isc in
amp.
Wattmeter readings W sc in
watts.
Ammeter readings Isc in
amp.
Wattmeter readings W sc in
watts.
Fundamentals of Electrical Engg. Lab Manual:2nd semester(ET&T)
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s.no.
Voltmeter readings VSC in
volt
1.
2.
3.
4.
5.
(B)for short circuit test :
s.no.
Voltmeter readings Vsc in
volt
1.
2.
3.
4.
5.
6.RESULT :
(i)
(ii)
With the parameters of equivalent circuit known, draw the equivalent circuit of the
transformer, referred to primary.
With the iron and copper loss known at ful rated load current (as well as other
values of load current) compute the efficiency at different values of output and
power factor.
7.PRECAUTIONS:
1. Connections should be tight .
2. Switch on power supply after checking circuit.
Fundamentals of Electrical Engg. Lab Manual:2nd semester(ET&T)
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EXPERIMENT NO 11
1.OBJECTIVE : Calculate transformation ratio of single phase transformer.
2.MATERIAL REQUIRED : 1. Single phase Autotransformer 1 No. 10 A, 0-270 V
2. Single phase transformer under test.
3. Ammeter MI type 1 No.
4. Voltmeter MI-type 1 No.
5. Wattmeter Dynamometer Type 2 Nos.
6. Connecting leads
3.THEORY : Conductors—the transformer's coils. A varying current in the first or primary
winding creates a varying magnetic flux in the transformer's core and thus a varying magnetic
field through the secondary winding. This varying magnetic field induces a varying electromotive
force (EMF) or "voltage" in the secondary winding. This effect is called mutual induction.
If a load is connected to the secondary, an electric current will flow in the secondary winding and
electrical energy will be transferred from the primary circuit through the transformer to the load. In
an ideal transformer, the induced voltage in the secondary winding (Vs) is in proportion to the
primary voltage (Vp), and is given by the ratio of the number of turns in the secondary (Ns) to the
number of turns in the primary (Np) as follows:
By appropriate selection of the ratio of turns, a transformer thus allows an alternating current (AC)
voltage to be "stepped up" by making Ns greater than Np, or "stepped down" by making Ns less
than Np.
In the vast majority of transformers, the windings are coils wound around a ferromagnetic core,
air-core transformers being a notable exception.
Transformers range in size from a thumbnail-sized coupling transformer hidden inside a stage
microphone to huge units weighing hundreds of tons used to interconnect portions of power
grids. All operate with the same basic principles, although the range of designs is wide. While
new technologies have eliminated the need for transformers in some electronic circuits,
transformers are still found in nearly all electronic devices designed for household ("mains")
voltage. Transformers are essential for high-voltage electric power transmission, which makes
long-distance transmission economically practical.
Adjust the autotransformer.
PROCEDURE :
1.Connect the circuit as figure and set the autotransformer to zero.
Fundamentals of Electrical Engg. Lab Manual:2nd semester(ET&T)
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2.Switch on power supply and
3..Record the voltages across primary and voltage across secondary.
4. vary the autotransformer and repeat step 3 for 5 readings.
5.Switch off power supply.
4.CIRCUIT DIAGRAM :
Transformer winding
5.OBSERVATION TABLE :
SR NO
V1
V2
K=V2/V1
6.RESULT : The transformation of given transformer is
7.PRECAUTIONS :
1. Connections should be tight.
2. check circuit before connecting to power supply.
Fundamentals of Electrical Engg. Lab Manual:2nd semester(ET&T)
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EXPERIMENT NO 12
1.OBJECTIVE :Identify various types of induction motor looking at the constructional details.
2.MATERIAL REQUIRED : Three phase induction motor, 3 phase transformer, tachometer.
3.THEORY : 1. Stator: It is the stationary part of the motor. It has three main parts, namely; (i)
Outer frame, (ii) Stator core and (Hi) Stator winding.
(0 Outer frame : It is the outer body of the motor. Its function is to support the stator core and to
protect the inner parts of the machine. For small machines the frame is casted but for large
machines it is fabricated. To place the motor on the foundation, feet are provided in the outer
frame .
