What Is Meant By Natural Commutation?

What is the difference between natural 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.


What is forced commutation in SCR?

Forced Commutation Thyristor current can be reduced to a value below the value of holding current. Since, the thyristor is turned off forcibly it is termed as a forced commutation process. … Forced commutation can be observed while using DC supply; hence it is also called as DC commutation.

Why is snubber circuit important?

Snubber circuits are needed to limit the rate of change in voltage or current (di/dt or dv/dt) and over voltage during turn-on and turn-off. These are placed across the semiconductor devices for protection as well as to improve the performance.

What are the types of commutation?

The reverse voltage which causes to commutate the SCR is called commutation voltage. Depending on the commutation voltage located, the commutation methods are classified into two major types. Those are 1) Forced commutation and 2) Natural commutation.

What is meant by load commutation?

Load commutation of SCR is a forced commutation technique in which SCR is forced to turn off. … In Load Commutation, Capacitor C & Inductor L are used as commutating element. Commutating element L and C are connected in series with the load resistance if the value of load resistance is low.

What is voltage commutation?

Commutation is the process when conduction switches from one supply phase to another. … If there is inductance in the supply circuit, a conducting diode will not switch off as soon as one of the other phase voltages exceeds the existing supply phase voltage.

Why is commutation needed?

The basic purpose of commutation is to ensure that the torque acting on the armature is always in the same direction. The voltage generated in the armature is alternating in nature, and the commutator converts it to direct current.

What is commutation problem in DC transmission?

Commutation failure can be defined as an adverse dynamic event that occurs when a converter valve that is supposed to turn off, continues to conduct without trans- ferring its current to the next valve in the firing sequence.

What is a firing circuit?

1. In land operations, an electrical circuit and/or pyrotechnic loop designed to detonate connected charges from a firing point. 2. In naval mine warfare, that part of a mine circuit which either completes the detonator circuit or operates a ship counter. Dictionary of Military and Associated Terms.

What is commutation in inverter?

Commutation is basically the. act of stopping or diverting current flow from a conducting. path in such a circuit. The inverter differs by requiring a. switching elementin which control can be regained be-

What is snubber circuit?

A snubber circuit limits or stops (snubs) switching voltage amplitude and its rate of rise, therefore reducing power dissipation. In its simplest form, a snubber circuit basically consists of a resistor and capacitor connected across the thyristor.

Can SCR convert AC to DC?

An SCR converts an AC voltage to a DC voltage. Unlike a diode that turns on when . … Once activated, it will remain on until the gate trigger voltage is removed or the anode to cathode current (also known as holding current IH) is reduced to a level below its designed operating threshold.

What is latching current in SCR?

Latching current can be defined as it is the least amount of anode current which is necessary to supply from the anode terminal to the cathode terminal to activate the SCR after detaching the gate terminal. This is allied with the turned-off method.

How is thyristor turned off?

Thus, a thyristor behaves like a normal semiconductor diode after it is turned on or “fired”. The GTO can be turned on by a gate signal, and can also be turned off by a gate signal of negative polarity. … Turn off is accomplished by a “negative voltage” pulse between the gate and cathode terminals.

Why do we use thyristors?

Thyristors are mainly used where high currents and voltages are involved, and are often used to control alternating currents, where the change of polarity of the current causes the device to switch off automatically, referred to as “zero cross” operation.

What is excitation angle?

The excitation angle or angle of incidence is the angle in which the horizontal seismic components are applied with respect to the principal structural axes during a time history analysis.

What is commutation in HVDC?

Most of the HVDC systems in operation today are based on line-commutated converters (LCC). The term line-commutated indicates that the conversion process relies on the line voltage of the AC system to which the converter is connected in order to effect the commutation from one switching device to its neighbour.

How is snubber circuit calculated?

Calculate the minimum value for the resistor in the RC snubber by dividing the voltage across the switch by the maximum current rating. For example, suppose the voltage measurement is 160 volts and the maximum current is 5 amps. … Your snubber must use a resistor that has a minimum resistance of 32 ohms.

Who is a snubber?

A snubber is a device used to suppress (“snub”) a phenomenon such as voltage transients in electrical systems, pressure transients in fluid systems (caused by for example water hammer) or excess force or rapid movement in mechanical systems.

What is a firing angle?

Firing Angle: The number of degrees from the beginning of the cycle when SCR is switched on is firing angle. Any SCR would start conducting at a particular point on the ac source voltage. The particular point is defined as the firing angle.

How is a thyristor controlled?

In an electric power transmission system, a thyristor-controlled reactor (TCR) is a reactance connected in series with a bidirectional thyristor valve. The thyristor valve is phase-controlled, which allows the value of delivered reactive power to be adjusted to meet varying system conditions.

What is natural or 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 failure?

Commutation failure (CF) is an adverse and frequent dynamic event in high-voltage direct current (HVDC) systems based on line-commutated converter technology. It is most often caused by AC system faults in the receiving-end grid [1].