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EE0314- POWER ELECTRONICS LAB

REFERENCE MANUAL

SEMESTER VI

DEPARTMENT OF ELECTRICAL AND ELECTRONICS

ENGINEERING

SRM UNIVERSITY

KATTANKULATHUR-603203

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EXPT. NO. 1 :

Pre lab Questions

Single Phase Half Converter

1. What is the delay angle control of converters?

2. What is natural or line commutation?

3. What is the principle of phase control?

4. What is extinction angle?

5. Can a freewheeling diode be used in this circuit and justify the reason?

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SINGLE PHASE HALF CONTROLLED BRIDGE RECTIFIER

Aim:

To study the operation of single phase half controlled converter using R and RL load and to

observe the output waveforms.

Apparatus required:

1. Power thyristors

2. Rheostat

3. CRO

4. Transformer (1-phase) 230V/24V

5. Connection wires

Single Phase Half Controlled Bridge Rectifier:

Circuit Diagram

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Model Graph:

Observation Table:

Serial

No.

Triggering angle

‘α’ degree

Output voltage

Vo

(volt)

(measured)

Time period(ms)

1

2

3

Procedure:

1. Make the connections as per the circuit diagram.

2. Connect CRO and voltmeter across the load.

3. Keep the potentiometer at the minimum position.

4. Switch on the step down ac source.

5. Check the gate pulses at G1-K1 & G2-K2, respectively.

6. Observe the wave form on CRO and note the triggering angle ‘α’ and

7. Note the corresponding reading of the voltmeter. Also note the value of Maximum amplitude Vm

from the waveform.

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8. Set the potentiometer at different positions and follow the step given in (6) for every position.

9. Tabulate the readings in the observation column.

Theory:

A semi converter uses two diodes and two thyristors and there is a limited control over the level of dc

output voltage. A semi converter is one quadrant converter. A one-quadrant converter has same polarity

of dc output voltage and current at its output terminals and it is always positive. It is also known as two-

pulse converter. Figure shows half controlled rectifier with R load. This circuit consists of two SCRs T1

and T2, two diodes D1 and D2. During the positive half cycle of the ac supply, SCR T1 and diode D2 are

forward biased when the SCR T1 is triggered at a firing angle ωt = α, the SCR T1 and diode D2 comes to

the on state. Now the load current flows through the path L - T1- R load –D2 - N. During this period, we

output voltage and current are positive. At ωt = π, the load voltage and load current reaches to zero, then

SCR T1 and diode D2 comes to off state since supply voltage has been reversed. During the negative half

cycle of the ac supply, SCR T2 and diode D1 are forward biased. When SCR T2 is triggered at a firing

angle ωt = π + α, the SCR T2 and diode D1 comes to on state. Now the load current flows through the

path N - T2- R load – D1 -L. During this period, output voltage and output current will be positive. At ωt

= 2π, the load voltage and load current reaches to zero then SCR T2 and diode D1 comes to off state since

the voltage has been reversed. During the period (π + α to 2π) SCR T2 and diode D1 are conducting.

Vout=(√2Vs)(1+Cosα)/π

Result:

Thus the operation of single phase half controlled converter using R and RL load has studied and the

output waveforms has been observed.

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Post lab Questions:

Single Phase Half Converter

1. What is conduction angle?

2. What are the effects of adding freewheeling diode in this circuit?

3. What are the effects of removing the freewheeling diode in single phase semi converter?

4. Why is the power factor of semi converters better than that of full converters?

5. What is the inversion mode of converters?

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EXPT. NO. 2: Pre lab Questions:

Single Phase Full Converter:

1. State the type of commutation used in this circuit?

2. What will happen if the firing angle is greater than 90 degrees?

3. What are the performance parameters of rectifier?.

4. What are the advantages of three phase rectifier over a single phase rectifier?

5. What is the difference between half wave and full wave rectifier?

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SINGLE PHASE FULLY CONTROLLED CONVERTER

Aim:

To study the operation of single phase fully controlled converter using R and RL load and to

observe the output waveforms.

Apparatus Required:

1. Power thyristors

2. Rheostat

3. CRO

4. Transformer (1-phase) 230V/24V

5. Connection wires

Circuit Diagram

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Model Graph:

Observation Table:

Serial

No.

Triggering angle

‘α’ degree

Output voltage

Voav

(volt)

(measured)

Time period(ms)

1

2

3

Procedure:

1. Single Phase Fully Controlled Bridge Rectifier

2. Make the connections as per the circuit diagram.

3. Connect CRO and multimeter (in dc) across the load .

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4. Keep the potentiometer (Ramp control) at the minimum position (maximum resistance).

