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8/9/2019 Www.srmuniv.ac.in Sites Default Files Files Power Electronics Lab Manual-withoutreadingsandprepostlab-EE0314
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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 t
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
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 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 T
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 t = , the SCR T1 and diode D2 comes t
the on state. Now the load current flows through the path L - T1- R load D2 - N. During this period, w
output voltage and current are positive. At t = , 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 hal
cycle of the ac supply, SCR T2 and diode D1 are forward biased. When SCR T2 is triggered at a firing
angle t = + , the SCR T2 and diode D1 comes to on state.Now the load current flows through th
path N - T2- R load D1 -L. During this period, output voltage and output current will be positive. At
= 2, 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 ( + to 2) SCR T2 and diode D1 are conducting.
Vout=(2Vs)(1+Cos)/
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 t
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
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 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 ove
the level of dc output voltage. With pure resistive load, it is single quadrant converter. Here, both th
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 th
quadrant operation of fully controlled bridge rectifier with R-load. Fig shows single phase full
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 t = , SCRs T1 and T3 ar
triggered, then the current flows through the L T1- R loadT3N. At t = , supply voltage falls tzero and the current also goes to zero. Hence SCRs T1 and T3 turned off. During negative half cycle (
to 2).
SCRs T3 and T4 forward biased. At t = + , SCRs T2 and T4 are triggered, then current flows through
the path NT2 R load- T4L. At t = 2, supply voltage and current goes to zero, SCRs T2 and T
are turned off. The Fig-3, shows the current and voltage waveforms for this circuit. For large power d
loads, 3-phase ac to dc converters are commonly used. The various types of three-phase phase-controlle
converters are 3 phase half-wave converter, 3-phase semi converter, 3-phase full controlled and 3-phas
dual converter. Three-phase half-wave converter is rarely used in industry because it introduces d
component in the supply current. Semi converters and full converters are quite common in industria
applications. A dual is used only when reversible dc drives with power ratings of several MW ar
required. The advantages of three phase converters over single-phase converters are as under: In 3-phas
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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 i
mostly continuous in 3-phase converters. The load performance, when 3- phase converters are used, i
therefore superior as compared to when single-phase converters are used.
Vout=(2Vs)(Cos)/ 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) Lamp60W
ii) Resistor - 100/ 1W
iii) Potentio meter100K
iv) Capacitor0.1F / 400V
v) Resistor1K
vi)
DIACDB3
vii) TRIAC BT 136
viii) Unearthed oscilloscope
Circuit Diagram
Circuit Operation:
1. When potentiometer is in minimum position drop across potentiometer is zero and henc
maximum voltage is available across capacitor. This Vcshorts the diac (Vc> Vbo) and trigger
the triac turning triac to ONstate there lamp glows with maximum intensity.
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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-MURRAYBEDFORD 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 i
shown in the figure.
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A half bridge modified Mc-Murray Bedford inverter uses lesser number of thyristors and diodes a
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 inducto
with a center rapped so that L1 = L2 = L. The inductance of the order 50H. The inductor is wound on
core with an air gap so as to avoid saturation. The value of the capacitance for the two capacitors is th
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 th
thyristors is turned on, then the other thyristor is turned off automatically. This type of commutation i
called complementary commutation.
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Result:
Thus the operation of a modified Mc-Murray Bedford full bridge inverter is studied and th
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 frequenc
potentiometer and by operating ON/OFF switch.
2. Then connect input DC supply to the power circuit. Connect trigger outputs to Gate and Cathod
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. Th
bottom of the commutating capacitor is charged to twice the supply voltage and remains at this value unti
TP is turned on. When TP is turned on, the current flows through lower half of the primary T P an
commutating inductance L. Since voltage across C cannot instantaneously, the common SCR cathod
point rises approximately to 2V dc and reverses bias TNThus TNturns off and C discharges through L, th
supply circuit and then recharges in the reverse direction. The autotransformer action makes C to charg
making now its upper point to reach +2V dc volts ready to commutate Tp, When TNis again turned o
and the cycle repeats.
