11

MARCH 1994 - REVISED MARCH 2000

TISP7072F3, TISP7082F3

TRIPLE BIDIRECTIONAL THYRISTOR OVERVOLTAGE PROTECTORS

P R O D UCT

INFORM A T ION

APPLICATIONS INFORMATION

deployment

These devices are three terminal overvoltage protectors. They limit the voltage between three points in the

circuit. Typically, this would be the two line conductors and protective ground (Figure 17).

In Figure 17, protectors Th2 and Th3 limit the maximum voltage between each conductor and ground to the

lightning surge

wave shape notation

Most lightning tests, used for equipment verification, specify a unidirectional sawtooth waveform which has an

exponential rise and an exponential decay. Wave shapes are classified in terms of rise time in microseconds

and a decay time in microseconds to 50% of the maximum amplitude. The notation used for the wave shape

is rise time/decay time, without the microseconds quantity and the “/” between the two values has no

mathematical significance. A 50A, 5/310 waveform would have a peak current value of 50 A, a rise time of

used surges.

generators

There are three categories of surge generator type: single wave shape, combination wave shape and circuit

defined. Single wave shape generators have essentially the same wave shape for the open circuit voltage and

short circuit current (e.g. 10/1000 open circuit voltage and short circuit current). Combination generators have

two wave shapes, one for the open circuit voltage and the other for the short circuit current (e.g. 1.2/50 open

circuit voltage and 8/20 short circuit current) Circuit specified generators usually equate to a combination

generator, although typically only the open circuit voltage wave shape is referenced (e.g. a 10/700 open

circuit voltage generator typically produces a 5/310 short circuit current). If the combination or circuit defined

generators operate into a finite resistance the wave shape produced is intermediate between the open circuit

and short circuit values.

ITU-T 10/700 generator

This circuit defined generator is specified in many standards. The descriptions and values are not consistent

between standards and it is important to realise that it is always the same generator being used.

Figure 18 shows the 10/700 generator circuit defined in ITU-T recommendation K.20 (10/96) “Resistibility of

telecommunication switching equipment to overvoltages and overcurrents”. The basic generator comprises

of:

switch SW to discharge the capacitor into the output shaping network

Figure 17. MULTI-POINT PROTECTION

Th3

Th2

Th1