P E Lab final

8/9/2019 P E Lab final

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1. (a) CHARACTERISTICS OF SCR

AIM:

To plot the characteristics of an SCR and also find the forwardresistance, holding current and latching current.

APPARATUS REQUIRED:

1. Characteristics study unit

2. 0- 50V DC Voltmeter

3. 0-500 mA DC Ammeter

4. 0-25mA DC ammeter

THEORY:

SCR stands for silicon controlled rectifier which is a PNPN 4 layerdevice. It is a unidirectional element and whose conduction can becontrolled by the gate triggering. The forward characteristics areplotted between VAK and IA at different gate currents. The breakdownoccurs at a relatively lower voltage as the gate current increases.

CIRCUIT DIAGRAM:


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PROCEDURE:

1. V-I Characteristics:

1. Make the connections as given in the circuit diagram including

meters.

2. Now switch ON the main supply to the unit and initially keep V1& V2 at minimum. Set load potentiometer R1 in the minimum

position.

3. Adjust IG-IG1 say 10 mA by varying V2 or gate current

potentiometer R2. Slowly vary V1 and note down VAK and 1A

readings for every 5V and enter the readings in the tabular

column.

4. Further vary V1 till SCR conducts. This can be noticed by

sudden drop of VAK and rise of 1A readings note down this

reading and tabulated.

5. Vary V1 further and note down 1A and VAK readings.

6. Draw the graph of VAKV/S 1A.

7. Repeat the same for IG = IG2/IG3 mA and the graph

2. To find VG/IG:

1. Set V2 to zero adjust VAKto V1- 10 Volts.

2. Connect voltmeter between VAK points slowly increase V2 till

SCR conducts.

3. Note down the corresponding IG&VAKvalues.

4. Repeat the procedure 2-3 times to accurately get the VG and IG

values.


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3.To

find latching current:

1. Apply about 20 V between Anode and Cathode by varying V1.

Keep the load potentiometer R1 at minimum position.

2. The device must be in the OFF state with Gate open.

3. Gradually increase Gate voltage V2 till the device turns ON.

4. This is the minimum Gate current (ig minimum) required to turn

ON the device.

5. Adjust the Gate voltage to a slightly higher. Set the load

potentiometer at the maximum resistance position. The device

should come to OFF state.

6. Otherwise decrease V1 till the device comes to OFF state. The

Gate voltage should be kept constant in this experiment.

7. By varying R1, gradually increase anode current 1A in steps open

and close the Gate voltage V2 switch after each step.

8. If the anode current is greater than the latching current of the

devise the device says ON even after the Gate switch is opened.9. Otherwise the devise goes in to blocking mode as soon as the

Gate switch is opened. Note the latching current obtain more

accurate value of the latching current by taking small steps of 1A

near the latching current values.

IG2(mA)

VAK (volts) IA(mA)

IG1 (mA)

VAK(volts) IA(mA)


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10. Increase the anode current from the latching current level by

load pot R1 or V1. Open the Gate switch permanently. The

thyristor must be fully ON.

11. Now start reducing the anode current gradually by adjusting R1.

If the thyristor does not turns OFF even after the R1 at maximum

position.

12.Then reduce V1 observe when the device goes to blocking mode.

The anode current through the devise at this instant is the

holding current of the device.

13. Repeat the steps again to accurately get the Ihnormally Ih


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RESULT:

The brake over voltages = Vb1 = ------------------

= Vb2 = ------------------

Latching current = ----------------------

Holding current = -----------------------

Forward resistance Rf = VAK/ IA==------------------------

VIVA VOCE:

1) Draw the characteristics of SCR.

2) Define holding current.

3) Define latching current.

4) What is meant by forward resistance?


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1. (b) CHARACTERISTICS OF MOSFET

AIM:To plot the input and transfer characteristics of MOSFET and to

find ON state resistance and Transconductance.

APPARATUS REQUIRED:


2. 0-50 volts DC voltmeter



THEORY:

A power MOSFET is voltage controlled device and requires only a

small input current. The switching N speed is very high and a switching

time is of order of nanoseconds. They are finding increasing application

in low power high frequency converters. MOSFETS have the problem of


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second break down phenomenon as do BJTS. However, MOSFET have

the problems of electrostatic discharge and require special care in

handling MOSFETS are of two types (1) Depletion MOSFETS (2)

Enhancement MOSFETS. Let us discuss n-channel depletion type

MOSFET type MOSFET, which is formed on a P-type silicon subtract,

with two heavily doped n silicon for low resistance connections. The

gate is isolated from the channel by thin oxide layer. If will have they

terminal gate, drain and source. The substrate is normally connected

to source.