Free wheeling diodes Dp and DNassist the inverter in handling a wide range of loads and the valu
of C may be reduced since the capacitor now does not have to carry the reactive current. To dampen th
feedback diode currents within the half period, feedback diodes are connected to tapping of th
transformer at 25V tapping.
(1) Firing Circuit:
This unit generates two pairs of pulse transformer isolated trigger pulses to trigger two SCR
connected in center tapped transformer type parallel inverter. Frequency of the inverter can be varie
from 75Hz to 200 Hz approximately.
(2) Power Circuit:This unit consists of two SCRs, two free wheeling diodes, commutation inductor, commutatio
capacitor and a center tapped transformer to be inter connected to make parallel inverter. All the point
are brought out to the front panel. A switch and fuse is provided for input DC supply. All the devices ar
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 : SCRs 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 : Primary30V-25V-025V30V
Secondary0-30V/2Amps.
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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: RTriggering Circuit:
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Model Graph: RTriggering Circuit:
Tabular Column
S.No.
Input
Voltage(V)
Input
CycleTime
(Ms)
Voltage
acrossResistor(V)
Voltage
across
zenerdiode
(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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Circuit Diagram: RC Triggering Circuit:
Model Graph:
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Theory:
RC Triggering:
By varying the variable resistance R, the firing angle can be varied from 0 180 .In the negativ
half cycle the capacitance C charges through the diode D2 with lower plate positive to, the peak suppl
voltage Emax .This Capacitor voltage remains constant at until supply voltage attains zero value. Durin
the positive half cycle of the input voltage, C begins to charge through R. When the capacitor voltag
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)
()
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 potentiomete
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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 Vd
zero. The voltage Vz is applied to the charging circuit RC. Current I, charges capacitor c at a rat
determined by R voltage across capacitor is marked by Vc as shown. When Vc reaches th
unijunction threshold voltage Vz, the t-B1 junction of UJT breaks down and the capacitor c discharge
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 a
their secondary terminals. Pulse at the two secondary windings feeds the same in phase pulse to tw
SCRs of a full wave circuits. SCR with positive anode voltage would turn ON. As soon as the capacito
discharges, it starts to recharge as shown. Rate of rise of capacitor voltage can be controlled by varyin
R. The firing angle can be controlled up to above 150o. This method of controlling the output powe
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 ha
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 modifie
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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Procedureo l o g y Page 58
1. To begin with switch on the power supply to the firing circuit check that Trigger pulses by varyin
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 SCRs connecte
as series inverter. ON/OFF switch is provided for the trigger pulses which can be used to switch ON th
inverter. Frequency of the inverter can be varied from 100 Hz to 1 KHz approximately.
Power Circuit: This part consists of two SCRs two diodes. A center tapped inductor with tappings an
4 capacitors. Input supply terminals with ON/OFF switch and a fuse is provided. All the devices in thi
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 interconnecte
as shown in the circuit diagram. Fly wheeling diodes can be connected across SCRs and its effect can bobserved.
Theory:
This circuit which converts DC power into AC power is called inverter. If the thyristo
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 ha
become zero and vice-versa. Therefore, the Modifed Series Inverter can be operated behond th
resonance frequency (fr) of the circuit. Inverter is operated at the resonance frequency (fr) if the loa
current waveform has low frequency and should not have zero current interval. The inverters resonanc
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 : SCRs TY 616.12A / 600V
10. D1 and D2 : Diodes BYQ28. 4A/200V
11. L2, L1, Lm, L1, L2 : 10mH5mH05mH10mH/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
USING1-PHASE HALF CONTROLLED RECTIFIER
Aim:
To study the speed control of a dc motor by varying armature applied voltage through phas
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 SCRs and three diodes. These devices can use to built singl
phase half wave converter, single phase full wave converter and single phase half controlled bridg
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 inpu
supply for over load protection and to switch ON/OFF the supply to the power circuit.
The Gate and Cathode of each SCRs 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 an
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 / 230VHeat 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 digit voltmeter to measure output voltage
Digital ammeter : 3 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
fuses in series with each SCRs.