(ii) Stator core : The stator core is to carry the alternating magnetic field which produces
hysteresis and eddy current losses, therefore^ core is built up of high grade silicon steel
stampings. The stampings are assembled under hydraulic pressure and are keyed to the frame.
Each stamping is insulated from the other with a thin varnish layer. The thickness of the stamping
varies usually from 0.3 to 0.5 mm. Slots are punched on the inner periphery of the stampings, as
shown in Fig. (6), to accommodate stator winding.
(Hi) Stator winding: The stator core carries a three-phase winding which is usually supplied from
a three-phase supply system. The six terminals of the winding (two of each phase) are connected
in the terminal box of the machine. The stator of the motor is wound for definite number of poles,
the exact number being determined by the requirement of speed. It will be seen that greater the
number of poles, the lower the speed and vice-versa, since
N =120 f. The three-phase winding may be connected in star or delta externally
through a starter.
2. Rotor : It is the rotating part of the motor. There are two types of rotors, which are employed in
3-phase induction motors :
(i) Squirrel cage rotor (ii) Phase wound rotor.
(i) Squirrel cage rotor : The motors employing this type of rotor are known as squirrel cage
induction motors. Most of the induction motors are of this type because of simple and rugged
construction of rotor. A squirrel cage rotor consists of a laminated cylindrical core having semiclosed circular slots at the outer periphery. Copper or aluminium bar conductors are placed in
these slots and short circuited at each end by copper or aluminium rings, called short circuiting
rings, as shown in Fig. (c). Thus, the rotor winding is permanently short circuited arid it is not
possible to add any external resistance in the rotor circuit.
The rotor slots are usually not parallel to the shaft but are skewed. Skewing of rotor has the
following advantages :
(a) It reduces humming thus ensuring quiet running of a motor,
(6) It results in a smoother torque curves for different positions of the rotor,
(c) It reduces the magnetic locking of the stator and rotor, ;
(d) It increases the rotor resistance due to the increased length of the rotor bar conductors.
(ii) Phase wound rotor. Phase wound rotor is also called slip ring rotor and the motors employing
this type of rotor are known as phase wound or slipring induction motors. Slip ring rotor consists
of a laminated cylindrical core having semi-closed slots at the outer periphery and carries a 3phase insulated winding. The rotor is wound for the same number of poles as that of stator. The
three finish terminals are connected together forming star point and the three start terminals are
connected to three copper sliprings fixed on the shaft [See Fig. (cQl.
In this case, depending upon the requirement any external resistance can be added in the rotor
circuit. In this case also the rotor is skewed.
Fundamentals of Electrical Engg. Lab Manual:2nd semester(ET&T)
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A mild steel shaft is passed through the centre of the rotor and is fixed to it with key. The purpose
of shaft is to transfer mechanical power.
Procedure:
(i) Study the constructional details of the stator and its winding, rotor and its winding,
slip rings etc. ,
-(ii) Note down the name plate specifications.
(Hi) Start the squirrel cage motor with the help of starter.
(iv) To reverse the direction of rotations interchange any two supply terminals.
:
4.CIRCUIT DIAGRAM :
Fundamentals of Electrical Engg. Lab Manual:2nd semester(ET&T)
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5.OBSERVATION TABLE : Synchronous speed =………rpm
S.No.
Line Voltage
Input Current
Rotor Speed
N8Nr
% Slip =
N8
1.
2.
3.
4.
5.
6. RESULT : Plot the curve between input current and rotor speed. 1.% slip at rated current
=………..
2. The various parts of induction motor are identified.
7.PRECAUTIONS :
1. Connections should be tight.
2. check circuit before connecting to power supply.
Fundamentals of Electrical Engg. Lab Manual:2nd semester(ET&T)
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EXPERIMENT NO 13 & 14
1.OBJECTIVE : Measure current & voltage in balanced star connection. Also verify the relation
of
phase and line value of voltage and current & Measure current & voltage in balanced Delta
connection. Also verify the relation.
