Partial Discharge Monitoring and Risk Reduction for Ageing Grids

Like many of the world’s regions, the electricity grids of the Middle East and North Africa are broadly characterised by a lack of investment that has been responsible for a declining asset base over many years. This has left the aging infrastructure poorly equipped and struggling to deal with new challenges such as the growing electrification of industry and a shift to a more distributed generation architecture.

There is an evident need to respond to this situation with large-scale investment in new grid infrastructure — replacing conductors and transformers and building new lines to reinforce the grid for example. However, according to a recent IEA report, Building the Future Transmission Grid: Strategies to Navigate Supply Chain Challenges, global grid expansion is struggling to keep pace with surging demand as supply chain bottlenecks have seen procurement lead times and costs for essential parts like transformers and cables nearly double since 2021. The IEA notes that while permitting remains the primary cause of delays in transmission projects, supply chain issues have emerged as a critical issue. An IEA survey on the issue found that procurement now takes two to three years for cables and up to four years for large power transformers. Meanwhile, real terms cable costs have nearly doubled since 2019 while transformer prices have increased by around 75%.

Despite these challenges though, there are alternative strategies available. The use of smarter grid-enhancing technologies (GETs) offers a route to reinforce the asset base without the need for wholesale replacement. GETs can thus reduce the need for capital investment while still improving system reliability and making the existing infrastructure far better equipped to cope with evolving demands.

The PD Problem

One of the tools available to improve grid reliability without the need for gross capital expenditure is the detection of partial discharge events, coupled with a strategy of early intervention. Partial discharge (PD) is caused by the breakdown of electrical insulation that results in a partial short circuit between conductors. Partial discharge can take place in any insulating medium with solid, liquid or gaseous types all potentially affected, although such events are often initiated in a gas void, such as gaps in solid epoxy insulation or bubbles in transformer oil.

While the partial discharge does not completely bridge the electrical gap it can nonetheless result in significant damage. When a partial discharge occurs over a long period, for example, it can cause a further breakdown in the insulating properties of the medium and eventually a complete failure. Inevitably, such failures result in a full short circuit and a sudden trip on any circuit affected. Where this occurs, such events are always costly for supply companies and consumers. Furthermore, replacing the failed elements can clearly be very expensive and it may take a long time to even secure replacement parts and effect a repair of the affected assets.

Monitoring the incidence of partial discharge thus not only allows potential failures to be addressed well ahead of time to avoid faults before they happen, but by deploying smart technologies partial discharge monitoring coupled with sophisticated analysis can also result in a predictive maintenance regime being implemented.

Detecting Partial Discharge

Partial discharge monitoring can be applied to assets running at voltage of 1 kV or more can be applied at any stage of an asset’s life, even during commissioning. However, it is particularly relevant to older assets that are at a higher risk of failure, especially those elements that are system-critical and which need to be rigorously monitored.

There are two ways of monitoring partial discharge events, off-line when the line is not energized, or online when the line is in use. Off-line monitoring can take place during commissioning or if the line is de-energized when there is no load and therefore no noise. Because the line is in use, online measurements can be more challenging as signal noise is generated that can interfere with the accuracy of any measurements. For example, high-intensity noise can obscure the pulses derived from small partial discharge problems and make them difficult to detect. In addition, it can make it harder to pinpoint the location of a particle discharge even if it is detected, the location is a key parameter to address any faults found.

There are also several possible monitoring strategies including punctual measurements that are performed at a specific time and usually last less than an hour, temporary measurements that can last perhaps hours or days and permanent measurements that monitor assets at all times and may be installed for months or years.

Finally, having obtained relevant data from the partial discharge monitoring, the interpretation of the signals is complicated and requires experienced personnel to derive actionable results.

Partial Discharge and Maintenance Strategies

With valid data in hand and a correct interpretation of the results available, this can be used to execute an effective maintenance strategy. There are broadly three types of maintenance strategies. Reactive or breakdown is a strategy of responding to a failure after it has occurred and when repairs are needed to restore function. A preventative or scheduled maintenance strategy requires periodic inspections and regularly timed interventions. Any defects are corrected as they are detected or components are replaced at scheduled intervals. A preventative strategy is designed to correct failures before they occur but can result in potential faults being missed or elements being replaced when they are still functional. Predictive maintenance is a data-driven, proactive strategy that relies on continuous data recovery and analysis to accurately forecast potential failures before they occur and allow timely intervention. While partial discharge monitoring can be used as part of a preventative maintenance strategy with more sophisticated analysis partial discharge monitoring can also be deployed as in important element in a predictive maintenance operation.

Partial Discharge Monitoring and the Future of an Ageing Grid

By detecting and taking action to address potential problems before they occur, grid reliability is improved. In addition, by acting early the cost impact of any emerging problems is mitigated. For an ageing asset base where reliability is already likely to be affected, advanced grid-enhancing technologies like partial discharge monitoring coupled with AI analytics are tools that serve a multitude of important functions. Indeed, a recent Credence Research report on the Middle East Grid Modernization Market found that the market is anticipated to reach $2.6 billion by 2032, at a CAGR of nearly 15%. It’s a market largely driven by increasing investments in smart grid technologies and digital transformation in the power sector as well as the influences of renewable energy integration. Partial discharge monitoring allows companies to be aware of the health of their assets and make better decisions about maintenance and repair. And, while it is worth noting that any defect that does not originate in the main insulation is not detectable by partial discharge monitoring, it can nonetheless serve as an important tool in the grid operator’s arsenal.