Protection 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 internal arc.

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 HV plants.
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.

Pressure arc detectors

Title Size in Kbytes Date

Pressure arc detector 106 21-11-01  View Online
MC40 Pressure arc detector 95 26-09-02  View Online

Light arc detectors

Title Size in Kbytes Date

Application guide 1373 15-05-09  View Online
LAD/X Light arc detector 989 28-06-13  View Online
Light arc detector with internal diagnostic 151 29-10-08  View Online
High sensitivity light arc detector 296 09-12-08  View Online
Triac light arc detector 267 07-02-05  View Online
Triac high sensitivity light arc detector 192 18-01-05  View Online
Optical cable for LAD 126 23-05-12  View Online
Cable for LAD 108 23-05-12  View Online