Ee 444 electrical drives be(tx) 2012

PRACTICAL WORK BOOK
For Academic Session 2012

ELECTRICAL DRIVES (EE-444)
For
BE (TX)

Name:
Roll Number:
Class:
Batch: Semester/Term :
Department :

Department of Electrical Engineering
NED University of Engineering & Technology

Electrical Drives Safety Rules
NED University of Engineering and Technology Department of Electrical Engineering

SAFETY RULES

1. Please don t touch any live parts.
2. Please don t work bare footed.
3. Never use an electrical tool near water.
4. Never use an electrical tool that has fallen into water.
5. Don t carry unnecessary item with you during performance (like water bottle,
bags etc.)
6. Before connecting any leads/Connecting Wires make sure power is switch off.
7. In case of emergency, push the nearby red color emergency switch of any panel
or immediately call the laboratory staff.
8. In case of electricity fire, never put water on it as it will further worse the
condition; use the class C fire extinguisher.

Fire is a chemical reaction involving rapid oxidation
(combustion) of fuel. Three basic conditions when met,
fire takes place. These are fuel, oxygen & heat, absence
of any one of the component will extinguish the fire.

Figure: Fire Triangle
A (think ashes): If there is a small electrical fire, be sure to use
paper, wood etc. only a Class C or multipurpose (ABC) fire
extinguisher, otherwise you might make the
B(think barrels): problem worsen.
flammable liquids
The letters and symbols are explained in left
C(think circuits): figure. Easy to remember words are also shown.
electrical fires

Don t play with electricity, Treat electricity with respect, it deserves

Electrical Drives Contents

CONTENTS

Lab. List of Experiments Page
Dated Remarks
No. No.

01 Introduction SACED TECNEL. 01
Introduction to the devices :
Diodes
02 SCR 03
IGBT s & MOSFET switches

(a) AC/DC Single-phase Not-
Controlled Half-wave Rectifier with 12
R load, RL Load.
03 (b) AC/DC Single-phase Not-
Controlled Full wave Rectifier with
R load and R-L load 17

To study the effect of Free Wheeling diode
on the output of single phase Not-controlled
04 half-wave rectifier.
22

(a) AC/DC Three-Phase Not-Controlled
Half-wave Rectifier with R load & 26
R-L load.
05 (b) AC/DC Three-Phase Not-Controlled
Full-wave Rectifier with R load & 32
R-L load

(a) AC/DC Single-phase Controlled
Half-wave Rectifier with R load,
37
R-L load
06 (b) AC/DC Single Controlled Full-
wave Rectifier with R load & R-L
43
load

Electrical Drives Contents

To study the effect of Free Wheeling diode
07 on the output of single phase controlled 49
half-wave rectifier.
(a) AC/DC Three-phase Controlled
Half-wave Rectifier with R load,
53
R-L load
08 (b) AC/DC Three-Phase Controlled
Full-wave Rectifier with R load &
59
R-L load

09 DC/DC Chopper (BUCK). 64

To draw the Magnetization curve of self-
10 excited Dc shunt Generator (Open circuit 70
Characteristics O.C.C)

To draw the load characteristics curve of
11 self-excited dc shunt generator
73

To draw the external and internal
12 characteristics of separately excited DC 76
generator
Speed control of a DC shunt motor by flux
13 variation method
78

Speed control of a D.C. Shunt Motor by
14 armature rheostat control method
81

To observe the starting of three phase
15 Synchronous and Induction motor
83

Electrical Drives Lab session 01

LAB SESSION 1
Object:-
Introduction to SACED TECNEL.

Apparatus:
SACED TECNEL (Software)
TECNEL
RCL3R Load module

Theory:
In electrical drives lab, we will use TECNEL/B hardware & RCL3R Load module.
The front panel of Tecnel /B consists of:

Diodes module: 6 diodes.
Thyristors module: 6 Thyristors.
IGBTS Module: 6 IGBTS.
Capacitor module
Sensors module: 4 Voltage sensors & 2 Current sensors.
Power supply connections for Red Yellow Blue Phases (R, S, T), Neutral and Ground.
Practices schemes.

PROCESS DIAGRAM AND ELEMENTS ALLOCATION

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RCL3R. Resistive, Inductive and Capacitive Loads Module:
Our Resistive, Capacitive and Inductive Loads Module (RCL3R) offers single and Three-phase
resistances, inductances & capacitances.

The values are as follows:
Variable resistive loads: 3 x [150 (500 W)]
Fixed resistive loads: 3 x [150 (500 W) + 150 x (500 W)]
Inductive loads: 3 x [0, 33, 78, 140, 193, 236mH]. (230V /2 A)
Capacitive loads: 3 x [4 x 7 µF]. (400V)

Now load the TECNEL software in PC, the main screen will be look like this:

And the Plot screen will be look like this:

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NED University of Engineering and Technology
Engineering Department of Electrical Engineering

LAB SESSION 2

Object:-
Introduction to the devices
devices:
Diodes
SCR
IGBT s & MOSFET switches

Theory:-
-

1. DIODE In electronics, a diode is a two terminal electronic component that conducts
DIODE:- two-terminal
electric current in only one direction. The most common function of a diode is to allow an
electric current to pass in one direction (called the diode's forward direction), while
blocking current in the opposite direction (the reverse direction). Thus, the diode can be
in
thought of as an electronic version of a check valve. This unidirectional behavior is called
rectification, and is used to convert alternating current to direct current, and to extrac
extract
modulation from radio signals in radio receivers.