2.MATERIALS REQUIRED : Ammeter, voltmeter .
3.THEORY:- In delta (∆) or mesh connections, the finish terminal of one winding is connected
terminal of the other phase and so on which gives a closed circuit. The three line conductors .
To obtain delta connection, a2 is connected with b1, b2 is connected with c1 and c2 is connected
with a1 as shown in Fig. The three conductors R, Y and B are run from the three junctions called
line conductors. The current flowing through each phase is called phase current (I ph) and the
current flowing through each line conductor is called line current (IL) as voltage across each
phase is called phase voltage (Eph) and voltage across tow line conductors is called line voltage
(EL). Since the system is balanced therefore, the three phase current I 12, I23 and I31are equal in
o
magnitude but displaced from one another by 120 electrical.
In start or wye (Y) connections, the similar ends (either start or finish) of the three windings are
connected to a common point called star or neutral point. The three line conductors are run from
the remaining three free terminals called line conductors. Ordinarily only three wire are carried to
the external circuit giving 3-phase, 3-wire star connected system. However, sometimes a fourth
wire is carried from the star point to the external circuit, called neutral wire, giving 3-phase, 4-wire
star connected system.
As shown in Fig. the finish terminals a2,b2 and c2 of the three windings are connected to
form a star or neutral point. From the remaining three free terminals three conductors are run,
named R, Y and B. The current flowing through each phase is called phase current I ph and
current flowing through each line conductor is called line current I L. Similarly, voltage across each
phase is called phase voltage (Eph ) and voltage across tow line conductors is called line voltage
(EL).
Relation between Phase voltage and Line voltage . Since the system is balanced, the three
o
voltages ENR, ENY and ENB are equal in magnitude but displaced from one another by 120
electrical. Their phasors are shown in Fig. The arrow heads on e.m.fs. and current indicate the
positive direction and their actual direction at any instant.
Relation between Phase current and Line current. From Fig. it is clear that same
current flows through phase winding as well as the line conductor is just connected in series with
the phase winding.
IR= INR
IY= INY
IB= INB
INR=INY=INB=IPH (phase current)
Fundamentals of Electrical Engg. Lab Manual:2nd semester(ET&T)
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IR=IY=IB=IN (line current)
Hence, in star connections Line current = phase current
4.CIRCUIT DIAGRAM :
Three-phase, four-wire “Y” connection uses a "common" fourth wire
Three-phase, three-wire “Y” connection does not use the neutral wire.
Fundamentals of Electrical Engg. Lab Manual:2nd semester(ET&T)
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Three-phase, three-wire Δ connection has no common.
5.OBSERVATION TABLE :FOR DELTA CONNECTION
S.No.
1.
2.
Phase Current
Phase Voltage
Line Current
Line Voltage
FOR STAR CONNECTION
S. No.
1.
2.
Line Current
Line Voltage
Phase Current
Phase Voltage
6.RESULT-: Hence, in star connections Line current = phase current
In delta connection
7.PRECAUTIONS:
1. Connections should be tight.
2. Check circuit before connecting to power supply.
Fundamentals of Electrical Engg. Lab Manual:2nd semester(ET&T)
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EXPERIMENT NO 15
1.OBJECTIVE : Measure the electrical power and energy in a given circuit & Measure active &
reactive power in 3-phase balance load circuit by one wattmeter method.
2.MATERIAL REQUIRED : 1. 1-Phase Auto transformer-1 No. (10A,-270V) 2.
Wattmeter – Dynamo meter type –1 No. (10A,250V) 3. Ammeter – Moving Iron type-1 No.
(0-10 ) 4.Voltmeter – Moving Iron type;1No.(0-250) 5 Resistive and Inductive load 6.
Connecting leads
3. THEORY : The power which is actually consumed or utilized in a.c. circuit is called
true power or active power or real power . As power is consumed only in resistance and a
pure inductor and a pure capacitor do not consume any power in a cycle. Since in a
half cycle what so ever power is received from the source by inductor and capacitor. Or
and the same amount of power is returned to the source. This power which flows back
and forth or reacts you upon itself is called reactive power. It does not do any useful
work in circuit.