The gate to source voltage VGS could be either + ve or ve. If VGS

is negative, some of the electrons in n- channel area will be repelled

and a depletion region will be created below the oxide layer, resulting

is a narrower effective channel and high resistance from the drain to

source, RDs

If VGSmade Ve high, the channel will be completely depleted,

offering a high value of RDS, and there will be no current flow from the

drain to source, Ids = 0,

The value of VGS is made +ve, the channel is called pinch off

voltage, Vp. On the other hand, VGS is made + ve, the channel

becomes wider and a DS increase due to reduction is Rds this is liner

region. In this region, the MOSFET operates as a switch with drain

current proportional to drain voltage. This is operative for low drain

voltage and high drain current. In pinch off or saturate region, the

device operate as an amplifier having very high current gain which is

the ratio or drain current to gate current . ID is independent of VD. Tranconductance, defined as the ratio of drain current to gate voltage ,

signifies the transfer capabilities of the device.

The output characteristic of a MOSFET is plot of drain current as

a function of drain source voltage, gate to source voltage is the


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parameter. In the cut off region, the gate voltage is less then the

threshold voltage. The device is in the non conducting state.

i) Cut off region VGS


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PROCEDURE:

Transfer characteristics:

1. Make the connections as shown in the circuit diagram with

meters initially keep V1 and V2 zero. Set V1 = VDS1 = say 10v.

2. Slowly vary V2 (VGS) and note down ID and VGS readings for every

0.5 volts enter in the tabular column.

3. The minimum Gate voltage VGS that is required for conduction to

start in the MOSFET is called threshold voltage VGS

is greaterthan VGS (Th).

4. If VGS is greater than VGS (Th) the drain current depends on

magnitude of the Gate voltage VGS varies from 2 to 5 volts.

5. Repeat the same for different values of VDS and draw the graph

of ID/VGS.

TABULAR COLUMN:

VDS1 (volts) 10V VDS2(volts)VGS (volts) ID (mA) VGS (volts) ID(mA)


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DRAIN CHARACTERISTICS:

Initially set V2 to VGS 1 = 3.5 volts. Slowly vary V1 and note down

ID and VDS. For a particular value of VGS1 there is a pinch off voltage

(Vp) between drain and source as shown in figure.

If VDS is lower than VP. The device works in the constant resistanceregion and ID is directly proportional to VDS if VDS is more than Vp.

Constant ID flows from the device and this operating region is called

constant current region.

Repeat the above for different values of VGS and note down ID v/s

VDS

Draw the graph of ID v/s VDS for different values of VGS.

TABULAR COLUMN:

VGS1 (volts) 10V VGS1 (volts)

VDS (volts) ID(mA) VDS (volts) ID(mA)

RESULT:

1. Rd= Vds/ Id =.

2. Gm = ID/VDS =.

VIVA VOCE:

1) Difference between MOSFET and SCR.

2) Draw transfer characteristics of MOSFET.

3) Write the formula for ON resistance and Transconductance.


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Expected Graph:


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1. (c) CHARACTERISTICS OF IGBT

AIM:

To plot the static characteristics of IGBT

APPARATUS REQUIRED:





THEORY:

IGBT combines the advantages of BJT and MOSFETS. If has ahigh input impedance like MOSFETS and low on state conduction

losses, like BJTS. But there is no second break down problem, like BJTS

The device has three terminals gate, collector an emitter instead

of gate , drain source for MOSFETS the output characteristics of IGBT is

the plot between the collector current Ic and collector to emitter

voltage VCE for various values of gate - emitter voltage VCE. The Ic

starts flowing beyond a particular gate voltage is called voltage.Device Power capability Switching speed

BJT Medium Medium

MOSFET Low Fast

GTO High SlowIGBT Medium Medium

MCT Medium Medium

CIRCUIT DIAGRAM:


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PROCEDURE:

Transfer characteristics:

1. Make the connections as shown in the circuit diagram with

meters initially keep V1 and V2 zero. Set V1 = VCE1 = say 10v.

2. Slowly vary V2 (VGE) and note down IC and VGE readings for every

0.5 volts and enter in the tabular column.

3. The minimum Gate voltage VGE which is required for conduction

to start in the IGBT is called Threshold voltage VGE is less than

VGE (Th).

4. If VGE is less than VGE (Th) only very small leakage current flows

from collector to Emitter.

5. If VGE is greater than VGE (Th) the collector current depends on

magnitude of the Gate voltage VGE varies from 5- to 6 volts.

6. Repeat the same for different values of VDS and draw the graph

of ID/VGS.

TABULAR COLUMN:

VGE1 (volts) VGE2(volts)VCE (volts) IE (Ma) VCE (volts) IE (mA)


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COLLECTOR CHARACTERISTICS:

Initially set V2 to VGE1 = 5 volts. Slowly vary V1 and note down ICand VGE. For a particular value of VGE1 there is a pinch off voltage (Vp)

between collector and Emitter as shown in figure.

If VGE is lower than VP the device works in the constant

resistance region and IC is directly proportional to VGE if VGE is more

than Vp. Constant IC flows from the device and this operating region is

called constant current region.

Repeat the above for different values of VGE and note down IC and VGE

values.

Draw the graph of IC Vs VGE for different values of VGE

TABULAR COLUMN:

VGE1 (volts) VGE2 (volts)

VCE(volts)

IC (mA)VCE

(volts)IC (mA)

EXPECTED WAVE FORMS:


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RESULT:

VIVAVOCE:

1) Difference between IGBT, MOSFET, and SCR.2) What is meant by the word called static?3) Explain switching speed of IGBT more or less compared to SCR.


