Can a 3 Phase SCR Unit be Used as a Voltage Stabilizer?

If your voltage sags by 10 percent, your power is reduced by 19 percent. The SCR controller can only reduce power from the maximum, so it would depend on how close the oven is to full capacity at the controlled temperature.

Not with a temperature control in place: were the supply voltage to sag, then it would simply take the <...oven...> a little longer than normal to come up to temperature, and were it to soar, then it would take a little less time than normal.

I will add that it will take longer only if the PI controller was at max during a warming cycle.

A thermostat is often good enough.

There should be a voltage requirement on the electrical tag on the appliance that will give acceptable variation in supply voltage, which is usually 10%± but can be 5%± on more sensitive equipment... so for a resistive load, such as a heater, it usually is 10%...

https://www.electricaltechnology.org/2016/11/what-is-voltage-stabilizer-how-it-works.html

..."An SCR is either ON or OFF, so it can’t regulate voltage.

But it is sometimes used as a “crowbar” to short a voltage to ground in case it gets too high. For this, you just connect a zener diode from the gate to the voltage supply.

In an SCR full wave bridge, each scr is triggered in each ac cycle and conducts until current reverses. Control is done by timing of triggering.

https://www.sciencedirect.com/topics/engineering/controlled-rectifier

SCRs are used quite commonly to regulate voltage, it’s just a matter of adjusting the phase angle. The output is dc, granted, but that works fine for heating.

To actually answer the OP’s question, there is likely no advantage whatsoever to putting a voltage stabilizer on the front end. In fact, it might even degrade the performance if the stabilizer controller transfer function was close to your heater. The heater controller makes firing angle corrections at line frequency, so can be quite responsive. Since there is no regeneration, the cleanliness of the line frequency clock signal is more important than the magnitude, so it even has been past practice on some equipment to set a lower than normal threshold on the line voltage sensing divider, to assure a good clock signal (set up 480v controller to sense as if 240v line voltage, for example). Not likely needed in your case, with the absence of fault firing indication.

How about cascade control? Temperature controller controls output voltage setpoint. Then SCR controller maintains output voltage. Assumes line voltage always exceeds power requirement of course.

So the suggested arrangement doesn’t care about <...oven...> temperature. What is the point of it?

If only the heating elements are a concern, the scr controller can be used to regulate the power sent to them but controlling the voltage for the rest of the equipment is possible but too complicated to be explained here.

In general, sags are short compared to the oven's time constant and will have little effect on its performance but...

In the case of overvoltage (the voltage rises above nominal) the heating elements are likely to overheat if operating at maximum (usually during a warmup cycle). It may be prudent to reduce the maximum on cycle of the SCR controller to 90% if this is a common occurrence and you want to maximize the life of the heating elements. It may take longer to heat up the oven though.

The maximum limit setting of the SCR controller influences the product. Very high settings can produce more roasting and burning of the product surface than lower limits where the elements don't turn red. So, experiment to find out the best result.

It sounds as though great care is being taken about this equipment and none at all about what is inside it and the equipment’s performance.

That’s sdrawkcab.