Download Observation Table: - Procedure: - 1) Study the circuit given on front

Experiment No: -1
Aim: - To study and plot the characteristics of SCR
Apparatus: SCR Kit
Voltmeter (0-50V)
Ammeter (0-50mA)
Ammeter (0-500mA),
Patch Chord
Theory: SCR is a four-layered PNPN switching device having three junctions and three terminals
known as Anode, Cathode and Gate terminals. When the end P-layer is made positive with
respect to the end N-layer, the two outer junctions J1 & J3 are forward biased but the middle
layer is reversed biased. Thus the junction J2 because of the presence of depletion layer does
not allow any current to flow through the device. Only leakage current negligibly small in
magnitude flows through the device due to the drift of the mobile charges. This current is
insufficient to make the device conduct. The depletion layer mostly of immobile charges does
not conduct. This is called forward blocking state of the device. On reverse biased conduction,
J1 & J3 are reverse biased while J2 is forward biased. The junction J1 & J3 do not allow any
current to flow through the device. Only very small leakage current flows through the device.
This is known as reverse blocking state or off state of the device.
Circuit Diagram: V-I Characteristics-
Observation Table: -
Procedure: 1) Study the circuit given on front panel of kit.
2) Connect milliammeter & voltmeter in the circuit
3) Connect dc power supply in gate & A to K circuit.
4) Keeping gate current constant increase VAK in steps to note anode- cathode
current IAK , for each step till SCR fires
5) Note the value of IH by gradually decreasing the voltage VAK
6) Plot SCR characteristics between IAK & VAK.
Result: Characteristics of SCR were studied & found that SCR turned on when IA > IL &
Remained in on state until IA >IH
Experiment No: -2
Aim: - To study and plot the characteristics of MOSFET , IGBT, TRIAC
Apparatus: MOSFET Kit,
IGBT Kit,
TRIAC Kit,
Voltmeter (0-50V)
Ammeter (0-25mA)
Ammeter (0-50mA)
Ammeter (0-500mA)
Multimeter.
Patch Chord
Theory:-1.MOSFET:MOSFET is an abbreviation for metal oxide semiconductor filed transistor. Like JFET,
it has a source (S), drain(D) and gate(G). However unlike JFET, the gate of MOSFET is
insulated from channel. Because of this, MOSFET is sometimes known as IGFET
(insulated gate FET). Basically MOSFET are of two types 1) depletion type MOSFET
and 2) enhancement type MOSFET. Enhancement MOSFET has no depletion mode and
only operates in enhancement mode. It differs in construction from depletion type
MOSFET in the sense that it has no
physical channel. The min gate-source voltage (VGS), which produces inversion layer,
called as threshold voltage.
Drain characteristics for enhancement MOSFET: When VGS< (VGS) the no drain current flows. However in actual practice, and
extremely small value of drain current does flow through MOSFET. This current flow is
generally due to presence of thermally generated electron in P type substrate when value
of VGS is kept above (VGS) significant drain current flow.
Transfer characteristics of MOSFET: When VGS=0 there is no drain current, however if VGS is increased rapidly as shown
in fig. The relation gives the drain current at any instant along the curve.
Circuit Diagram: -
Transfer
Characteristics
Output characteristics
Observation
Table: -
Procedure: 1) Keep VDS say 5 V & vary VGS in steps & note down corresponding value of
drain current.
2) When keeping VGS at VGS & vary VDS in steps to note corresponding value of
drain current.
3) Then repeat for different values of constant VGS & constant VDS.
4) Plot the drain characteristics VDS, VS ID for constant value of VGS & plot the
graph for transfer characteristics where VGS VS ID is plotted keeping VDS
constant.
2.TRIAC:TRIAC is three terminal bi-directional high power devices. Conduction takes place in
both directions i.e. from MT1 to MT2 or MT2 to MT1. Gate terminal is towards MT1 in
operation TRAIC is equivalent to two SCR’s connected in anti parallel. The layer
diagram symbolic representation of TRAIC is as shown VI characteristic of SCR and
TRAIC are similar. The only difference is that VI Characteristics is symmetrical in
TRAIC.