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2. GATE TRIGGERING CIRCUITS

AIM:

To study various firing schemes for triggering SCRs when theyare used in different converter topologies employ line commutation.

1. Resistance firing circuit.

2. Resistance capacitance (RC) firing circuit.

3. UJT firing scheme.

APPARATUS REQUIRED:

1. R, RC triggering module and UJT triggering module.

2. Resistive load.

3. 20 MHz dual trace oscilloscope with 1:10 BNC probes.

SPECIFICATIONS:

1. SCRs : 400V, 4A, type 106 D

2. Diodes : 1N4007


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3. Diacs : D3202 U

4. Zeners : 20 V, 1W

5. UJTs : 2N2646

6. NPN Transistors : BC 107

7. PNP Transistors : BC 177

8. Pulse transformers : 1:1:1

THEORY:

This is the most commonly used method for triggering SCRs. In

laboratories almost all the SCR devices are triggered by this process.

By applying the positive signal at the gate terminal of the device, it

can be triggered much before the specified break over voltage.

The conduction period of the SCR can be controlled by varying

the gate signal within specified values of the maximum and minimum

gate currents.

CIRCUIT DIAGRAM:

PROCEDURE:


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1. Make the connections as per the circuit diagram.

2. Vary the control pot and observe the voltage wave

forms across load, SCR and at different points in the

circuit, using oscilloscope.

3. Draw the wave forms in the graph at firing angles

0o,45o, 90o, 135oand 180o.

TABULAR COLUMN:

S.NO Resistance () Firing angle (o)

PRECAUTIONS:

1. Make sure all the connections are tight.

2. Ensure all the controlling knobs are kept in fully counter

clock wise position before starting experiment.

3. Handle every thing with care



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RESULT:

VIVA VOCE:

1) What is meant by triggering?2) Why we need to employ different triggering circuit to trigger

SCR?3) What is the use of UJT in UJT triggering circuits?4) What happens when BJT is used instead of UJT in UJT triggering

circuit?


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3. SINGLE PHASE CYCLO - CONVERTER

AIM:

To study the module and wave forms of a 1 center tapped cyclo

- converter with R and RL loads.

APPARATUS REQUIRED:

1. 1 cyclo - converter firing circuit and power circuit units.

2. 1 230 V /230 V -0-230 V center- tapped transformer.

3. 1 230 V / 0-270 V auto transformer.

4. Loading Rheostat: 50 Ohms, 2 A..5. Loading inductor; 50 mH, 2 A.


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SPECIFICATIONS:

1. Input : 0-230 V 1- AC supply.

2. Load : 15 A

3. Thyristor : 25 A, 1200 V, type 25 RIA 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 SCRs,

SCRs,T1,T2 are responsible for generating there positive halves forming

the positive group. The other two SCRs T3&T4 are responsible for

producing negative halves forming the negative group. This

configuration is meant for generating 1/3 of the input frequency i.e this

generates a frequency of 16 2/3 Hz at its output.

Depending upon the polarities of the transformer, SCRS are gated.

Natural commutation process is used for turning off the SCRS.

the circuit configuration is analyzed for purely resistive load.

CIRCUIT DIAGRAM:


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PROCEDURE:

1. Switch ON the main supply to the firing circuit and power

circuit. Observe the trigger outputs by changing frequency

division push buttons and varying the firing angle control

knob. Make sure the firing pulses are proper before

connecting to the power circuit.


3. Connect firing pulses from the firing circuit to the

respective SCRs in the power circuit.

4. Initially connect the input terminals to the 30V- 0 -30V

terminals of the center tapped transformer.

5. Set the frequency division to 2. Switch ON the trigger

pulses. And switch ON the MCB.

6. Vary the firing angle potentiometer and observe the

voltage wave forms across load using oscilloscope.

7. Note down the reading in the tabular column.

8. After ensuring correct output at low voltage, increase the

input voltage to 230V-0-230V in steps and note down the

corresponding readings.

9. Follow the above procedure for frequency divisions 3 to 9.


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10. Draw the wave forms in the graph at firing angles 0o, 45o,

90o, 135oand 180o..

TABULAR COLUMN:

S.NO. Inputvoltage(V)

Frequency

divisions

Firingangle

(o)

Outputvoltage

(V)

Outputcurrent

(A)

PRECAUTIONS:

1. Make sure all the connecting links are tightly fixed.

2. Ensure all the controlling knobs in fully counter clock wise

position before starting experiment.

3. Handle everything with care.

4. Change the frequency divisions only when the trigger pulse

switches at OFF position.

5. Make sure the firing pulses are proper before connecting to

the power circuit.

6. If the out put is zero even after all power connections,

switch OFF the MCB and adjust interchange AC input

connections to the power circuit. This is to make the firing

circuit and power circuit to synchronize.



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RESULTS:

VIVA VOCE:

1) Define cyclo converter?

2) Which commutation process is used in cyclo converters?

3) Applications of cyclo converters?


