*4.2.3. The interrupted conductor with ground contact towards the customer fault*

For this simulation VSGOL is opened , as if the phase conductor would be interrupted, and with a 20ms delay VSa is connected (simulating the ground contact of the broken conductor). The switch VSb remains opened.

The MVN functioning at resonance, with compensation inductor, was simulated with three values of Rt, namely 1Ω, 10Ω, 100Ω. Two values for α were taken into account, 0°, respectively 90°.

The equivalent capacitance of the phase conductor from the fault to the consumers is simulated by:


Two possible situations are considered: C101a = C102a, and C102a = 0,1C101a.

482 Numerical Simulation – From Theory to Industry

this events are situated near the earth plate.

conductor). The switch VSb remains opened.

respectively 90°.

simulated by:

transformer station

grounding methos is used for the neutral point of the MVN.

place to the consumers supplied by the faulty line.

**Figure 60.** Time variation of the voltages when the neutral point of MVN is isolated, Rt = 1000Ω, α = 90°

The greater values of the currents at the two fault places, when the double phase to ground fault is produced, give high thermic solicitation to the instalation, as well as, higher values of the step voltages. This situatiom is dangerous for human being and animals, especially if

The time variation at the two fault places is far from being the same, no matter what

For this simulation VSGOL is opened , as if the phase conductor would be interrupted, and with a 20ms delay VSa is connected (simulating the ground contact of the broken

The MVN functioning at resonance, with compensation inductor, was simulated with three values of Rt, namely 1Ω, 10Ω, 100Ω. Two values for α were taken into account, 0°,

The equivalent capacitance of the phase conductor from the fault to the consumers is

C101a is simulating the capacitance of phase 1 from the fault place to the bars of the MV

C102a represents the model for the capacitance of the phase conductor from the fault

*4.2.3. The interrupted conductor with ground contact towards the customer fault* 

**Figure 61.** Time variation of the currents, neutral point of MVN is grounded by resistor and Rt = 1Ω, α = 90°, C101a = 9C102a

**Figure 62.** Time variation of the voltages, neutral point of MVN is grounded by resistor and Rt = 1Ω, α = 90°, C101a = 9C102a

In the oscillograms of the currents I(S) is the current to ground at the place of the fault, I(R7) is the current flowing trough the grounding resistor and the zero sequence current of the faulty line is (I(R1a) + I(R2a) + I(R3a))/3. In the oscillogramms (I(R1b + I(R2b) + I(R3b))/3 is the zero

The phase voltages are V(7), V(8), V(9), the zero sequence voltage on the bars of the MV transform station is (V(7) + V(8) + V(9))/3 and V(71) is the voltage of the broken conductor

In each situation, either the grounding resistance is 1Ω, or 100Ω, the transient regime is stronger in the very moment of broking the phase conductor (t = 40 ms) than in the moment when the broken conductor contacts the ground (t = 60 ms). The voltage on the broken conductor might reach very high, dangerous values, jeopardizing the insulation of the line

In Figs. 65 to 78 the oscillograms correspond to the MVN at resonance, with compensation inductor for grounding the neutral point. In this cases the current trough the compensation inductor is not represented because the protections used in MVN do not survey this current. By the point of view of the overvoltages that might appear when the conductor is broken are more dangerous than the overvoltages in the case when the broken conductor is in contact

**Figure 65.** Time variation of the currents when MVN is at resonance, Rt = 1Ω, α = 0°, C101a = C102a

sequence current of the healty "b" line.

as well as the insulation of the consumer.

behind the fault place.

with the ground.

**Figure 63.** Time variation of the currents, neutral point of MVN is grounded by resistor and Rt = 100Ω, α = 90°, C101a = 9C102a

**Figure 64.** Time variation of the voltages, neutral point of MVN is grounded by resistor and Rt = 100Ω, α = 90°, C101a = 9C102a

In the oscillograms of the currents I(S) is the current to ground at the place of the fault, I(R7) is the current flowing trough the grounding resistor and the zero sequence current of the faulty line is (I(R1a) + I(R2a) + I(R3a))/3. In the oscillogramms (I(R1b + I(R2b) + I(R3b))/3 is the zero sequence current of the healty "b" line.

