Tech View

Innovation in Arc Extinguishing Technologies

New- generation technologies (Arc Accelerated Rapid Cooling) increase compactness and performance.

Here we discuss on the invention related to the integral design of high permeability plates housing and ferromagnetic de-ion plates housing. The innovators have provided grooving in the high permeability plates housing to increase the speed of air circulation so that the arc movement speed will be faster. Along with this feature, a U-shape fixed contact is also provided for high repulsion force and thermoplastic material is used for housing to get ablation effect for de-ionisation of ionised gases. As the three forces acting on the optimised space the ionised gases will be evacuated very quickly from the outlet.

Low resistance or current zero method
This method is employed for arc extinction in AC circuits only. In this method, arc resistance is kept low until current zero where the arc extinguishes naturally and is prevented from restriking in-spite of the rising voltage across the contacts. All modern high power AC circuit breakers employ this method for arc extinction.
Lengthening of the gap: The dielectric strength of the medium is proportional to the length of the gap between contacts. Therefore, by opening the contacts rapidly, higher dielectric strength of the medium can be achieved. (Patent applied)

Multi-finger concept results in reduced electromagnetic repulsive forces of the contact region and gives good short time current resistant performance.

Detailed description
A current limiting circuit breaker comprising of a hiperm treated material enclosing the moving contact as magnetic accelerator. The threshold value of tripping current is reduced by concentrating the magnetic flux lines to drive the contact arm faster and produce enhanced current limiting effect. The technology of decarburising reduces the percentage of carbon & Watt-Loss in ferromagnetic material.

The Hiperm treated material leads in increased permeability leading to higher concentration of flux, thus, higher magnetic force. The steel piece is Nickel plated so as to further increase the magnetic effect utilising the ferromagnetic property of nickel.

Extreme over current conditions through the contacts generate magnetic flux in the magnetic accelerator across the open end of the slot which interacts with current flow through the contact arm to produce a magneto dynamic force driving the contact arm from the first position to second position. This accelerator includes a saturable magnetic core which increases the magnetic flux intensity and magnetic force on the arc to move it faster towards arc splitter plates.

Arc Chute for MAX3Air Circuit Breaker
The arc chute of low-voltage air circuit breaker comprises of a stack of steel plates. These plates have high magnetic permeability. The volume between arc chute chamber and arc ignition point is decreased which increases the velocity of arc towards arc chutes due to increased pressure. Above the arc chute plates there is a wire mesh and a ferromagnetic plate. Between the wire mesh and ferro-magnetic plate is a chamber in which the deionisation of gases takes place. This prevents the interaction of the ions between different phases and reduces the chances of phase to phase short circuit. (Patent applied)

The volume between arc chute chamber and arc ignition point is decreased which increases the velocity of arc towards arc chutes due to increased pressure

Detailed description
Decarburised Hi-perm treated Nickel plated Deion grids are placed close to the contacts and a close ended steel grid is placed on the top of the splitter plates to create deionisation chamber.

During short circuit: Under such high currents a high magnetic force is created which blows apart the arc that strikes between the contacts. Decarburised hi-perm treated Deion grids have high permeability which leads to higher magnetic field intensity and increased magnetic force on the arc. The movement of arc that constitutes ionised particles is assisted by increased magnetic field intensity which is directly related to permeability. This results in quicker arc quenching.

The arc chute plays a major role in proper arc quenching in a low voltage circuit breakers. The arc chute consist of stack of de-ion plates made up of magnetic material to attract, split-up and cool the arcs. The stack of de-ion plates is trapped between two plates known as lining made up of electrically insulated material. The function of de-ion plates is to split the arc in a plurality of arcs of approximately equal length which results in higher arc voltage and distinctly greater dielectric strength after current zero. The assembly was enclosed in a thermoplastic housing with basic design of gas evacuation and high permeability plates were enclosed in separated housing.

The Invention
The invention relates to electric circuit breakers for interrupting low voltage power circuits and more particularly to Moulded Case Circuit Breakers and Air Circuit Breakers.

The magnetic field produced by the current carrying contact forces the arc towards arc chute. The high interrupting capacity in air circuit breaker is achieved by intensifying this magnetic field around the arcing contact. The fixed arcing contact support is so designed that it increases the magnetic field around the arcing contact.

The main U shape fixed contact is the integral part of arc chute body which is totally enclosed giving excess to exhaust gases from single exhaust port in MCCB design.

Authored by:

Suresh Duggal
General Manager
Havells India Ltd

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