TRAIC can be run on in four modes
I+ Mode: In this mode MT2 is positive with respect to MT1 and gate is made positive w.r.t. MT1.
I- Mode: In this mode MT2 is positive with respect to MT1 and gate is made negative w.r.t. MT1.
III+ Mode: In this mode MT2 is negative with respect to MT1 and gate is made positive w.r.t. MT1.
III- Mode: In this mode MT2 is negative with respect to MT1 and gate is made negative w.r.t.
MT1.
Circuit diagram: -
Observation Table: Forward characteristics – IG (CONSTANT) = 4, 8.
Reverse characteristics – IG (CONSTANT) = 15, 16.
Procedure:1) Connect the circuit as shown in circuit diagram.
2) Make the connections for I + mode.
3) Keep the IG constant and note down the voltmeter and ammeter reading.
4) Now make the connections in III - mode.
5) Keep IG constant and note down the voltmeter and ammeter reading.
6) Plot the graph for both the characteristics.
3.IGBT:- An IGBT Insulated Gate Bipolar Transistor combines advantages of both
BJT and MOSFET. An IGBT have high input impedance like MOSFET and low on
state conduction loses like BJT. It has three terminals namely Gate, Collector and
Emitter instead of Gate, Drain and Source as in MOSFET. The parameters and their
symbols are similar to that of MOSFET except that the subscript D and S have been
changed. The current rating of single IGBT can be up to 400A, 1200V and switching
frequency can be up to 20 KHz. An IGBT is inherently faster than a BJT. The structure
of IGBT is quite similar to MOSFET. The IGBT conducts in two modes reverse
blocking mode and forward blocking mode. If gate – emitter voltage applied is of
sufficient magnitude to surface the base region under gate, device switches to its
positive forward conduction state and current can flow from collector N-region to base
N- region.
Circuit Diagram:-
Symbol of IGBT:-
VI & transfer characteristics
\
Observation
Table:-
VCE = 5v(const..)
VGE = 5v(const..)
Procedure :1. Make connections as shown in circuit diagram.
2. Apply same positive collector to emitter voltage keeping collector at higher
potential with gate.
3. Apply gate to emitter voltage at VGE and base different values of I CE for
constant value VCE.
4. Plot graph of VGE VS I CE for constant value of V CE .
5. For dynamic characteristics, apply suitable gate to emitter voltage keeping its
constant VGE and examining the readings VCE and I CE .
6. Plot graph of VCE vs I CE.
Result: 1.The transfer & drain characteristics of power MOSFET has been plotted
2.Characteristics of TRIAC were studied and plot the graph from the reading
3.I/p &o/p characteristics of IGBT can be studied.
Experiment No:-04
Aim : To study class A commutation of a Thyristor.
Apparatus :
Commutation Circuit
Patch cords
Wires
CRO.
Theory:-
The commutation techniques are broadly classified into four types depending
upon how the device forward current is reduced to zero to turn it off.
1. Natural or Line commutation
2. Load commutation
3. External Pulse commutation
4. When Thyrister is turned off by external pulse causing reverse voltage through a
pulse transformer, the technique is called “External Pulse commutation”. This
technique is used in AC choppers.
The types are
1.Class A : Load Commutation
2.Class B : Resonant Pulse Commutation
3.Class C : Complementary Commutation
4.Class D : Auxiliary Commutation
5.Class E : External Pulse Commutation
6.Class F : AC line Commutation
Class A Commutation:
When load resistance ‘R’ is low, the elements L,C & R are connected in series.