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4. SINGLE PHASE FULLY CONTROLLED BRIDGECONVERTER

AIM:

To study the module and waveforms of a 1 Full Bridge

converter with R, RL and RLE loads.

SPECIFICATIONS:

1. Input : 0 -230 V 1- phase AC supply

2. Load : R RL and RLE load

3. Thyristor : 25A, 1200V, type 25 RIA 120.4. Diodes : 25A 1200V.

5. MCB : Two pole 230 V/16A.

6. Fuses : 16A HRC.

7. Field supply Bridge rectifier: 10A, 600 V.

8. Field supply : 220 V 10 %

APPARATUS REQUIRED:

1. 1 Full Bridge converter firing circuit and power circuit

units.

2. 1 auto transformer : 230V/0-270V, 10A

3. 1 isolation transformer : 230V/230V.

4. Loading inductor : 50 mH,

5. Loading Rheostat : 50 Ohms 2A.

6. DC Motor load (RLE) : 230 V, 1 hp, Field 220 V @ 2A.

7. Volt meter : 0 300 V, MI.

8. Shunt : 0.1 Ohm, 5W.



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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 is

i) SCRs are subjected to a peak inverse voltage of 2Em in mid-point

converter K Em is fully converter bridge converter.

ii) In midpoint configuration each secondary should be able to

supply the load power. As such, the rating in mid-point converter is

double the load-rating this however is not the case in single phase

bridge converter.


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PROCEDURE:

1. Make the connection as per the circuit diagram.

2. Switch ON (SW1) the main supply to the firing circuit.

Ensure switch SW2 in OFF position as a precaution. Identify

different blocks of the triggering circuit and different

waveforms may be observed at the test points provided on

left hand side of the panel.

3. Now ensure that the lamp load is to the twelve pin socket

provided on

The front panel of the controller and the potentiometer

marked SPEED CONTROL is in minimum position.

4. Switch ON SW2 i.e power circuit. Press the speed control

pot P1 (infect

armature voltage control pot) slightly in the anti-

clockwise direction.

This turns ON the soft start relay and output d.c voltage is

made available to the load.

5. Vary the speed control pot in smooth fashion in the

clockwise direction.

The lamp intensity increases with the increase with the

output voltage.

6. Connect the CRO to main supply to the isolating

transformer at point

TP (test point).You may connect isolating transformer

provided along with to the 5 amp 3-pin socket located on

the right hand side panel. Do not touch the metallic parts of

the CRO. Keep CRO in minimum sensitivity position that is


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about 20V per division. Now you may observe waveforms of

the output voltage.

7. Now switch OFF SW1, SW2. Connect the twelve pin Johnson

plug into the twelve pin socket at the centre of the front

panel. Switch SW3 may be kept in NO choke position that is

most anticlockwise position (this is very much important

and it should be always checked before switching

SW2).Keep no load on the motor.

8. Switch on SW1 first and then SW2 .The motor parts rotating

at low speed. Vary the speed control pot in smooth and slow

fashion. We can get a speed variation from 10% to

90%.Gently increase the load on.

9. Observe waveform on CRO.

TABULAR COLUMN:

S.NO. Inputvoltage(v)

Firing angle(o)

Outputvoltage(V)

Outputcurrent (A)

PRECAUTIONS:


2. Ensure all the controlling knobs in fully counter clock wise

position before starting experiment.


4. Make sure the firing pulses are proper before connecting to

the power circuit.


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5. If the output is zero even after all power connections,

switch OFF the MCB and just interchange AC input

connections to the power circuit this is to make the firing

circuit and the power circuit to synchronize.

RESULTS:

VIVA VOCE:

1) What is meant by phase controlled rectifier?2) In which quadrants we can operate this converter?3) What are the advantages of fully controlled converter compared

to semi controlled converter?

Expected Waveforms


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5. SINGLE PHASE PARALLEL INVERTER

AIM:

To study module and waveforms of a 1- parallel inverter

power circuit with R and RL loads.

SPECIFICATIONS:

1. Input : 230V, 50Hz, 1- AC supply

2. Load : Rand RL

3. Thyristors : 10 A, 600V.

4. Diodes : 10A, 600V.

5. Capacitor : 6.8 f, 100V.

6. Inductor : 300 H, 2A.

7. Fuses : 2A Glass fuse

APPARATUS REQUIRED:


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1. 1- parallel inverter firing circuit and power circuit unit

2. Inductor : 300mH, 2A.

3. Capacitor : 6.8 f, 100V.

4. Output transformer : Primary - 30V-25V-0-

25V-30V

Secondary- 0-30V2A

5. Loading Rheostat : 50 Ohms 2 A.

6. Loading Inductor : 50 mH, 2A

7. 20 MHz dual trace oscilloscope with 1:10 BNC probes

THEORY:

A Parallel inverter is used top produce a square wave from a

DC source is connected in alternative sense to the two halves of the

transformer primary, there by inducing a square wave voltage

across the load in the transformer secondary.

In this inverter, the commutating capacitor comes in parallel

with the load during the operation of the inverter and hence this

inverter is called as a parallel inverter. The capacitor in the given

figure is required for commutation, but as the capacitor is

effectively in parallel with the load via the transformer, an inductor

L is required in series with the DC source to prevent the instant

discharge of capacitor C via the source when thyristor switching

occurs.

