Protection stages usually a varistor. Varistors are variable resistances. Their impedance is very high when voltage is normal, and it lowers in a non-linear way when voltage increases. In general, they are faster than gas discharge tubes but their disadvantage is that, while voltage is normal, their impedance is very high but still produces current leakage.
Usually, the first protection is a spark gap. Spark gaps typically remain completely open, with no flowing current, while signal is normal. Each one has its characteristic breakdown voltage (although it varies slightly with the wave form). When this voltage is surpassed, then the component becomes short-circuited, driving all the current to ground. When the high level voltage disappears, these components return to inactive status, that is, to be an open circuit.
The third protection barrier is normally Transient Voltage Suppressor Diodes, very fast elements, capable of letting very low residual voltages but unable to withstand currents over several amperes.
The element forming the second protection, tighter than the first one, is
COORDINATION IMPEDANCE: DECOUPLING CONDUCTOR OR MORE THAN 10 METERS OF CABLE EQUIPMENT PROTECTED
TYPE 1
TYPE 2
PROTECTOR
kV
TYPE 3
PROTECTOR
PROTECTOR
V
V
V
12
600
600
600
10
500
500
500
8
400
400
400
6
300
300
300
4
200
200
200
2
100
100
100
0
0
0
0
20
40
60 µs
0
1
2
µs
0
0
1
2
µs
0
1
2
µs
Reduction of transient overvoltages by means of a stepped protection.
Many SPDs are formed by the combination of these elements or by several of them coordinated in a single device. Decoupling elements are normally resistances or inductors with very low impedances because, being in series with the line, the current flows through them continuously. If impedances were high, they would cause unnecessary losses and consumptions.
Aplicaciones Tecnológicas, S.A. Surge Protective Devices have been tested not only individually but also in coordination with other protectors of different stages.
Normally the problem of electrical consumptions is worse in power supply lines, where flowing current is of amperes. For data lines, the current flowing is of miliamperes, hence the consumption is not important. However, the working voltages of electronic components are usually very low thus a significative voltage drop at the decoupling impedance must be avoided, since it could cause disturbances in data transmissions. For power supply lines, different combinations of ATSHOCK, ATSUB and ATCOVER have been tested, using ATLINK devices as decoupling inductors, verifying their coordination and proper working even with lightning impulse waves (100kA, 10/350μs). Concerning SPDs for telephone, data lines, etc., our protectors internally coordinate several protection stages.
ATBARRIER, Combined protectors
INTERNAL PROTECTION
97