5. Switch on the step down ac source.

6. Check the gate pulses at G1-K1, G2-K2,G3-K3,& G4-K4 respectively.

7. Observe the waveform on CRO and note the triggering angle ‘α’ and note the corresponding

reading of the multimeter. Also note the value of maximum amplitude Vm from the waveform.

8. Set the potentiometer at different positions and follow the step given in (6) for every position.

9. Tabulate the readings in observation column.

10. Draw the waveforms observed on CRO.

Theory:

A fully controlled converter or full converter uses thyristors only and there is a wider control over

the level of dc output voltage. With pure resistive load, it is single quadrant converter. Here, both the

output voltage and output current are positive. With RL- load it becomes a two-quadrant converter. Here,

output voltage is either positive or negative but output current is always positive. Figure shows the

quadrant operation of fully controlled bridge rectifier with R-load. Fig shows single phase fully

controlled rectifier with resistive load. This type of full wave rectifier circuit consists of four SCRs.

During the positive half cycle, SCRs T1 and T2 are forward biased. At ωt = α, SCRs T1 and T3 are

triggered, then the current flows through the L – T1- R load – T3 – N. At ωt = π, supply voltage falls to

zero and the current also goes to zero. Hence SCRs T1 and T3 turned off. During negative half cycle (π

to 2π).

SCRs T3 and T4 forward biased. At ωt = π + α, SCRs T2 and T4 are triggered, then current flows through

the path N – T2 – R load- T4 – L. At ωt = 2π, supply voltage and current goes to zero, SCRs T2 and T4

are turned off. The Fig-3, shows the current and voltage waveforms for this circuit. For large power dc

loads, 3-phase ac to dc converters are commonly used. The various types of three-phase phase-controlled

converters are 3 phase half-wave converter, 3-phase semi converter, 3-phase full controlled and 3-phase

dual converter. Three-phase half-wave converter is rarely used in industry because it introduces dc

component in the supply current. Semi converters and full converters are quite common in industrial

applications. A dual is used only when reversible dc drives with power ratings of several MW are

required. The advantages of three phase converters over single-phase converters are as under: In 3-phase

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converters, the ripple frequency of the converter output voltage is higher than in single-phase converter.

Consequently, the filtering requirements for smoothing out the load current are less. The load current is

mostly continuous in 3-phase converters. The load performance, when 3- phase converters are used, is

therefore superior as compared to when single-phase converters are used.

Vout=(2Vs)(Cosα)/π Iavg=Vavg/R

Result:

Thus the operation of single phase fully controlled converter using R and RL load has been

studied and the output waveforms has been observed.

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Post lab questions

Single phase full converter

1. If firing angle is greater than 90 degrees, the inverter circuit formed is called as?

2. What is displacement factor?

3. What is Dc output voltage of single phase full wave controller?

4. What are the effects of source inductance on the output voltage of a rectifier?

5. What is commutation angle of a rectifier?

6. What are the advantages of three phase rectifier over a single phase rectifier?

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EXPT. NO: 3 Pre lab questions

Single phase AC voltage controller using TRIAC

1. Why should the two trigger sources be isolated?

2. What are the advantages and the disadvantages of phase control?

3. What is phase control?

4. What are the advantages of bidirectional controllers?

5. What is meant by duty cycle in ON-OFF control method?

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1-PHASE AC VOLTAGE CONTROL USING TRIAC

Aim:

To study the 1-phase AC voltage control using TRIAC.

Apparatus Required:

i) Lamp – 60W

ii) Resistor - 100 / 1W

iii) Potentio meter – 100K

iv) Capacitor – 0.1F / 400V

v) Resistor – 1K

vi) DIAC – DB3

vii) TRIAC BT 136

viii) Unearthed oscilloscope

Circuit Diagram

Circuit Operation:

1. When potentiometer is in minimum position drop across potentiometer is zero and hence

maximum voltage is available across capacitor. This Vc shorts the diac (Vc > Vbo) and triggers

the triac turning triac to ON – state there lamp glows with maximum intensity.

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2. When the potentiometer is in maximum position voltage drop across potentiometer is

maximum. Hence minimum voltage is available across capacitor (Vc M Vbo) hence triac to is

not triggered hence lamp doesnot glow.

3. When potentiometer is in medium position a small voltage is available across capacitor hence

lamp glows with minimum intensity.

Tabular Column:

S.No. Firing Angle(α) Output Voltage(Volts) Time period(ms)

1

2

3

Procedure:

1. Connections are given as per the circuit diagram

2. Initially potentiometer kept at minimum position so lap does not glow at this instant.

3. Note the voltage across the diac and triac.

4. Capacitor and potentiometer using multimeter and CRO.

5. Potentiometer is now placed at medium and then to minimum position and their voltages were

noted.