CIRCUIT DIAGRAM:


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PROCEDURE:

1. Switch ON the main supply to the firing circuit. Observe

the trigger outputs in the firing circuit by varying frequency

potentiometer and by operating ON/OFF switch. Make sure the firing

pulses are proper before connecting to the power circuit.


3. Connect the firing pulses from the firing circuit to the


4. Connect the DC input from 30V, 2A regulated power

supply.

5. Switch ON the DC supply, set input voltage to 15 V and

switch ON the trigger pulses by operating ON/OFF/ switch in the

firing circuit.

6. Observe the voltage waveform across load using

oscilloscope.

7. Vary the frequency, load and observe the voltage

waveform across load with and with out freewheeling diode.8. Draw the waveforms in the graph at different

frequencies.

9. To switch OFF the inverter, switch OFF the input supply

first and then trigger pulses.


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10. Since the parallel inverter works on forced

commutation, there is a chance of failure. If the commutation fails,

switch OFF the DC supply and then trigger outputs. Check the

connections and try again.

PRECAUTIONS:


2. Ensure all the controlling knobs in fully counter clock

wise position before starting experiment.


4. Make sure the firing pulses are proper before


5. Make sure to connect firing pulses from the firing circuit

to their respective SCRs in the power circuit.

6. Ensure switch OFF the input supply first and then trigger

pulses to avoid short circuit.



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RESULT:

VIVA VOCE:

1) Define inverter.2) Explain different types of inverters.

3) Difference between inverter and converter.


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6. FORCED COMMUTATION CIRCUITS

AIM:

To study the module and waveforms of forced commutation

circuits.

1. Class A commutation Self commutation by resonating load

2. Class B commutation self commutation by IC circuit

3. Class C commutation Complementary commutation.

4. Class D commutation Auxiliary commutation.

5. Class E commutation External commutation.

APPARATUS REQUIRED:

1. Forced commutation unit.

2.

3. Loading Rheostat : 50 Ohms, 2A.

4. Regulated power supply : 0-30VDC, 2A.


SPECIFICATIONS:

1. Thyristors : TYN 612.

2. Diodes : BYQ 28-200

3. Transistor : TIP 122.

4. Capacitor : C1= 6.8 f , 100V C2= 10 f , 100V

6. Inductor : L1=250 H, 2A. L2=500 H, 2A.L3 =

1m H.

7. Fuses : 2A Glass fuse

THEORY:

i). Class A- self commutation by resonating load:

This is also known as resonant commutation. This type of

commutation circuit using L - C components in series with load.


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In this process of commutation, the forward current passing

through the device is reduced to less then the level of holding

current of the device. Hence this method is also known as the

current commutation method.

ii). Class B- self commutating by an LC circuit:

In this method, the LC resonating circuit is across the SCR and

not in series with the load.

Initially as soon as the supply voltage Edc is applied, the

capacitor C starts getting charged with its upper plate positive and

lower plate negative, and it charges up to the voltage Edc.

When thyristor T is triggered, the circuit current flows in two

directions:

i) the load current IL flows through the path Edc+ T-RL-Edc-

ii) Commutating current Ic.

iii) Class D auxiliary commutation:

In this commutation method, an auxiliary thyristor is required

to commutate the main thyristor (T1), assuming ideal thyristor andthe lossless components; here inductor L is necessary to ensure the

correct polarity on capacitor C.

Thyristor T1 and load resistor RL from the power circuit, Where

as LDK T2 from the commutation circuit.

iv) Class E External pulse commutation:

In this type of commutation method, the reverse voltage is

applied to the current carrying thyristor from an external pulse

source.

Here, the commutating pulse is applied through a pulse

transformer which is suitably designed to have tight coupling

between the primary and secondary


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This type of commutation method is capable of very high

efficiency as minimum energy is required and both time ratio and

pulse width regulation are easily incorporated.

CIRCUIT DIAGRAM:


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PROCEDURE:

1. Switch ON the mains supply to the firing circuit. Observe the trigger

outputs in the firing circuit by varying frequency potentiometer and

duty cycle potentiometer. Make sure the firing pulses are proper

before connecting to the power circuit.

2. Check the DC power supply between the DC input

points.

3. Check the resistance between anode and cathode

of all SCRs.4. Check the resistance between the Gate and

cathode of SCRs.

5. Check the diode and Transistor and their

polarities.

6. Check the fuse in series with the DC input.

7. Make sure that all the components are good and

firimg pulses are correct before starting the experiment.

CLASS A&B:


2. Connect the trigger output T1 from the firing circuit

to the Gate and cathode of SCR T1.


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3. Switch ON the DC supply and switch ON the trigger

pulses by operating ON/OFF switch in the firing circuit

4. Observe the voltage waveform across load using

oscilloscope by varying the frequency potentiometer. Duty cycle

potentiometer is of no use in this experiment.

5. Repeat the same for different values of R, L and C.

6. Draw the waveforms in the Graph for different R, L

and C.

