On-line Partial Discharge Monitoring & Location on a 33kV Offshore Wind Farm Export Cable

Published 19 Apr 2022

Partial Discharge

Special thanks to Jordan Edmenson at HVPD for the kind permission to republish
Link to the original article can be found here

Partial Discharge

Monitoring & Location on a 33kV Offshore Wind Farm Export Cable

Project

An offshore wind farm operator in the UK requested On-Line Partial Discharge monitoring and cable fault location on two 33kV XLPE land sea export cables to an offshore wind farm. The 33kV circuit began from a grid-connected onshore substation feeding a 2 km long land subsea transition joint, which in turn fed a 12 km 3-core cable directly to the offshore wind farm.

Onshore & Offshore Network | 33kV Cables

Solution

Short-term continuous monitoring was conducted using an HVPD diagnostic device connected to High Frequency Current Transformer (HFCT) and a Transient Earth Voltage (TEV) sensor.

The HFCT and TEV sensors were installed at the cable terminations during a temporary outage
The HFCT sensors are split core enabling them to be easily installed around the cable core and earth for detection of PD activity within the cable
The TEV is a capacitive probe designed to detect local, high frequency PD pulses originating within the switchgear and terminations

Conducting short-term continuous monitoring over a number of days enables intermittent PD activity to be captured and correlated with other parameters such as load, temperature and humidity.

HFCT and TEV Sensors

Background Theory

If significant levels of PD activity were detected, fault location could be carried out using the cable mapping function of the HVPD diagnostic device. Cable mapping is conducted by detecting the an original PD pulse from the fault location as well as a reflected PD pulse (caused when the original PD pulse reaches the far end of the cable). Using the time delta between these pulses, and the signal propagation speed (which is provided in the cable data sheet) the approximate location of the PD source can be identified.

Results

During the short-term monitoring period, high levels of PD activity were detected with the HFCT on Phase L3 of Circuit 1. Cable mapping on this circuit was then carried out to confirm the location of the fault, with the results indicating that the source was located 800m from the onshore substation.

This result was then corroborated with the cable schedule which confirmed the presence of cable joint no.7 at this location. Based on these findings, it was recommended that the affected joint no.7 be replaced. Following this replacement a forensic analysis on the joints was conducted in which significant insulation damage and tracking within the inner insulation section was found.

Partial Discharge Map Showing PD Location

Forensic Examination of Cable Joint

PD Trend Line Before Replacement

PD Trend Line After Replacement

Conclusions and Recommendations

During the short-term monitoring period, high levels of PD activity were detected and cable mapping on this circuit then confirmed the location of the fault. The affected joint was able to be taken out of service and replaced during a scheduled outage, avoiding the risk of an in-service cable failure.

HVPD

About HVPD

HVPD supplies a comprehensive range of equipment to detect and monitor On-line PD for the condition assessment of in-service power cables, switchgear, motors and generators, and transformers rated at 3.3kV and above. Our PD testing and monitoring technology provide you with an early warning of developing insulation faults, helping you to avoid costly failures and resulting unplanned network outages.

To find out how we can test and monitor your cable network for PD and locate any faults, terminations or joints, get in touch today at [email protected] or call us on 0161 877 6142.

Thorne & Derrick

Specialist Electrical Distributor

Established since 1985, T&D International based in the UK distribute the most extensive range of LV, MV & HV Cable Jointing, Terminating, Pulling & Installation Equipment – contact us today for a competitive quotation.

Key Products : MV Joints & Terminations, Access Chambers, Cable Cleats, Duct Seals, Cable Transits, Jointing Tools, Feeder Pillars, Cable Duct, Earthing & Lightning Protection, Electrical Safety, Cable Glands, Arc Flash Clothing Protection & Fusegear.

Distributors for : 3M, Pfisterer CONNEX, Nexans Euromold, Elastimold, Catu, Roxtec, Emtelle, Centriforce, Lucy Zodion, Alroc, Cembre, Prysmian, Ellis Patents, ABB & Furse.