Procedure:
Switch ON the mains supply to the single phase converter firing circuit. Observe the test point
and trigger outputs. Verify the trigger outputs and their phase sequence. Vary the firing angl
potentiometer and observe the trigger outputs. The pulse train width will increase as we decrease th
firing angle from 180o to 0
o. It is 0
o to 180
oand 50% at 90
osoft start and stop feature is provided fo
trigger outputs. When we press of ON/OFF switch the trigger outputs will start at 180o and slowl
increased to the firing angle set by firing angle potentiometer. The acceleration time is set in the facto
(10 seconds).
When we release the ON/OFF switch the trigger outputs will slowly decreased to 180o from th
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 trigge
outputs are proper before connecting to the power circuits. Make the connections in the power circuit a
given in the circuit through isolation transformer. Initially keep the input supply at low voltage say 3volts. Connect the trigger outputs from firing circuit to the corresponding SCRs Gate and Cathode
Initially connect a Rheostat of 50 Ohms / 5amps. Switch ON the trigger outputs observe the voltag
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 fiel
terminals of DC motor to the field supply points in the power circuit. The connect armature terminal o
the DC motor through the rheostat and the rheostat and the ammeter provided in the unit to the output o
rectifier. Switch ON the field supply. Set the field voltage to some value 150Volts. This voltage ca
be measured using the voltmeter provided in the rectifier. Set the input voltage to 100Volts. Initiall
keep the firing angle pot at 180o. Initially keep the resistance at maximum position and cut off once th
DC motor starts. This is to limit the starting current. Switch On the MCB and trigger outputs. Vary th
firing angle potentiometer and note down the output voltage, output current and measure the speed of th
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DC motor for different values of firing angle. Note down these values in the tabular column. And als
observe the voltage waveforms. We can observe that back emf will increase as the speed increases. Nex
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 phas
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.
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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?
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SPEED CONTROL OF UNIVERSAL MOTOR
Aim:
To study the speed control of a Universal motor by varying armature applied voltage through phas
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
VoltageV0Output
Current I0
Speed
RPM
a) Firing Circuit:
This unit, generates line synchronized 2 pulse transformer isolated trigger pulses. These trigge
pulses can be used to trigger.
(i)
Single phase AC phase control using SCRs (Antiparallel SCRs)
(ii) Single phase AC phase control using triac.
(iii) Single phase Half wave rectifier (single SCR)
(iv) Single phase Full wave rectifier (Two SCRs)
(v) Single phase Half controlled bridge rectifier (Two SCRs & Two diodes) power circuits.
The firing circuit is based on zero crossing detector, ramp generator, op-amp comparator and amplifie
/ 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 180oto 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 SCRs, 3 diodes and a Triac. The power devices are mounted o
suitable heat sink for power dissipation. The snubber circuit is connected for dv/dt protection. A fuse i
also provided in series with the devices for short circuit or over current protection. In the input side
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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 : SCRs 16 Amps / 600 volts
5. D3& D4 : Diodes16amps / 600V
6. Dm : Free wheeling diode
7. TR : Triac10 amps / 600 volts
8. Voltmeter : 3 Digit digital AC/DC Voltmeter to measure input /
output voltage
9. Ammeter : 3 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 th
firing circuit and observe the trigger outputs. Make sure that the firing pulses are proper beforconnecting to the power circuit.
Then connect the trigger output from firing circuit to corresponding SCRs / Triac . In the powe
circuit Initially set the AC input to 30 volts. Switch ON and MCB. Switch ON the Trigger output
switch. Select the SCR / Triac selection switch and observe the output wave forms across R load b
varying the firing angle potentiometer. If the output wave form is proper then you can connect the moto
& increase the input voltage to rated value 0-230V gradually. Vary the firing angle and note down outpu
voltage and speed of the motor.
Note:
1) If you are not getting the output after all proper connections interchange AC output terminals, afte
switch OFF the MCB. This is just to synchronize the power circuit with firing circuit.
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Result:
Thus the speed control of Universal motor is performed by varying armature voltage through phas
controlled converter
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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?
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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?
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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 position6) From the capacitor output waveform we can measure the turn on time and turn off time of mai
SCR as well as auxiliary SCR
7) Verify the unity and frequency of the triggering circuit using parts provided on the triggerin
circuit.
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Result:
Thus the operation of class D commutated technique has been obtained.
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