LTspice GDT simulation

 This document develops a two-electrode gas discharge tube bidirectional model using a
circuit of LTspice elements (two switches and six voltage sources) and parametric equations.
Four operational examples are given using the following surge generators; 8/20, 1.2/50-8/20,
10/700 and a high impedance 10/700.


LTspice MOV simulation

With the knowledge that the logarithm of MOV resistance (R) has a reasonably linear relationship with the logarithm of MOV current (i), a function may be derived of the form LOG(R) =F(LOG(i)). In LTspice, this relationship allows the simulation of an MOV using a variable resistor controlled by R = 10^ F(LOG(i)), see Figure 5.

Three MOV circuit LTspice simulations are given; use with an 8/20 current generator (Figure 6), use with a 1.2/50-8/20 generator (Figure 11) and current sharing in paralleled MOVs (Figure 16).

Surge generator values and simulations

Using SPICE (Simulation Program with Integrated Circuit Emphasis) simulations, this tutorial analyses the 10/700, circuit defined, surge generator and the 1.2/50-8/20, waveform defined, surge generator. The ITU-T originated the 10/700 surge generator for long distance network line testing and many of the ITU-T Recommendations use the 1.2/50-8/20 surge generator for short distance network line testing.

SPICE simulation was used to analyse the surge generator performances. The Linear Technology LTspice IV software was used for this tutorial. The 10/700 simulation objective was to define the tolerance of the component values used in the 10/700 circuit diagram given in ITU-T Recommendation K.44. The 1.2/50-8/20 simulation objective was to identify the most appropriate generator circuit diagram for modelling the 1.2/50-8/20 generator.