Medium and low voltage switchgear are becoming increasingly prevalent in modern substations and industrial power systems as electrical infrastructure continues to expand and evolve. As utilities and industrial facilities upgrade their systems to meet growing demand and incorporate new technologies, such as renewable energy sources and smart grid capabilities, the deployment of sophisticated switchgear solutions has accelerated significantly.

Many older installations are now beginning to experience failure modes as these assets are reaching the end of their serviceable life. Common issues include insulation degradation, contact wear, mechanical fatigue, and environ-

mental deterioration that naturally occur after years of operation under demand­ing conditions. These age-related failures can result in unexpected outages, safety hazards, and costly emergency repairs that disrupt operations and im­pact service reliability.

Therefore, the need for cost-effective monitoring technologies is becom­ing critical to mitigate the substantial costs associated with both scheduled offline maintenance and unanticipated in-service failures. By implementing condition-based monitoring systems that can detect early warning signs of equipment deterioration, operators can transition from reactive maintenance strategies to proactive approaches that extend asset life, optimize mainte­nance budgets, and improve overall system reliability.

Challenge

A South African mining company operating smelting furnaces was experi-encing a high failure rate of cable terminations, resulting in costly downtime and complete production disruption. To prevent these costly interruptions, a comprehensive partial discharge (PD) was installed. The online monitor identi-fied abnormally high levels of PD activity which were coming from the high-volt-age furnace cable terminations, exceeding established threshold limits. The identified defects were continuously monitored and trended until an emergency planned shutdown was strategically arranged for a detailed physical inspec-tion, root cause investigation, and corrective maintenance interventions.

Solution

To resolve the issue, a multi-phase approach was deployed combining ad-vanced testing techniques with corrective actions. As part of the investigation of the 33kV cable terminations, high voltage (50Hz) was applied to the termi-nation under controlled test conditions. During this examination, the termi-nation earth strap was found to be improperly folded over the black heat shrink tube and secured with roll springs, creating an unexpected discharge path. The discharges were clearly identified on the black heat shrink tube surface, indicating significant surface degradation.

Further inspection revealed that the screen of the terminations had been incorrectly installed during the original commissioning, shown in Figure 1. Critical voids were identified between the screen and XLPE insulation, creating cavities where partial discharges could initiate and propagate. Discharges could be measured at phase voltage, confirming active defects under normal operating conditions.

Based on these findings, immediate remedial action was taken. The two terminations exhibiting the highest discharge magnitudes were replaced with properly installed units. A detailed investigation and comprehensive electrical tests were then conducted on the removed terminations to definitively de-termine the root cause of the discharges and prevent recurrence across the fleet. By performing diagnostic analysis of the PD activity, the source of the discharges was successfully identified and repaired, preventing unwanted premature failure.

To ensure ongoing asset health and enable proactive maintenance stra-tegies, a permanent PD monitoring system, including the Dynamic Ratings Switchgear and Cable Monitor (SCM), was installed on the 33kV switchgear to continuously measure electrical partial discharges within the switchgear components. This strategic decision was based on the well-established fact that 90% of cable failures occur at splices and terminations, and as these accessories break down, they generally produce partial discharges prior to complete failure.

The SCM takes data from radio frequency current transformers (RFCTs) placed around the cable termination shields or uses a GPCS sensor when shields are ungrounded. The system continually monitors partial discharge activity, stores and correlates operating dynamics, and provides comprehensive information on the health of the medium voltage insulation systems of switch-gear, cables, bus duct, and unit substations.

For enhanced protection, the Switchgear and Cable Partial Discharge Monitor may be paired with Dynamic Ratings Switchgear Performance Monitor to identify slow or malfunctioning breakers as shown in figure 2. Combining these two technologies offers a comprehensive solution to prevent switchgear breaker and cable failures.

The Switchgear Performance Monitor utilizes smart capture technology to monitor the open and close operation of each breaker in the switchgear. Figure 3

shows a slow breaker operation detected by the Switchgear Performance Monitor.

Seventy days after the monitor was installed, a slow operation was detected which was 33 milliseconds slower than the baseline. The monitor alerted the customer of a lubrication problem with the breaker, allowing them to repair the problem and prevent an arc flash incident and catastrophic failure.

Combined, these two technologies offer one of the most comprehensive monitoring solutions available in the market. By implementing this integrated monitoring approach, facilities can transform their maintenance strategy from reactive emergency responses to proactive condition-based interventions, sig­nificantly reducing the risk of costly unplanned outages and production disrup­tions. This case study demonstrates how modern online monitoring systems can effectively detect degradation and mechanical issues in aging infrastructure, enabling operators to extend asset life while maintaining operational reliability and safety.

This article was originally published in the February 2026 issue of the Advanced Diagnostics & Analytics magazine.

View Magazine