**6. Conclusions**

496 Numerical Simulation – From Theory to Industry


Symbol of quantities

component,

Regime of the network

Resonance I<sup>0</sup>

10% Overcompensated I0

I0

I0

corresponding values obtained by numeric simulation.



The significance of the symbols from the table is as follows:



Values obtained by

> Simulation

Experiment

simulation and the values measured during the experiment are reasonably small.

Table 1, campare some of the values measured during the experiment with the


From Table 1. results that the differences between the values obtained by the numerical

Error [%]

Rt[Ω]

5 250 500

Simulation

Error [%]

Values obtained by

> Simulation

Experiment

Error [%]

Values obtained by

Experiment

max[A] 21,7 24,6 13,4 4,8 4,5 6,3 2,8 2,6 7,1

IB [A] 26,16 24,3 7,1 17,81 16,2 9,1 14,37 12,84 10,6

stab[A] 2,28 2,42 6,1 1,94 1,75 9,8 1,64 1,49 9,1

tam [ms] 126 130 3,2 38 34 10,5 57 54 5,3

U0 [kV] 3,6 3,55 1,4 2,62 2,43 7,3 2,31 2,17 6,1

Uf [kV] 6,22 6,03 3,1 5,6 5,46 2,5 5,3 4,78 9,8

max[A] 17,8 58 226 4,2 4,5 7,1 3,2 2,9 9,4

IB [A] 26,69 24,82 7,0 19,6 18,3 6,6 15,16 13,86 8,6

stab[A] 2,2 2,06 6,4 2,64 2,42 8,3 2,53 2,27 10,3

tam ms] 80 86 7,5 35 32 8,6 41 37 9,8

U0 [kV] 3,63 3,55 2,2 2,73 2,47 9,5 1,91 1,7 9,9

Uf [kV] 6,24 5,96 4,5 5,69 5,21 8,4 4,38 4,76 8,7

The numerical simulator designed by us allows the analysis of transients caused by diferent types of faults, such as simple groundings, double groundings, or broken conductor grounded towards the consumer.

We have compared results obtained by simulation with measured values only for simple grounding faults.

In this type of fault the simulator is validated by the measurements, no matter how the neutral point of the medium voltage network is grounded and whatever are the functioning conditions of the electrical network.

The results from Table 1. show that the simplificatory conditions, taken into account for developing the simulator, are correct.

The numerical simulation of the transient regimes caused by simple grounding faults produced in medium voltage networks shows to be an efficient method for analyzing such faults.

The most dangerous transient regimes occur when the initial phase of the voltage of the faulty line is near 90°.

The initial phase of the voltage, that happen to be in the very moment of producing the fault, was taken with the same value in simulation. The differences between the maximal

values of zero sequence component, obtained by the two methods, are quite acceptable from a technical point of view and this concordance validates the model.

Numerical Methods for Analyzing the Transients in Medium Voltage Networks 499

*Electric Power Systems High Voltages, Electric Machines Control & Signal Processing,* 

Curcanu, G., Toader, D. & Pandia, T. (2006). Determination of overvoltages in high voltage networks at single phase faults by numarical simulation and experiments, *Proceedings* 

Danyek, M., Handl, P.& Raisz, D. (2002). Comparison of Simulation Tools ATP-EMTP and MATLAB-Simulink for Time Domain Power System Transient Studies, *Proceedings of the* 

Dessaint, L.-A., Al-Haddad, K., Le-Huy, H., Sybille, G. & Brunelle, P. (1999). *A power system simulation tool based on Simulink*, IEEE Trans. on Ind. Electronics, vol. 46, no. 6, pp. 1252-

Dommel, H.W. (1995). *ElectroMagnetic Transient Program. Theory Book*, Bonneville Power

Drapela, J. (2009). Performance of a Voltage Peak Detection-Based Flichermeter, *Proceedings of the 8thWSEAS International Conference on Circuits, Systems, Electronics, Control & Signal* 

