Fault location algorithms according to position

As mentioned before the analysis of the position of the fault according to the section of the network or even the substation outgoing where the fault has appeared is other possible classification which describes a fault location algorithm.

5.3.3.1 Fault section location

5.3.3.1.1 Direct method

The direct method defines a matrix in order to describe the network structure. These algorithms can be based in the structure shape or in base structure or even the overhead arc algorithm. This method is simple to implement but the complexity will depend on the network size. If the network expands the complexity of the computation will increase considerably, therefore several operations with matrix have to be avoided. Although nowadays the evolution of the Data Processing Centre (DPC) and in general terms the IT could increase the application of this kind of algorithms.

Several publications such as [111] and [112] depend on the structure of the network, so they are focused on networks with stable operation mode. This kind of algorithms use the known loads in the network to establish some calculus, but normally it is not easy to get the rated loads.

5.3.3.1.2 Indirect method

contribute specially in the location of a fault. This methodology has been classified in four main areas as described below:

• Artificial Intelligence. The use of ANN can contribute as mentioned before in the possibility to search the section where the fault is. As mentioned before the ANN is a connectionism of several artificial networks which simulate the empirical thinking mechanism. At the end, the ANN can produce reasonable outputs in order to detect a fault in distribution networks [113].

• Optimization algorithms. The optimization algorithms can build an evaluation function and convert the location of the fault in a minimum and maximum problem. Examples of this optimization problems are the genetic algorithms such as [114] or even the ant colony optimization such as [115].

• Expert system. As mentioned before a high system control can integrate this kind of algorithms which can use other auxiliary systems such as GIS and historical information. As mentioned in [116] and in [117] to share information and the use of GIS in a ADMS can contribute considerably in the fault location.

• Rough set method. This method is adequate for small-scale distribution network. In fact, the method proposes that when fault happens, the operator can detect the fault by means of the information from historical information with decision table in order to reduce the fault location. Algorithms such as [118] can reduce this operation time.

5.3.3.1.3 Practical method

The practical method uses the information from field devices in order to identify where is the fault. The use of FPIs or IEDs with communication to control centre or to local devices such as telephone mobile can give information to the operator in order to guess where the fault is. This method can combine with rough set method which has been explained before. The problem of this kind of methodology is focused mainly for radial distributions without DG.

5.3.3.2 Fault line selection

As mentioned before the fault line selection method has as goal to identify the outgoing of the substation where the fault is in a distribution network in order to avoid a bad recognition due to a weak fault current or unstable arc. The table 5.4 identifies three important methods inside this category which are based in steady state fault component, in transient state fault component and active selecting method.

5.3.3.2.1 Steady state information

This fault line selection methodology uses methods such as zero-sequence current magnitude and phase comparison method as it has been explained before with the flow current in electrical distribution networks. This method calculates each zero-sequence magnitude from each line and can compare the direction of the flow to determinate the line with the fault and also to discriminate is there is a fault in the busbar of the substation.

Also, this methodology uses other very similar technique such as fifth harmonic method which can compare the magnitude and phase of fifth harmonic current. The harmonic magnitude is much smaller that fundamental current. Then for a fault with large transient resistance it will be difficult to extract this information.

Other important method within steady state information is the active component method or zero- sequence admittance method which make a phase comparison in order to determinate in which line is the fault. These methodologies are very similar than the implemented algorithms in IED such as protection ANSI 67N, then it is possible to use this direct field device information to have more information to locate the fault.

5.3.3.2.2 Transient state information

These algorithms use the information during the fault in order to determinate the affected outgoing of the substation. One of the methods is the first half-wave, in this case the different zero-sequence transient states from each feeder are compared and the feeder with the fault will have the largest magnitude and also compare the phases and the different one is fault line. If the signals are the same the fault will be in the busbar of the substation. In fact, is a similar process to steady state zero sequence which has been described before.

Another efficient transient state information method is continuous wavelet transform. The application of this wavelet packet is more accurate that the signal analysis method due to the frequency band is divided into multilevel parts and the spectrum of the signal is matched then the resolution time-frequency is improved [119].

In this case it will be necessary to compare between feeders such as in last method but in this case the accuracy can contribute significantly in use it in several earth neutral systems. As mentioned before the isolated earth system has a lower zero-sequence current then to identify the feeder with the fault will be difficult in comparison with resistance earth system. This method can provide a better observation of transient variation instead of the Fourier transform, which is used by AEDs and FPIs in order to identify a fault.

5.3.3.2.3 Active selecting methods

The active selecting methods has the principle to modify the system doing several specific actions in order to locate correctly the fault. For example, the fact modifying the impedance in the Petersen coil or injecting some signal in the network.

A modification in the Petersen Coil makes a modification of the zero sequence and then it will help to detect the fault. Other modification could be to inject a signal to the neutral earth system and see the magnitude of the fault. Although this kind of method could be more interesting for an end user installation that not in a distribution network from utilities.