Electric arc & arc-suppression elements
About this app
Contact opening under load in super slow motion: the arc ignites, travels and extinguishes at the current zero crossing — AC vs. DC, four suppression concepts (free, deion plates, RC element, varistor) with a synchronous U/I plot and accumulating contact erosion.
How a switching arc forms
When a contact opens under load, the current does not stop instantly. The load inductance keeps it flowing, the air in the narrow gap ionises, and an arc of conductive plasma carries the current across the gap. It heats the contact surfaces and erodes material. With alternating current at 50 Hz, the current passes through zero 100 times per second, and the arc can go out there if the gap is already wide enough. Direct current has no zero crossing, so the arc keeps burning until it is drawn out long enough. Switching DC is therefore much harder.
Arc suppression methods
Several measures help to extinguish the arc. An arc chute with splitter plates above the contacts breaks the arc into many short partial arcs with a high total voltage. An RC snubber across the contact briefly takes over the current and damps the voltage spike. A varistor or freewheeling diode across the contactor coil clamps the turn-off spike of the coil inductance. Utilisation category AC-3 covers squirrel-cage motors: starting and switching off during running. A contactor must extinguish the arc reliably many times over.
What the app shows
Press “Switch” to separate the contacts under load, with adjustable slow motion. The 3D scene shows the arc igniting, moving and going out. You choose AC or DC, the load current (1 to 100 A) and one of four modes: no suppression, arc chute, RC snubber or varistor. The measurement plot records u(t) and i(t) in sync and marks contact opening, ignition, zero crossing, re-ignition and extinction. A counter accumulates switching cycles and contact wear until you reset it.
Frequently asked questions
- Why does an arc form when a switch opens?
- When a circuit is broken under load, its inductance tries to keep the current flowing. This creates a high field strength in the still narrow contact gap, the air ionises and a conductive plasma channel forms. This arc keeps carrying current until it is extinguished.
- Why is DC harder to switch than AC?
- Alternating current passes through zero every half cycle, 100 times per second at 50 Hz. At the zero crossing the arc loses its energy and can go out. Direct current has no zero crossing, so the arc must be extinguished by lengthening, cooling or splitting it.
- How does an arc chute work?
- An arc chute consists of parallel metal splitter plates above the contacts. The arc is driven into it and divided into many short partial arcs. Each partial arc needs its own burning voltage, the total exceeds the driving voltage, and the arc goes out.
- What can I compare in the switching arc app?
- You compare AC and DC and four variants: no suppression, arc chute, RC snubber and varistor. For every switching operation the app plots voltage and current and tracks contact wear over many cycles.
Subject: Electrical & Control Engineering
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