systems for minimising the consequences of an electrical internal arc
when, in spite of alarm systems, an electric fault takes place in the
device it is very important to minimize the damage caused from the
Pressure Arc Detectors
When arc fualt is generated into a closed or semiclosed environment a
pressure wave, moving at sound speed, spreads all around. Pressure
sensors are able to signal (with a delay of 9-10 ms) the relevant
pressure peak. This signal operates immediately on the breaker that
causes failure without waiting the longer operating time of the
selective protections. This system don't need any electronic processing
device and operates in a steady way directly on the tripping coil of
the breaker which cause failure by means of a simple wired logics.
Light arc detectors
When a fault arc is generated a flash light, with all IR and visible
radiation spectra, is emitted. Of course light reaches each point
around the fault instantaneously. Optical electronic receivers are very
quick to response and acording to their technology can react with fast
timing (5-10ms) or ultrafast (1-5 us).
This protection is so quick that is commonly used when there's the
necessity to cut the energy of fault in a very short time such as for
Light detectors are the preferred ones not only when a very fast
reaction is required but also when the compartment is quite open and it
is not possible to create a sufficient peak pressure to operate with
pressure arc detectors.
Nevertheless attention must be taken using light arc detectors as they
are not able to distinguish between the light coming from a fault
arc to the light coming from an operation arc: in these situations the
proceeding is to enable tripping coil only if both light and
overcurrent are simultaneously present.
A hint to solve previous situation is obtained by using low sensitivity
IR light arc detectors where the compartment is not dark and a high
sensitivity when the compartment is sealed.