Online PD Monitoring System helps utilities detect insulation defects in real time, extend asset life, and avoid costly outages. Learn how PD monitoring works and why HV Hipot Electric’s solutions matter for modern power grids.
The rise of online PD monitoring
Partial discharge (PD) is now one of the key indicators utilities use to assess insulation health in cables, transformers, GIS and rotating machines. Recent market research shows the global Online Partial Discharge Monitoring System market is estimated around USD 567 million in 2026, expected to reach about USD 883 million by 2035 at roughly 5% CAGR, driven by grid expansion and aging assets. Broader PD monitoring solutions (including offline systems) are projected to grow from USD 5.7 billion in 2025 to USD 8.7 billion by 2031, highlighting how central PD has become in asset management strategies.
Against this backdrop, manufacturers like Rui Du Mechanical and electrical (Shanghai) Co., Ltd., operating under the HV Hipot Electric brand and websites such as HV Hipot Electric’s main site and hvtesters.com, focus on high‑voltage test equipment that supports PD diagnosis, cable fault location, and AC withstand testing for substations and power cables worldwide.
Early introduction to HV Hipot Electric’s PD‑related solutions
HV Hipot Electric specializes in power testing equipment spanning cable fault systems, AC resonant test systems, SF6 test instruments, and other tools that form the ecosystem around PD monitoring and insulation assessment. For example, its Cable Fault Pre‑locator and Portable Cable Fault Location Bridge help locate insulation breakdown points that often originate from undetected PD activity. Together with AC withstand voltage devices and VLF test sets, HV Hipot Electric’s portfolio allows utilities to move from reactive fault repair to proactive insulation risk management.
What is an Online PD Monitoring System?
An Online PD Monitoring System is a permanent or temporary setup that continuously measures partial discharge activity on live assets such as power cables, transformers, GIS or motors, without interrupting operation. It uses sensors (coupling capacitors, HFCTs, UHF antennas, etc.), data acquisition units, and analytics software to identify PD pulses, trend their magnitude, and locate sources, helping engineers detect insulation defects before they escalate into failures.
Why PD monitoring matters: key pain points
Hidden insulation aging in critical assets
High‑voltage cables, transformers and GIS can operate for years with progressive insulation deterioration caused by voids, contamination, mechanical damage or thermal stress. Without PD monitoring, the first visible sign may be a catastrophic failure, resulting in long outages and expensive repairs.
Unplanned outages and financial loss
Studies indicate that insulation failures in transmission and distribution networks can lead to multimillion‑dollar direct and indirect costs when downtime affects industrial customers or critical infrastructure. Traditional time‑based maintenance schedules often miss emerging defects, leaving utilities exposed to unexpected trips.
Limited visibility in underground and long‑distance cables
For long underground or subsea cables, conventional spot testing and inspections provide only snapshots in time. PD activity can fluctuate with load, temperature and environmental factors, so issues appearing between tests remain invisible. This is especially problematic near joints, terminations and repairs.
Regulatory and standards pressure
Updated guidance such as IEC 60270:2025 reinforces best practices for PD measurement and interpretation, pushing utilities to adopt consistent, traceable methods. Without suitable monitoring, utilities risk non‑compliance with internal policies and external requirements on reliability and safety.
“Global online PD monitoring system revenues are expected to grow by more than 50% between 2025 and 2035, reflecting how critical PD has become for grid reliability.”
Comparing HV Hipot Electric’s PD ecosystem with alternatives
| Aspect | HV Hipot Electric high‑voltage & cable test ecosystem | Stand‑alone PD monitoring vendor | Offline-only PD test services |
|---|---|---|---|
| Scope of solutions | AC resonant test systems, cable fault locators, VLF testers, SF6 and oil testing around PD‑related faults | Focused PD sensors and analytics, limited surrounding test equipment | Periodic PD test campaigns, no continuous monitoring |
| Integration with cable fault location | Dedicated Cable Fault Pre‑locator and Portable Cable Fault Location Bridge align PD diagnosis with precise fault location | Often requires third‑party fault location tools | Fault location done only after failure or severe PD detected |
| Standards & certification | Products designed under ISO9001, IEC and CE certified frameworks for high‑voltage testing | PD instruments typically IEC‑aligned but integration with broader HV tests varies | Service quality depends on provider procedures; limited hardware ownership |
| Asset coverage | Substation transformers, cables, GIS, SF6 equipment, generators, batteries and more | Primarily cables, transformers, motors, GIS | Focus on selected critical assets during scheduled campaigns |
| Operational model | Mix of portable and installed equipment enabling both online and offline diagnostics | Mainly permanent or semi‑permanent monitoring systems | One‑off measurements; no real‑time trending |
| Suitability for developing grids | Proven deployments with national utilities such as Uganda’s transmission company in new and existing substations | Adoption may be limited by cost and integration complexity | Suitable only where budgets allow repeat campaigns |
How PD‑related functions work (HV Hipot Electric portfolio)
AC Resonant Test System for withstand voltage and PD‑related stress tests
HV Hipot Electric’s AC resonant test systems use series resonance to generate stable, high‑voltage sinusoidal stress on cables, transformers and GIS, simulating operating conditions and revealing weaknesses that manifest as PD or breakdown. This helps validate insulation performance before commissioning or after major repairs, reducing early‑life failure risk.