484 Numerical Simulation – From Theory to Industry

α = 90°, C101a = 9C102a

α = 90°, C101a = 9C102a

**Figure 63.** Time variation of the currents, neutral point of MVN is grounded by resistor and Rt = 100Ω,

**Figure 64.** Time variation of the voltages, neutral point of MVN is grounded by resistor and Rt = 100Ω,

The phase voltages are V(7), V(8), V(9), the zero sequence voltage on the bars of the MV transform station is (V(7) + V(8) + V(9))/3 and V(71) is the voltage of the broken conductor behind the fault place.

In each situation, either the grounding resistance is 1Ω, or 100Ω, the transient regime is stronger in the very moment of broking the phase conductor (t = 40 ms) than in the moment when the broken conductor contacts the ground (t = 60 ms). The voltage on the broken conductor might reach very high, dangerous values, jeopardizing the insulation of the line as well as the insulation of the consumer.

In Figs. 65 to 78 the oscillograms correspond to the MVN at resonance, with compensation inductor for grounding the neutral point. In this cases the current trough the compensation inductor is not represented because the protections used in MVN do not survey this current.

By the point of view of the overvoltages that might appear when the conductor is broken are more dangerous than the overvoltages in the case when the broken conductor is in contact with the ground.

**Figure 65.** Time variation of the currents when MVN is at resonance, Rt = 1Ω, α = 0°, C101a = C102a

**Figure 68.** Time variation of the voltages, when MVN is at resonance, Rt = 1Ω, α = 90°, C101a = C102a

**Figure 69.** Time variation of the currents when MVN is at resonance, Rt = 1Ω, α = 90°, C101a = 9C102a

**Figure 66.** Time variation of the voltages, when MVN is at resonance, Rt = 1Ω, α = 0°, C101a = C102a

**Figure 67.** Time variation of the currents when MVN is at resonance, Rt = 1Ω, α = 90°, C101a = C102a

**Figure 66.** Time variation of the voltages, when MVN is at resonance, Rt = 1Ω, α = 0°, C101a = C102a

**Figure 67.** Time variation of the currents when MVN is at resonance, Rt = 1Ω, α = 90°, C101a = C102a

**Figure 68.** Time variation of the voltages, when MVN is at resonance, Rt = 1Ω, α = 90°, C101a = C102a

**Figure 69.** Time variation of the currents when MVN is at resonance, Rt = 1Ω, α = 90°, C101a = 9C102a

**Figure 72.** Time variation of the voltages. when MVN is at resonance, Rt = 1MΩ, α = 90°, C101a = 9C102a

**Figure 73.** Time variation of the currents when MVN is at resonance, Rt = 100Ω, α = 90°, C101a = 9C102a

**Figure 70.** Time variation of the voltages, when MVN is at resonance, Rt = 1Ω, α = 90°, C101a = 9C102a

**Figure 71.** Time variation of the currents when MVN is at resonance, Rt = 1MΩ, α = 90°, C101a = 9C102a

**Figure 70.** Time variation of the voltages, when MVN is at resonance, Rt = 1Ω, α = 90°, C101a = 9C102a

**Figure 71.** Time variation of the currents when MVN is at resonance, Rt = 1MΩ, α = 90°, C101a = 9C102a

**Figure 72.** Time variation of the voltages. when MVN is at resonance, Rt = 1MΩ, α = 90°, C101a = 9C102a

**Figure 73.** Time variation of the currents when MVN is at resonance, Rt = 100Ω, α = 90°, C101a = 9C102a


The experiment was made in order to verify the concordance with the numeric simulation

The experiment consisted on producing on purpose faults of the type single-phase


The three recordings, corresponding to the three functioning regimes for metallic grounding

Figures 75 to 83 show the following:

station U0.

grounding, namely:

overcompensation,

are shown in Figs. 75, 76 and 77.




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

The functioning regimes of the MV network were:

and to validate the accuracy of the simulator.


**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 occur a transient regime.

When the fault is of the type interrupted conductor with ground contact towards the customer the heavyest situation is shown to be when the phase is near 90°.

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