However if ‘R’ is high, then C is connected across it and then this parallel combination
is connected in series with inductor ‘L’ and thyrister. Load in series :
Initially the thyrister is off, hence entire supply voltage ‘E’ appears across it in
forward biased. Once turned on, it acts as short circuit, thereby connecting series R-L-C
circuit across DC source. Load in parallel : When the load resistance ‘R’ is not low and
cannot form under damped series RL- C circuit then ‘R’ is connected in parallel with
‘C’. Initially ‘C’ has zero voltage when first firing pulse is applied to it, it conducts. The
capacitor acts as short circuit, hence entire supply voltage ‘E’ appears across an
inductor. The current starts to flow and capacitor charges. Capacitor charges to a voltage
greater than ‘E’. At zero current thyrister is turned off. Reversed biased is maintained as
VC > ‘E’. Once thyrister is turned off, Capacitor starts discharging through load.
Circuit Diagram :
Procedure :
1.Study the circuit provided.
2.Switch on the power supply.
3.note the output waveforms.
4.Plot the waveforms.
Result : Class A commutation technique is studied and graphs are plotted.
Experiment No :- 05
Aim:- To study the step up and step down chopper.
Apparatus:Experimental kit
Patch chord
CRO probe
Rheostat
Supply voltage
Theory:Operation of DC CHOOPER
Chopper is a switching circuits, which converts the fixed I/p dc
voltage into variable dc o/p voltage. Chopper can be used where the variable o/p dc
voltage is required .e.g.
trolley cars, buses, marine hoists, lift, electrical locomotives in which speed control &
breaking can be achieved using DC chopper.
Chopper system enables smooth control , fast response and high frequency .there are
basically of two types of chopper:a) step up chopper.
b) step down chopper.
a) Step down chopper:-In step down chopper the average o/p load voltage is less
than I/p voltage.
b) Step up chopper :-In step up chopper ,the average o/p and load voltage is more
than I/p supply voltage.
Circuit diagram:-
Procedure :1) Study the circuit diagram.
2) Make connections as shown in circuit diagram.
3) Supply a trigger pulse to the gate terminal of thyristor .
4) Switch on the DC supply .
5) Connect CRO probe to obtained the output.
6) Note the TON and TOFF time of wave form obtained on screen and plot the output
on graph paper.
Result :- DC chopper is studied and o/p waveform is plotted.
Experiment no :- 03
Aim :- To study 1-phase full wave controlled rectifier and semi controlled rectifier with
R, R-L, and R-L-E Load.
Apparatus: 1.1ФFull Bridge converter firing circuit and power circuit nits.
2.1Фa u t o t r a n s f o r m e r : 2 3 0 V / 0 - 2 7 0 V , 1 0 A
3. 1Фi s o l a t i o n t r a n s f o r m e r : 2 3 0 V / 2 3 0 V .
4.Loading inductor : 50 mH,
5.Loading Rheostat : 50 Ohms 2A.
6.DC Motor load (RLE) : 230 V, 1 hp, Field 220 V
@ 2A.
SPECIFICATIONS:
1.
2.
3.
4.
5.
6.
7.
8.
Input : 0-230V 1- phase AC supply.
Load: R,RL,RLE load.
Thyristor: 25A,1200V,type 25RIA 120.
Diodes: 25A,1200V.
MCB : two pole 230V/16A.
Fuse: 16A HRC.
Field supply Bridge rectifier: 10A, 600 V.
Field supply: 220v± 1 0 %
.
Theory: In the single phase full bridge circuit, diagonally opposite pair of thyristor are made to
conduct and are commutated simultaneously.
The advantage of single phase bridge converter
over single phase mid point converter
i ) S C R ’ s a r e s u b j e c t e d t o a p e a k i n v e r s e v o l t a g e o f 2 E m in midpointconverter K Em is fully converter – bridge converter.
i i ) I n mi d p o i n t c o n f i g u r a t i o n e a c h s e c o n d a r y s h o u l d b e a b l e t o supply the
load power. As such, the rating in mid-point converter isdouble the load-rating this
however is not the case in single phasebridge converter.
CIRCUIT DIAGRAM:
PROCEDURE:
1.Make the connection as per the circuit diagram.
2.Switch ON (SW1) the main supply to the firing circu
i t . Ensure switch SW2 in OFF position as a precaution.
