the fire angle is the angle at which the thyristor starts working...
not a clue a A: It all depends on the thyristor. There are no calculation involved not until you look up the thyristor specifications and decide on the load of the thyristor then you may calculate or more likely choose.
Thyristor is used for Rectifiying and inverting the power supply in induction furnace. The parallel Resonance Coils (Current Control Furnaces) Control the Furance power up to 40% by controlling the firing angle of the rectifier inverter and remaining 60% controlled by inverter thyristor control. In rectifier they are varying the thyristor firing angle from 15 deg to 45 deg. (in sin wave)
In a single-phase semi-converter operating under discontinuous conduction, each thyristor conducts for a conduction angle of α to β, where α is the firing angle and β is the extinction angle. The conduction angle for each thyristor is therefore given by the formula ( \theta = \beta - \alpha ). Since the conduction is discontinuous, this angle is typically less than 180 degrees, resulting in each thyristor conducting for a part of the AC cycle, followed by a period where it is off. In general, the conduction angle can vary based on the firing angle and load conditions, but the key point is that it occurs only for the duration between firing and extinction.
Types of thyristor firing art
The turn off and turn off mechanism of a thyristor can be best explained by the gate turn-off thyristor. The thyristor uses the reverse bias mechanism.
A thyristor is a semiconductor device which acts as a switch.
Thyristor is a kind fast acting switch. These are fully controlled switches
The term "Forced commutation" is used when a thyristor is turned off using external components. If a thyristor is used in a DC circuit, when first turned on, it will stay on until the current goes to zero. To turn off the thyristor it is possible to use a Forced commutation circuit. The circuit creates a reverse voltage over the thyristor (and a small reverse current) for a short time, but long enough to turn off the thyristor. A simple circuit consist of a precharged capacitor and a switch (e.g. another thyristor) parallel to the thyristor. When the switch is closed, the current is supplied by the capacitor for a short while. This cause a reversed voltage over the thyristor, and the thyristor is turned off.
No because a mosfet does not work the same as a thyristor. In a thyristor the current flows even when the gate pulse is removed, until the current stops. That is not the case for a FET.
There are more than two conditions that can make a thyristor conduct, but the general (functional) ones are: 1) positive voltage form anode to cathode, and 2) a positive voltage on the trigger input (referenced to the cathode) for a standard polarity thyristor. Other conditions can be: A) Anode-Cathode Voltage exceeding thyristor witholding voltage. B) Overtemperature of the thyristor chip C) Faulty thyristor (can be caused by overloads)
A conducting thyristor can be turned off by reducing the current flowing through it below the holding current value. This can be achieved by interrupting the current flow using a circuit breaker, reverse biasing the thyristor, or triggering the thyristor with a gate signal that transitions it into a non-conducting state.