Performance analysis of Single Phase AC voltage controller with different load inductance.

Experiment No.: – 08

Aim of the Experiment: –

Performance analysis of Single Phase AC voltage controller with Lamp load.

Objective: – Understand how AC voltage controller using SCRs 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: –

The above circuit is a AC voltage controller. During the positive half cycle of input AC supply TH1 conducts and voltage appears across load. During negative half cycle TH3 conducts and negative voltage appears across the load. Changing the firing angle of both the SCRs can control the load voltage. Thus we get controlled AC voltage across the load. The direction of load current reverses in every half cycle of Input AC and the firing instance within these cycles can be controlled as such this arrangement is used for controlling AC power to load. Typical electrical heater based Ovens or Industrial furnaces employ this type of control. Here two distinct types are possible.

1. Integral cycle control- Here the control circuits ensures that SCRs are kept ON for required number of FULL AC cycles and then they are OFF. This cycle repeats so as to control average power delivered to load. This arrangement minimizes generation of unwanted EMI and RFI noise while switching power through SCRs, as the switching takes place almost near to load current zero. This type is demonstrated in a separate unit on application of SCR namely 6.1
2. AC phase control- This is demonstrated in PE trainer. Here SCR phase control is achieved in every cycle as per power requirement of load.

Procedures: –

1. For this unit we can use any two SCRs from CON/INV panel. Input AC should be used from top board. Lamp load is provided on top board.
2. Make the connections as per circuit diagram given above to form AC voltage controller. A 100W/230V lamp from top board should be used for load. 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. Now put on AC mains. Connect CRO across load and observe the load voltage. You can also observe change in conduction angle by varying the conduction angle control pot on LSPT panel.
4. Take the readings as per following table. Use 300V AC meter from top board for this purpose.

Observation Table: –

Sl. No.	Firing angle α	Input AC voltage on meter	AC voltage across load on meter
1
2
3
4
5

Conclusion: –

Written by student.