Therefore true power or active power=Voltage Current in phase with voltage =V*I cos ф = VI
cos ф watt And Reactive Power =Voltage* Current 90˚ out of phase with voltage = V*I sinф
=VI sinф.
It is important not to confuse power and energy, although they are closely related. Just remember
that power is the rate at which energy is delivered, not an amount of energy itself. With simple
algebra, can turn the formula above for power around to solve for energy instead, and write:
Energy = Power x Time.
For example, using the definition of the word watt given above, a 100 watt light bulb is a device
that converts 100 joules of electrical energy into 100 joules of electromagnetic radiation (light)
every second. If you leave a 100 watt light on for one hour, that is, 3600 seconds, then the total
energy you used was:
Energy = Power x Time = (100 Joules/Second) x (3600 Seconds) = 360,000 Joules
An electric meter or energy meter is a device that measures the amount of electrical energy
consumed by a residence, business, or an electrically powered device.
Electric meters are typically calibrated in billing units, the most common one being the kilowatt
hour. Periodic readings of electric meters establishes billing cycles and energy used during a
cycle.
In settings when energy savings during certain periods are desired, meters may measure
demand, the maximum use of power in some interval. In some areas, the electric rates are higher
during certain times of day, to encourage reduction in use.
PROCEDURE : (1) Connect the Instruments, Autotransformer and load as shown in Fig . (a)
and setup to auto transformer to zero position.
Fundamentals of Electrical Engg. Lab Manual:2nd semester(ET&T)
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(2) Switch on the supply and adjust the autotransformer till a suitable voltage
(3) Vary the voltage by autotransformer and take down the various readings of voltmeter,
Ammeter
4.CIRCUIT DIAGRAM :
Three-phase electromechanical induction meter, metering 100 A 230/400 V supply.
Horizontal aluminum rotor disc is visible in center of meter
CALCULATIONS :
(1) Calculate the value of P.F. cos ф from different readings as cosф= ( Wattmeter
Reading)/(Voltmeter * Ammeter )Reading .
(2) Calculate the value of Reactive power as Q=VI sin ф =VI (1-cos ² ф) ½.
5.RESULT : Power at different voltages is……..watts and conclusion is that power varies as
square of the applied voltage.
6.PRECAUTIONS :
1. Connections should be tight.
2. check circuit before connecting to power supply.
Fundamentals of Electrical Engg. Lab Manual:2nd semester(ET&T)
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EXPERIMENT NO 16
1.OBJECTIVE : Use analog and digital multimeter for testing voltage, current and resistance.
2.MATERIAL REQUIRED :Multimeter, signal generator,dry cell,power supply,resistors of
assorted value.
3.THEORY : multimeter or a multitester, also known as a volt/ohm meter or VOM, is an
electronic measuring instrument that combines several measurement functions in one unit. A
typical multimeter may include features such as the ability to measure voltage, current and
resistance. Multimeters may use analog or digital circuits—analog multimeters and digital
multimeters (often abbreviated DMM or DVOM.) Analog instruments are usually based on a micro
ammeter whose pointer moves over a scale calibration for all the different measurements that can
be made; digital instruments usually display digits, but may display a bar of a length proportional
to the quantity measured.
A multimeter can be a hand-held device useful for basic fault finding and field service work or a
bench instrument which can measure to a very high degree of accuracy. They can be used to
troubleshoot electrical problems in a wide array of industrial and household devices such as
electronic equipment, motor controls, domestic appliances, power supplies, and wiring systems.
PROCEDURE : Measuring voltage and current with a multimeter
1. Select a range with a maximum greater than you expect the reading to be.
2. Connect the meter, making sure the leads are the correct way round.
Digital meters can be safely connected in reverse, but an analogue meter may be damaged.
3. If the reading goes off the scale: immediately disconnect and select a higher
range.