Theory:

Triac is a bidirectional thyristor with three terminals. Triac is the word derived by combining the capital

letters from the words TRIode and AC. In operation triac is equivalent to two SCRs connected in anti-

parallel. It is used extensively for the control of power in ac circuit as it can conduct in both the direction.

Its three terminals are MT1 (main terminal 1), MT2 (main terminal 2) and G (gate).

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Result:

Thus the operation and performance of the 1-phase AC voltage control using DIAC and TRIAC.

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Post lab questions

Single Phase AC voltage controller using TRIAC

1. What type of commutation is used in this circuit?

2. What are the effects of load inductance on the performance of AC voltage controllers?

3. What is extinction angle?

4. What are the disadvantages of unidirectional controllers?

5. What are the advantages of ON-OFF control?

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EXPT. NO. 4: Prelab questions

Modified Mc Murray Full bridge Inverter

1. What is the difference between Mcmurray half bridge and full bridge inverter?

2. What is meant by Mcmurray inverter?

3. What is the type of commutation used in this circuit?

4. What is the other name for this inverter circuit?

5. Advantages of Mc Murray inveter?

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MODIFIED MC-MURRAY – BEDFORD FULL BRIDGE INVERTER

Aim:

To study the operation of a modified Mc-Murray Bedford full bridge inverter.

Apparatus Required:

i) Modified Mc-Murray Bedford inverter kit

ii) Connecting wires

iii) CRO and probes

Circuit Diagram

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Model Graph

Tabular Column:

S.No Frequency Voltage Amplitude(V) Time

period(ms)

1 Minimum

2 Maximum

Procedure:

i) Connections are made as per the circuit diagram

ii) Power supply is switched ‘ON’ and the output waveforms are noted.

Theory:

The power circuit diagrams of a modified Mc-Murray Bedford half and full bridge inverter is

shown in the figure.

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A half bridge modified Mc-Murray Bedford inverter uses lesser number of thyristors and diodes as

compared with the full bridge one.

The inverter consists of main thyristors T1,T2 and feedback diodes D1, D2 commutation circuitry

consists of two capacitors C1, C2 and magnetically coupled inductors L1 and L2 constitute one inductor

with a center rapped so that L1 = L2 = L. The inductance of the order 50H. The inductor is wound on a

core with an air gap so as to avoid saturation. The value of the capacitance for the two capacitors is the

same (C1=C2=C). It is a voltage commutated VSI.

In a branch consisting of two tightly coupled inductors in series with two thyristors if the

thyristors is turned on, then the other thyristor is turned off automatically. This type of commutation is

called complementary commutation.

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Result:

Thus the operation of a modified Mc-Murray Bedford full bridge inverter is studied and the

waveforms are drawn.

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EXPT. NO. 5: Pre lab Questions

Single Phase parallel Inverter

1. What is parallel inverter? Why is it called so?

2. What is the purpose of capacitor in the parallel inverter?

3. What is the purpose of transformer in the parallel inverter?

4. IS the parallel inverter naturally commutated or force commutated?

5. What are the advantages of parallel resonant inverters?

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PARALLEL INVERTER

Aim:

To study the operation of parallel inverter.

Apparatus Required:

i) Parallel inverter kit

ii) Inductor

iii) Transformer

iv) CRO

This module consists of two units – (1) Firing circuit and 92) Power circuit.

Circuit Diagram

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Model Graph

Tabular Column:

S.No. Frequency Voltage Amplitude(V) Time period(ms)

1 Minimum

2 Maximum

Procedure:

1. Switch on the firing circuit. Observe the trigger outputs TP and TN by varying frequency

potentiometer and by operating ON/OFF switch.

2. Then connect input DC supply to the power circuit. Connect trigger outputs to Gate and Cathode

of SCR TP & TN.

3. Apply trigger pulses to SCR

4. Observe voltage waveforms across load. Output voltage is square wave only.

5. Vary the load, vary the frequency and observe waveforms.

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Theory:

The circuit is a typical class C Parallel inverter. Assume TN to be ON and TP to be OFF. The

bottom of the commutating capacitor is charged to twice the supply voltage and remains at this value until

TP is turned on. When TP is turned on, the current flows through lower half of the primary TP and

commutating inductance L. Since voltage across C cannot instantaneously, the common SCR cathode

point rises approximately to 2V dc and reverses bias TN Thus TN turns off and C discharges through L, the

supply circuit and then recharges in the reverse direction. The autotransformer action makes C to charge

making now its upper point to reach +2V dc volts ready to commutate Tp, When TN is again turned on

and the cycle repeats.

Free wheeling diodes Dp and DN assist the inverter in handling a wide range of loads and the value

of C may be reduced since the capacitor now does not have to carry the reactive current. To dampen the

feedback diode currents within the half period, feedback diodes are connected to tapping of the

transformer at 25V tapping.