Figure: (a) Construction of a semi conductor diode
semi-conductor (b) symbol of diode

A diode is formed by joining two equivalently doped P Type and N-Type semiconductor. When
P-Type N-Type
they are joined an interesting phenomenon takes place. The P Type semiconductor has excess
P-Type
holes and is of positive charge. The N Type semiconductor has excess electrons. At the point of
N-Type
contact of the P Type and N Type regions, the holes in the P Type attract electrons in the N Type
P-Type N-Type P-Type N-Type
material. Hence the electron diffuses and occupies the holes in the P Type material. Causing a
aterial. P-Type
small region of the N type near the junction to loose electrons and behaves like intrinsic
N-type
semiconductor material, in the P type a small region gets filled up by holes and behaves like an
P-type
intrinsic semiconductor
semiconductor.
This thin intrinsic region is called depletion layer, since it is depleted of charge (see diagram
s
above) and hence offers high resistance. It s this depletion region that prevents the further
diffusion of majority carriers. In physical terms the size of the depletion layer is very thin.
he

Page | - 3 -


Figure: (a) Formation of depletion Layer. (b) Forward characteristics of diode

Due to formation this depletion layer the diode will not conduct until the depletion layer voltage is
overcome, that is 0. V for Germanium and 0. V for silicon. An increase in the applied voltage
, 0.3 0.7
above that narrow depletion layer (0. V for Germanium and 0. V for silicon) results in rapid rise
(0.3 0.7
in the flow of current. Graphs depicting the current voltage relationship for forward biased PN
of the
junction, for both silicon and germanium are called forward characteristics and shown below.
Diode is mainly used to perform rectification, converting A.C into unidirectional D.C. In half
mainly rectification, .
wave rectification, either the positive or negative half of the AC wave is passed, while the other
rectification,
half is blocked. Because only one half of the input waveform reaches the output, it is very
inefficient if used for power transfer. Half wave rectification can be achieved with a single diode
Half-wave
in a one-phase supply, or with three diodes in a three-phase supply.
phase phase

Figure:- Half wave rectification process in which negative half cycle is annulled by diode

Review

A diode is an electrical component acting as a one way valve for current.
one-way
When voltage is applied across a diode in such a way that the diode allows current, the
diode is said to be forward-biased
biased.
When voltage is applied across a diode in such a way that the diode prohibits current, the
di
diode is said to be reverse-biased
biased.
The voltage dropped across a conducting, forward
forward-biased diode is called the forward
voltage.
voltage. Forward voltage for a diode varies only slightly for changes in forward current and
temperature, and is fixed by the chemical composition of the P N junction.
and P-N
Silicon diodes have a forward voltage of approximately 0.7 volts.
Germanium diodes have a forward voltage of approximately 0.3 volts.
The maximum reverse bias voltage that a diode can withstand without breaking down is
reverse-bias
called the Peak Inverse Voltage or PIV rating.
Voltage,

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Figure: V-I characteristics of Diode

THRYRISTOR (SCR):-A silicon-controlled rectifier is a four-layer semiconductor
device that controls current. SCR consists of four layers of alternating P and N type
semiconductor materials and it has three terminals called anode, cathode and gate. The
SCR is uni-directional device, meaning it passes electron current only in one direction,
from cathode to anode when positive gate signal is applied. It is named as controlled
rectifier because it can control the amount of power flowing from source to load. It can be
made to conduct for whole part of positive half cycle or for small part of positive half
cycle.
The SCR will turn on and conduct current when following two conditions are satisfied.
1. It has forward biased voltage across its anode and cathode of at least 0.7 Volts. Forward
biased condition exists when anode is more positive than cathode.
2. It has a positive voltage applied across the gate.

Figure: Thyristor Construction, schematic symbol, forward biasing for normal operation

Volt-Ampere Characteristics
Figure below illustrates the volt-ampere characteristics curve of an SCR. The vertical axis + I
represent the device current, and the horizontal axis +V is the voltage applied across the device

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anode to cathode. The parameter IF defines the RMS forward current that the SCR can carry in the
ON state, while VR defines the amount of voltage the unit can block in the OFF state.

Figure:- V-I Characteristics of SCR

Biasing
The application of an external voltage to a semiconductor is referred to as a bias.
Forward Bias Operation
A forward bias, shown above in figure as +V, will result when a positive potential is
applied to the anode and negative to the cathode.
Even after the application of a forward bias, the device remains non-conducting until the
positive gate trigger voltage is applied.
After the device is triggered ON it reverts to a low impedance state and current flows
through the unit. The unit will remain conducting after the gate voltage has been removed.
In the ON state (represented by +I), the current must be limited by the load, or damage to
the SCR will result.

Reverse Bias Operation
The reverse bias condition is represented by -V. A reverse bias exists when the potential
applied across the SCR results in the cathode being more positive than the anode.
In this condition the SCR is non-conducting and the application of a trigger voltage will
have no effect on the device. In the reverse bias mode, the knee of the curve is known as
the Peak Inverse Voltage PIV (or Peak Reverse Voltage - PRV) and this value cannot be
exceeded or the device will break-down and be destroyed. A good Rule-of -Thumb is to
select a device with a PIV of at least three times the RMS value of the applied voltage

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SCR Phase Control
In SCR Phase Control, the firing angle, or point during the half-cycle at which the SCR is
triggered, determines the amount of current which flows through the device. It acts as a high-speed
switch which is open for the first part of the cycle, and then closes to allow power flow after the
trigger pulse is applied. Figure two below shows an AC waveform being applied with a gating
pulse at 45 degrees. There are 360 electrical degrees in a cycle; 180 degrees in a half-cycle. The
number of degrees from the beginning of the cycle until the SCR is gated ON is referred to as the
firing angle, and the number of degrees that the SCR remains conducting is known as the
conduction angle. The earlier in the cycle the SCR is gated ON, the greater will be the voltage
applied to the load. Figure Three shows a comparison between the average output voltages for an
SCR being gated on at 30 degrees as compared with one which has a firing angle of 90 degrees.
Note that the earlier the SCR is fired, the higher the output voltage applied to the load.

Figure:- SCR output waveform (a) When forward biased (b) Triggering at different angles

The voltage actually applied to the load is no longer sinusoidal, rather it is pulsating DC having a
steep wave front which is high in harmonics. This waveform does not usually cause any problems
on the driven equipment itself; in the case of motor loads, the waveform is smoothed by the circuit
inductance.

