Power Electronics Laboratory Reg. No. ______________________

Session 2011 Seventh Semester EED,UET, Lahore

Experiment No. 3

Full Wave Rectifier Using R-Triggering and R-C Triggering Objectives:

1. To analyze full wave R- firing network of SCR. 2. To analyze full wave RC- firing network of SCR.

Equipment: AC supply, oscilloscope, SCR (MCR 100-6), single phase Diode Bridge, load resistor of designed value, variable gate resistance, connecting wires and breadboard. Circuit Diagram:

Figure 4a Task: Vary the firing angle (0 to 90 degree) by changing the gate resistance and observe load voltage and voltage across thyristor on the oscilloscope. Sketch waveforms for selected values of firing angle. Design Procedure: The design equations are same as used in experiment number 2 for half wave R-triggering.

• Load Resistance = ____________ ohms • Rmin = ______________________ ohms • Gate resistance = ______________ohms

Procedure:

1. Adjust the supply voltage as used in design procedure. Recommended is 10 V peak at

frequency of 50

2. Arrange the circuit as shown in Figure 4a.

Power Electronics Laboratory Reg. No. ______________________

Session 2011 Seventh Semester EED,UET, Lahore

3. Keep the potentiometer resistance RG to its maximum value so IG is very small and

SCR is not triggered. Measure and observe the voltage across load and SCR.

4. Decrease the resistance of potentiometer RG such that SCR is now fired and almost all

the input voltage appears across the load. Measure and observe the change in voltage

across load and SCR

5. Record your observations for at least ten different firing angles over the entire range

of observation.

6. Record your observations and calculations in tabular form and also plot the

waveforms observed on oscilloscope.

7. Compare the practical output voltage with theoretical output voltage.

Observation Table:

No. Firing Angle α Vo (dc)

(Practically using DMM)

Vo (dc)

(Theoretically using

calculations)

1.

2.

3.

4.

5.

6.

7.

8.

9.

10.

Power Electronics Laboratory Reg. No. ______________________

Session 2011 Seventh Semester EED,UET, Lahore

Sketch voltage waveform across load resistance for firing angle in reading 2

Sketch voltage waveform across thyristor for firing angle used above

Sketch voltage waveform across load resistance for firing angle in reading 4

Sketch voltage waveform across thyristor for firing angle used above

Power Electronics Laboratory Reg. No. ______________________

Session 2011 Seventh Semester EED,UET, Lahore

Sketch voltage waveform across load resistance for firing angle in reading 6

Sketch voltage waveform across thyristor for firing angle used above

Power Electronics Laboratory Reg. No. ______________________

Session 2011 Seventh Semester EED,UET, Lahore

Show your calculations for voltage with firing angle in reading 3

Show your calculations for voltage with firing angle in reading 7

Sketch the variation of output voltage with firing angle.

Comments:

___________________________________________________________________________

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___________________________________________________________________________

___________________________________________________________________________

___________________________________________________________________________

Power Electronics Laboratory Reg. No. ______________________

Session 2011 Seventh Semester EED,UET, Lahore

Performance Parameters: Evaluate the following parameters by consulting the suggested pre-lab reading. Also consult the lab manual handout of Experiment No. 1 (use a separate paper sheet if required, to record the required observations and details of calculations): Rectifier Efficiency = _______________ Form Factor = _______________ Ripple Factor = ________________ Transformer or Source Utilization Factor (TUF) = _________________ Express the output voltage (at firing angle of 30 degree) with Fourier series.

Power Electronics Laboratory Reg. No. ______________________

Session 2011 Seventh Semester EED,UET, Lahore

Now update the circuit in Figure 4a to look like as shown in Figure 4b.

Figure 4b Task: Vary the firing angle (90 to 180 degree) by changing the gate resistance and observe load voltage and voltage across thyristor on the oscilloscope. Sketch waveforms for selected values of firing angle. Design Procedure: The design equations are same as used in experiment 3 for half wave RC-triggering.

• Load Resistance = ____________ ohms • Rmin = ______________________ ohms • Gate resistance = ______________ohms • Capacitor =___________________

Procedure:

1. Keep the potentiometer resistance RG to its maximum value so IG is very small and

SCR is not triggered.

2. Decrease the resistance of potentiometer RG such that SCR is now fired and almost all

the input voltage appears across the load. Measure and observe the change in voltage

across load and SCR

3. Record your observations for at least ten different firing angles over the entire range

of observation.

4. Compare the practical output voltage with theoretical output voltage.

Power Electronics Laboratory Reg. No. ______________________

Session 2011 Seventh Semester EED,UET, Lahore

Observation Table:

No. Firing Angle α Vo (dc)

(Practically using DMM)

Vo (dc)

(Theoretically using

calculations)

1.

2.

3.

4.

5.

6.

7.

8.

Sketch voltage waveform across load resistance for firing angle in reading 2

Sketch voltage waveform across thyristor for firing angle used above

Power Electronics Laboratory Reg. No. ______________________

Session 2011 Seventh Semester EED,UET, Lahore

Sketch voltage waveform across load resistance for firing angle in reading 4

Sketch voltage waveform across thyristor for firing angle used above

Sketch voltage waveform across load resistance for firing angle in reading 6

Power Electronics Laboratory Reg. No. ______________________

Session 2011 Seventh Semester EED,UET, Lahore

Sketch voltage waveform across thyristor for firing angle used above

Sketch voltage waveform across load resistance for firing angle in reading 8

Sketch voltage waveform across thyristor for firing angle used above

Power Electronics Laboratory Reg. No. ______________________

Session 2011 Seventh Semester EED,UET, Lahore

Show your calculations for voltage with firing angle above 90 degree.

Sketch the variation of output voltage with firing angle.

Comments:

___________________________________________________________________________

___________________________________________________________________________

___________________________________________________________________________

___________________________________________________________________________

___________________________________________________________________________

___________________________________________________________________________

___________________________________________________________________________

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Assignment:

1. Simulate the two circuits in MultiSim/Orcad and attach the circuit diagram and waveforms with this manual.