Reverse Parallel Thyristor Configuration

The other half of the sine wave.

But with a sine wave voltage source, how do you know which thyristor is the reverse thyristor?

The three that are upside-down/backwards compared to the other three?

To be certain you must test them out of circuit. Cut the leads. Shake them. The electrons will only fall from one lead. Mark that lead on each. Then install three with the mark down, three with the mark up.

Fwd & Reverse connected SCRs to conduct on both the 1/2 cycles to pass current [controlled as per gate signal to the relative scr alternately] .

It is posted in simple words by #1.

I understand that it's difficult to grasp at first, but draw out a 3 phase circuit with 6 thyristors paired as inverse parallel sets. Then visualize each of the 3 sine waves and how turning on only one thyristor in each pair will affect the shape and magnitude of the sine waves. Remember that the voltage must flow from one phase to another in order to be valid, and an SCR that is not gated blocks the flow. When you follow the COMPLETE logic sequence it becomes evident.

Side note: you can use 3 triacs or 3 thyristors and 3 diodes to allow current to flow, but think of that scenario in terms of the goal, that of reducing the RMS voltage in the circuit as smoothly as possible. What you will see is a very misshapen sine wave, which is why it is not done very often that way.

Dear JRaef,

I now understand it. First we have to visualize it for single phase then extend it to 3-phase pattern. The forward biased thyristror will pass the positive cycle while negative cycle will pass through the reverse biased thyristor depending upon the firing angle. The average voltages pass to the load.

Kid question; Because it is AC!