MOSFET (Metal oxide Semiconductor Field Effect Transistor):-
The metal oxide semiconductor field-effect transistor (MOSFET, MOS-FET, or MOS FET) is a
transistor used for amplifying or switching electronic signals. It has three terminals gate, source
and drain as shown below. Unlike the bipolar junction transistor (BJT), the metal-oxide-
semiconductor field effect transistor (MOSFET) is composed of a bulk substrate of metal oxide
ions, which form n- and p-charged regions in order to amplify analog voltages across a circuit.
Figure shows the basic of a MOSFET. Note the charged n-regions in the substrate and the four

Page | - 7 -


terminals (3 active, 1 grounded). Furthermore, unlike the BJT, the operation of the MOSFET is
determined by a voltage rather than a current.
Gate

Source Drain
n+ n+
p

Bulk (or substrate)

Diagram of the composition of a MOSFET

Like the bipolar junction transistors, the MOSFETs are composed of two different semiconductor
regions, n and p. Instead of creating a current through the device by filling of holes in the p
region, the MOSFET forms a channel of the positively charged n layer between the two n
sections, as shown in Figure 1. This channel forms when a voltage is applied across the gate,
attracting the electrons in the n region nearer to the gate charge. The strength of the gate voltage
determines the geometry of the channel and the current that passes through it. Figure below shows
the drain characteristic of the MOSFET, the relationship between the drain-source voltage and the
drain current. Like the collector characteristic of the BJT, the MOSFET drain characteristic uses
two voltages and the gate voltage to construct a series of characteristic curves for the device.

Figure 1 Drain characteristic for a MOSFET

Two voltages are keys to the operation of the MOSFET, the threshold voltage and the gate
voltage. The threshold voltage VT is the voltage at which the MOSFET begins to conduct the
electrons from the drain to the source. The difference between it and the gate voltage, VG ,
determines the flow of the electrons through the channel. If the difference between the threshold
and the gate is negative, no current flows. If this difference is greater than zero, current flows
between the two terminals.

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At a certain point within the saturation region a pinch-off occurs. The pinch
region, -off pinch-off means that
the channel thins , not allowing electron flow between the two terminals. Generally, if the
termi
difference between the gate voltage and the threshold voltage is greater than or equal to the
threshold voltage, this pinch off occurs
pinch-off

Figure:- MOSFET schematic symbols
Figure:

IGBT (INSULATED GATE BIPOLAR TRANSISTOR):-
A power transistor that has characteristics of both MOSFET and bipolar junction transistors
(BJTs).is called IGBT. IGBT handles high current, a characteristic of BJTs, but enables fast
is
switching with greater ease of control. IGBTs are found in home appliances, electric cars and
electric
digital stereo power amplifiers The insulated gate bipolar transistor or IGBT is a three terminal
three-terminal
power semiconductor device, noted for high efficiency and fast switching. It switches electric
power in many modern appliances: electric cars, trains, variable speed refrigerators, air air-
conditioners and even stereo systems with switching amplifiers. Since it is designed to turn on and
off rapidly, amplifiers that use it often synthesize complex waveforms with pulse width
modulation and low pass fi
low-pass filters. The IGBT combines the simple gate drive characteristics of the
gate-drive
MOSFETs with the high current and low saturation voltage capability of bipolar transistors by
high-current saturation-voltage
combining an isolated gate FET for the control input, and a bipolar power transistor as a switch, in
a single device. The IGBT is used in medium- to high-power applications such as switched mode
medium- power switched-mode
power supply, traction motor control and induction heating. Large IGBT modules typically consist
of many devices in parallel and can have very high current handling capabilities in the order of
current
hundreds of amperes with blocking voltages of 6000 V, equating to hundreds of kilowatts.
,

Figure:- Electronic symbol of IGBT

IGBT switching characteristics: The switching characteristics of an IGBT are very much similar to
GBT characteristics:-The
that of a Power MOSFET. The major difference from Power MOSFET is that it has a tailing
collector current due to the stored charge in the N drift region. The tail current increases the turn
N--drift turn-
off loss and requires an increase in the dead time between the conduction of two devices in a half
time half-

Page | - 9 -


bridge circuit. The Figure shows a test circuit for switching characteristics and the Figure 9 shows
the corresponding current and voltage turn-on and turn-off waveforms. IXYS IGBTs are tested
with a gate voltage switched from +15V to 0V. To reduce switching losses, it is recommended to
switch off the gate with a negative voltage (-15V).

The turn-off speed of an IGBT is limited by the lifetime of the stored charge or minority carriers in
the N--drift region which is the base of the parasitic PNP transistor. The base is not accessible
physically thus the external means cannot be applied to sweep out the stored charge from the N--
drift region to improve the switching time. The only way the stored charge can be removed is by
recombination within the IGBT. Traditional lifetime killing techniques or an N+ buffer layer to
collect the minority charges at turn-off are commonly used to speed-up recombination time.

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The main advantages of IGBT over a Power MOSFET and a BJT are:
1. It has a very low on-state voltage drop due to conductivity modulation and has superior on-state
current density. So smaller chip size is possible and the cost can be reduced.
2. Low driving power and a simple drive circuit due to the input MOS gate structure. It can be
easily controlled as compared to current controlled devices (Thyristor, BJT) in high voltage and
high current applications.
3. Wide SOA. It has superior current conduction capability compared with the bipolar transistor. It
also has excellent forward and reverse blocking capabilities.

The main drawbacks are:
1. Switching speed is inferior to that of a Power MOSFET and superior to that of a BJT. The
collector current tailing due to the minority carrier causes the turn off speed to be slow.
2. There is a possibility of latch up due to the internal PNPN Thyristor structure.

