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The thyristor is basically used a switch in an AC circuit to control the amount of power fed to the load. To turn on this switch an "electric" pulse should be applied to the Gate terminal of the Thyristor. A circuit which supplies the "electric" pulse is called the firing circuit.
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What is a line commutation?
it is the natural commutation ...by making open circuit or short circuit on the thyristor to make it turn off.
What is the difference between firing and triggering a thyristor?
There is no difference. The terms "firing" and "triggering" both mean exactly the same.As long as the voltages applied to both the anode and the gate have the correct values and polarities for a particular design of thyristor, "firing" or "triggering" will cause current to switch on between the thyristor's anode and cathode. The current will then continue to flow for as long as the correct source voltage polarity is maintained onto the anode.Another opinionIf the input signal is given to a thyristor, it is said to be gated. Because of gating pulse the thyristor gets triggered ( cause & effect relationship). Once the thyristor is triggered the charged particles starts moving inside the different layers. A noise is created called "SHOT NOISE", due to the movement of charged particles. Heat energy is dissipated due to this movement of charged particles. Once the thyristor reaches this stage it is said to be fired. Hence, there is a minute difference between these three terms. But all these terms are being used interchangeably.
Why would you color code a Thyristor?
The 3 wires on a Thyristor are colour coded in order not to connect the wrong wire to the incorrect part of the circuit. The three wires are called: anode (OV), cathode (output) and gate (input signal). Sorry I don't know the colours but I hope this helps.
How does a thyristor function?
A thyristor is a semiconductor device which acts as a switch.
What is ac chopper?
AC chopper is also called AC voltage controller. In AC voltage controller, we use 2 thyristors as switching element. In AC chopper we use MOSFET or IGBT as switching element with diodes in bridge rectifier for bidirectional flow of current. This use of mosfet switch has the following advantages over thyristor: * no separate firing circuit are needed for Mosfet ( it can be driven directly by interfacing it with MC) whereas firing circuits are needed for SCR. *when the line current drops to zero SCR turns off due to natural commutation( when it reaches 172 deg) ; mosfet- user control - we can turn on and off as per our requirement. * snubber circuit is needed for thyristor phase control method. By using mosfet in diode rectifier provides internal snubber
What are types of thyristor?
Types of thyristor firing art
What does forced commutation mean?
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.
How thyristor used in induction furnace?
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)
What is a line commutation?
it is the natural commutation ...by making open circuit or short circuit on the thyristor to make it turn off.
What is thyristors?
A thyristor is a part of a alarm circuit you use it so the alarm stays on
What circumstances led to the invention of the transistor in 1947?
before the invention of transistor,thyristor was used instead of transistor but thyristor produces more heat in the circuit and size is more when compared to transistor
Why thyristor used in resistance welding machine?
For firing current between the the moving arm of the gun and the fixed arm
What is the difference between firing and triggering a thyristor?
There is no difference. The terms "firing" and "triggering" both mean exactly the same.As long as the voltages applied to both the anode and the gate have the correct values and polarities for a particular design of thyristor, "firing" or "triggering" will cause current to switch on between the thyristor's anode and cathode. The current will then continue to flow for as long as the correct source voltage polarity is maintained onto the anode.Another opinionIf the input signal is given to a thyristor, it is said to be gated. Because of gating pulse the thyristor gets triggered ( cause & effect relationship). Once the thyristor is triggered the charged particles starts moving inside the different layers. A noise is created called "SHOT NOISE", due to the movement of charged particles. Heat energy is dissipated due to this movement of charged particles. Once the thyristor reaches this stage it is said to be fired. Hence, there is a minute difference between these three terms. But all these terms are being used interchangeably.
Can a thyristor work as a circuit breaker?
A thyristor is primarily a very fast "switch-on" device and is not designed to be used as a "switch-off" device.A circuit breaker is primarily a "switch-off" device which is used to automatically break the flow of current from a source to a load whenever the amount of current exceeds the rated current value of the breaker.So, because a thyristor does not, all by itself, "open" a circuit, a thyristor cannot be used to work as a circuit breaker.NotesCurrent flow through a thyristor can only stop if - external to it - the current flowing through it gets reduced to below its minimum holding current or, of course, to zero, as would happen either:i) if the load was disconnected from it by a separate circuit breaker that is wired into the circuit between the thyristor and the load;orii) if the source was disconnected from it by a separate circuit breaker that is wired into the circuit between the supply and the thyristor.Further notesA thyristor is designed to close or "make" a circuit whenever:a) an appropriate value of trigger voltage is put onto its gateand then only if:b) the current from the source to the load can flow through it in its "forward" direction.One way of ensuring it automatically disconnects the load from the source is to use an alternating current supply and always "trigger" the thyristor so that it turns on during each positive-going part of each ac cycle.Then, whenever the ac supply voltage returns to zero at the end of each positive half-cycle (after which it goes into the negative half-cycle) the thyristor will automatically break any further flow of current.By using other electronic circuitry to determine exactly when the gate is triggered (earlier or later in each positive-going part of each cycle) the amount of power supplied to the load can be controlled very accurately.That is why the main application for thyristors is to provide a precisely controlled way too use alternating currents to allow varying amounts of power to be supplied to electrical loads.
State one example of an automatic Voltage system that is error actuated?
An AVR circuit, the voltage sensing unit measures the incoming voltage and compares it to the set point. Then an error signal is produced and sent to the amplifier,the error signal then reaches a firing circuit which consists of a thyristor with a field current which will adjust alternators output current. Dependant on the signal from the actuating unit.
How does the turn off circuit on a Class B type thyristor work?
The Class B type of commutation circuit uses an LC circuit in parallel with the thyristor. During initial power up, the capacitor C charges to the supply voltage (Edc) and the thyristor is OFF. The initial charging current of the LC branch flows thru the load. When the thyristor is fired, the supply DC voltage is applied across the load, and the voltage across the LC branch goes to almost zero (the forward drop of the thyristor). Then the LC circuit enters a resonant discharge with an angular frequency of the square root of the inverse of LC product. The LC resonant cycle supplies a peak forward current thru the thyristor of Edc times the square root of C/L. This peak current must exceed the load current in order to effect the turn-off of the thyristor during the second half of the discharge resonant cycle. This peak current is usually designed to be twice the load current. The thyristor is reversed biased (and turned OFF) during the first quarter cycle of this second half of the resonant cycle - thus allowing the supply to recharge the capacitor in the LC parallel branch. Then the cycle can repeat.
What does a thyristor works as a circuit breaker?
A thyristor is a type of semi-conductor and is used in a circuit to control the application of electrical power to a load. They are often found as the switching element in light dimmers and can be used as control elements in power supplies (variable or regulated). Types of thyristors are diacs, triacs, sidacs and SCRs (silicon controlled rectifier).
