A Study of Single-Phase Full-Wave Controlled Rectifier Using R-Load and RL-Load

#LAB 2

STUDY OF SINGLE PHASE FULL WAVE CONTROLLED RECTIFIER USING R - LOAD AND RL - LOAD

OBJECTIVE

To familiarize with the SCR in controlled rectification with resistive (R) and inductive

(L) load.

APPRATUS REQUIRED

1. Thyristor Kit

2. Connecting Wires

3. Oscilloscope

4. Multi-meter

THEORY

Single-Phase Full-Wave Controlled Rectifier using R - load Single-Phase Bridge Rectifier

Figure 1(a)shows a fully controlled bridge rectifier, which uses four thyristors and a

resistive load and also the resulting voltage and current waveforms are shown infigure 1(b).

During the positive half cycle of source voltage, thyristors T1 and T2 are in forward blocking mode and T3 and T4 are in reverse blocking mode. The thyristor does not conduct until they are triggered. When thyristors T1 and T2 are triggered at [illustration not visible in this excerpt] and [illustration not visible in this excerpt] go in forward conduction mode and thus starts conducting upto ωt = π. The output voltage appears for the period of [illustration not visible in this excerpt] and T2 goes turned off by natural commutation.

During the negative half cycle of source voltage, thyristors T1 and T2 are in reverse blocking mode and T3 and T4 are in forward blocking mode. The thyristors does not conduct until they are triggered. When thyristors T3 and T4 are triggered at [illustration not visible in this excerpt]

and T4 go in forward conduction mode and thus starts conducting upto [illustration not visible in this excerpt] The output voltage appears for the period of [illustration not visible in this excerpt].

The average value of load voltage (output voltage) is given by,

illustration not visible in this excerpt

Figure 1: (a) Single phase full wave (bridge) controlled rectifier circuit with R - load and (b) Waveforms

Single-Phase Full-Wave Controlled Rectifier using RL - load

Figure 1(a)shows a fully controlled bridge rectifier, which uses four thyristors and a load is depicted as series combination of resistance (R) and inductance(L). The inductance is very high considered here for constant current. The waveforms output voltage and current with current in individual components are shown infigure 2.

During the positive half cycle of source voltage, thyristors T1 and T2 are in forward blocking mode and T3 and T4 are in reverse blocking mode. When thyristors T1 and T2 are triggered [illustration not visible in this excerpt] go in forward conduction mode and thus starts conducting. Due to the highly inductive load, current doesnot decay to zero ωt = π and negative voltage will appear across load from [illustration not visible in this excerpt] The thyristors T1 and T2 remains in forward conduction mode due to the inductor current and therefore T1 and T2 conduct from [illustration not visible in this excerpt]

At [illustration not visible in this excerpt] thyristors T1 and T2 are undergoes reverse blocking mode and T3 and T4 are already in forward blocking mode at [illustration not visible in this excerpt] and when it is triggered at [illustration not visible in this excerpt] then it starts conducting and continues to conduct upto [illustration not visible in this excerpt]. Each pair of thyristors conduct 180[0] conduction angle.

illustration not visible in this excerpt

Figure 2: Waveform of fully controlled single phase bridge rectifier with resistive-inductive (RL) load

illustration not visible in this excerpt

Full wave controlled rectifier with R - load

illustration not visible in this excerpt

Full wave controlled rectifier with RL - load

illustration not visible in this excerpt