17

MARCH 1994 - REVISED MARCH 2000

TISP7125F3, TISP7150F3, TISP7180F3, TISP7240F3, TISP7260F3,

TISP7290F3, TISP7320F3, TISP7350F3, TISP7380F3

TRIPLE BIDIRECTIONAL THYRISTOR OVERVOLTAGE PROTECTORS

P R O D UCT

INFORM A T ION

The combination generator has three testing configurations; directly applied for testing between equipment

a.c. supply connections, applied via an external 10

Ω resistor for testing between the a.c. supply connections

and ground, and applied via an external 40

Ω resistor for testing all other lines. For unshielded unsymmetrical

data or signalling lines, the combination generator is applied via a 40

Ω resistor either between lines or line to

ground. For unshielded symmetrical telecommunication lines, the combination generator is applied to all lines

viaaresistorof n x 40

Ω, where n is the number of conductors and the maximum value of external feed

resistance is 250

Ω. Thus for four conductors n = 4 and the series resistance is 4 x 40 = 160 Ω.For ten

conductors the resistance cannot be 10 x 40 = 400

Ω and must be 250 Ω. The combination generator is used

for short distance lines, long distance lines are tested with the 10/700 generator.

When the combination generator is used with a 40

Ω, or more, external resistor, the current wave shape is not

8/20, but becomes closer to the open circuit voltage wave shape of 1.2/50. For example, a commercial

generator when used with 40

Ω produced an 1.4/50 wave shape.

The wave shapes of 1.2/50 and 8/20 occur in other generators as well. British Telecommunication has a

combination generator with 1.2/50 voltage and 8/20 current wave shapes, but it has a fictive resistance of 1

Ω.

ITU-T recommendation K.22 “Overvoltage resistibility of equipment connected to an ISDN T/S BUS” (05/95)

has a 1.2/50 generator option using only resistive and capacitive elements, Figure 34.

The K.22 generator produces a 1.4/53 open circuit voltage wave. Using 25

Ω output resistors, gives a single

short circuit current output wave shape of 0.8/18 with 26 A/kV and a dual of 0.6/13 with 20 A/kV. These

current wave shapes are often rounded to 1/20 and 0.8/14.

There are 8/20 short circuit current defined generators. These are usually very high current, 10 kA or more

and are used for testing a.c. protectors, primary protection modules and some Gas Discharge Tubes.

impulse testing

To verify the withstand capability and safety of the equipment, standards require that the equipment is tested

with various impulse wave forms. The table in this section shows some common test values.

Manufacturers are being increasingly required to design in protection coordination. This means that each

protector is operated at its design level and currents are diverted through the appropriate protector e.g. the

primary level current through the primary protector and lower levels of current may be diverted through the

secondary or inherent equipment protection. Without coordination, primary level currents could pass through

the equipment only designed to pass secondary level currents. To ensure coordination happens with fixed

voltage protectors, some resistance is normally used between the primary and secondary protection (R1a

and R1b Figure 36). The values given in this data sheet apply to a 400 V (d.c. sparkover) gas discharge tube

primary protector and the appropriate test voltage when the equipment is tested with a primary protector.

Figure 34.

C

2

30 nF

R

1

76

Ω

Ω

Ω

Ω

C

1

1µF

R

2

13

Ω

Ω

Ω

Ω

SW

V

C

1kV

K.22 1.2/50 GENERATOR

C

3

8nF

C

4

8nF

NOTE: SOME STANDARDS

REPLACE OUTPUT

CAPACITORS WITH

25

Ω

Ω

Ω

Ω RESISTORS