Using UHF for Partial Discharge Monitoring and Location

Advancements in Transformer Health: Implementing UHF-Based Online Partial Discharge Monitoring and Localisation

This is a Qualitrol Case Study.

Overview

Keeping power transformers running reliably is essential for a stable electricity grid. Even small faults inside a transformer can grow over time and lead to major failures if they go unnoticed.

One of the earliest warning signs is something called partial discharge (PD)—tiny electrical sparks inside the insulation. To detect these early, Qualitrol uses Ultra High Frequency (UHF) monitoring, a modern method that can pick up these signals in real time and help pinpoint exactly where they are coming from.

Challenge

Traditional PD detection methods can struggle in real-world conditions. They can be affected by electrical noise, making it harder to tell the difference between a real fault and background interference.

On top of that, even if PD is detected, finding the exact location inside a transformer is difficult. Without accurate location data, maintenance teams may not know where to look, which can lead to longer outages and higher costs.

For older transformers, adding monitoring equipment can also be challenging, as they were not originally designed for it.

Solution

Qualitrol’s UHF monitoring system offers a more advanced way to detect and locate partial discharge activity.

Specialised sensors are installed on the transformer, either built in during manufacturing or retrofitted onto existing units through access points like hatch covers or drain valves. These sensors detect high-frequency signals created by PD events.

By comparing how quickly the signal reaches different sensors, the system can pinpoint where the discharge is happening inside the transformer. This allows for accurate fault location, not just detection.

Benefits

With UHF monitoring in place, operators gain a clearer and more reliable view of transformer health.

The system is highly sensitive and less affected by external noise, making it easier to detect real issues early. It also provides location data, helping maintenance teams act faster and more precisely.

This reduces the risk of unexpected failures, lowers maintenance costs, and improves overall system reliability.

Results

In one case, a 132kV/25kV transformer showed warning signs through gas analysis, suggesting a possible internal issue.

UHF sensors were installed, and the system quickly confirmed partial discharge activity. By analysing the signal timing, the exact location of the fault was identified.

When the transformer was opened for inspection, the issue was found exactly where the system had indicated.

This result showed how effective UHF monitoring can be not just in detecting problems early, but in helping teams find and fix them with confidence before they lead to bigger failures.