Why Annual PD Inspections Aren’t Enough
One in four medium-voltage failures involve Partial Discharge (PD).
It’s a silent, early-stage fault that can go undetected for months before suddenly bringing critical systems to a halt. For operators in energy-intensive industries, that can mean the difference between reliable production and a six-figure outage.
Annual PD inspections have long been a cornerstone of electrical maintenance strategies. They are valuable, they highlight risk, and they tick a compliance box. But here’s the problem: a once-a-year snapshot simply can’t keep pace with real-world conditions.
Today, technology and cost finally make continuous monitoring of PD and environmental conditions a practical reality — and it’s time for operators to rethink their approach.
The limits of annual inspections
Standards such as IEC 60270 and IEEE 400.3 recognise PD as a leading indicator of insulation degradation. Annual inspections will tell you whether activity is present in that moment — but PD is dynamic. It can appear suddenly, accelerate under environmental stress, and escalate from minor activity to catastrophic failure in a matter of weeks.
Humidity, for example, is a well-known trigger. A switchgear panel that tests clean in July may be under very different conditions by October, when moisture, dust, or contamination combine to lower insulation strength. By the time the next annual inspection comes around, PD could already have been the root cause of serious damage.
The real cost of waiting: a pharmaceutical case
Consider a pharmaceutical manufacturing facility. Electrical resilience isn’t just about uptime — it directly underpins product integrity and regulatory compliance.
At one such site, a switchgear failure linked to undetected PD led to an unplanned shutdown.
The result:
- Major safety incident
- Production halted for several days.
- Replacement switchgear had a 12-week lead time.
- Temporary switching arrangements and emergency repairs caused immediate impact to operations.
The financial impact on this site? Production loss + reactive operational impact + new switchgear + installation. More than £450,000 for a single event, not including the impact to resource availability for existing projects.
This is not unusual.
Continuous monitoring: now practical, now essential
Until recently, continuous PD monitoring was seen as complex and expensive. But advances in sensing and software mean that operators can now deploy permanent, automated monitoring systems at a fraction of the historical cost.
With continuous monitoring, operators gain:
- Early detection of PD activity, even months before failure.
- Environmental insight, tracking humidity and conditions that raise PD risk.
- Trend data, showing whether PD is stable, worsening, or linked to operating cycles.
- Actionable intelligence, enabling maintenance teams to intervene before a fault escalates.
In short, continuous monitoring transforms PD management from a reactive inspection into a proactive, condition-based maintenance strategy.
Why Acteniq and ndb
At Acteniq, we specialise in helping operators strengthen the reliability of their electrical networks through advanced monitoring and sensing. We use ndb Technologies’ test and measurement portfolio because of its proven quality and innovation in detecting PD across medium- and high-voltage assets.
By combining ndb’s world-class technology with our local engineering expertise, we enable customers in the UK and Ireland to move confidently towards condition-based
Take the next step
Annual inspections remain a valuable baseline — but they are no longer enough on their own. The technology is here, the cost barrier is gone, and the risks of waiting are too high.
Start your move towards condition-based maintenance today.
