Thyristorised Heater Control System

I dont know what is Sailent feature. silent? static? I can only explain that the scr controller change its stroble angle or control angle of the electric cureent to get the goal of change heating power. it can also change periodic on/off of current to change the heating ppower. most of the controler use pi or pid control. now more and more heater use igbt instead of scr.

A thyristor is used to reduce the power sent to a downstream load while dissipating rather less waste heat in itself than if a series resistance had been used to the same effect. In the case of an electrically-powered furnace, electricity costs have dictated the use of thyristors, as less heat is wasted. Thyristors, being electronic devices akin to a voltage- or phase-operated switch, lend themselves readily to the use of electronic control techniques to effect the power reduction required. In the furnace there will be a measuring instrument, providing an electronical analog of the furnace temperature and connected to a control system.

Somewhere in the control system there will be a set-point input, and somewhere there will be a device producing an output proportional to the error, proportional to the integral of the error over a particular time, and proportional to the rate of change of error with respect to time, where "error" is defined as "setpoint minus measured value". The proportional, integral and derivative characteristics can be set by the user in a process called "tuning", and this operation can sometimes be carried out automatically by algorithm(s) within the control equipment, and this paragraph can be applied to all feedback control loops where proportional-integral-derivative feedback control techniques are in use.

Try that.

That's an excellent description of PID in one paragraph!!

Back in the days before auto loop tuning controllers, it was nescessary to manually tune the control loops.Several methods were used, but I had much success using the 1/4 wave decay method.Adjust gain until a process upset results in an oscilaltion, with each succesive wave 1/4 the ampliude of the previous wave.The period of one cycle was used as the integral. The Derivitive was usually set at 1/8 of the integral.This was a good starting point, and you had to make minor adjustments for best performance.The first self-tuning loops were not very good, and were only good for a starting point.The new ones are much better.

Hi

using thyristor controller we can provide soft start. we can apply low power. in certain furnace silicon carbide heaters are used which need to start at low voltage to avoid thermal sock. Silicon carbide elements' resistance changes as it becomes old. it requies certain voltage reserve. so by varying firing angle we apply reqiures voltage to obtain same power after ageing.

This is my stock and trade, I build transformer coupled molybdenum disilicide glass furnaces for studio artists.

I build both single and polyphase equipment. One problem with these is that at low power settings the partially transmitted sine wave (how a current limiting S.C.R. lowers voltage) results in poor power factor. Not in the sense of leading and lagging that can be corrected with a capacitor, but the current stays fairly constant and you can have high apparant power useage (and you will get billed for it).

You also need the supply transformers to be oversized, if you tell the utility you are installing 75 kilowatts of equipment and they hang 75kva of transformers on the pole outside you will be sorely dissapointed with the equipment performance, you will end up with real soft voltage to the equipment and lots of transients on the line.

A thyristor (SCR silicon controlled rectifier) is a DC device that can be controlled by pulsing the gate with a control voltage. The device will hold on if the current flowing from the anode to cathode is above the hold voltage. If this voltage falls bellow the hold voltage the current is cut off until the gate is made positive again. So a pulse wave variable mark space signal can control another voltage on off. (burst fire).

The voltage can be an ac voltage if two SCRs are used. Another method is to use a triac three terminal ac device. These us a diac like a double diode to control the triac on of these can be used for proportional control, as well as burst fire. They are most commonly found in dimmer circuits. Thyristors are used in industrial equipment because the interface with digital controllers and computers more easily. Large motor control units or power sharing circuits, heating control, process controllers.