When testing circuits you often need to find the voltages at various points, for example the voltage at pin
2 of a 555 timer IC. This can seem confusing - where should you connect the second multimeter lead
1. Connect the black (negative -) lead to 0V, normally the negative terminal of the battery or
power supply.
2. Connect the red (positive +) lead to the point you where you need to measure the voltage.
3. The black lead can be left permanently connected to 0V while you use the red lead as a probe
to measure voltages at various points.
4. You may wish to fit a crocodile clip to the black lead of your multimeter to hold it in place while
doing testing like this.
Voltage at a point really means the voltage difference between that point and 0V (zero volts)
which is normally the negative terminal of the battery or power supply. Usually 0V will be labelled
on the circuit diagram as a reminder.
Measuring resistance with a DIGITAL multimeter
1. Set the meter to a resistance range greater than you expect the resistance to be.
Notice that the meter display shows "off the scale" (usually blank except for a 1 on the
left). Don't worry, this is not a fault, it is correct - the resistance of air is very high!
Fundamentals of Electrical Engg. Lab Manual:2nd semester(ET&T)
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2. Touch the meter probes together and check that the meter reads zero.
If it doesn't read zero, turn the switch to 'Set Zero' if your meter has this and try again.
3. Put the probes across the component.
Avoid touching more than one contact at a time or your resistance will upset the reading!
4.CIRCUIT DIAGRAM :
DIGITAL MULTIMETER
ANALOG MULTIMETER
Fundamentals of Electrical Engg. Lab Manual:2nd semester(ET&T)
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5.OBSERVATION TABLE :
VOLTAGE OF DRY CELL :
VOLTAGE OF AC SUPPLY :
VOLTAGE OF DC SUPPLY :
RESISTANCE MEASUREMENT :
SR NO
MEASURED
VALUE
VALUE INDICATED
IN COLOUR CODE
TOLERANCE
DIFFERENCE IN
MEASURED AND
GIVEN VALUE
6.RESULT : The value of resistance, current and voltage are measured with help of multimeter.
7.PRECAUTIONS : Multimeters are easily damaged by careless use so please take these
precautions:
1.Always disconnect the multimeter before adjusting the range switch.
2.Always check the setting of the range switch before you connect to a circuit.
3.Never leave a multimeter set to a current range (except when actually taking a reading).
The greatest risk of damage is on the current ranges because the meter has a low resistance.
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EXPERIMENT NO 17
1.OBJECTIVE : Measure circuit parameters by L.C.R. meter.
2.MATERIAL REQUIRED : LCR meter, voltmeter, ammeter and ohmmeter.
3.THEORY : LCR meter (Inductance (L), Capacitance (C), and Resistance (R)) is a piece of
electronic test equipment used to measure the inductance, capacitance and, resistance of a
component. In the usual versions of this instrument these quantities are not measured directly,
but determined from a measurement of impedance. The necessary calculations are, however,
incorporated in the instrument's circuitry; the meter reads L, C and R directly with no human
calculation required.
Usually the device under test (DUT) is subjected to an AC voltage source. The meter detects the
voltage over, and the current through the DUT. From the ratio of these the meter can determine
the magnitude of the impedance. The phase angle between the voltage and current is also
detected and between that and the impedance magnitude the DUT can be represented as an L
and R or a C and R. The meter must assume either a parallel or a series model for these two
elements. The most useful assumption, and the one usually adopted, is that LR measurements
have the elements in series (as would be encountered in an inductor coil) and that CR
measurements have the elements in parallel (as would be encountered in measuring a capacitor
with a leaky dielectric).It can also be used to judge the inductance variation with respect to the
rotor position in permanent magnet machines.
The Q meter can be used for many purposes. As the name implies, it can measure Q and is
generally used to check the Q factor of inductors. As the internal tuning capacitor has an air
dielectric its loss resistance is negligible compared to that of any inductor and hence the Q
measured is that of the inductor.
