**4. Numeric simulation of transients triggered by faults in medium voltage networks**

Faults in medium voltage networks (MVN) generate transient regimes with duration depending on the networks parameters, on the contact type at the fault place and on the default type itself. The numeric simulation performed in this chapter is based on PSPICE and the transient regimes are caused by simple and double grounding faults, as well as, by the fault produced by a broken conductor, grounded towards the consumer. A fault of the type broken conductor grounded towards the source can be treated similar as the simple grounding fault, with an insignificant error, so shall be no more analyzed in the followings (Sybille et al., 2000).

The elements that are important in the analysis are:


## **4.1. The structure of MVN**

450 Numerical Simulation – From Theory to Industry

Resistor R17 has a value that is corresponding to the conditions of the fault.

**Figure 5.** MVN represented as a complex circuit in SPICE drawing

**Figure 6.** Current and voltages representation as SPICE output oscillogrames

resulting, calculated, currents values.

Currents and voltages can be represented, as on a "soft" oscilloscope, after solving the transient regime, using the elements of the V[t] matrix, calculated for each time step, and the The single line diagram of the MVN whose behavior is studied in case of transient caused by faults is presented in Fig. 7.

**Figure 7.** Single Line Diagram of the MVN

The MVN in Fig. 7 contains the following elements:



Numerical Methods for Analyzing the Transients in Medium Voltage Networks 453

the same time, the switch VSa it is possible to simulate a fault of the type broken conductor

The fault of the type double grounding is simulated by closing the switch VSa connected to

If a fault of the type double grounding on the same line is wanted to be simulated, the

The parameters of the Earth (resistance, inductance) are encompassed in the parameters of

The line "b" can simulate a simple grounding fault by closing the switch VSb.

the line "a" and closing the switch VSb connected to the line "b", as well.

switch VSb should be moved from line "b" to line "a".

**Figure 8.** Three phased circuit simulating a MVN

and grounded on the consumer's side.

the electric line.


The model is designed with the possibility of changing the values of parameters.
