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Client objective

To identify cable runs in need of urgent attention, as well as longer term maintenance or replacement, via the of ranking of the 27.6kV XLPE cable runs, in terms of high / medium / low risk.

Scope of work

Partial discharges (PD) are essentially ‘electrical sparks’ that occur in the bulk of high voltage insulation materials. In polymeric-based cable systems (EPR or XLPE cables) partial discharges primarily occur along dielectric interfaces and / or impurities in cable accessories, such as cable joints or splices and cable terminations.  Partial discharges may also occur within the cable insulation itself around mechanically degraded spots and / or impurities, resulting in the formation of electrical trees.

Measurement of PD activity is by no means a new technical accomplishment.  For decades, cable manufactures have been using PD testing for quality assurance purposes.  However, recent technological advancements in on-line PD detection and instrumentation, allowing for measurement of a range of PD parameters, greatly enhances interpretation of the data.

Work performed

An on-line PD survey of the client’s XLPE cables was carried out by Kinectrics using an in-house developed sensor, coupled with an instrument, PDBase that was developed by a European manufacturer, TechImp.  Fundamentally, PDBase is a sophisticated data logger having three input channels that allow for sequential acquisition of PD signals.

Unlike conventional PD monitors, PDBase acquires and stores the actual pulse shape of each signal measured.  This enables both frequency and time-domain analysis.Specifically, for cables, the data acquired via PDBase allows for identification of internal discharges, surface discharges and corona discharges. 

The cables tested were ranked into three risk different categories:  LOW, MEDIUM and HIGH. Specific recommendations and order of priority was given to cables being considered for possible replacement programs.

Test results

From the on-line PD tests Kinectrics was able to predict there would be tracking along spacers or terminations on several cable runs at the main sub-station, and that they should take the system off-line to look for it.  

During visual Inspections, it was found that the spacers on several XLPE cables (see photo above) were tracking heavily. These cables were replaced.

Direct client benefits

The client was exceptionally satisfied with the findings, since an in-service failure would have produced significant costs, both in terms of downtime and repairs, coupled with the fact that a plant restart after shutdown would have required three days.

For more information

Mark Fenger, 416.207.6000x6347, mark.fenger@kinectrics.com