(1) Firing Circuit:

This unit generates two pairs of pulse transformer isolated trigger pulses to trigger two SCR’s

connected in center tapped transformer type parallel inverter. Frequency of the inverter can be varied

from 75Hz to 200 Hz approximately.

(2) Power Circuit:

This unit consists of two SCR’s, two free wheeling diodes, commutation inductor, commutation

capacitor and a center tapped transformer to be inter connected to make parallel inverter. All the points

are brought out to the front panel. A switch and fuse is provided for input DC supply. All the devices are

mounted on proper heat sink. Each device is protected by snubber circuit.

Front Panel Details:

1. Frequency : Potentiometer to vary the inverter frequency from 75Hz

to 200 Hz approximately.

2. ON / OFF : Switch for trigger outputs

3. T1 & T2 : Trigger outputs

4. Power : Mains switch for firing circuit

5. Vdc in : Terminals for DC input from 30V/2A RPS unit

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6. ON : Switch for DC input

7. Tp & Tn : SCR’s 10A/600V

8. Dp & Dn : Diodes 10A/600V

9. L : Inductance - 300H/2A

10. C : 6.8F/100V

11. Load : Terminals to connect load.

12. O : Transformer center tap point which should be

connected to positive of DC supply after fuse.

13. Fuse : 2A Glass fuse.

14. Output Transformer : Primary – 30V-25V-025V – 30V

Secondary – 0-30V/2Amps.

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Result:

Thus the operation of a parallel inverter is studied and the output waveforms are measured and

drawn.

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Post lab questions

Single phase parallel Inverter

1. What is the purpose of the inductor in the parallel inverter?

2. During its operation, capacitor voltage reaches 2Vs. How?

3. What is the significance of the split phase transformer?

4. During operation, what is the voltage across primary winding of the transformer?

5. Capacitor current flows in how many modes of the operation of parallel inverter?

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EXPT.NO 6: Pre Lab questions

R, R-C AND UJT TRIGGERING CIRCUITS

1. UJT triggering circuit is also known as?

2. Types of triggering circuit?

3. What is the purpose of series resistor?

4. What is the condition for triggering the circuit?

5. What is the function of pulse transformer in firing circuit?

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R, R-C AND UJT TRIGGERING CIRCUITS

Aim:

To study the operation of resistance, resistance capacitance and UJT triggering circuits of SCR

Circuit Diagram: R – Triggering Circuit:

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Model Graph: R – Triggering Circuit:

Tabular Column

S.No.

Input

Voltage

(V)

Input

Cycle

Time

(Ms)

Voltage

across

Resistor(V)

Voltage

across

zener

diode

(V)

Voltage

across

capacitor

(V)

Voltage

across

load

(V)

1

Procedure

R Firing

1. Connections are made as shown in fig.

2. Switch on the power supply to the CRO.

3. Set the CRO to the line trigger mode.

4. Switch on power supply to the SCR trainer.

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5. Observe the waveform on the CRO.

6. Study the waveforms for various firing angle by varying the pot in R trigger circuit.

7. Observe the range of firing angle control.

8. For any one particular firing angle plot the waveforms of the ac voltage, voltage across the load

and the SCR.

9. Measure the average dc voltage across the load and rms value of the ac input voltage using a

digital multimeter.

10. Calculate the dc output voltage using the equation.

V - Vrms value of ac input voltage

Vm - \/2Vrms.And compare the measured value.

Theory:

Resistance Triggering:

Resistance trigger circuits are the simplest & most economical method. During the positive half cycle of

the input voltage, SCR become forward biased but it will not conduct until its gate current exceeds Igmin

. Diode D allows the flow of current during positive half cycle only. R2 is the variable resistance & R is

the stabilizing resistance .R1 is used to limit the gate current. During the positive half cycle current Ig

flows. Ig increases and when Ig= Igmin the SCR turns ON .The firing angle can be varied from 0 — 90°

by varying the resistance R.

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Circuit Diagram: RC Triggering Circuit:

Model Graph:

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Tabular Column:

S.No.

Input

Voltage

(V)

Input

Cycle

Time

(Ms)

Resistance

Value

(K _ )

O/P

Voltage

V rms (V)

Voltage

Across

(Anode-

Cathode)

V rms (V)

Procedure:

RC FIRING:

1. Connections are made as shown in fig.

2. Switch on the power supply to the CRO .

3. Set the CRO to the line trigger mode.

4. Switch on power supply to the SCR trainer.

5. Observe the waveform on the CRO.

6. Study the waveforms for various firing angle by varying the pot in R trigger circuit.

7. Observe the range of firing angle control. t u t e o f T e c h n o l o g y Page 53

8. For any one particular firing angle plot the waveforms of the ac voltage, voltage across the load

and the SCR.

