What is line commutation?
Natural or Line commutation is a Class-F SCR commutation technique in which, a thyristor is turned off due to natural current zero and voltage reversal after every half cycle.
What is commutation of a thyristor?
Commutation is defined as the process of turning-off a thyristos. – Turn-off of a thyristor means, bringing the device. from forward-conduction mode to forwarda blocking mode. – Turn-off process of thyristor requires. @ Anode current to be reduced below holding current.
What are the methods for commutation of a thyristor?
Thyristor Commutation Techniques
- Natural Commutation.
- Forced Commutation. Class A: Self or Load Commutation. Class B: Resonant-Pulse Commutation. Class C: Complementary Commutation. Class D: Impulse Commutation. Class E: External Pulse Commutation.
What are the two methods of commutation?
There are two types of commutation viz. current and voltage based. There are two methods for commutation viz. natural commutation and forced commutation.
How would the need of commutation in thyristor circuit?
Commutation means transfer of current from one circuit to another. The anode or forward current of SCR must be reduced to zero or below the level of holding current and then, A sufficient reverse voltage must be applied across the SCR to regain its forward blocking state.
What do you mean by commutation?
Commutation refers to the right that a beneficiary has to exchange one type of income for another. Commutation is offered to annuitants and to the beneficiaries of life insurance policies so that they might receive a lump-sum payment instead of a series of future payments.
What are the two conditions of commutation of a thyristor?
This external circuit is known as commutation circuit. To turn off an SCR / thyristor, it is required that its anode current should fall below the holding current and a reverse voltage should be applied across the SCR for the sufficient time so that it regains to forward blocking mode from forward conduction mode.
What is line commutation and forced commutation?
It is also called as phase commutation, line commutation or AC commutation. The SCR turns off automatically during negative half cycle of alternating supply when reverse voltage applied across SCR for sufficient time. The time period of the negative half cycle should be more than the turn off time of the SCR.
What are different types of commutation?
Three types of commutation are identified: i) Voltage commutation, ii) Current commutation and iii) Load commutation.
Why is commutation needed?
The commutator assures that the current from the generator always flows in one direction. On DC and most AC motors the purpose of the commutator is to insure that the current flowing through the rotor windings is always in the same direction, and the proper coil on the rotor is energized in respect to the field coils.
Which of the following is also known as line commutation?
The class F commutation is also called as line or natural commutation because the SCR is turned off automatically during negative cycle of alternating supply.
How are the commutation methods of the thyristor used?
So, the thyristor commutation methods or thyristor commutation techniques are used to turn off. The commutation techniques of thyristors are classified into two types: Generally, if we consider AC supply, the current will flow through the zero crossing line while going from positive peak to negative peak.
What is the process of turning off a thyristor?
The process used for turning off a thyristor is called as commutation. By the commutation process, the thyristor operating mode is changed from forward conducting mode to forward blocking mode. So, the thyristor commutation methods or thyristor commutation techniques are used to turn off.
Which is a subclass of forced commutation?
A sub-classification of forced commutation in which the device is commutated by transferring the load current of the main thyristor to another thyristor in the circuit is Class C Commutation of the Thyristor. Another name for this type of commutation is complementary commutation.
When to use line commutation in SCR circuit?
This commutation method is only applicable for AC circuit and mostly used in Phase-Controlled Converters, Line-Commutated Inverters, AC voltage controllers and Step-down cycloconverters. When an SCR circuit is energized from an AC source, current has to pass through its natural zero at the end of every half cycle.