Overhead distribution lines cover more distance than any other grid asset, and their insulation – porcelain and composite insulators, line terminals and arrester connections – weathers directly: sun, rain, salt, pollution and mechanical stress. Partial discharge (PD) on line equipment is both a cause and an early indicator of insulator degradation, tracking and flashover risk. Detecting it on the open line is more challenging than in a substation, and this guide sets out the practical methods.
What PD means on an overhead line
Insulator surface discharge
Pollution, moisture and salt create surface conduction on insulators, producing discharge that erodes the surface and can lead to tracking and flashover. The discharge activity is measurable before it becomes critical.
Line equipment defects
Loose connections, damaged arcing horns and defective arrester leads produce corona and PD at specific line positions.
Detection methods for line PD
1. Ceramic insulator sensors (installed)
Specialised ceramic insulator sensors can be installed on distribution lines to detect PD and overvoltage activity at the line, transmitting condition data to a monitoring platform. They suit critical spans and known problem routes where continuous observation earns its cost.
2. Ultrasonic inspection from the ground or vehicle
Ultrasonic detectors, including parabolic or focused types, pick up the airborne acoustic emission of surface discharge and corona from insulators and fittings. Ground-based or vehicle-mounted ultrasonic patrols screen long line sections quickly, prioritising positions for closer inspection.
3. Infrared thermography
Thermal imaging from the ground or a drone finds hot connections, damaged insulators and contaminated surfaces – complementary to acoustic methods in a line patrol.
Practical limits of line PD detection
- Access – line equipment is physically distant; ground-based detection sees what is audible or visible from the patrol point.
- Ambient noise – corona from nearby hardware and environmental noise complicate acoustic interpretation.
- Coverage economics – installed sensors pay on critical spans; patrol-based methods cover the fleet.
Building a line inspection programme
- Screen with ultrasonic and thermal patrols, prioritising routes with pollution, coastal exposure or a flashover history.
- Investigate flagged positions with closer inspection, including climbing or drone-based checks where warranted.
- Install ceramic insulator sensors or line monitors on the highest-risk spans for continuous observation.
- Record findings per span and trend across patrols, feeding the insulator replacement programme.
About HUWOR
Zhuhai Huawang Technology Co., Ltd. (HUWOR) manufactures ceramic insulator sensors for distribution lines and ultrasonic inspection instruments used in overhead line patrols, supporting utilities worldwide with OEM/ODM supply and application guidance. Contact the HUWOR sales team for a line inspection configuration.