Identifyd i f f e r e n t b l o c k s o f t h e t r i g g e r i n g c i r c u i t a n d d i f f e r e n t waveforms
may be observed at the test points provided onleft hand side of the panel.
3. Now ensure that the lamp load is to the twelve pin socketprovided on The front
panel of the controller and the potentiometer marked Speed Control in the minimum
position.
4. Switch ON SW2 i.e power circuit. Press the speed controlpot P1 (infectarmature
voltage control pot) slightly in the anti-clockwise direction. This turns ON the soft
start relay and output d.c voltage ismade available to the load.
5. Vary the speed control pot in smooth fashion in theclockwise direction. The
lamp intensity increases with the increase with the output voltage.
6. Connect the CRO to main supply to the isolatingtransformer at
point T P ( t e s t p o i n t ) . Yo u ma y c o n n e c t i s o l a t i n g t r a n s f o r me r provided
along with to the 5 amp 3 -pin socket located onthe right hand side panel. Do not
touch the metallic parts of the CRO. Keep CRO in minimum sensitivity position
that is about 20V per division. Now you may observe waveforms of the outputvoltage.
7.Now switch OFF SW1, SW2. Connect the twelve pin Johnsonplug into the twelve
pin socket at the centre of the front panel. Switch SW3 may be kept in NO choke
position that is almost anticlockwise position. Keep no load on the motor.
8.Switch on SW1 first and then SW2 .The motor parts rotatingat low speed. Vary the
speed control pot in smooth and
slowf a s h i o n . W e c a n g e t a s p e e d v a r i a t i o n f r o m 1 0 % t o 90%.Gentl
y increas
e the load on.
9.Observe waveform on CRO.
PRECAUTIONS:
1. Make sure all the connecting links are tightly fixed.
2.Ensure all the controlling
w i s e position before starting experiment.
knobs
in
fully
counter
clock
3. Handle everything with care.
4 . M a k e s u r e t h e f i r i n g p u l s e s a r e p r o p e r b e f o r e c o n n e c t i n g t o the
power circuit.
5.If the output is zero even after all power connection
s , s w i t c h O F F t h e M C B a n d j u s t i n t e r c h a n g e A C i n p u t connection
s to the power circuit this is to make the firingcircuit and the power circuit to
synchronize.
Result :-
Experiment No:-08
Aim: - To study the circuit of series inverter & parallel inverter.
Apparatus: - Experimental kit
Dual channel COR
Patch chords
Ammeter (0-5A)
Voltmeter (0-50V)
Diodes D1 and D2CRO dual channel multimeter
Components: Thyrister T1 and T2
Inductor L
,
Theory: -
1. Theory of series inverter:Fig shows the schematic diagram of modified series inverter. Here inductor L1 and L2
are identifies and coupled capacitor C1 and C2 are also identical. Let the initial voltage
across capacitor C2 be EC, with the polarity as shown lower plate positive. Then
capacitor C1 will be charged to voltage (VDC+Ec) in the opposite direction.
When SCR1 is fired, and then will be tow parallel paths for load current i2 current i1
will flow from the positive DC terminal through SCR1-L1-load-capacitor C2 to the
negative terminal of supply current i2 will flow from C1, through SCR1-L1-Load. The
driving voltage (VDC+Ec) the circuit elements. The initial condition is identical for
both those paths. Therefore the two current s will be equal hence one half of the load
current will come from the DC supply and other half form the discharge of the capacitor
at the end of the half cycle. When the load current becomes zero, SCR1 will be turn off
and the voltage across the capacitor reversed.
In the steady state capacitor C2 will be charged to voltage (VDC+Ec) in the opposite
direction and capacitor C1 To E2. Identical operation will take place in the following
negative half cycle whenSCR2 is triggered. Then one half of the load current will
supply form the input and other half from the discharge of capacitor C2.