The value of Q varies considerable with different types of inductors used over different ranges of
frequency. Miniature commercial inductors, such as the Siemens B78108 types or the LenoxFugal Nanored types, made on ferrite cores and operated at frequencies up to 1 MHz, have
typical Q factors in the region of 50 to 100. Air wound inductors with spaced turns, such as found
in transmitter tank circuits and operating at frequencies above 10 MHz, can be expected to have
Q factors of around 200 to 500. Some inductors have Q factors as low as five or 10 at some
frequencies and such inductors are generally unsuitable for use in selective circuits or in sharp
filters. The Q meter is very useful to check these out.
The tuning capacitor (C) of the Q meter has a calibrated dial marked in pico-farads so that, in
conjunction with the calibration of the oscillator source, the value of inductance (Lx) can be
derived. The tuned circuit is simply set to resonance by adjusting the frequency and/or the tuning
capacitor for a peak in the output voltage meter and then calculating the inductance (Lx) from the
usual formula:
Lx = 1/4π²f²C
Direct measurement of Q in an inductor, as discussed in previous paragraphs. is based on the
circuit having two components, inductance and capacitance. Inductors also have distributed
capacitance (Cd) and if this represents a significant portion of the total tuning capacitance, the Q
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value read will be lower than its actual value. High distributed capacitance is common in large
value inductors having closely wound turns or having multiple layers.
Actual Q can be calculated from Qe, as read, from the following:
Q = Qe (1 + Cd/C)
where Cd = Distributed capacitance
and C = Tuning Capacitance
Q value error is reduced by resonating with a large value of tuning capacitance, otherwise
distributed capacitance can be measured and applied to the previous formula. Two methods of
measuring distributed capacitance are described in the "Boonton Q Meter Handbook". The
simplest of these is said to be accurate for distributed capacitance above 10 pF and this method
is described as follows:
1. With the tuning capacitor (C) set to value C1 (say 50 pF), resonate with the sample inductor by
adjusting the signal source frequency.
2. Set the signal source to half the original frequency and re-resonate by adjusting C to a new
value of capacitance C2.
3. Calculate distributed capacitance as follows: Cd = (C2 -4C1) /3
4.CIRCUIT DIAGRAM :
LCR METER
5.RESULT :The value of inductance, capacitance and resistance is measured with LCR meter.
6.PRECAUTIONS :
.Always disconnect the multimeter before adjusting the range switch.
2.Always check the setting of the range switch before you connect to a circuit.
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EXPERIMENT NO 18
1.OBJECTIVE :Calculate fusing current of a fuse wire.
2.MATERIAL REQUIRED : Ammeter, fuse wire.
3.THEORY : In electronics and electrical engineering a fuse (from the French fusée, Italian.
I
fuso, "spindle" s a type of sacrificial overcurrent protection device. Its essential component is a
metal wire or strip that melts when too much current flows, which interrupts the circuit in which it
is connected. Short circuit, overload or device failure is often the reason for excessive current.
A fuse interrupts excessive current (blows) so that further damage by overheating or fire is
prevented. Wiring regulations often define a maximum fuse current rating for particular circuits.
Overcurrent protection devices are essential in electrical systems to limit threats to human life
and property damage. Fuses are selected to allow passage of normal current and of excessive
current only for short periods.
In 1847, Breguet recommended use of reduced-section conductors to protect telegraph stations
from lightning strikes; by melting, the smaller wires would protect apparatus and wiring inside the
building.
A fuse consists of a metal strip or wire fuse element, of small cross-section compared to the
circuit conductors, mounted between a pair of electrical terminals, and (usually) enclosed by a
non-conducting and non-combustible housing. The fuse is arranged in series to carry all the
current passing through the protected circuit. The resistance of the element generates heat due
to the current flow. The size and construction of the element is (empirically) determined so that
the heat produced for a normal current does not cause the element to attain a high temperature.
If too high a current flows, the element rises to a higher temperature and either directly melts, or
else melts a soldered joint within the fuse, opening the circuit.
