Name / Giuseppe Rizzi / Session / ALPHA 1
Company / CESI / Block / 2
Address / Via Rubattino , 54 / Question n° / Presentation
202134 Milano Italy / Language used on the floor / English
Phone / + 39 02 21255387 / Accompanying visuals on file ? / Yes
e-mail /
Presentation of the paper
Condition assessment of power cables in the ENEL distribution network
The paper reports the preliminary results of a very extensive program on condition assessment of ENEL power cables network.
The drivers of the project are the following:
- Rate of failure of cable network for the choice of the sections to be tested
- The choice of a unique indicator: partial discharge measurement and location
- The preparation of a central data base for the evaluation of the results obtained
- The visual inspection of the defected parts to evaluate the validity of the method and the Services
The information asked by ENEL at the three Services performing the tests are:
- The determination of the electrical position of the cable joints in each cable section
- The PD map for each cable section
- The ranking of the defected points in 4 levels
- The indication, on the terrain, of the defected points to be fixed in a short time interval
The project, that includes 12500 sections to be tested, started 2002 and will last till the end of this year.
The main results achieved by CESI are reported in the following:
- Most of the tests were performed on South Italy
- The rate of the critical defects detected is higher than the failure rate. In particular this difference is much higher for North Italy probably for a more accurate choice of the section to be tested
- Approximately 90% of the defects are located in cable accessories as expected.
- The rate of the non critical defects is much higher (more than one order of magnitude) than the rate of the critical defects.
- The results obtained by CESI are good considering that the analysis of the removed part as shown, in more than 90% of the case, the evidence of PD activity. Similar results are obtained in the identification on the terrain of the defected points
The return of experience from the field has highlighted also few weak or critical points and namely:
- The failure on critical points remained is service is negligible (2 out of 100)
- It was experienced the failure of sections already tested for which no critical defects were determined. The analysis of the parts put in evidence large extent of carbonised parts (low PD activity)
- Visual inspection can be used to supplement PD measurement mainly for termination
As conclusion the following remarks can be derived from the results obtained:
- The selected method is valid for the determination of defect producing PD, that normally are defects induced by a bad manipulation. The PD activity is higher in the initial stage and tends to decrease as the carbonisation of insulation media increases
- The selected method presents lower performances in case of defects that have already produced large carbonisation of the insulation.
- The use of more diagnostic indicators seems to be more adequate.