9. Measure the average dc voltage across the load and rms value of the ac input voltage using g' a

digital millimeter.

10. Calculate the dc output voltage using the equation.

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Theory:

R —C Triggering:

By varying the variable resistance R, the firing angle can be varied from 0 —180° .In the negative

half cycle the capacitance C charges through the diode D2 with lower plate positive to, the peak supply

voltage Emax .This Capacitor voltage remains constant at until supply voltage attains zero value. During

the positive half cycle of the input voltage, C begins to charge through R. When the capacitor voltage

reaches the minimum gate trigger voltage SCR will turn on.

Circuit Diagram: UJT Triggering Circuit

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Model Graph:

Tabular Column:

Resistor

value(r)

(ω)

Capacitor

voltage

Vc

Charging

time

(ms)

Discharging

Time

(ms)

Voltage vo

(v)

Time

Period

(ms)

Procedure:

1. Connect a & k terminal of UJT triggering circuit to the gate cathode terminals of SCR.

2. Give a 24 V ac supply.

3. Observe the waveforms and plot it for one particular firing angle by adjusting the potentiometer

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and observe the range over which firing angle is controllable.

4. Observe that capacitor voltage is set at every half cycle.

Theory:

A synchronized UJT triggered circuit using an UJT is shown in the figure. Diodes ‘D1’ to ‘D4’

rectify ac to dc. Resistor R1 lowers Vdc to a suitable value for the zener diode and UJT. Zener diode ‘Z’

functions to clip the rectified voltage to a standard level, ‘Vz’ which remains constant except near the Vdc

zero. The voltage Vz is applied to the charging circuit RC. Current ‘I’, charges capacitor ‘c’ at a rate

determined by ‘R’ voltage across capacitor is marked by ‘Vc’ as shown. When ‘Vc’ reaches the

unijunction threshold voltage Vz, the t-B1 junction of UJT breaks down and the capacitor ‘c’ discharges

through the primary of pulse transformer sending a current ‘C2’ as shown.

As the current ‘i2’ is in the form of pulse, windings of the pulse transformer have pulse voltages at

their secondary terminals. Pulse at the two secondary windings feeds the same in phase pulse to two

SCRs of a full wave circuits. SCR with positive anode voltage would turn ON. As soon as the capacitor

discharges, it starts to recharge as shown. Rate of rise of capacitor voltage can be controlled by varying

‘R’. The firing angle can be controlled up to above 150o. This method of controlling the output power

by varying the charging resistor ‘r’ is called ramp control, open loop control (or) manual control.

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Result:

Thus the operation of resistance, resistance capacitance and UJT triggering circuits of SCR has

been studied.

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Post lab questions

R, R-C AND UJT TRIGGERING CIRCUITS

1. Explain how synchronization of the triggering circuit with the supply voltage across SCR is achieved? 2. How can the capacitor charging be controlled?

3. What is the maximum value of firing angle which can be obtained from the circuit?

4. How is the output power to the triggering circuit controlled?

5. Compare UJT triggering circuit with RC firing circuit?

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EXPT. NO. 7: Pre lab questions

SERIES INVERTER

1. Why is this circuit called as series inverter?

2. What is the type of commutation for series inverter?

3. What is the configuration of inductor?

4. What is the principle of series inverter?

5. Disadvantages of series inverter?

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SERIES INVERTER

Aim:

To study the operation of series inverter and to obtain variable AC from DC input.\

Apparatus Required:

i) Series inverter module

ii) Loading rheostat - 50

iii) CRO

iv) Connection wire

This unit consists of power circuit and firing circuit sufficient to build and study the modified

series inverter.

Circuit Diagram

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Model Graph:

t u t e o f T e c h n o l o g y Page 56

Observation Table:

A

S. No

Amplitude (volt)

Ton (ms)

Toff (ms)

1

2

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Procedure o l o g y Page 58

1. To begin with switch on the power supply to the firing circuit check that Trigger pulses by varying

the frequency.

2. Connections are made as shown in the circuit diagram.

3. Now connect trigger outputs from the firing circuits to gate and cathode of SCRs T1 & T2.

4. Connect DC input from a 30v/2A regulated power supply and switch on the input DC

supply.

5. Now apply trigger pulses to SCRs and observe voltage waveform across the load.

6. Measure Vrms & frequency of o/p voltage waveform.

Firing Circuit: This part generates two pairs of pulse transformer isolated trigger two SCR’s connected

as series inverter. ON/OFF switch is provided for the trigger pulses which can be used to switch ON the

inverter. Frequency of the inverter can be varied from 100 Hz to 1 KHz approximately.

Power Circuit: This part consists of two SCR’s two diodes. A center tapped inductor with tappings and

4 capacitors. Input supply terminals with ON/OFF switch and a fuse is provided. All the devices in this

unit mounted on a proper heat sink, snubber circuit for dv/dt protection and a fuse in series with each

device for short circuit protection.