When the metal conductor parts, an electric arc forms between the un-melted ends of the
element. The arc grows in length until the voltage required to sustain the arc is higher than the
available voltage in the circuit, terminating current flow. In alternating current circuits the current
naturally reverses direction on each cycle, greatly enhancing the speed of fuse interruption. In the
case of a current-limiting fuse, the voltage required to sustain the arc builds up quickly enough to
essentially stop the fault current before the first peak of the AC waveform. This effect significantly
limits damage to downstream protected devices.
The fuse element is made of zinc, copper, silver, aluminum, or alloys to provide stable and
predictable characteristics. The fuse ideally would carry its rated current indefinitely, and melt
quickly on a small excess. The element must not be damaged by minor harmless surges of
current, and must not oxidize or change its behavior after possibly years of service.
The fuse elements may be shaped to increase heating effect. In large fuses, current may be
divided between multiple strips of metal. A dual-element fuse may contain a metal strip that melts
instantly on a short-circuit, and also contain a low-melting solder joint that responds to long-term
overload of low values compared to a short-circuit. Fuse elements may be supported by steel or
nichrome wires, so that no strain is placed on the element, but a spring may be included to
increase the speed of parting of the element fragments.
The fuse element may be surrounded by air, or by materials intended to speed the
quenching of the arc. Silica sand or non-conducting liquids may be used.
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4. CIRCUIT DIAGRAM :
5.RESULT :
6. PRECAUTIONS :
.1.Always disconnect the multimeter before adjusting the range switch.
2.Always check the setting of the range switch before you connect to a circuit
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EXPERIMENT NO 19
1.OBJECTIVE : Observe different waveform on C.R.O. to calculate time period, maximum
value,
cycle, frequency etc. of A.C. waveform.
2.MATERIAL REQUIRED : CRO, signal generator, probes.
3.THEORY : Both the CRO and the signal generator are important test instruments. The signal
generator contains an oscillator and produces sine-(and also square-)wave voltage of adjustable
frequency and magnitude. this voltage can be for testing the performance of electronic circuits.
The main purpose of a CRO is to display waveshapes. The heart of a CRO is its cathode ray
tube(CRT).to operate this CRT, The oscilloscope has a sweep (sawtooth) oscillator, deflection
amplifiers (horizontal and vatical),power supply circuite and a number of controls,switches and
input terminals on the front panel.
An electron beam produced by the electron gun in the CRT strikes the flouroscent screen. As
a result, a bright spot is observed on the screen of the CRT. By applying voltages to the
horizontal and vertical deflection plates (in the CRT), the beam (and hence the bright spot) is
deflected in any desired direction. To display a voltage wave, it disconnected to the vertical
input of he scope. To the horizontal deflection plate, a sawtooth-wave voltage is applied
internally.
If we connect sine wave voltages to both the vertical and horizontal inputs, we get a
display called Lissajous pattern. The shape of these patterns depends upon the frequency
ratio of the two sine waves.
PROCEDURES:
1. sketch the front panel diagrams of CRO and signal generator. Mark the functions of each
control.
2. switch on the CRO. Rotate the intensity control clockwise. After sometime, you will see either
a bright spot or a line on the screen. If you see non, adjust X-POS and Y-POS controls to get
the display in the center of the screen.
3. operate the INTEN and FOCUS controls and observe the effect on the spot (or line). Adjust
them suitably.
4. connect the output from the audio signal generator to the Y-INPUT terminal of the CRO. By
adjusting attenuator of the signal generator, adjust the output voltages at about 1V. adjust
the frequency at 1 KHz. Now adjust the sensitivity of the vertical section to about 1V/cm. the
time base may be adjusted to about 1 ms/cm. if a stationary display is not observed, adjust
the TRIGG LEVEL.
5. to measure the voltage of the signal generator, adjust the vertical amplifier sensitivity suitably,
so as to get a sufficiently large display. Read on the calibrated graticule, the vertical length of
the display. This corresponds to peak-to-peak value of the signal. Multiply this length by the
sensitivity (in V/cm). dividing this result by 2√2 gives the rms value of the signal voltage.
Repeat the measurement procedure for two or three other values of output signal voltages.