CLASS C:2. Make the connections as per the circuit diagram.

3. Connect the trigger output T1 &T2 from the firing

circuit to the Gate and cathode of SCR T1 &T2.

4. Switch ON the DC supply and switch ON the trigger

pulses by operating ON/OFF switch in the firing circuit.

5. Observe the voltage waveform across R1, R2 and C

using oscilloscope by varying the frequency and duty cycle

potentiometers.

6. Repeat the same for different values of R & C.

7. L is of no use in this circuit.

8. Draw the waveforms in the graph for different R & C.CLASS D:


2. Connect the trigger outputs T1 and T2 from the firing

circuit to gate and cathode of SCRs T1 & T2.

3. Initially keep the trigger ON/OFF switch at OFF

position to charge the capacitor. This can be observed by

connecting CRO across the capacitor.4. Switch ON the DC supply and switch ON the trigger


5. Observe and note down the voltage waveform across

the load. T1, T2 and C using oscilloscope by varying the frequency

and duty cycle potentiometers.


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6. Repeat the same for different values of load. L & C.

CLASS E:


2. Connect V2 supply from an external DC power supply

unit.3. Connect the trigger output T1 from the firing circuit

to gate and cathode of SCR T1.

4. Connect T2 to the transistor base and emitter points.

5. Switch ON the DC supply, external DC supply and the

trigger pulses by operating ON/OFF switch in the firing circuit.

6. Observe and note down the voltage waveform across

the load.7. Repeat the same by varying the frequency and duty

cycle potentiometers.

8. Draw the waveforms in the graph for different

frequency and duty cycle.

PRECAUTIONS:


2. Ensure all the controlling knobs in fully counter clockwise position before starting experiment.




5. Make sure to connect firing pulses from the firing

circuit to their respective SCRs in the power circuit.

6. Ensure switch OFF the input supply first and then

trigger pulses to avoid short circuit.


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RESULT:

VIVA VOCE:

What is meant by commutation?Generally how to turn off a SCR?Generally how to turn on a SCR?


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7. DC JONES CHOPPER

AIM:

To study the module and waveforms of a DC Junes chopper

power circuit with R, RL loads.

APPARATUS REQUIRED:

1. Jones chopper firing circuit unit and power circuit

unit

2. Loading Rheostat : 50 Ohms, 2A.

3. Loading Inductor : 50 mH,

4. DC motor load (RLE) : 220V, 1hp, Field 220V,

@2A

5. 20MHz dual trace oscilloscope with 1:10 BNC

probes.

SPECIFICATIONS:

1.Input : 0 -230V 1- AC supply.

2. Load : R, RL and RLE loads.

3. Thyristor : 25A, 1200V, type 25 RIA 120.

4. Diodes : 25A, 1200V.

5. Communicating capacitors : 25 f, 440 V.

6. Commutating Inductor : 500 0 - 500 H, 10A.

7. MCB : Two pole 230V/16A.

8. Fuses : 16A HRC.

THEORY:

This chopper circuit is an example of class D commutation. In thecircuit, SCR T1 is the main thyristor where as SCR T2 is the auxiliarythyristor. The special feature of this circuit is the tappedautotransformer. If the main thyristor T1 is on for a long period thenthe motor will reach the maximum steady state speed determinedby the battery voltage, the motor, and the mechanical load


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characteristics. If the thyristor T1 is off, the motor will not rotate.Now, if thyristor T1 is alternatively on and off in a cyclic manner, themotor will rotate at some speed between maximum and zero.

CIRCUIT DIAGRAM:

PROCEDURE:

1. Switch ON the mains supply to the firing circuit. Observe

the trigger outputs by varying duty cycle and frequency

potentiometer by keeping the control switch in `INT` position. Make

sure the firing pulses are proper before connecting to the power

circuit.


3. Connect firing pulses from the firing circuit to the


4. Initially set the input DC supply to 5V.

5. At the beginning, keep the ON/OFF switch in the firing

circuit in OFF position.


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6. Switch ON the DC supply and now switch ON the trigger


7. Observe the DC chopped voltage waveform across load

using oscilloscope.

8. If the commutation fails, pure DC voltage can be observed

across the load; then switch OFF the DC supply and trigger pulses,

Check the connections and try again.

9. Observe the voltage waveforms across load, capacitor,

main, SCR and auxiliary SCR by varying the duty-cycle

potentiometer and frequency potentiometer, using oscilloscope.

10. Now, vary the DC supply up to the rated voltage, 30VDC.

11. Note down the readings in the tabular column.

12. Draw the waveforms in the graph at different duty cycle

and at different frequency.

PRECAUTIONS:


2. Ensure all the controlling knobs in fully counter clock

wise position before starting experiment.




5. Make sure to connect firing pulses from the firing

circuit to their respective SCRs in the power circuit.

TABULAR COLUMN:


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EXPECTED WAVEFORMS:

S.NO

Inputvoltage(V)

Ton(s)

Toff(s)

Dutycycle (%)

Outputvoltage

(V)

Outputcurrent

(A)


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RESULT:

VIVA VOCE:

Define chopper.

