TISP7125F3, TISP7150F3, TISP7180F3, TISP7240F3, TISP7260F3,

TISP7290F3, TISP7320F3, TISP7350F3, TISP7380F3

TRIPLE BIDIRECTIONAL THYRISTOR OVERVOLTAGE PROTECTORS

MARCH 1994 - REVISED MARCH 2000

shunt resistor R1, series resistor R2 and shunt capacitor C2 form the output shaping network.

series feed resistor R3 to connect to one line conductor for single surge

series feed resistor R4 to connect to the other line conductor for dual surging

VC

2.8 kV SW

R2

15 Ω

C1

20 µF

R1

50 Ω

C2

200 nF

R3

25 Ω

70 A

5/310

R

T

R

R

T

70 A

5/310

G

G

G

T

10/700 GENERATOR - SINGLE TERMINAL PAIR TEST

T AND G

TEST

R AND G

TEST

R AND T

TEST

VC

5.2 kV SW

R2

15 Ω

R4

25 Ω

R3

25 Ω

95 A

4/250

95 A

4/250

C1

20 µF

R1

50 Ω

C2

200 nF

10/700 GENERATOR - DUAL TERMINAL PAIR TEST

Figure 33.

T

R

190 A

4/250

G

DUAL

T AND G,

R AND G

TEST

In the normal single surge equipment test configuration, the unsurged line is grounded. This is shown by the

dotted lines in the top drawing of Figure 33. However, doing this at device test places one terminal pair in

parallel with another terminal pair. To check the individual terminal pairs of the TISP7xxxF3, without any

paralleled operation, the unsurged terminal is left unconnected.

With the generator output open circuit, when SW closes, C1 discharges through R1. The decay time constant

will be C1R1, or 20 x 50 = 1000 µs. For the 50% voltage decay time the time constant needs to be multiplied

by 0.697, giving 0.697 x 1000 = 697 µs which is rounded to 700 µs.

The output rise time is controlled by the time constant of R2 and C2. which is 15 x 200 = 3000 ns or 3 µs.

Virtual voltage rise times are given by straight line extrapolation through the 30% and 90% points of the

voltage waveform to zero and 100%. Mathematically this is equivalent to 3.24 times the time constant, which

gives 3.24 x 3 = 9.73 which is rounded to 10 µs. Thus the open circuit voltage rises in 10 µs and decays in

700 µs, giving the 10/700 generator its name.

When the overvoltage protector switches it effectively shorts the generator output via the series 25 Ω resistor.

Two short circuit conditions need to be considered: single output using R3 only (top circuit of Figure 33) and

dual output using R3 and R4 (bottom circuit of Figure 33).

For the single test, the series combination of R2 and R3 (15 + 25 = 40 Ω) is in shunt with R1. This lowers the

discharge resistance from 50 Ω to 22.2 Ω, giving a discharge time constant of 444 µs and a 50% current

decay time of 309.7 µs, which is rounded to 310 µs.

For the rise time, R2 and R3 are in parallel, reducing the effective source resistance from 15 Ω to 9.38 Ω,

giving a time constant of 1.88 µs. Virtual current rise times are given by straight line extrapolation through the

10% and 90% points of the current waveform to zero and 100%. Mathematically this is equivalent to 2.75

PRODUCT INFORMATION

15