Page | - 11 -

Electrical Drives Lab Session 03 (a)

LAB SESSION 3 (a)

Object:
AC/DC Single phase Not Controlled Half-wave Rectifier with R load, RL Load.
Single-phase Not-Controlled wave load,
Apparatus:
SACED TECNEL
TECNEL or TECNEL/B
RCL3R Load module
Connecting Wires

Theory:
Single-phase half wave not controlled rectifiers:
phase half-wave not-controlled
Not-controlled rectifiers are constituted by diodes that, a
controlled acts
as not-controlled elements, provide a dependent output
controlled
voltage of fixed magnitude. In half wave rectifiers, diode
conducts only in half cycle of the input, otherwise open.

From a theoretical point of view, they may be considered as
switches that are opened or closed depending on the direction of the voltage applied. That is with a
voltage
positive voltage between anode (A) and cathode (K) the switch is closed, and it is opened if the
voltage is negative.

The behavior of the rectifier will depend considerably on the used load type, so we may have:

Pure resistive load (R) where the voltage is annulled when its direction changes.
(R):
Inductive load (R L), where the conduction continues until the moment when the current in the
(R-L),
coil is annulled, although the output voltage inverts its polarity.

Circuit Diagram
Diagram:

E1UK Model
Procedure:
1. Carry out the assembly E1UK shown in the above figure
2. Connect the respective load to its terminals one by one.
For R Load
Use Fixed R= 300ohms plus variable resistance in series.

Page | - 12 -


And sample the following parameters:
Input voltage V2, Output voltage V1, Output current I2, Diode voltage V3 (as shown in
figure)

Figure: Uncontrolled Half Wave Rectifier R Load
For different values of R the RMS voltage will vary across the load, which can be
calculated using multi meter.

S. No Load Resistance V rms Voltage Across Diode
1. 300 + 75
2. 300 + 120

For RL Load
Observe how the conduction angle increases as we increase L (0to 236mH) with R=375 ,
measuring with the voltmeter the average output voltage.

S. No Load Impedance V rms Voltage Across Diode
1. 300 + 75 + 140mH
2. 300 + 75 + 236mH

Observe how the output current varies for different L values with R=375 . Save the
different samples.
figure)

Page | - 13 -


Figure: Uncontrolled Half Wave Rectifier RL Load

3. Load the SACED TECNEL program in PC and the window corresponding to this practice
Select Practice Option
AC/DC Single-phase Not-Controlled Half wave Rectifier option
4. Select the respective sample sensors
5. Check the connections and switch on the equipment.
6. Press the Data Capture button.
7. Visualize the parameters measured and save them in the corresponding file.
8. Switch off the equipment.

Question:
Define the following terms:
1. Ripple Factors:
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________

2. Harmonics:
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________

3. Fundamental Frequency:
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________

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4. Power Factor:
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________

5. Rectifiers:
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________

Waveforms:
R LOAD

Fig: Input Voltage Fig: Output Voltage across R Load

Fig: Load Current IL Fig: Output Voltage across Diode

Page | - 15 -


R-L LOAD

Fig: Input Voltage Fig: Output Voltage across RL Load

Fig: Load Current IL Fig: Output Voltage across Diode D1

Page | - 16 -

Electrical Drives Lab Session 03 (b)

LAB SESSION 3 (b)

Object:
AC/DC Single-phase Not-Controlled Full wave Rectifier with R load and R-L load.

Apparatus:
SACED TECNEL
TECNEL or TECNEL/B
RCL3R Load module
Connecting Wires

Theory:
Single-phase full-wave not-controlled rectifiers:
By the use of four diodes, rectifier circuit performance can be greatly improved. The entire supply
voltage wave is utilized to impress current through the load.

Figure: Single-phase, full-wave diode rectifier:
(a) Circuit diagram and (b) load voltage and current waveforms for R load.

The behavior of the rectifier will depend considerably on the used load type, i.e. R Load or RL
Load.

Circuit Diagram:

B2U Model

Page | - 17 -


Table 1: Single-Phase Diode Rectifier Circuits with Resistive Load

Procedure:
1. Carry out the assembly B2U shown in the above figure
For R Load

figure)

Figure: Uncontrolled Full Wave Rectifier with R load

Page | - 18 -


And measure the following quantities
S. No Load Resistance V rms Voltage Across D1
1. 300 + 75
2. 300 + 120
For RL Load

1. 300 + 75 + 140mH
2. 300 + 75 + 236mH

different samples.
figure)

Figure: Uncontrolled Full Wave Rectifier with RL load

AC/DC Single-phase Not-Controlled full wave Rectifier option

Page | - 19 -


Waveforms:
R LOAD


Fig: Load Current IL Fig: Supply Current IS

Fig: Output Voltage across Diode D1 Fig: Output Voltage across Diode D3

Page | - 20 -


R-L LOAD

Fig: Input Voltage Fig: Output Voltage across RL Load


Fig: Output Voltage across Diode D1 Fig: Output Voltage across Diode D3

Page | - 21 -

Electrical Drives Lab Session 04

LAB SESSION 4

Object:
To study the effect of Free Wheeling diode on the output of single phase Not-controlled half-wave
rectifier.

Apparatus:
SACED TECNEL
TECNEL or TECNEL/B
RCL3R Load module
Connecting Wires

Theory:
Freewheeling diode:-
when using a load with inductive character, the following effects appear:
when the input voltage is inverted, a peak of negative voltage appears in the output, and it
is not annulled until the current becomes zero.
In a part of the cycle, the current is interrupted, that is, the conduction is discontinuous.

These two effects may be eliminated, as well as the reduction of the harmonic content, with the
introduction in parallel with the load of a diode called Freewheeling Diode (FWD) or Flying
Diode.
When the input voltage is annulled at the end of the positive semi cycle, the voltage in the coil is
inverted. It begins to act as a generator, forcing the conduction of the FWD and the load current
going through it, annulling the peak of negative voltage, as we can see in the following.

