BlueBOX technology by Ampacimon has been developed to assist TSOs & DSOs, cable engineers, contractors, manufacturers, and suppliers with the ability to measure partial discharges in underground cables in power transmission and distribution networks. Partial discharge (PD) measurements are increasingly used for insulation diagnostics of medium and high voltage cable systems to improve network reliability. Ampacimon has outlined some key challenges, and applications companies and engineers face monitoring and maintaining power systems.

PD measures are a real asset in today’s electrical world because of the following challenges: 

Cable demand and applications are increasing and changing:

Overhead power lines (OHLs) are increasingly being “retrofitted” and placed underground for aesthetic and resilience reasons. Subsea cables are increasing with offshore wind power development. Finnish undergrounding strategy is considered exemplary for climate adaptation.

Cables are prone to significant impact risks:

Cable failure is the number one cause of power outages. Therefore, maximising performance and reducing downtime is always essential. Inter-regional interconnectors and critical supply lines are often cables, which must be monitored closely for maximum capacity utilisation and critical asset integrity.

Cable structures are complex:

Various forms of degradation of cable insulation layers, joints and terminations can occur, each requiring different detection techniques. Locating a cable failure can also be done before and after a fault: Post-fault: High resistance fault or Low resistance fault; Pre-fault: Degradation type and Component/location.

Long delays in locating and repairing faults

Cables are assets with the highest rate of sustained failure and the longest repair times. The cables are buried and therefore not visible, making it challenging to identify the location of the fault. It is even more difficult to predict the likely location of the fault. The time required for fault location and repair is longer for cables than for OHLs.

There are three different approaches to on-site PD measurements in installed cable systems: 

  • Off-line PD measurements: the easiest way to detect PDs but requires service interruption. 
  • Online PD measurements are more attractive than off-line measurements for maintenance because they do not require service interruption and are a little bit more complicated because noise interference can be more significant. Mixed signals interpretation requires advanced analysis tools when several PD defects appear simultaneously.
  • In-service continuous PD monitoring: is an extension of online PD measurements for extended periods and is recommended to reduce the likelihood of catastrophic failures. 

BlueBOX technology has been deployed globally by Red Electrica Spain, Unión Fenosa Distribución, AENA (the company responsible for managing and maintaining Spanish airports), Elia Belgium, ENEDIS France, PEA Thailand, TEPCO Power Grid Japan, and more. From their experiences, it appears:

“Continuous monitoring systems allowed for early detection of insulation defects to prevent uncontrolled failures in the cable systems where they were operated. Experience shows that PD magnitude is not always the most relevant parameter to correlate the level of degradation caused by an internal fault. Once a PD source is located, and the phase-resolved PD pattern is associated with an internal fault, the trend of the PD amplitude and the rate of number of PD pulses per grid cycle should be used to support the decision-making process.”

Image source: Stock image for illustration purposes only, courtesy of Ampacimon

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