Experiment No
SINGLE PHASE SEMI CONVERTER
Specification:
Kit working voltage
Input voltage
Controlled Output Voltage
:
:
:
220-240V AC
110V AC (±5)
130 V DC (variable)
Circuit Details:
T1 , T 3 act as converter circuit.
G1 , G3 used as test point for gate pulse.
Incandescent lamp (100W) load is used for load.
SW1 switch is used for the main power circuit.
SW2 switch is used for the Triggering Pulse circuit.
Pulse is generated by TCA785IC.
α Potentiometer is used to vary the firing angle
Components Details:
SCR Pulse Laod -
TYN612
TCA785
Incandescent Lamp (100W)
INTRODUCTION TO CONTROLLED RECTIFIERS
Controlled rectifiers are line commutated ac to dc power converters which are used to
convert a fixed voltage, fixed frequency ac power supply into variable dc output voltage.
Type of input: Fixed voltage, fixed frequency ac power supply
Type of output: Variable dc output voltage
The input supply fed to a controlled rectifier is ac supply at a fixed rms voltage and at a
fixed frequency. We can obtain variable dc output voltage by using controlled rectifiers. By
employing phase controlled thyristors in the controlled rectifier circuits we can obtain variable
dc output voltage and variable average dc output current by varying the trigger angle at which
the thyristors are triggered. We can obtain a uni-directional and pulsating load current
waveform, which has a specific average value.
The thyristors are forward biased during the positive half cycle of input supply and can
be turned ON by applying suitable gate trigger pulses at the thyristor gate leads. The thyristor
current and the load current begin to flow once the thyristors are triggered at ωt=α. The load
current flows when the thyristors conduct from ωt=α to π. The output voltage across the load
follows the input supply voltage through the onducting thyristor. At ωt= π, when the load
current falls to zero, the thyristors turn off due to AC line commutation.
The thyristor remains reverse baised during the negative half cycle of input supply. The
type of commutation used in controlled rectifier circuit is referred to AC line commutation or
natural commutation AC commutation.
When the input ac supply voltage reverses and becomes negative during the negative
half cycle, the thyristor becomes reverse baised and hence turns off.
APPLICATIONS OF PHASE CONTROLLED RECTIFIERS
1. DC motor control in steel mills, paper and textile mills employing dc motor drives.
2. AC fed traction system using dc traction motor.
3. Electro chemical and electro-metallurgical processes.
4. Magnet power supplies.
5. Reactor controls
6. Portable hand tool drives.
7. Variable speed industrial drives.
8. Battery charges
9. High voltage dc transmission.
10. Uninterruptible power supply system (UPS)
SINGLE-PHASE SEMI CONVERTER
AIM:
To obtain DC voltage from AC input using single phase semi converter with R load and to plot
the variation of output voltage with respect to different values of α.
APPARATUS REQUIRED:
Sl.No.
1
2
3
4
5
Item
SCR
Power diode
CRO
Bread board
Triggering Kit
Specification
TYN612
IN 4001
-
Quantity
2
2
1
1
1
THEORY:
Figure 1 shows the circuit diagram of single phase semi converter supplying a R load. The output
voltages vo across load terminals is controlled by varying the firing angles of SCRs T1 and T2.
The diodes D1 and D2 provide merely a return path for the current to the most negative line
terminal. Figure 2 shows voltage and current waveforms for a 1-phase semiconverter for
different firing angles At any instant thyristor connected to most positive line terminal and diode
connected to most negative line terminal conducts. During positive cycle thyristor T1 and diode
D2 conducts. During negative cycle thyristor T2 and diode D1 conducts. As the triggering angle
α increases, the output voltage decreases.
Output voltage, Vo= (Vm [1+cos α])/ π
Where α=firing angle of SCR, Vm= maximum value of phase voltage.
PROCEDURE:
Initial Settings

Ensure the 230V power supply is in proper with tester
 Ensure the CRO is working properly with probe checking and proper ground line axis.
Experimental Steps
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The connections are made as per the circuit diagram
The R load must be 60W bulb or 200Ω/2A rheostat. The load is 120mH/2A.
When the load is rheostat,it must be in maximum position
Turn ON the SW2 and observe the wave form across G1 & K1, G2 & K2. And ensure it
is like triggering pulse given in model graph.
Turn ON SW1 and observe the wave form across the R load.
Measure the X-axis time interval of ON time of load voltage and OFF time of load
voltage.
Adjust the value of firing angle and note down the load voltage and current.
Repeat the experiment for different values of α and note down Vo
CONNECTION DIAGRAM:
Figure 1:Connection diagram for 1 phase semi converter with R load.
WAVEFORM:
Figure 2: Input Voltage and output voltage waveform for a 1-phase semiconverter for a particular
firing angle α.
Figure 3: Waveform showing the variation of output voltage with respect to α.
RESULT:
Connections were made as given in the diagram and the wave forms were observed in the CRO.