All the points are brought out to front panel for inter connections. They have to be interconnected

as shown in the circuit diagram. Fly wheeling diodes can be connected across SCR’s and its effect can be

observed.

Theory:

This circuit which converts DC power into AC power is called inverter. If the thyristor

commutation circuit of the inverter is in series with the Load, then the inverter is called “Series are tightly

coupled. In this circuit, it is possible to turn-on-thyristor Tp before the current through thyristor Tn has

become zero and vice-versa. Therefore, the Modifed Series Inverter can be operated behond the

resonance frequency (fr) of the circuit. Inverter is operated at the resonance frequency (fr) if the load

current waveform has low frequency and should not have zero current interval. The inverter’s resonance

frequency depends on the values of L, R and C in the circuit.

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Front Panel Details:

1. Frequency : Potentiometer to vary the inverter frequency.

From 100 Hz to 1 KHz approximately.

2. Gate, Cat : Trigger outputs to connect to Gate and

Cathode of SCR

3. ON / OFF : Switch for trigger outputs

4. T1 and T2 : Trigger outputs

5. Power : Mains switch for firing circuit

6. Vdc in : Terminals for DC input 30V/2A max from

RPS

7. ON / OFF : Switch for DC input

8. Fuse : Fuse for dc input-2 Amps Glass Fuse

9. T1 and T2 : SCR’s TY 616.12A / 600V

10. D1 and D2 : Diodes BYQ28. 4A/200V

11. L2, L1, Lm, L1, L2 : 10mH – 5mH – 0 – 5mH – 10mH/2 Amps

12. C1 and C1 : 6.8 farad / 100V

13. C2 and C2 : 10 farad / 100V

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Result:

Thus the operation of a series inverter is studied.

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Post lab questions

SERIES INVERTER

1. What is the dead zone of an inverter?

2. Up to what maximum voltage will the capacitor charge during circuit operation?

3. What is the amount of power delivered by capacitor?

4. What is the purpose of coupled inductors in half bridge resonant inverters?

5. Types of resonant pulse inverters?

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EXPT. NO.8: Pre lab questions

SPEED CONTROL OF DC MOTOR

1. What type of commutation is applied to Jones Chopper?

2. Give the commutating element to form the commutating circuit for the main thyristor?

3. Give the reason for the high efficiency of this chopper.

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SPEED CONTROL OF DC MOTOR

USING – 1-PHASE HALF CONTROLLED RECTIFIER

Aim:

To study the speed control of a dc motor by varying armature applied voltage through phase

controlled converter.

Apparatus Required:

i) DC motor control unit

ii) DC ammeter

iii) DC voltmeter

iv) CRO

v) DC motor

Circuit Diagram

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DC Motor Speed Control Unit (Power Circuit) 230V/5A

This power circuit consists of two SCR’s and three diodes. These devices can use to built single

phase half wave converter, single phase full wave converter and single phase half controlled bridge

converter, and also single phase AC voltage controller power circuits.

Each device in the unit is mounted on an appropriate heat sink and is protected by snubber circuit.

Short circuit protection is achieved using glass fuses. A circuit breaker is provided in series with the input

supply for over load protection and to switch ON/OFF the supply to the power circuit.

The Gate and Cathode of each SCR’s brought out on the front panel for firing pulse connection. A

digital voltmeter and an ammeter is mounted on the front panel to measure the armature voltage and

current. All devices schematic is printed on the front panel.

Specifications:

Input : 10V to 230V single phase

SCR : (V) rrm 1200V, (I) av : 10 amps, 25TTS12

International rectifier make.

Power diodes & Free

Wheeling diode : (V) rrm : 1200V, (I) 16 amps, 12KLR 16DS

Fuses : 6 Amps Glass fuses

MCB : Two pole 6 amps / 230V

Heat Sink : PI-46, 50mm

Snubber : R-250 Ohms / 5 Watts c-0.1 Microfarad / 1000V

Front Panel Details:

AC Input : Terminals to connect 1-phase AC input from single phase

isolation transformer.

Output : Terminals after the MCB to be connected to power circuit

Digital voltmeter : 3 ½ digit voltmeter to measure output voltage

Digital ammeter : 3 ½ digital ammeter to measure output voltage

Circuit Breaker : 6 Amps, AC power ON/OFF to the circuit and for protection

T1, T2 : Trigger pulse connections from the firing circuit

D2, D4 : Power diodes

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Dm : Free wheeling diode

Field (+and-) : Field supply for DC motor for motor control experiments.

(With indicator)

Back Panel Details:

3 pin mains socket for AC mains supply to field supply bridge rectifier Glass fuse holders for 6

fuses in series with each SCR’s.