6. for measuring the frequency of the signal, adjust the TIME BASE control suitably so as to get
about 2-3 cycles of the signals displayed on the screen. Rotate the VERNIER control clock
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wise to CAL position. Read on the calibrated graticule, on the screen, the length of one cycle.
Multiply this by the time base setting (in ms/cm or µs/cm). this gives the time period of the
signal. Taking inverse of this time period gives the frequency of the signal (i.e. f = 1/T Hz).
7. many CROs do not have a calibrated time base. We can measure frequency of a signal using
such a CRO. For this, feed the unknown signal (taken from the signal generator) to the YINPUT terminals. Take a standard signal generator till you get a Lissajous pattern. For the
various frequency ratios, fv/fh, the Lissajous patterns are shown in Fig.E.14.2.2. the unknown
frequency can thus be determined.
8. to measure the phase shift introduced by an RC phase shift network, connection as shown in
. put the TIME BASE control at EXT position. Adjust the vertical and horizontal amplifier gains
(sensitivities) so as to get an ellipse of suitable size, as shown in measure the lengths Y1
and Y2 (or X1 and X2). Calculate the phase difference between the two waves using the
relation
sin θ = Y1/Y2 = X1/X2
4.CIRCUIT DIAGRAM :
5.OBSERVATIONS TABLE :
1. Measurement of voltage:
S.NO
Signal
generator
output (measured by
a voltmeter)
Measurement on CRO
(p-p)valum in cm
Fundamentals of Electrical Engg. Lab Manual:2nd semester(ET&T)
Sensitivity in V/cm
Rms value
50
1.
2.
3.
6.RESULT :
The CRO can be used to measure time period, maximum value,cycle, frequency
etc. of A.C. waveform.
7. PRECAUTIONS :
.1.Always disconnect the CRO before adjusting the range switch.
2.Always check the setting of the range switch before you connect to a circuit
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EXPERIMENT NO 20 & 21
1.OBJECTIVE : Calibrate given voltmeter/ammeter & Calibrate energy meter at various P.F. by
Standard energy meter.
2.MATERIAL REQUIRED :1.Auto transformer (0-270V)
2.
3.
4.
5.
6.
7.
MI type ammeter (0-10A)
MI type voltmeter (0-300V)
Energy meter 5A , 230V
Lamp load 5Amp
Stop Watch
Connecting leads
3.THEORY - Single phase energy meters are extensively used for measurement of electrical
energy in a.c. circuits. It consists of (1) two a.c. electromagnets ; the series and shunt magnet ,
(2) an aluminium disc or rotor placed between the two electromagnets ,(3) brake magnet and (4)
counting mechanism .The shunt coil is wound with a fine wire of many turns and connected
across the supply .the series coil is wound with a heavy wire of few turns and connected in seiries
with the load so that it carries the ioad current .The No. of revolutions , N is directly proportional to
energy and the counting mechanism is so arranged that the meter indicates kilowatt hour .(k Wh)
directly 1 unit indicates one kilowatt hour.
4.CIRCUIT DIAGRAM :
Recorder
Shunt magnet
supply
load
disc
Series magnet
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PROCEDURE :
1. Connect the ammeter , voltmeter and energy meter through autotransformer as shown
in Figure and setup the auto transformer to zero position .
2. Switch on the supply and adjust the autotransformer till a rated voltage. Note down the
reading of voltmeter and ammeter.
3. Now start the loading with the lamp load up to 1000 watts.
4. Record the Reading of ammeter , voltmeter and energy meter just at 1 hr. after start.
5. Switch off the supply.
5.OBSERVATION :
S no.
Voltmeter Reading
Ammeter Reading
Energy Meter Reading
1.
2.
3.
4.
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CALCULATION: The energy E =V I . t
If the Reading of energy meter shows one unit i. e, 1 k Wh then it shown that the energy
meter is properly calibrated.
6.RESULT – The energy meter is properly calibrated.
7. PRECAUTIONS :
1. wattmeter should be checked before connecting.
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