Electrical faults rarely happen out of nowhere. In most cases, small, undetectable issues start developing long before a major failure occurs. These early-stage faults don’t immediately shut down systems—but they silently chip away at the health and safety of your infrastructure. Left unaddressed, they can trigger outages, equipment damage, or worse.
This is where Partial Discharge Testing becomes a powerful tool. It allows businesses to detect and locate insulation faults in high-voltage systems before they escalate—providing critical insight into the condition of your assets and helping you take action while you still have time.
What Is Partial Discharge?
Partial discharge (PD) refers to small electrical sparks or discharges that occur when insulation within high-voltage equipment breaks down but doesn’t yet lead to a full electrical short. Think of it like a slow leak in a pipe—it’s not causing total failure now, but if ignored, it could result in a burst down the line.
PD often goes unnoticed because it happens inside cable joints, switchgear, transformers, or other enclosed systems. But even these tiny discharges can cause significant long-term damage to insulation materials, eventually leading to breakdowns, unplanned downtime, or equipment replacement.
Why Early Detection Matters
Catching PD early provides more than just peace of mind—it gives you time. Time to plan maintenance instead of responding to a crisis. Time to budget for repairs instead of absorbing emergency costs. And time to avoid major disruptions that could halt operations, especially in high-dependence environments like manufacturing plants, data centres, or hospitals.
Key benefits of regular PD testing include:
- Preventing outages and equipment failures
- Reducing downtime and repair costs
- Improving worker safety by identifying at-risk components
- Extending the life of high-voltage assets
- Supporting asset management and maintenance planning
Where Partial Discharge Happens
PD is most common in aging or poorly installed insulation but can also result from environmental factors like moisture, contaminants, or mechanical stress. Here’s where it typically occurs:
- Cable joints and terminations
- Power transformers
- High-voltage switchgear
- Rotating machines (e.g., motors, generators)
- Busbars and insulators
Because these components are often critical to operations, catching PD in these areas early is essential.
Types of Partial Discharge Testing
There’s no one-size-fits-all method for PD detection. The approach depends on the equipment involved, whether it’s in service, and how accessible the area is. Two main types of testing are typically used:
Online Testing
Performed while the equipment remains live, online PD testing is ideal for facilities that can’t afford downtime. Sensors are used to monitor PD activity without interrupting operations, making this approach fast and non-intrusive.
Online testing is great for:
- Ongoing condition monitoring
- Spot checks during normal operations
- Identifying trends or degradation over time
Offline Testing
Offline testing is done when equipment is de-energised, usually during scheduled maintenance or commissioning of new systems. It offers a deeper dive into insulation performance and can be useful for pinpointing fault locations.
Offline testing is useful for:
- Detailed diagnostics during planned shutdowns
- Post-repair verification
- Factory acceptance testing (FAT) and commissioning
When to Schedule Testing
Regular PD testing doesn’t need to be frequent, but it should be part of your broader electrical maintenance schedule—especially if your facility has:
- Aging electrical infrastructure
- High loads or mission-critical systems
- A history of electrical faults or unexplained equipment failures
- Harsh operating environments (e.g. humidity, dust, corrosive atmospheres)
- New equipment installations that require baseline readings
Even new installations can benefit from PD testing to confirm that joints and terminations were properly completed before the system goes live.
What Happens After Testing
The real value of PD testing lies not just in detection, but in what you do with the results. A professional testing provider will not only identify PD activity but also help you interpret the data and prioritise next steps.
A good test report should include:
- Clear readings of PD magnitude and frequency
- Location mapping of affected components
- Severity analysis (e.g., low, medium, high risk)
- Maintenance or replacement recommendations
- Suggested re-testing intervals if monitoring is required
By combining this data with your asset management system, you can create smarter, risk-based maintenance schedules and reduce the chance of unexpected failure.
A Smarter Way to Manage Electrical Risk
Running a facility or business means managing hundreds of moving parts—and electrical systems are often expected to “just work” in the background. But like any complex system, they need monitoring. They need attention. And most importantly, they need proactive care.
Partial discharge testing helps you stay ahead of the fault curve. It’s not about finding problems—it’s about preventing them before they cost you time, money, and safety.