Page | - 22 -


We may see here that from 10ms the waveform of the current load (graph in previous page) is an
exponential one, that proves the discharge of the coil for the resistance through the FWD. This is
corroborated by the input current, ceasing at 10ms.
Circuit Di
Diagram:-

Figure:- E1UK Model
Figure:
Procedure:
1. Carry out the assembly E1UK shown in the above figure
2. Now connect a diode in anti-Parallel manner with the First diode as shown below
anti
3. Connect the respective RL load to its terminal.
For RL Load with FWD
mH) R=37

Voltage Across Diode
S. No Load Impedance V rms
D1 D2
1. 300 + 75 + 140mH
140
2. 300 + 75 + 236mH
23

Observe how the output current varies for different L values with R=375 .
R=3
sample
figure)

Page | - 23 -


Figure: Uncontrolled single phase Half Wave Rectifier RL Load & FWD.

5. Select Practice Option
6. AC/DC Single-phase Not-Controlled Half wave Rectifier option
Switch off the equipment

Question:

1. Free Wheeling Diode
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________

2. Effect of FWD on RL Load Output
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________

Page | - 24 -


__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________
5. Rectifiers:
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________

Waveforms:-

R-L LOAD WITH FWD

Fig: Input Voltage Fig: Output Voltage across R-L Load

Fig: Load Current IL Fig: Diode Voltage

Page | - 25 -

Electrical Drives Lab Session 05(a)

LAB SESSION 5 (a)

Object:
AC/DC Three-Phase Not-Controlled Half-wave Rectifier with R load& R-L load.

Apparatus:
SACED TECNEL
TECNEL or TECNEL/B
RCL3R Load module
Connecting Wires

Theory:
Three-phase half-wave not-controlled rectifiers:
Three-phase electricity supplies with balanced, sinusoidal voltages are widely available. It is found
that the use of a three-phase rectifier system, in comparison with a single-phase system, provides
smoother output voltage and higher rectifier efficiency. Also, the utilization of any supply
transformers and associated equipment is better with poly-phase circuits. If it is necessary to use
an output filter this can be realized in a simpler and cheaper way with a poly-phase rectifier.

Figure: Three-phase, half-wave diode rectifier with resistive load: (a) circuit connection,
(b) phase voltages at the supply, (c) load current.

Page | - 26 -


Table: Three Phase Uncontrolled Rectifier with Ideal Supply

Circuit Diagram:

M3UK Model
Procedure:
1. Carry out the assembly M3UK shown in the above figure
For R Load
Input voltages (V2, V3, V4), Output voltage V1, Output current I1, Diode voltage V5 (as
shown in figure)

Page | - 27 -


Figure: Uncontrolled Three Phase Full Wave Rectifier with R load

Also measure the following quantities using multi-meter.

S. No Load Resistance V rms Voltage Across D1
1. 300 + 75
2. 300 + 120

For RL Load

1. 300 + 75 + 140mH
2. 300 + 75 + 236mH

different samples.
Input voltages (V2, V3, V4), Output voltage V1, Output current I1, Diode voltage V5 (as
shown in figure)

Page | - 28 -


Figure: Uncontrolled Three Phase Full Wave Rectifier with RL load

AC/DC Three-phase Not-Controlled Half wave Rectifier option

Here you can also study and visualize what will be the effect of inverting the polarization
of the three diodes.

Secondly suppose that, due to an over-voltage, one of the diodes is in open circuit. Study
and visualize what effect provokes the output voltage.

Page | - 29 -


Waveforms:
R LOAD

Fig: Input Voltages R,S,T Fig: Output Voltage across R Load


R-L LOAD


Page | - 30 -



Page | - 31 -


LAB SESSION 5 (b)

Object:
AC/DC Three-Phase Not-Controlled Full-wave Rectifier with R load& R-L load.

Apparatus:
SACED TECNEL
TECNEL or TECNEL/B
RCL3R Load module
Connecting Wires

Theory:
Three-phase full-wave not-controlled rectifiers:
The basic full wave uncontrolled (diode) rectifier circuit is shown in the following figure. The
diodes D1, D3, D5 are sometimes referred to as the upper half of the bridge, while diodes D2, D4
and D6 constitute the lower half of the bridge. As with the half wave operation the voltages at the
anode of the diode valves vary periodically as the supply voltages undergo cyclic excursions.
Commutation or switch off of a conducting diode is therefore accomplished by natural cycling of
the supply voltages and is known as natural commutation. The load current IL is now
unidirectional but the supply currents are bi-directional. In order to permit load current to flow, at
least one diode must conduct in each half of the bridge. When this happens the appropriate line to
line supply point voltage is applied across the load. In comparison with the half wave bridge, in
which supply phase voltage is applied across the load, the full wave bridge has immediate
advantage that peak load voltage is 3 times as great.
Circuit Diagram:

B6U Model
Procedure:
1. Carry out the assembly B6U shown in the above figure
For R Load


Page | - 32 -


figure)

Figure:- Three phase not controlled full wave rectifier with R load

Also measure following quantities using multi-meter

S. No Load Resistance V rms Voltage across D1
1 300 + 75
2 300 + 120

For RL Load
measuring with the voltmeter the average output voltage. V av =

S. No Load Impedance V rms Voltage across D1
1 300 + 75 + 140 m
H
2 300 + 120 + 236mH

Observe how the output current varies for different L values with R=375. Save the
different samples.
Input voltage V4, Output voltage V1, Diode voltage V3, Output current (load) I1 (as
shown in figure)

Page | - 33 -


Figure:- three phase not controlled full wave rectifier with RL load

AC/DC Three-phase Not-Controlled full wave Rectifier option

Page | - 34 -


Waveforms:
R LOAD



R-L LOAD


Page | - 35 -


Fig: Load Current IL with L=140mH Fig: Load Current IL with L=236mH

Fig: Output Voltage across diode

Page | - 36 -


LAB SESSION 6 (a)

Object:
AC/DC Single-phase Controlled Half-wave Rectifier with R load, R-L load and R-L load.