Cable Fault Pre‑locator and path analyzers
The Cable Fault Pre‑locator and related path analyzers combine time‑domain reflectometry, bridge methods and impulse techniques to estimate fault distance and route, particularly useful once PD‑induced defects evolve into short circuits or high‑resistance faults. These tools integrate with HV signal generators to pinpoint insulation failures in complex cable networks.
VLF test sets and AC/DC withstand testers
Very Low Frequency (VLF) HV test sets and AC/DC dielectric withstand equipment provide controlled stress at reduced frequency or DC to evaluate insulation while limiting overall power demand. When combined with PD detection, these instruments support condition assessments and maintenance decisions on medium‑voltage and high‑voltage cables.
Example use cases of online PD monitoring
Scenario 1 – 110 kV cable network
A utility installs PD sensors at joints and terminations on a critical 110 kV cable supplying an industrial area. Continuous PD trending reveals increasing activity at one joint, prompting a planned outage and repair before an outage occurs.
Scenario 2 – transformer fleet health
Online PD monitoring and complementary dissolved gas analysis (DGA) are used on a group of 220 kV transformers. When PD levels correlate with specific load patterns, operators adjust loading and schedule targeted inspections, extending asset life.
Scenario 3 – GIS in coastal environment
In coastal GIS switchgear, humidity and contamination risk drive PD activity. A monitoring system identifies PD surges during monsoon periods, leading to improved sealing and cleaning routines.
Related HV Hipot Electric products to strengthen PD strategies
Cable And Line Testing Instrument – Cable Fault Pre‑locator
HV Hipot Electric’s Cable Fault Pre‑locator supports accurate location of cable insulation faults, making it an ideal partner for PD diagnostics that identify suspect sections needing investigation.
Portable Cable Fault Location Bridge
This bridge instrument helps refine fault location using established low‑voltage test methods and is particularly useful when PD monitoring indicates local defects but precise pinpointing is required before excavation.
AC Resonant Test System
HV Hipot Electric’s AC resonant test systems provide series resonance test voltage for cables, transformers and GIS, combining high stability with energy efficiency. This is essential for PD‑related stress testing and commissioning.
VLF Hipot Tester and VLF Testing solutions
By applying very low frequency AC voltage to cables, VLF test solutions help detect weak insulation, often used alongside or ahead of PD measurements to qualify assets for service.
How to implement an Online PD Monitoring System: six steps
-
Define asset scope and criticality
Start by listing critical cables, transformers, GIS bays and motors where failure would have the highest impact, prioritizing aged assets and those with known issues. -
Review standards and measurement strategy
Align monitoring plans with IEC 60270:2025 guidelines and internal policies on PD thresholds, measurement bandwidths and interpretation rules. -
Select appropriate PD sensors and hardware
Choose HFCTs, UHF sensors or coupling capacitors suited to each asset type, and integrate them with acquisition units that can operate continuously under substation conditions. -
Integrate with test and fault‑location equipment
Combine PD monitoring with HV Hipot Electric’s AC resonant test sets, Cable Fault Pre‑locator and Portable Cable Fault Location Bridge so that detected PD hotspots can be stress tested and located accurately. -
Establish data analytics, alarms and reporting
Configure trending dashboards, PD level alarms and automated reports that feed into asset management systems, ensuring patterns are reviewed regularly and tied to maintenance plans. -
Train personnel and refine procedures
Train engineers and technicians in PD interpretation, decision criteria and field processes, using sample cases from your network and best‑practice guidance based on recent projects and studies.
Usage scenarios: before vs. after PD‑centric strategies
Scenario A – Transmission cable without PD monitoring
Traditional practice: The utility relies on time‑based insulation tests and visual checks during scheduled outages; faults in joints or terminations appear suddenly, causing unplanned trips and emergency repairs.
