1. THE VERIFICATION OF SHUNTING METHOD FOR LIMITATION OF EARTH FAULT CURRENT IN MV COMPENSATED NETWORKS Petr TOMAN Jaroslava ORSÁGOVÁ David TOPOLÁNEK Vladimír BLAŽEK Brno University of Technology Jaromír DVOŘÁK E.ON Czech Republic

2. Objectives Try to find out the reason of damaged concrete towers in the distribution network

4. Objectives Try to find out the reason of damaged concrete towers in the distribution network To measure the voltage and currents during the earth fault for fault on unearthed console of concrete tower and for other types of fault The method of shunting (connecting affected phase to earth system in substation) should be tested The conditions during the fault state should be the same as in normal operation

5. The network The distribution grids (22 and 35 kV) in the Czech Republic are operated as compensated via Petersen coil or as earthed via resistor (urban predominantly cable grids) When the earth fault comes the automatic of coil tuning stops and the dispatcher tries to find out the point of fault. During this process the mistuning caused by switching operation could rise

6. The measuring Six types of fault were realized –Low impednace – conductor lying on the earth –Arc - spark gap –Arc - damaged MV cable –400  –1600  –Unearthed console of concrete tower

7. The measuring The size of the network was 140 A: –Tuned Petersen coil –Mistuned Petersen coil about 40 A low All experiments was made in three places of fault: –Close to substation (busbar) –The long distance (about 25 km) from busbar –The middle distance (about 12 km) from busbar

9. The time sequence of fault 1.Switch on the fault 2.Switch on the shunting circuit breaker 3.Switch off the fault 4.Switch off the shunting circuit breaker

10. Tuned coil

11. Mistuned coil

12. Earth fault on unearthed console of concrete tower -tuned coil

13. Earth fault on unearthed console of concrete tower - mistuned coil

14. Earth fault on unearthed console

15. Conclusion The longer operation of earth fault on unearthed console of concrete tower could be very dangerous for the lifecycle of towers Fault currents after closing shunting circuit breaker decreased practically to zero during all experiments

16. Conclusion DSO on the base of series of experiments decided about the pilot project of shunting in substation Medlanky in the periphery of Brno city. The equipment could shortly make the second earth fault in substation in the other phase.

17. Conclusion The next series of experiments are prepared. The main aim is to verify touch voltage for specified cases and evaluate the possibilities of fault location by distance principle (during double earth fault)

18. Thank you for your attention!