Foltin, M., Ernek, M. & Hnat, J. (2006). SimPowerSystems in Education, *Mezinarodni* 

Hasler, M. & Neirynck, J. (1985). *Circuits non lineares*, Presses Polytechniques Romandes,

Iordache, M. & Mandache, A. (2004). *Computer Aided Analyse of Nonlinear Circuits (in* 

Istrate, M., Gavrilas, M., Istrate, C. & Ursuleanu, R. (2009). Algorithms in Transmission Grids Using ATP Simulations, *Proceedings of the 9thWSEA/IASMES International Conference on Electric Power Systems High Voltages, Electric Machines Control & Signal* 

Karlsson, A. (2005). *Evaluation of Simulink/SimPowerSystems and other Commercial Simulation Tools for the Simulation of Machine System Transient*, Swedish Royal Institute of

Mandache, L. & Topan, D. (2009). *Algorithms for Electric Circuit Simulation,* Universitaria

Radoi , C. (1994). *SPICE Simulation and Analysis of Electronic Circuits,* Ameo Press Bucureşti. Rashid, M.H. & Rashid, H.M. (2006) *SPICE for Power Electronics and Electric Power,* Taylor &

Sybille, G., Brunelle, P., Hoang Le-Huy, Dessaint, L.A. & Al-Haddad, K., (2000). *Theory and applications of power system blockset, a MATLAB/Simulink-based simulation tool for power systems*, Power Engineering Society Winter Meeting 2000, IEEE, Vol.1, pp.774-

Genova, Italy, October 17-19, 2009, pp.65-70

*12th International IGTE Symposium,* Gratz

*Konference Technical Computing,* Prague

*Romanian)* , Politehnica Press Bucharest

1254, Dec. 1999

Lausannes.

Administration, Portland

Technology, Stockholm

Francis Group, Boca Raton

Press Craiova

779

*European EMTP-ATP Conference*, Sopron, Hungary

Chuco, B. (2005). Electrical Software Tools Overview *in* SINATEC-IEEE

DeCarlo, R & Lin, P. (2001). *Linear Circuit Analysis,* Oxford University Press

*Processing,* Teneriffe, Spain, December 14-16, 2009, pp.296-301

*Processing,* Genova, Italy, October 17-19, 2009, pp.109-114

Ross, C.C. (2004). *Differential Equations,* Springer Science, pp.51-56

The resistance of the broken conductor to ground is extremely important, small values of Rt implying long damping periods. If this undesirable condition happens the currents might have high values, as well as important values of the over voltages leading to important supplementary mechanical stress and damages of the insulating devices and, eventually a simple fault can turn to a multiple fault situation.

For small values of the grounding resistance at the fault location (Rt < 10Ω) difference between measured and simulated values is a litle higher than in the case of greater values (Rt > 100Ω).

The model is very useful by giving the values of the voltages on the healthy lines (over voltages that might jeopardize the insulation) and zero sequence currents of the faulty lines (fixing the condition of the fault detection by protection devices).

Using the conclusions of the simulation of a MVN for the values of the currents and voltages during different types of faults it is possible to adjust the prescribed values of the protection.

Simulation of the broken conductor fault, either connected to the ground or not, shows that resonance might occur, over voltages due to this resonances being dangerous to the equipments.

When double phase to ground fault was simulated the values of the voltages showed dangerous voltages for step or touch voltage.

The numerical simulator has the advantage of analyzing rapidly several variants as models of different possible situations.

The simulator is flexible and all kinds of faults can be simulated for different MVN, just by making the proper modification in the parameters of the simulator. These modifications are slightly easier to be performed when PSPICE simulating model is used.

Either using PSPICE or Mathlab-Simulink the accuracy of the analysis is similarly good.

The precision of the results obtained by simulation depends essentially on the accuracy of the MVN parameters.
