**5. Measurement on real MVN**

The results obtained during the measurements in the experiment area, while faults were produced on purpose, are shown in the followings.

The fault produced was of type single phase grounding.

The experimental aria contains 7 electric lines of 6kV, with total value of the capacitive current of 27A From the 7 electric linea 6 are connected at first system of bars and at the second bar system was connected the line on which the faults were produced. The capacitive current of this line is 2.7A.

The transformer station contains a transversal switch in connected position.

For recording the currents and the voltages during the experiment was used a CDR oscilloperturbograph.

Figures 75 to 83 show the following:

490 Numerical Simulation – From Theory to Industry

occur a transient regime.

**5. Measurement on real MVN** 

capacitive current of this line is 2.7A.

oscilloperturbograph.

**Figure 74.** Time variation of the voltages, when MVN is at resonance, Rt = 100Ω, α = 90°, C101a = 9C102a

When Rt = 1MΩ the fault becomes of the type broken conductor and at t=60ms does not

When the fault is of the type interrupted conductor with ground contact towards the

The results obtained during the measurements in the experiment area, while faults were

The experimental aria contains 7 electric lines of 6kV, with total value of the capacitive current of 27A From the 7 electric linea 6 are connected at first system of bars and at the second bar system was connected the line on which the faults were produced. The

For recording the currents and the voltages during the experiment was used a CDR

customer the heavyest situation is shown to be when the phase is near 90°.

The transformer station contains a transversal switch in connected position.

For higher values of Rt the transient regime is less dangerous.

produced on purpose, are shown in the followings.

The fault produced was of type single phase grounding.


The experiment was made in order to verify the concordance with the numeric simulation and to validate the accuracy of the simulator.

The experiment consisted on producing on purpose faults of the type single-phase grounding, namely:


The functioning regimes of the MV network were:


The three recordings, corresponding to the three functioning regimes for metallic grounding are shown in Figs. 75, 76 and 77.

**Figure 75.** Single phase metallic grounding, Rt= 5 Ω, network at resonance

This difference is due to a greater equivalent resistance of the experimental equivalent

In the same maner, as for the metallic grounding, but with a 250Ω grounding resistance for the three functioning regimes of the network the, results are presented in Figs. 78, 79 and 80.

**Figure 78.** Single phase grounding with Rt=250 Ω, network at resonance

**Figure 79.** Single phase grounding with Rt=250 Ω, 10% over-compensated network

circuit than the simulated one.

**Figure 76.** Single phase metallic grounding, Rt= 5 Ω, network at 10% over-compensation network

**Figure 77.** Single phase grounding with Rt=5 Ω, 10% under-compensated network

By comparing the shape of the current of the faulty line during the transient regime (the zero sequence current of the faulty line) obtained by numeric simulation with the one obtained by recording the same current during experiment it can be observed that the simulated current has an oscillating component greater than in recorded experiment.

This difference is due to a greater equivalent resistance of the experimental equivalent circuit than the simulated one.

In the same maner, as for the metallic grounding, but with a 250Ω grounding resistance for the three functioning regimes of the network the, results are presented in Figs. 78, 79 and 80.

**Figure 78.** Single phase grounding with Rt=250 Ω, network at resonance

492 Numerical Simulation – From Theory to Industry

**Figure 76.** Single phase metallic grounding, Rt= 5 Ω, network at 10% over-compensation network

**Figure 77.** Single phase grounding with Rt=5 Ω, 10% under-compensated network

By comparing the shape of the current of the faulty line during the transient regime (the zero sequence current of the faulty line) obtained by numeric simulation with the one obtained by recording the same current during experiment it can be observed that the

simulated current has an oscillating component greater than in recorded experiment.

**Figure 79.** Single phase grounding with Rt=250 Ω, 10% over-compensated network

**Figure 82.** Single phase grounding resistance Rt= 500 Ω, network at 10% overcompensation

**Figure 83.** Single phase grounding with Rt=500 Ω network at 10% undercompensation

**Figure 80.** Single phase grounding with Rt=250 Ω, 10% under-compensated network

The third value for the grounding resistance used in the experiment is 500Ω and the results for the resonant regime, for 10% overcompensated and for 10% undercompensated are presented, respectively, in the figures 81, 82 and 83.

**Figure 81.** Single phase grounding resistance, Rt= 500 Ω, network at resonance

494 Numerical Simulation – From Theory to Industry

**Figure 80.** Single phase grounding with Rt=250 Ω, 10% under-compensated network

**Figure 81.** Single phase grounding resistance, Rt= 500 Ω, network at resonance

presented, respectively, in the figures 81, 82 and 83.

The third value for the grounding resistance used in the experiment is 500Ω and the results for the resonant regime, for 10% overcompensated and for 10% undercompensated are

**Figure 82.** Single phase grounding resistance Rt= 500 Ω, network at 10% overcompensation

**Figure 83.** Single phase grounding with Rt=500 Ω network at 10% undercompensation

Table 1, campare some of the values measured during the experiment with the corresponding values obtained by numeric simulation.

Numerical Methods for Analyzing the Transients in Medium Voltage Networks 497

Rt[Ω]

5 250 500

Simulation Error [%]

Values obtained by

> Simulation

Experiment

Error [%]

Values obtained by

Experiment

max[A] 20,99 43 105 4,3 4,5 4,7 3,1 2,8 9,7

IB [A] 22,82 21,28 6,7 17,77 16,5 7,1 9,44 9,22 2,3

stab[A] 2,5 2,32 7,2 2,05 1,91 6,8 2,53 2,31 8,7

tam ms] 198 210 6,1 31 28 8,6 23 21 8,7

U0 [kV] 3,59 3,56 0,84 2,8 2,53 9,6 1,84 1,67 9,1

Uf [kV] 6,2 5,97 3,7 5,71 5,39 5,6 5,35 4,81 10,1

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

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

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

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

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

The most dangerous transient regimes occur when the initial phase of the voltage of the

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

Regime of the network

10% Under compensated

**6. Conclusions** 

grounding faults.

faults.

faulty line is near 90°.

Symbol of quantities

I0

I0

grounded towards the consumer.

conditions of the electrical network.

developing the simulator, are correct.

**Table 1.** Comparison of measured and simulated values

Values obtained by

> Simulation

Experiment

Error [%]

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


From Table 1. results that the differences between the values obtained by the numerical simulation and the values measured during the experiment are reasonably small.



**Table 1.** Comparison of measured and simulated values
