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Arc extinction |
| Arc extinction is about electricity, and
particularly enters the picture when switching DC electricity. AC is alternating current. DC is direct current. Current is a measure of heat or power on circuit. The more current flowing along the wire, then the more power or heat is available to do the work of rotating motor shaft etc With AC, the current or flow of electrons reverses 60 times per second in US. This is because the generator rotates 60 times per second. Each rotation has North and South poles of a magnet pass next to a coil of wire. As the N and S poles pass the coil of wire, they reverse the flow of electrons on the wire. The current oscillates or reverses direction. The entire grid energized by the generator(s) DC is different. DC current flows one direction. It does not 'alternate' directions like AC Resource: Difference between AC and DC power |
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DC arc extinction/ controlling high voltage DC"the higher the number of contacts opening the circuit, the higher the breaking capacity of the circuit-breaker.This means that, when the voltage rises, it is necessary to increase the number of current interruptions in series, so that a rise in the arc voltage is obtained and consequently a number of poles for breaking operation suitable to the fault level." What this quote means: A DC circuit breaker or any DC switchgear must have multiple contacts that disconnect as illustrated in diagrams below You want to increase the number of contact points, so the arc from DC power can be extinguished AC electricity oscillates. The voltage rises and falls. 60 times each second, the voltages drops to zero. Of course you notice this when grabbing a hot wire, because there is voltage on the line. There is a difference when choosing switchgear. Each time a switch is thrown, there is an arc (or spark) that continues to jump between the contact points of the switch. With AC power, the arc is 'extinguished' more easily because voltage reaches zero at some point and the arc stops. With DC power, the arc is more difficult to extinguish. DC never reaches zero volts, because it doesn't change direction... it doesn't oscillate.... and so electrons keep piling against one another, forcing the front ones to jump across the switch contacts. So switchgear must be rated for DC. Using AC switchgear will sometimes work, BUT careful attention must be paid to rating label. Each switch has a rating label or rating specifications. For example a switch might be rated 240 volt 30 amp AC, but only rated 48 volt 3 amp DC. If a device does not show DC rating, then assume it is not sufficient for DC application, and might be fire hazard. "the higher is the number of contacts opening the circuit, the higher is the breaking capacity of the circuit-breaker. This means that, when the voltage rises, it is necessary to increase the number of current interruptions in series, so that a rise in the arc voltage is obtained and consequently a number of poles for breaking operation suitable to the fault level." So a DC circuit breaker or any DC switchgear must have multiple contacts that disconnect as illustrated in diagram below. Resource: DC arc extinction .pdf Read about difference between AC and DC |
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Or use a 3-pole for better arc extinguish using six contact pointsSwitchgear for DC::
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3-pole contactor wired for DC loadsDC direct current is different than AC alternating current.AC current is a wave that crosses zero volts each time generator rotates 50-60 times per second,. US 60 cycles. Europe Asia 50 cycles. DC current is a straight line. The voltage does not oscillate or vary like AC. Electrons flow through circuit at same voltage at all times. When high voltage AC is turned off, the voltage drops to zero frequently. When AC voltage hits zero, then the arc or spark or heat is easy to extinguish. Result: AC switchgear like contactors last million repetitions without melting the points High voltage DC is different. When high voltage DC is turned off, the electrons keep pushing. Voltage never reaches zero. Result: DC voltage causes arc or spark or heat that is difficult to stop. Basically the electrons keep piling into the contactor. DC switchgear must be rated for DC voltages, and be capable of extinguishing DC arc. Illustration shows one method of extinguishing DC arc using 3-pole contactor. The circuit has 3 parallel switches on the positive wire. With a 4-pole contactor, 3 poles can be used to turn off Positive, and 1 pole to turn off Negative Add resistor in parallel with inductive winding* helps eliminate arcs. *Inductive winding is motor load Buy: 3-pole contactors at Amazon Resources: Contactors Solar contactor/ pdf DC relays for solar DC contactor wiring diagrams/ pdf What is 3-phase electricity Can AC circuit breaker be used for DC |
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