We need protection from fires resulting from an electrical overload caused by a faulty device or an accidental short circuit. The huge current from the overload heats up wires and their insulation may go up in flames. There are several ways to activate this protection.
The oldest method consists of a fuse wire. Usually, this is a thin wire enclosed in a casing. The material of the fuse wire is carefully chosen to heat up and melt (blow) when a certain current level is exceeded. Melting of the wire disconnects the circuit and interrupts the current, preventing heat buildup. Once a fuse wire blows, it has to be replaced by a similar wire to continue protection and reestablish electrical operation.
Nowadays, it is common to see switchboards where the fuse holder has been replaced by a miniature circuit breaker (MCB). The device has a bi-metallic spring holding pair of mechanical contacts, which can establish connection by throwing an external switch. An electrical overload causes the bi-metallic spring to trip and the contacts open up, disconnecting the fault from the rest of the circuit. Once the fault has been cleared up, the MCB can simply be rearmed by flipping the external switch.
Although simpler to operated compared to the fuse wire, MCBs have their own disadvantages of being slow to react and expensive, with their cost going up proportional to their trip current. Over time, the bimetallic strip tends to deform, reducing the current capacity of the breaker and its accuracy. The mechanical construction of an MCB makes it prone to wear and tear.
Opening mechanical contacts to interrupt high currents often causes an arc flash to jump across the contacts. It is necessary to quench the arc flash within a short time to prevent incidence of fires.
For overcoming the above problems, using a digital circuit breaker offers the most convenient solution. The device has an all-electronic construction involving an electronically controlled automatic switch. There are no mechanical components involved, no bi-metallic strips, and no electromagnetic coils inside.
Atom Power is proposing a solid-state digital circuit breaker to replace the traditional types and thereby avoiding the related problems. Currently awaiting approval from the Underwriters Laboratory (UL), Atom Power has two models, one each for AC and DC circuits.
So far, Atom Power was producing only a few numbers of their digital circuit breakers, using their in-house 3-D printers for producing the plastic parts of the housing. With increase in production, they will use the resources of an external rapid manufacturing company, and will move to injection molding for higher volumes of commercial operations.
The Atom Switch, within the breaker, responds to a digital signal generated whenever the current exceeds a certain level, whether due to overload or short-circuits. With tripping speeds exceeding 16,000 times those of its mechanical counterparts, the arc flashes simply do not happen.
Another technique used to prevent arc flashes is to switch the device off when the AC voltage passes through zero. This is called zero voltage switching or ZVS, and is a very useful technique to prevent arcing across the open ends of the circuit.