Apparatus:
SACED TECNEL
TECNEL or TECNEL/B
RCL3R Load module
Connecting Wires

Theory:
Single-phase half-wave controlled rectifiers:
The controlled rectifiers are constituted by Thyristors. The Thyristor
is basically a diode controlled by positive voltage among gate (G)
and anode (A).
The main difference between controlled rectifiers and not controlled
Rectifiers is based on the fact that the Thyristor conduction and non-conduction
states can be controlled externally.

Figure:- single phase half wave controlled rectifier a) circuit connections
b) output voltage waveform

The Thyristors can be made to conduct during the whole part of positive cycle or for some part of
positive cycle, in this way we can control the amount of power flowing from source to load in
controlled rectifiers.
In this lab session we will deal with rectifiers which are capable to decide the moment when we
may trigger the Thyristor by using PC.

The behaviour of controlled rectifier will depend, to a great extent, on the load type used.
Pure resistive load (R): where the voltage is annulled when its direction changes. The average
output voltage for resistive load will be :
V average = [1 + cos ] V/2
Inductive load (R-L), where the conduction continues until the moment when the current in the
coil is annulled, although the output voltage inverts its polarity.
The average output voltage for RL load will be :

Page | - 37 -


V average = [ cos {cos( + )}] V/2

In order to separate the output voltage and the load type, we may use the freewheeling diode
(FWD), which avoids the inversion of polarization in the output voltage.

Circuit Diagram:

E1CK Model

Procedure:
1. Carry out the assembly E1CK shown in the above figure
For R Load
Use Fixed R= 300 ohms plus variable resistance in series.
Input voltage V2, Output voltage V1, Output current I2, Thyristor voltage V3 (as shown in
figure)

Figure: Controlled Half Wave Rectifier with R Load

Page | - 38 -


For different values of R the RMS voltage will vary across the load, which can be
calculated using multi meter.

S. No Load Resistance V rms Voltage Across
Thyristor
1. 300 + 75
2. 300 + 120
For RL Load

S. No Load Impedance V rms Voltage Across
Thyristor
1. 300 + 75 + 140mH
2. 300 + 75 + 236mH

different samples.
Input voltage V2, Output voltage V1, Thyristor voltage V3, Output current (load) I2 (as
shown in figure)

Figure: Controlled Half Wave Rectifier RL Load

Page | - 39 -


AC/DC Single-phase Controlled Half wave Rectifier option

Question:
1. Ripple Factors:
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________
2. Harmonics:
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________

__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________

4. Power Factor:
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________

5. Rectifiers:
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________

Page | - 40 -


Waveforms:
R LOAD

Fig: Input Voltage Fig: Output Voltage across R load

Fig: Load Current IL Fig: Output Voltage across Thyristor

R-L LOAD

Fig: Input Voltage Fig: Output Voltage across R-L load

Page | - 41 -


Fig: Load Current IL Fig: Output Voltage across Thyristor Th 1

Page | - 42 -


LAB SESSION 06 (b)

Object:
AC/DC Single-phase Controlled Full wave Rectifier with R load and R-L load.

Apparatus:
SACED TECNEL
TECNEL or TECNEL/B
RCL3R Load module
Wires

Theory:
Single-phase full wave controlled rectifiers:
By the use of four Thyristor, rectifier circuit performance can be greatly improved. In full control
single phase rectifier the Thyristor are divided into the two group, one with common anodes and
other with common cathodes as shown below in the figure.

Figure: Single-phase, full-wave controlled rectifier:
(a) circuit diagram and (b) load voltage and current waveforms for R load.

Thyristor Th 1 and Th 4 will conduct when input voltage is positive.
Thyristor Th 2 and Th 3 will conduct when input voltage is negative.

The average output voltage for R load will be:
V average = (1 + cos ) V/
The average output voltage for RL load will be:
V average = ( cos ) 2V/

The behavior of the rectifier will depend considerably on the used load type, i.e. R Load or RL
Load.

Page | - 43 -


Circuit Diagram:

B2C Model

Table 1: Single-Phase Controlled Rectifier Circuits with Resistive Load

Procedure:
1. Carry out the assembly B2C shown in the above figure
For R Load

Input voltage V4, Output voltage V1, Output current I2, Thyristor voltage (V2 , V3) as
shown in figure

Page | - 44 -


Figure: Controlled Full Wave Rectifier with R load

And measure the following quantities

S. No Load Resistance V rms Voltage Across
Thyristor
1. 300 + 75
2. 300 + 120

For RL Load
Observe how the conduction angle increases as we increase L (0 to 236mH) with R=375 ,

S. No Load Impedance V rms Voltage Across
Thyristor
1. 300 + 75 + 140mH
2. 300 + 75 + 236mH

different samples.

Input voltage V4, Output voltage V1,Thyristor voltage (V2, V3), Output current (load) I2,
Supply current I1 , as shown in figure

Page | - 45 -


Figure: Controlled Full Wave Rectifier with RL load

AC/DC Single-phase Controlled full wave Rectifier option
Waveforms:
R LOAD

Fig: Input Voltage Fig: Output Voltage across R load

Page | - 46 -



Fig: Output Voltage across Thyristor Th 1 Fig: Output Voltage across Thyristor Th 3
R-L LOAD


Page | - 47 -



Fig: Output Voltage across Thyristor Th 1 Fig: Output Voltage across Thyristor Th 3

Page | - 48 -


LAB SESSION 07

Object:
To study the effect of Free Wheeling diode on the output of single phase controlled half-wave
rectifier.

Apparatus:
SACED TECNEL
TECNEL or TECNEL/B
RCL3R Load module
Connecting Wires

Theory:
Freewheeling diode:-

when using a load with inductive character, the following effects appear:
when the input voltage is inverted, a peak of negative voltage appears in the output, and it
is not annulled until the current becomes zero.
In a part of the cycle, the current is interrupted, that is, the conduction is discontinuous.