Types of choppers.Explain the operation of DC Jones chopper.


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8. SINGLE PHASE HALF CONTROLLED BRIDGE

CONVERTER

AIM:

To study the module and waveforms of a 1 Half Bridge

converter with R, RL and RLE loads.

APPARATUS REQUIRED:

1. 1 Half Bridge converter firing circuit and power circuit

units.

2. 1 auto transformer : 230V/0-270V, 10A

3. 1 isolation transformer : 230V/230V.

4. Loading inductor : 50 mH,

5. Loading Rheostat : 50 Ohms 2A.

6. DC Motor load (RLE) : 230 V, 1 hp, Field 220 V @ 2A.

7. Volt meter : 0 300 V, MI.

8. Shunt : 0.1 Ohm, 5W.


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Specifications:

1. Input : 0 -230 V 1- phase AC supply

2. Load : R RL and RLE load

3. Thyristor : 25A, 1200V, type 25 RIA 120.

4. Diodes : 25A 1200V.

5. MCB : Two pole 230 V/16A.

6. Fuses : 16A HRC.

7. Field supply Bridge rectifier: 10A, 600 V.

8. Field supply : 220 V 10 %

THEORY:

The phase controlled converter circuit are capable of operating withboth positive and negative mean voltages at the dc terminals, manyapplications actually require operation only with a positive voltage,that is only in the rectifying mode. In such cases it is generallyadvantageous to connect uncontrolled diodes into certain parts of thecircuits. When one pair of SCRs is replaced by diodes in single phasefully controlled bridge circuit, the resultant circuit obtained is called asa half controlled bridge circuit.PROCEDURE:


2. Ensure Switch SW2 in the off position. Plug in the supply

and withSW1 on. Observe the trigger outputs by varying

firing angle potentiometer. Use CRO through an isolating

transformer.

3. Keep the speed control knob in the minimum position.

Ensure that a lamp bank is connected to the front side of

the panel in the 12 pin socket. Switch on SW2, keep SW3 in

NO CHOKE position. (upward position).

4. Vary the speed control pot in smooth and gentle fashion to

observe variation in the lamp intensity. This completes

initial testing of the system.


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5. To observe the wave forms at the attenuated test point,

connect a CRO through an isolating transformer as a

source of its supply. Observe poarity.

6. Now switch off the power circuit of the unit and connect

the 12-pin Johnson plug in the socket on the front panel

provided along with the DC motor.( Motor is optional with

the system). Ensure pot P1 is in most anticlockwise

position. Now keep SW3 in upward position. Switch on the

power circuit (SW2 ON). Increase speed of the motor in

gentle fashion. Observe the effect of load change on the

output voltage. Apply load in a very slow fashion. Do not

put load in a jerky manner.

7. Now reduce the speed to minimum level and switch on

SW3. Ensure motor load is about 1.5A. Start increasing of

the load in a smooth fashion and note down the effect of

load variation on the output voltage and speed motor also.

8. Load the motor slowly with max. current up to 4A. Observe

the wave forms in the CRO.

TABULAR COLUMN:

S.NO. Inputvoltage(v)

Firing angle(o)

Outputvoltage(V)

Outputcurrent (A)


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PRECAUTIONS:

1. Switch SW3 should be operated with minimum speed of

the motor.

2. Motor should be provided with the good earthing.

3. Motor loading should be done carefully.

4. Unit should not be turned on with motor loaded.

5. Ensure that armature and field cable of the motor is not

damaged by rotating parts of the motor.

RESULTS:

VIVA VOCE:

1) What is meant by phase controlled rectifier?2) In which quadrants we can operate this converter?3) What are the disadvantages of half controlledconverter compared to fully controlled converter?

9. LAMP DIMMER USING DIAC AND TRIAC

AIM:

To study lamp dimmer circuit using Diac and Triac.

APPARATUS:

1. Lamp dimmer using Diac and Triac circuit,

2. 40W, 230Vlamp,

3. CRO.

THEORY:


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A DIAC is a two electrode, bidirectional avalanche diode which can beswitched from the off state to the on state for either polarity of appliedvoltage. The two leads are labeled as terminals T1 and T2 instead ofthe conventional anode-cathode designations. DIAC is mainly used as atrigger device for triacs which require either positive or negative gatepulse to turn on. DIAC-TRIAC pairs are available in the market forvarious types of control circuits. Two thyristors may be connected ininverse parallel, but at moderate power levels the two antiparallelthyristors can be integrated into a single device structure.

CIRCUIT DIAGRAM:

PROCEDURE:

1. Connect the bulb (40w) witch form load.

2. Switch on the experiment board by connecting the power cord tothe AC mains.

3. By varying the 250 K potentiometer the gate current and there

by the firing angle of the TRIAC varies.

4. Finally the intensity of lamp varies as the potentiometer is

moved from clock wise potentiometer to the vice versa.


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5. Now observe the wave form at different positions by connecting

C R O through 10:1 through resistance allowed alternator prob.

6. Compare the wave forms with expected and note down the

readings.

OBSER VATIONS :

S L NO.

