Lightning effect is generated using the Heidler block. The lightning of 100 kA will strike on the shielding wire in case of mitigation due to shielding and on phase A in case where surge arresters are considered. Below is a figure of a 100 kA lightning strike. This current is measured at the node where the lightning strikes.

Fig. 5.1 Lightning strike current of 100 kA

When lightning strikes on the shielding conductors the current induces a voltage on the phase conductors. Here we are generating a case of induced voltage on the line. The induced voltage then should be mitigated by shielding. Here we see a voltage of 155 kV has been induced due to the lightning strike on the phase line. Such induced voltages cause the sensitive

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The approach that we have taken is not practical however to see the effect of grounding we have changed the resistances of the ground and observed that the induced voltage on the line is seen to be reduced as the resistances were lowered.

Induced voltage due to lightning on shield wires when the ground resistances are taken to be 50 ohms. In this case the induced voltage reaches almost 1 MV this is because of the higher resistance. Due to high resistances the conductance is less and the current does not pass through the grounding of the shielding wires. The resistances were then reduced and the results are shown below. Fig 5.1.1. Induced voltages on the line due to lightning at 50 ohms grounding resistance

Induced voltage due to lightning on shield wires when the ground resistances are taken to be 30 ohms the induced voltage has a peak voltage of 678 kV. Comparing with the case where the resistance was 50 ohms this case shows that the induced overvoltage has a mitigating effect. Fig 5.1.2. Induced voltages on the line due to lightning at 30 ohms grounding

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CONCLUSION

The system that developed in ATP for grounding or the shielding effect is impractical because the grounding resistances considered cannot be achieved in reality. However, for the purpose of understanding the concept and visualizing them this model is very helpful. Grounding the shielding wire will not always prove to be effective and there are chances that the system would collapse since considered lightning strike is of 100 kA. This would not be the case every time and there could be surges of high amplitude.

Surge arresters have proved to be more reliable than the shielding wires. They show a very fast response of mitigating the surges in under 1s. The maximum amplitudes reached by the over voltages is the same as presented in [8].

7. RECOMMENDED CONTINUED WORK

The system developed for this project have a few impractical approaches like the location of lightning strike. The lighting strike is considered only at a single point. On the shield wire in Case 1 and on phases in Cases 2 and 3. In the future, we would like to analyze our system for lightning at different locations and also an indirect lighting strike could be considered. For the improvement of the system, we would like to implement surge arresters of better and practical characteristics. The project has not considered distances of surge arrester and location taken are random to get varied results. Therefore for future work we may the distances. In [8] it has been mentioned that when surge arresters