These two effects may be eliminated, as well as the reduction of the harmonic content, with the
introduction in parallel with the load of a diode called Freewheeling Diode (FWD) or Flying
Diode.
When the input voltage is annulled at the end of the positive semi cycle, the voltage in the coil is
inverted. It begins to act as a generator, forcing the conduction of the FWD and the load current
going through it, annulling the peak of negative voltage, as we can see in the following.

Consider the above figure which shows the assembly of Thyristor and Free Wheeling diode.

Figure:- Controlled Half wave rectifier with FWD

Page | - 49 -


The circuit works as follows:
In the positive semi cycle, during the interval in which the Thyristor is switched on, the input
voltage appears in the output with no changes. When the input voltage is annulled at the end of the
positive semi cycle, the voltage in the coil is inverted, thus, the coil works as a generator. As a
consequence, the freewheeling diode is directly polarized, and the load current circulates through.
The negative peak of the output voltage that took place in the previous paragraph is annulled. This
may be better
appreciated in the following graphs

Circuit Diagram:-

Procedure:
1. Carry out the assembly E1CK shown in the above figure
2. Now connect a diode in anti-Parallel manner with the Thyristor as shown below
3. Connect the respective RL load to its terminal .

For RL Load with FWD
Voltage Across
S. No Load Impedance V rms Thyristor
Th 1
1. 300 + 75 + 140mH
2. 300 + 75 + 236mH

Page | - 50 -


Observe how the output current varies for different L values with R=375 .
Input voltage V2, Output voltage V1, Output current I1, Thyristor Voltage V3

Figure: Controlled Half Wave Rectifier RL Load with FWD

AC/DC Single-phase Controlled Half wave Rectifier option

Question:

1. Free Wheeling Diode
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________

2. Effect of FWD on RL Load Output
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________

Page | - 51 -


__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________
5. Rectifiers:
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________

Waveforms:-
R-L LOAD WITH FWD


Fig: Load Current IL Fig: Thyristor voltage

Page | - 52 -


LAB SESSION 08 (a)

Object:
AC/DC Three phase Controlled Half-wave Rectifier with R load & R-L load.

Apparatus:
SACED TECNEL
TECNEL or TECNEL/B
RCL3R Load module
Wires

Theory:
Three-phase half-wave controlled rectifiers:
Three-phase electricity supplies with balanced, sinusoidal voltages are widely available. It is found
that the use of a three-phase rectifier system, in comparison with a single-phase system, provides
smoother output voltage and higher rectifier efficiency. Also, the utilization of any supply
transformers and associated equipment is better with poly-phase circuits. If it is necessary to use
an output filter this can be realized in a simpler and cheaper way with a poly-phase rectifier.

Figure: Three-phase, half-wave controlled rectifier with resistive load: (a) circuit connection,
(b) phase voltages at the supply, output voltage, output current.

Page | - 53 -


Table: Three Phase Controlled Rectifier with Ideal Supply

Circuit Diagram:

B6C Model
Procedure:
For R Load

Input voltage (V2,V3, V4), Output voltage V1, Output current I1, Thyristor voltage V5 as
shown in the above figure.

Page | - 54 -


Figure: Controlled Three Phase Full Wave Rectifier with R load

Also measure the following quantities using multi-meter.

S. No Load Resistance V rms Voltage across Th 1
1. 300 + 75
2. 300 + 120

For RL Load
Observe how the conduction angle increases as we increase L (0 to 236mH) with R=375 ,

S. No Load Impedance V rms Voltage across Th 1
1. 300 + 75 + 140mH
2. 300 + 75 + 236mH

different samples.

Input voltage (V2,V3, V4), Output voltage V1, Output current I1, Thyristor voltage V5 as
shown in the above figure.

Page | - 55 -


Figure: Controlled Three Phase Full Wave Rectifier with RL load

AC/DC Three Phase Controlled Half wave Rectifier option

Here you can also study and visualize what will be the effect of inverting the polarization
of the three Thyristor.

Secondly suppose that, due to an over-voltage, one of the Thyristor is in open circuit.
Study and visualize what effect provokes the output voltage.

Page | - 56 -


Waveforms:
R LOAD



R-L LOAD


Page | - 57 -



Page | - 58 -


LAB SESSION 08 (b)

Object:
AC/DC Three-Phase Controlled Full-wave Rectifier with R load& R-L load.

Apparatus:
SACED TECNEL
TECNEL or TECNEL/B
RCL3R Load module
Connecting Wires

Theory:
Three phase controlled full wave rectifier:-
Three phase controlled full wave rectifier is just like assembly of two controlled, three phase half
wave rectifiers. One with common anodes and other with common cathodes as shown below.

Figure:- Three Phase controlled full wave rectifier with resistive load
a) Circuit connections with load b) load voltage and load current
waveforms.

Th 1, Th 2, Th 3, conduct when the voltages Vr, Vs, Vt respectively are most positive
provided that the Thyristor have been triggered.
Th 4, Th 5, Th 6, conduct when the voltages Vr, Vs, Vt respectively are most negative
provided that the Thyristor have been triggered.

The average output voltage for R load will be:
60 (direct conduction ) V average = (cos wt) 3 3V/
60 (discontinuous conduction) V average = (1 - 3/2 sin + 1/2 cos )3 3V/

The average output voltage for RL load will be:

Page | - 59 -


60 (direct conduction ) V average = (cos ) 3 3V/
60 (discontinuous conduction) V average = (sin wt - 3/2 sin + 1/2 cos )3 3V/

Circuit Diagram:-

B6C Model

Procedure:
For R Load

figure)

Figure:- Three Phase controlled full wave rectifier with R load.