IN PUTVOLTAGE

FIRING ANGLE

RADFIRNG ANGLE

Expected Waveforms:


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RESULT:

VIVA VOCE:

1) What is DIAC.2) What is TRIAC.3) Dereference between DIAC and TRIAC.


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10. STUDY OF MORGANS CHOPPER

AIM:

To study the module and wave form for DC Morgans chopper.

APPARATUS:

1. Morgans chopper firing circuit and power circuit unit.


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2. 40w lamp load.

3. 20 M H Z Dual trace Oscilloscope with 1:10 B N C Probe.

THEORY:

The following figure shows the power circuit of Morgan Chopper. In

this circuit, T1 is the main thyristor where as capacitor , saturablereactor SR and diode, forms the commutating circuit. The excitingcurrent of the saturable reactor is assumed to be negligible small.When the saturable reactor is saturated, it has very low inductance.When the main SCR T1 is off, capacitor C will be charged to the supplyvoltage. When the core flux reaches the negative saturation, thecapacitor discharges through the SCR T1 and the post saturationinductance of SR.

CIRCUIT DIAGRAM:

PROCEDURE:

1. Connect 250 V D C Power supply to approximate terminals of

the Morgan chopper circuit.

2. Connect isolated firing pulse G1 K1 and G2 K2 to the S C R i gate

and in minimum frequency portion.

3. Connect 40w lamp load and switch ON the system.


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4. Observe the wave form across load, SCR ON CRO by increasing

the frequency.

5. Compare the wave forms.

OBSERVATIONS:

SL NO INPUT VOLTS T. ON T. OFF % DUTY CYCLE

RESULT:

VIVA VOCE:

1) Define chopper.Types of choppers.Explain the operation of MORGANs chopper.

11. A.C PHASE CONTROL FULL WAVE (USING SCR)

AIM:To study the principle of half wave and full wave phase control

using RC triggered Circuits and SCR.

APPARATUS:

1. Power electronics Kit - 1No

2. Lamp,230V,60W - 1No


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3. CRO - 1No

THEORY:

Because of the unidirectional characteristics of the SCR it conductscurrent in only one direction. so SCR individually will not control both

the positive and negative cycles. So for this purpose a bridge rectifieris formed. So the out put of the bridge rectifier is having only positivehalves and is able to control both positive and negative cycles. Firingof the scr depends upon the RC time constant and firing of the DIACwhich is on the gate circuit of the SCR.

CIRCUIT DIAGRAM:

PROCEDURE:

1. Switch on the experimental kit.

2. Connect isolated A.C source (230V) to the input of the half wave

control circuit.

3. Connect the external lamp load provided on the trainer board in

place of load.


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4. Vary the potentiometer in clockwise direction and observe the

light intensity is varying.

5. Observe the waveforms (by using attenuators).Note down the

readings.

6. Now connect isolated A.C source (230V) to the input of full wave

control circuit.


place of load.

8. Vary the potentiometer in clockwise direction and observe the

varying.

9. Observe the waveforms (by using attenuators).Note down the

readings.

OBSERVATIONS:

Sl.NoInput voltage(V)

(Volts)Firing Angle()

(Radians)Firing Angle()

(Degrees)

RESULT:


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VIVA VOCE:

1) What is power electronics?2) Compare half and full wave converter.3) Which commutation process is used in phase controlled rectifier?

11. A.C PHASE CONTROL HALF WAVE (USING SCR)


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AIM:To study the principle of half wave and full wave phase control

using RC triggered Circuits and SCR.

APPARATUS:

4. Power electronics Kit - 1No

5. Lamp,230V,60W - 1No

6. CRO - 1No

THEORY:

The simple RC circuit for triggering SCRs by means of gate control isshown below. The gate current magnitude can be changed by varyingR the SCR triggers when there is a sufficient gate current. A control on

the firing angle can be easily attained when the applied voltage is AC.Capacitor C gets charged through diode D2 to the negative peak valueof the applied AC voltage during every negative half cycle charging inthe positive direction takes place in the following positive half cycle.The charging rate is controlled by resistance R when there is asufficient positive voltage across capacitor C, the SCR fires. Diodes D1is used for preventing reverse break down of the gate to cathodejunction in the negative half cycle.

CIRCUIT DIAGRAM:


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PROCEDURE:

10. Switch on the experimental kit.

11. Connect isolated A.C source (230V) to the input of the half

wave control circuit.

12. Connect the external lamp load provided on the trainer

board in place of load.

13. Vary the potentiometer in clockwise direction and observe

the light intensity is varying.

14. Observe the waveforms (by using attenuators).Note down

the readings.

15. Now connect isolated A.C source (230V) to the input of full wave

control circuit.


place of load.

17. Vary the potentiometer in clockwise direction and observe

the varying.

18. Observe the waveforms (by using attenuators).Note down

the readings.

OBSERVATIONS:

Sl.NoInput voltage(V)

(Volts)Firing Angle()

(Radians)Firing Angle()

(Degrees)


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RESULT:

VIVA VOCE:

4) What is power electronics?5) Compare half and full wave converter.6) Which commutation process is used in phase controlled rectifier?

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