Procedure:

Switch ON the mains supply to the single phase converter firing circuit. Observe the test points

and trigger outputs. Verify the trigger outputs and their phase sequence. Vary the firing angle

potentiometer and observe the trigger outputs. The pulse train width will increase as we decrease the

firing angle from 180o to 0

o. It is 0

o to 180

o and 50% at 90

o soft start and stop feature is provided for

trigger outputs. When we press of ON/OFF switch the trigger outputs will start at 180o and slowly

increased to the firing angle set by firing angle potentiometer. The acceleration time is set in the factor

(10 seconds).

When we release the ON/OFF switch the trigger outputs will slowly decreased to 180o from the

set firing angle. The deceleration time is set in the factory.(-2 seconds)

The deceleration time is very short compared to acceleration time. Make sure that all the trigger

outputs are proper before connecting to the power circuits. Make the connections in the power circuit as

given in the circuit through isolation transformer. Initially keep the input supply at low voltage say 30

volts. Connect the trigger outputs from firing circuit to the corresponding SCR’s Gate and Cathode.

Initially connect a Rheostat of 50 Ohms / 5amps. Switch ON the trigger outputs observe the voltage

waveforms across load by varying the firing angle potentiometer. Compare with the expected waveforms,

if the unit is working properly switch OFF the trigger outputs and switch OFF the MCB. Connect field

terminals of DC motor to the field supply points in the power circuit. The connect armature terminal of

the DC motor through the rheostat and the rheostat and the ammeter provided in the unit to the output of

rectifier. Switch ON the field supply. Set the field voltage to some value – 150Volts. This voltage can

be measured using the voltmeter provided in the rectifier. Set the input voltage to 100Volts. Initially

keep the firing angle pot at 180o. Initially keep the resistance at maximum position and cut off once the

DC motor starts. This is to limit the starting current. Switch On the MCB and trigger outputs. Vary the

firing angle potentiometer and note down the output voltage, output current and measure the speed of the

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DC motor for different values of firing angle. Note down these values in the tabular column. And also

observe the voltage waveforms. We can observe that back emf will increase as the speed increases. Next

vary the input voltage upto 230 volts in steps and note down the readings in the tabular column.

Armature Control:

S.No. Output

Voltage(V)

Duty Cycle(%) Frequency Speed(RPM) Current

1

2

3

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Result:

Thus the speed control of DC motor is performed by varying armature voltage through phase

controlled converter

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Post lab questions

SPEED CONTROL OF DC MOTOR

1. How the load current is smooth other than pulsating? 2. The inductance L maintains the load current to diodes D when SCR T is not conducting. Hence, the motor

torque and load current is smooth rather than pulsating. 3. What is the commutating voltage across capacitor C?

4. Give the torque equation for speed control of DC machine.

55

EXPT. NO. 9: Pre lab questions

SPEED CONTROL OF UNIVERSAL MOTOR:

1. What is universal motor?

2. How speed is controlled by using a thyristor?

3. What is delay angle?

4. What is duty cycle?

5. What is meant by controlled rectifier?

56

SPEED CONTROL OF UNIVERSAL MOTOR

Aim:

To study the speed control of a Universal motor by varying armature applied voltage through phase

controlled converter.

Apparatus Required:

i) Universal kit

ii) CRO

iii) Batch cards motor

iv) Universal motor

This unit consists of two parts:

(a) Firing circuit and (b) Power circuit

Speed Control of Universal Motor Using AC Voltage Control

Circuit Diagram:

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Speed control of DC motor using Single phase Half wave converter

Speed control of DC motor using Single phase full wave converter

Single phase Half controlled bridge rectifier

Tabular Column:

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Sl.

No.

Input Voltage

Vin

Firing Angle

Output

Voltage – V0

Output

Current I0

Speed

RPM

a) Firing Circuit:

This unit, generates line synchronized 2 pulse transformer isolated trigger pulses. These trigger

pulses can be used to trigger.

(i) Single phase AC phase control using SCR’s (Antiparallel SCR’s)

(ii) Single phase AC phase control using triac.

(iii) Single phase Half wave rectifier (single SCR)

(iv) Single phase Full wave rectifier (Two SCR’s)

(v) Single phase Half controlled bridge rectifier (Two SCR’s & Two diodes) power circuits.

The firing circuit is based on zero crossing detector, ramp generator, op-amp comparator and amplifier

/ pulse transformer isolation method.