2.Theory of parallel inverter:The process of converting DC into AC is known as inverting. In other words we can
define it as reverse process of rectification .the device, which performs this process, is
called as inverter. The basic principle of inverter can be explained with the help of
simple circuit shown in figure. Here we have used SCR for switching due to high
current of the circuit according to the connection of thyrister and commutating
components the device may be classified into three groups. All the basic commutation
components are L & C. The capacitor is connected in parallel with the load therefore it
is called as parallel inverter. The parallel inverter consists of two feedback diodes D1 &
D2. The function of this feedback diode is that they feedbacks the reactive power i.e. the
energy stored by the commutation capacitor C, L and load induction back to DC supply.
Circuit diagram:-
Circuit diagram for Series Inverter:-
Circuit diagram for Parallel Inverter:-
Procedure: 1. Connect the circuit as shown in figure.
2. Make the connection with the help of patch cords on series inverter experimental
kit.
3. Give DC input to the series inverter.
4. Observe the waveforms on dual channel CRO by connecting on output of series
inverter to the CRO.
5. The output of series inverter is AC, is noted carefully.
6. Measure the output F and A.
7. Plot the graph.
Result:- 1.Modified series inverter has been studied successfully.
Input amplitude=
Output amplitude=
Time period=
Frequency=
Experiment No:-07
Aim: - To study 1-phase cycloconverter.
Apparatus:1.1Фcyclo - converter firing circuit and power circuit units.
2.1Ф230 V /230 V -0-230 V center- tapped transformer.
3.1Ф230 V / 0-270Vauto transformer.
4. Loading Rheostat: 50 Ohms, 2 A.
5. Loading inductor;50mh,2A.
6. 20MHz dual trace oscilloscope with 1:10BNC probs.
SPECIFICATIONS:
1. Input: 0-230V 1- ФAC supply.
2. Load: 15A.
3. Thayristor: 25A,1200V type 25RIA 120
4.MCB: two pole 230 V /16A.
THEORY:
In a single phase cyclo - converter employing a center tapped transformer
has four thyristers, namely T1,T2, T3, T4 Out of four SCR’s,SCR’s,T1,T2 are
responsible
for
generating
there
positive
halves
forming
t h e p o s i t i v e g r o u p . Th e o t h e r t wo S C R ’s T3&T4are responsible forp r o d
u c i n g n e g a t i v e h a l v e s f o r m i n g t h e n e g a t i v e g r o u p . T h i s configur
ation is meant for generating 1/3 of the input frequency i.e thisgenerates a frequency of
16 2/3 Hz at its output.Depending upon the polarities of the transformer, SCR’S are
gated.Natural commutation process is used for turning off the SCR’S.the circuit
configuration is analyzed for purely resistive load.
CIRCUIT DIAGRAM:
PROCEDURE:
1.Switch ON the main supply to the firing circuit and
p o w e r circuit. Observe the trigger outputs by changing frequencydivision push
buttons
and
varying
the
firing
angle
controlk n o b . M a k e s u r e t h e f i r i n g p u l s e s a r e p r o p e r b e f o r e connecting
to the power circuit.
2. Make the connections as per the circuit diagram.
3 . C o n n e c t f i r i n g p u l s e s f r o m t h e f i r i n g c i r c u i t t o t h e respective
SCRs in the power circuit.
4. Initially connect the input terminals to the 30V- 0 -30Vterminals of the
center tapped transformer.
5.Set the frequency division to 2. Switch ON the trigg
e r pulses. And switch ON the MCB.
6.Vary the firing angle potentiometer and observe t
h e voltage wave forms across load using oscilloscope.
7.Note down the reading in the tabular column.
8 . A f t e r e n s u r i n g c o r r e c t o u t p u t a t l o w v o l t a g e , i n c r e a s e t h e input
voltage to 230V-0-230V in steps and note down thecorresponding readings.
9.Follow the above procedure for frequency divisions 3 to
9.
1 0 . D r a w t h e w a v e f o r m s i n t h e g r a p h a t f i r i n g a n g l e s 0 o, 45 o,90o,
135oand 180o.
TABULAR COLUMN:
S.No.
Input
voltage(V)
Frequency
division
EXPECTED WAVE FORMS:
RESULTS :-
FiringAngle(o) Output
vloltage
(V)
Output
current(I)