Performance of half wave SCR controlled Rectifier with R load.

Experiment No.: – 04

Aim of the Experiment: –

Performance of half wave SCR controlled Rectifier with R load.

Objectives: – Understand how controlled Half wave SCR based converter functions and also it’s associated waveforms.

Apparatus Required: –

Sl. No.	Name	Specification	Quantity
1	Experimental Kit	PE trainer with INV/CON panel	1 no.
2	DSO/CRO	Two channel	1 no.
3	Connecting wire	Patch cord	as per required.
4	Resistive load	100 W bulb.	1 no.
5	Multimeter/Voltmeter		1 no.

Circuit Diagram: –

Theory: –

Th1 conducts only when it’s anode is positive w.r.t. cathode and a synchronized gate pulse is applied to it.

During positive half cycle of input AC, ( as anode is positive w.r.t. cathode) if gate pulse is given at an angle α (ref wave form fig. 2.1) then SCR will conduct for π-α and voltage appears across load for the period (π-α). During negative half cycle of input this SCR is reversed biased so it will not conduct even gate pulse is applied.

We can vary the conduction period of an SCR by varying the firing angle. The angle between starting of  AC waveform and firing instance is known as firing angle.

Where as the angle between firing instance and end of the respective half cycle is known as conduction angle. If firing angle increases then conduction angle decreases and vice versa.

Using standard integration method as follows one may derive the formula for Average load voltage, 

Procedures: –

1. For this configuration, only one SCR is required. Choose any one SCR from con/Inv panel. The lamp load is available on top board. For input AC use 230 volt AC banana sockets from top board. Use 100 W lamp as load.
2. Make the connections as per circuit diagram given above to form half wave-controlled converter. All connections should be done using patch cords provided.
3. The firing pulse selector switch should be kept on 4^th position for getting required gate pulses. By doing so you are selecting UJT relaxation oscillator based SCR firing. Now put on AC mains.
4. Connect CRO across load and observe the output waveforms. You can also observe change in conduction angle by varying the conduction angle control pot on LSPT panel.
5. Take the reading as per following table. Use 300V DC meter from top board for this purpose.

Observation Table: –

Sr. No.	Firing angle α	Peak voltage Vin(mV)	Average voltage Vdc
			As per formula	On 300V DC meter
1
2
3
4
5

Conclusion: –

Written by student.