Page | - 60 -


Also measure the following quantities using multi meter.
S. No Load Resistance V rms Voltage across D1
1 300 + 75
2 300 + 120
For RL Load
measuring with the voltmeter the average output voltage. V av =

S. No Load Impedance V rms Voltage across D1
1 300 + 75 + 140 m
H
2 300 + 120 + 236mH

Observe how the output current varies for different L values with R=375. Save the
different samples.
figure)

Figure:- Three Phase controlled full wave rectifier with RL load.

AC/DC Three-Phase Controlled Full-wave Rectifier option

Page | - 61 -


Waveforms:
R LOAD

Fig: Input Voltage R, S, T Fig: Output Voltage across R Load


R-L LOAD

Fig: Input Voltage R , S , T Fig: Output Voltage across RL load

Page | - 62 -


Fig: Load Current IL with L=140mH Fig: Load Current IL with L=236mH

Fig: output voltage across Thyristor

Page | - 63 -


LAB SESSION 09

Object:-
DC/DC Chopper.
Apparatus:
SACED TECNEL
TECNEL or TECNEL/B
RCL3R Load module
Connecting Wires
Theory:-
Chopper is used to convert the unregulated DC input to a controlled DC output with a desired
voltage level. It is a static device which gives variable dc voltage from a constant dc voltage
source. Chopper is also known as dc-to-dc converter.
There are basically two types of the chopper:
1. Step down chopper (BUCK) :- In step down chopper output voltage is less than input
voltage.
2. Step up chopper (BOOST) :- In step up chopper output voltage is more than input voltage.

Basically, we may obtain a variable voltage from a fixed direct voltage by way of connecting and
disconnecting the source from the load by using a switch, so the average value of the output
voltage may depend on the opening and closing rhythm of the controllable switch. In this case it
will be an IGBT. They are, thus, called Commuted Direct Current Converters.

The input voltage chopping to obtain a lower average value is the Chopper operation principle.
The average value of this voltage will depend on the ratio of the T on time (conduction time) and
the period T, called work cycle.

The average value of voltage is given by above formula;

Therefore, the variation of the average output voltage can be made in three ways:

Page | - 64 -


By closing the switch at a fixed frequency (1/T) and delaying its opening (varying the
work cycle using Ton).
By acting on the switch with a variable frequency, but always leaving the switch closed at
the same time (fixed Ton).
By acting on the switch in a mixed way, that is, acting the same as in the latter case only
with a variable conduction time.

The most general sketch for this type of converters is the following one:

Figure:- BUCK chopper

The function of the output filter is to cut down the output intensity. The freewheeling diode
prevents any dangerous over voltages that may damage the switch, since the current in the load
circulates through it as soon as it is annulled, and there is no abrupt variation of the current in
Lout. The source possesses internal impedance Rg, and Lin and Cin constitute the input filter,
which has a double function:

Limiting the over voltages that will take place in Lg when the switch is opened.
To cut down the intensity supplied by the source, and consequently the curling of its output
voltage.

There are two ways of operation of a chopper which are given as under :
Direct conduction mode
The intensity that circulates through the load fluctuates between maximum and minimum values,
never to the point of being annulled. As it will be seen later on, it is caused by the ratio of the
period of time that the switch is closed and the time that the coil needs to discharge all its energy
previously stored. This is also called direct current regime.
Discontinuous conduction mode
The intensity for the load is annulled at a certain moment during the Toff period (time during
which the switch is opened). The time during which the switch is opened is bigger than the one

Page | - 65 -


required by the coil to give away all its energy, therefore when the following period starts the
intensity will be zero. Also called regime of discontinuous current.

To study the circuit operation, we will analyze the two states that the switch may present (opened
or closed).

when switch is closed as , as shown in figure the diode is reversed biased . switch
conducts the inductor current , this results in positive voltage across inductor.

when switch is opened , as shown in figure the current iL continues to flow. The
diode is forward biased and current now flows (free-wheeling) through the diode

Page | - 66 -


CIRCUIT DIAGRAM:-

Figure:- BUCK model

PROCEDURE:-
1. Carry out the assembly BUCK as shown in the above figure.
2. Connect the respective load to its terminal .
3. Select the following sensors.
Input Voltage (V1), Output Voltage (V2), Input Current (I1) and Output current (I2)
4. Introduce 500 Hz as frequency and 50% as duty cycle.
5. Obtain and analyze the output voltage, determine its average value and check it with
voltmeter, analyze how R variations effect the voltage
6. Obtain and analyze output current and determine its average value. Analyze how variations
of R effect the maximum and average value.

For RL Load
S. No Load Impedance Input Voltage (V1) Output Voltage (V2) V av
1. 600 +236mH
2. 600 + 472mH

Page | - 67 -


S. No Load Impedance Input Current (I1) Output Current(I2)
1. 600 +236mH
2. 600 +472mH

Figure:- Circuit Diagram of DC/DC Chopper with RL Load.

AC/DC CHOPPER option
Switch off the equipment.

Page | - 68 -


Waveforms:-

Fig: Input Voltage Fig: Output Voltage across load

Fig: Load Current Fig: Input Current

Page | - 69 -


LAB SESSION 10

OBJECT
To draw the magnetization curve of self-exited DC shunt generator (open circuit
characteristics curve O.C.C).

APPARATUS
1. Bench 10-ES/EV or Bench 14-ES/EV
2. DC multi-range ammeter
3. DC multi-range voltmeter

CIRCUIT DIAGRAM

THEORY
The magnetization characteristics, also known as No load or Open circuit
characteristics, is the relation between emf generated and field current at a given speed.

Due to residual magnetism in the poles, some emf is generated even when filed current is
zero. Hence the curve starts a little way up. It is seen that the first part of the curve is practically
straight. This is due the fact that at low flux densities reluctance of iron path is being negligible,
total reluctance is given by air gap reluctance which is constant. Hence the flux and consequently
the generated emf is directly proportional to exciting current. However at high flux densities iron

Page | - 70 -

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