FAULT MANAGEMENT IN ELECTRICAL …

1 FAULT MANAGEMENT IN ELECTRICAL distribution SYSTEMSF inal report of the CIRED Working Group WG03 FAULT ManagementFOREWORDThis text comprises the final report of CIRED WorkingGroup 03 FAULT MANAGEMENT . The working group wasestablished in November 1995. The initiative came fromMr. Yves Harmand of Electricit de France, who was theconvenor of the predecessor working group DistributionAutomation .On behalf of CIRED organisation, the work has beensupported and supervised by Dr. Frank Otto, StadtwerkeDresden, members of WG 03 have beenDr. Matti Lehtonen, VTT Energy, Finland (convenor)Dr. Damian Cortinas, Electricit de France, (secretary)Mr.

2 Rino Anelli, ENEL, ItalyMr. Jean-Paul Krivine, Electricit de FranceMr. I aki Ojanguren, Iberdrola, SpainMr. Philippe Perusset, Electricit Neuch teloise,SwitzerlandProf. Peter Schegner, TU Dresden, germanyMr. Philip Tempelaere, Electrabel, BelgiumDr. Walter Tenschert, OKA, AustriaMr. Antonio Gomes Varela, Electricidade de Lisboa,PortugalI wish to thank all the working group members and alsoDr. Otto for a very good and pleasant co-operation whenworking towards this final report on FAULT Espoo, Finland 22. December 1998 Matti LehtonenINTRODUCTIONIn ELECTRICAL distribution systems, FAULT MANAGEMENT is oneof the main functions to reduce outage times.

3 For thispurpose, various methods are used in different report is an attempt to estimate the current state ofthese functions and to give recommendation forimprovement of the present approach of the report is to find the different technicaland organisational solutions for FAULT MANAGEMENT ,depending on network structure, protection philosophy andother circumstances. Various methods are presented andcompared for advantages and disadvantages, as well asfor costs and of the main issues is the techniques for FAULT locationand FAULT indication. For these, both different equipmentand functions are considered.

4 Of high importance also, arethe various computer systems used in network analyse the state of art of these, also a detailed analysisof the properties of present SCADA-systems is the latter part of the report, two special issues areconsidered. One is the comparison of different solutions offault statistics and FAULT indices. The second subject is thevarious approaches when assessing the economic feasibilityof FAULT MANAGEMENT OF ABBREVIATIONSAMA utomatic mappingDCCD istribution control centreDLCD istribution line carrierDMSD istribution data MANAGEMENT systemENDE nergy not deliveredFMFacilities managementGISG raphic information systemHVHigh voltage (> 60 kV)LVLow voltage (< 1 kV)LEDL ight emitting diodeMMIMan machine interfaceMV Medium voltage (1 kV.)

5 60 kV)NCCN etwork control centreRTUR emote terminal unitSCADA Supervisory control and data acquisition1 NETWORK distribution network structuresThis section focus on the structure of MV (1 kV to 60 kV)and LV (1 999 V) networks. The distribution utilities thathave been studied in this report are very heterogeneous insize (they operate from 1 to 100 distribution networks HV/MV substations) and in structure. Nevertheless, thegroup has managed to produce a summary of networkstructures of all utilities that highlights the differences andthe similarities between them. We will show only thosecharacteristics that will be useful for the discussion of is one major issue that differentiate thecharacteristics of a network : its urban or rural networks are usually short and underground, ruralnetworks are usually long (but not necessarily overhead : insome parts of Germany and in Electrabel they are mostlyunderground, and we see a trend in all utilities to increasethe part of underground in rural networks).

6 Manycharacteristics of networks can be explained whenconsidering the urban or rural remarks should be made about this chapter: This document reflects the state of the art on networkstructures, and some changes might occur in the future. All the utilities contributing to this survey use MVnetworks without distribution of the neutral conclusions don t apply to networks of the distributed neutral kind (very common in the UnitedStates and Canada). Structure and operationThe structure of the MV networks is mainly meshable, sothat feeders can be backfeed by adjacent lines. Urbannetworks are almost completely meshable, but that is notthe case of rural networks for obvious reasons of cost.

7 Thepercentage of rural networks that can be backfeed variesbetween 50% and 90% on the utilities networks are much less meshable than MV only some urban networks can be backfeed. Thepercentage varies between 0% and 30%.MV and LV networks are almost always operated utility have plans to loop networks in the Primary substationsPrimary substations (HV/MV substations) have generallyfrom 1 to 4 power transformers. 2 transformers is the mosttypical average number of MV feeders by substation variesbetween 4 and 20, most typical values being around we find differences in the typical numbers offeeders of rural and urban substations, but the trends aredifferent from one utility to tendencies regarding the total number of primarysubstations are not same around Europe: In Finland the number is decreasing, in order todiminish the maintenance costs.

8 In Austria the number is increasing in order to copewith new demand. In EDF and ENEL the number is increasing in order toimprove the quality of MV feeder profileRural MV feeders are much longer than urban MV values vary from 10 to 35 km for rural feeders, andfrom 3 to 10 km for the urban the typical load of a MV feeder, there is noobvious trend to differentiate urban and rural lines. Someutilities design rural feeders more loaded than urban ones,other utilities do the contrary, and sometimes there is nosignificant difference. Typical loads of rural feeders varyfrom 1 to 8 MVA, typical loads of urban ones vary from 1to 10 networks are almost always 3-phased in the utilitiesthat have contributed to this report.

9 Some 2-phase branches(connected to a 3-phase backbone) are used by EDF to feedlow-consumption rural Secondary substationsThe average numbers of secondary substations (MV/LV) byMV feeder are different for rural and urban feeders : Averages from 5 to 15 secondary substations by urbanMV feeder. Averages from 15 to 50 secondary substations by ruralMV average number of LV customers by secondarysubstation varies from 40 to 100, the maximal numberbeingalways under Power generationAll the utilities reflect a step increase in the number ofpower generators that apply for connection in MV and range of rated power of the dispersed generatorsconnected to MV networks varies largely from one utility toanother.

10 The minimum rated power goes from 25 kW(ENSA) to 1 MW (Iberdrola), the maximum power allowedfor connection at MV level goes from 1 MW (Finland) to25 MW (Iberdrola). PROTECTION Short Circuit protectionsShort Circuit Faults are usually the easiest to detect, as thefault current is important when compared to the loadcurrent. All the utilities studied use definite time currentrelays to detect this kind of faults: if the measured time issuperior to a fixed threshold, the protection considers that afault is present on the network. Time delays are used to co-ordinate the transformer, the busbar and the utilities (Austria, Germany, ENSA) install distanceprotections that measure the current and the voltage at thetime of a FAULT , and calculate the impedance of the FAULT thatis a good indicator of the FAULT distance to the information is very useful to locate the the protection directly calculates the Earth FAULT protectionsNeutral groundingThe type of neutral grounding has important consequencesover the earth FAULT protection scheme and the types offaults encountered by each company.