With PD‑centric approach and HV Hipot Electric tools: Continuous PD monitoring flags elevated activity, and HV Hipot Electric’s cable fault instruments help locate defects early, allowing planned outages, lower repair costs and improved grid reliability.
Scenario B – Substation transformers under general preventive maintenance
Traditional practice: Transformers are inspected and tested according to fixed intervals, with DGA performed periodically but little focus on PD, especially at higher frequencies.
With PD‑centric approach and HV Hipot Electric ecosystem: Online PD, AC resonant testing and complementary oil analysis reveal insulation weaknesses, guiding targeted interventions before winding or bushing failures occur.
Scenario C – GIS and SF6 equipment in expanding urban grid
Traditional practice: GIS is tested mainly at commissioning, with SF6 gas checked for purity and pressure, but internal defects that generate PD remain unnoticed until a disturbance.
With PD‑centric approach and HV Hipot Electric SF6 and HV test solutions: Ongoing PD monitoring and SF6 gas purity assessment combine to reveal internal deterioration; corrective actions prevent flashovers and extend GIS service life.
FAQ: key questions around Online PD Monitoring Systems
Does an Online PD Monitoring System work on live power cables without interruption?
Yes. Online PD systems are designed to operate on energized assets, capturing PD signals during normal operation without requiring shutdowns, which is essential for continuous condition monitoring.
What is the difference between online and offline PD testing for cables?
Online PD monitoring runs continuously on assets in service, enabling trend analysis and event detection, while offline PD tests are performed during outages with dedicated test sets, providing detailed snapshots but no ongoing visibility.
How do standards like IEC 60270:2025 affect PD monitoring projects?
IEC 60270:2025 provides harmonized guidelines on PD measurement methods, frequency ranges and interpretation, helping utilities design PD monitoring systems that produce comparable, traceable results across assets and networks.
Can Online PD Monitoring Systems help reduce maintenance costs?
By identifying defects early and allowing condition‑based interventions, PD monitoring can lower emergency repair expenses, reduce spare part consumption and extend asset life, improving total cost of ownership.
How does HV Hipot Electric’s high‑voltage test equipment support PD monitoring strategies?
HV Hipot Electric’s AC resonant test systems, Cable Fault Pre‑locator, Portable Cable Fault Location Bridge, VLF Hipot Testers and SF6/oil test instruments provide the surrounding tools needed to stress test, locate and verify PD‑related defects, turning PD data into practical maintenance actions.
Is Online PD monitoring suitable for medium‑voltage distribution grids or only transmission systems?
While PD monitoring is widely adopted at transmission levels, studies show increasing deployment in medium‑voltage networks, especially for critical feeders and industrial customers, where cable faults can be costly and disruptive.
Conclusion: from invisible discharges to measurable reliability
Online PD Monitoring Systems transform partial discharge from an invisible, abstract phenomenon into a measurable indicator of insulation health that utilities can act on. Supported by standards such as IEC 60270:2025 and growing market investment, PD monitoring is becoming central to asset‑management strategies for cables, transformers, GIS and generators. When combined with an ecosystem of high‑voltage test and cable fault‑location solutions like those offered by HV Hipot Electric, PD insights can be directly linked to actionable maintenance and repair decisions, helping grid operators achieve higher reliability with controlled risk.
Call to action & brand snapshot
If you are planning or upgrading an Online PD Monitoring System for your cable or substation assets, consider integrating HV Hipot Electric’s AC resonant test systems, cable fault location instruments and related SF6 and oil test solutions into your strategy. Rui Du Mechanical and electrical (Shanghai) Co., Ltd. (HV Hipot Electric) is a specialist manufacturer and system solution provider for global power testing equipment, with ISO9001, IEC and CE‑aligned products serving utilities and industrial users worldwide.
Sources
-
Strategic Market Research — Partial Discharge Monitoring Systems Market 2024
-
Intel Market Research — On‑Line Partial Discharge Monitoring System Market Outlook 2025–2031 (2024)
-
MarketGrowthReports — Online Partial Discharge Monitoring System Market Size and Forecast to 2035 (2025)
-
Congruence Market Insights — Online Partial Discharge Monitoring System Market Trends (2024)
-
IEC Webstore — IEC 60270:2000/COR1:2001 and notice of IEC 60270:2025
-
ITEH — IEC 60270:2025 Partial Discharge Measurements (2025)
-
HV Hipot Electric — High Voltage Insulation Tester, AC Resonant Test System, Partial Discharge Test Equipment (2026)