Front Panel Details:

1. Power : Mains switch for firing circuit with built in indicator

2. Firing angle : Potentiometer to vary the firing angle from 180o to 0

o

3. SCR / Triac : Selection switch for trigger O/P 1 for SCR/Triac

4. OFF/ON : Switch for trigger O/Ps with soft start feature.

5. Trigger O/Ps :

T1 / TR :

T2 : Trigger O/P for SCR2

Power Circuit:

The power circuit consists of 2 SCR’s, 3 diodes and a Triac. The power devices are mounted on

suitable heat sink for power dissipation. The snubber circuit is connected for dv/dt protection. A fuse is

also provided in series with the devices for short circuit or over current protection. In the input side a

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MCB is provided to switch ON/OFF the supply to the power circuit.

A voltmeter and an ammeter is provided to measure the Input / Output voltage and current.

Front Panel Details:

1. AC input : Terminals to connect AC input

2. AC output : AC supply terminals after the MCB to be connected to

power circuit.

3. MCB : A 6A / 2 pole MCB for ON/OFF the AC supply to the

power circuit

4. T1 & T2 : SCR’s 16 Amps / 600 volts

5. D3 & D4 : Diodes – 16amps / 600V

6. Dm : Free wheeling diode

7. TR : Triac – 10 amps / 600 volts

8. Voltmeter : 3 ½ Digit digital AC/DC Voltmeter to measure input /

output voltage

9. Ammeter : 3 ½ Digit digital AC/DC Ammeter to measure current

Procedure:

Make the inter connections in the power circuit as given is the circuit diagram. Switch ON the

firing circuit and observe the trigger outputs. Make sure that the firing pulses are proper before

connecting to the power circuit.

Then connect the trigger output from firing circuit to corresponding SCR’s / Triac. In the power

circuit Initially set the AC input to 30 volts. Switch ON and MCB. Switch ON the Trigger outputs

switch. Select the SCR / Triac selection switch and observe the output wave forms across ‘R’ load by

varying the firing angle potentiometer. If the output wave form is proper then you can connect the motor

& increase the input voltage to rated value 0-230V gradually. Vary the firing angle and note down output

voltage and speed of the motor.

Note:

1) If you are not getting the output after all proper connections interchange AC output terminals, after

switch OFF the MCB. This is just to synchronize the power circuit with firing circuit.

60

Result:

Thus the speed control of Universal motor is performed by varying armature voltage through phase

controlled converter

61

Post lab questions

SPEED CONTROL OF UNIVERSAL MOTOR

1. What is Circuit Breaker & Fuse? 2. What are the different operating regions of SCR?

3. What is gate pulse?

4. What is snubber circuit?

5. Different methods of speed control?

62

EXPT. NO.12: Pre lab questions

VOLTAGE COMMUTATED CHOPPER

1. What are the other names of this circuit?

2. What are the commutating components of this circuit?

3. What are the different types of commutated choppers?

4. Give the expression for commutating elements L and C for the voltage commutated chopper.

5. What is the purpose of freewheeling diode?

63

VOLTAGE COMMUTATED CHOPPER

Aim:

To observe the operation of class D commutated technique.

Apparatus Required:

1. Force commutation trainer kit.

2. Patch chord

3. CRO

CIRCUIT DIAGRAM

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Model Graph:

Tabular Column:

S.No. Duty Cycle(%) Output Voltage(V) Time

period(ms)

1

2

3

Procedure:

1) Patch the voltage commutated chopper as per the circuit diagram

2) Connect the CRO probe across the commutated chopper

3) Give the input dc voltage (0-30)v, 2amps from the external power supply.

4) Switch ON the trainer then switch ON the input dc suuply circuit breaker.

5) After then switch ON the trigger OFF-ON position

6) From the capacitor output waveform we can measure the turn on time and turn off time of main

SCR as well as auxiliary SCR

7) Verify the unity and frequency of the triggering circuit using parts provided on the triggering

circuit.

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8) Also observe the voltage across main SCR and auxiliary SCR and load

9) Take the turn on and turn off time at main so auxiliary SCR from the capacitor waveform at

various values of unity cycle and frequency and tabulate them

10) Also find out the peak value of current through the capacitor

Theory:

MODE-1

Main SCR is triggered to make source current to flow in two path one is load current and other

path with triggering of SCR load get connected to supply and load voltage.

MODE-2

At a desired instant the auxiliary SCR is to be triggered for turning OFF the main SCR T1 with the

switch ON, T2 reverse capacitance voltage appears across T1 which reverse biases it and turn it OFF.

MODE-3

SCR T2 turn OFF since the capacitance is slightly changed after the freewheeling diode set

frequently forward biased.

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Result:

Thus the operation of class D commutated technique has been obtained.

67

Post lab questions

VOLTAGE COMMUTATED CHOPPER

1. What are the initial conditions to be attained before the circuit can be operated? 2. What are the components required for commutating the thyristor?

3. What is the main disadvantage of this circuit?

4. In what mode does the diode and inductor operate?

5. Give the classification of the choppers.

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