TISP7072F3, TISP7082F3
TRIPLE BIDIRECTIONAL THYRISTOR OVERVOLTAGE PROTECTORS
MARCH 1994 - REVISED MARCH 2000
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
via a resistor of 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 19.
C4
8 nF
VC
1 kV
R2
13 Ω
C3
8 nF
SW
NOTE: SOME STANDARDS
REPLACE OUTPUT
CAPACITORS WITH
25 Ω RESISTORS
R1
76 Ω
C1
1 µF
C2
30 nF
K.22 1.2/50 GENERATOR
Figure 19.
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 21). The coordination resistance values given in here 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.
P R O D U C T
I N F O R M A T I O N
14
POINN [ POWER INNOVATIONS LTD ]
