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Partial Discharge Testing Services
Last Updated: 2026
Partial discharge (PD) testing detects tiny electrical sparks inside insulation before they grow into a complete failure. Elion performs non-invasive PD testing on transformers, switchgear, and cables per IEC 60270, using advanced PD detection instruments, and delivers a report with severity assessment and repair recommendations — trusted since 2010 across 30,000+ audits.
What Is Partial Discharge and Why Does It Matter?
Partial discharge is a small electrical spark that occurs within a gap, void, or defect in insulation — it doesn’t immediately disrupt equipment operation, but over time it degrades the insulation further, eventually leading to complete failure and unplanned outages. PD testing identifies these discharges early, before they cause costly downtime or safety incidents.
Why is Partial Discharge Testing Important?
- Detects insulation defects early before catastrophic failure.
- Extends equipment life by allowing timely corrective actions.
- Prevents unplanned outages and production losses.
- Enhances safety by reducing the risk of arc flash and equipment explosion.
- Supports condition-based maintenance over reactive maintenance.
- Complies with IS/IEC standards and best practices for asset management.
What Equipment Requires PD Testing?
- Power Transformers (66 kV, 132 kV, 220 kV, 400 kV and above)
- Gas-Insulated Switchgear (GIS)
- Air-Insulated Switchgear (AIS)
- High Voltage Cables
- Rotating Machines (Motors & Generators)
- Bus Ducts and Terminations
Elion’s Partial Discharge Testing Services
- Offline PD Testing: Performed during planned shutdowns using coupling capacitors and PD detectors.
- Online PD Testing: Without interrupting operations, identifying active discharges under real load conditions.
- PD Mapping & Localization: Identifying exact locations of discharges using advanced detection methods.
- Frequency & Time Domain Analysis: Advanced waveform analysis for accurate diagnosis.
- PD Pattern Analysis: Identifying the nature of defects (corona, surface, internal discharge).
- Data Logging & Trending: Long-term monitoring for condition-based maintenance planning.
- Reporting: Detailed reports with PD levels, location, severity assessment, and actionable recommendations.
- Post-Test Advisory: Guidance on insulation repair, monitoring, and retesting schedules.
Standards We Follow
- IEC 60270 (High-voltage test techniques – Partial discharge measurements)
- IS 6209 (Partial discharge measurement)
- IEC 60076-3 (Transformers)
- IEEE 400 Series (Cable PD testing)
- OEM guidelines for transformers and GIS
Benefits of Choosing Elion for PD Testing
- 20+ years of high-voltage testing and condition monitoring expertise.
- Advanced PD detection instruments with high sensitivity.
- Pan-India testing capability for substations, industries, and utilities.
- Expert engineers trained in PD interpretation and analysis.
- Non-invasive testing without system damage.
- Quick turnaround with on-site reporting options.
- Actionable recommendations for asset life extension.
Our Partial Discharge Testing Process
- Pre-test Consultation: Identify critical assets and testing objectives.
- On-site Testing: Using advanced PD measuring instruments under offline or online conditions.
- Analysis: PD pattern recognition, localization, and severity assessment.
- Reporting: Detailed technical report with graphs and actionable insights.
- Recommendations: Maintenance or insulation repairs as needed.
- Post-Test Support: Planning for monitoring and retesting for continuous asset health management.
Definition – Partial Discharge Testing
Partial Discharge (PD) Testing is a diagnostic technique used to detect early electrical breakdowns or weak points in insulation systems of high-voltage electrical equipment such as transformers, switchgear, cables, generators, and motors.
Partial discharges are tiny electrical sparks that occur within insulation defects before a complete failure happens. These tiny sparks may not immediately disrupt operation but over time can grow, weakening insulation and eventually leading to costly outages or catastrophic equipment failure.
PD Testing identifies and measures these microscopic discharges so you can address issues early — improving safety, reliability, and asset life.
What Types of Partial Discharge Does Testing Detect?
Corona discharge — occurs at sharp points or edges in high-voltage equipment exposed to air.
Surface discharge — occurs along the surface of insulation due to contamination or tracking.
Internal discharge — occurs within voids or gaps inside solid insulation material.
Online vs. Offline Partial Discharge Testing
| Parameter | Online PD Testing | Offline PD Testing |
|---|---|---|
| Equipment Status | Equipment remains energized and in normal operation | Equipment is de-energized and taken out of service |
| Best For | Routine condition monitoring and continuous asset health assessment | Detailed diagnostics, commissioning, and acceptance testing |
| Operational Disruption | No disruption to plant operations | Planned shutdown or maintenance outage required |
| Typical Use Cases | Substations, transformers, switchgear, cable systems, and other critical infrastructure that cannot be shut down | New equipment commissioning, post-repair verification, factory/site acceptance testing, and detailed fault investigation |
Factors That Decide Partial Discharge Testing Cost in India
Partial discharge testing cost depends on: number and type of assets tested (transformers, switchgear, cables), voltage class of the equipment, whether testing is done online or offline, and site accessibility. Request a fixed-fee quote with your asset list.
Contact Elion for Partial Discharge Testing
Enhance your asset reliability and prevent unplanned outages with Elion’s expert Partial Discharge Testing services.
Request a Quote or contact us at [email protected].
Client Testimonial
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Frequently Asked Question (FAQs)
Partial discharge is a small electrical spark that occurs within a gap or defect in insulation, without immediately causing complete failure — but it worsens over time if left undetected.
It’s a non-invasive test that detects and measures these discharges in transformers, switchgear, and cables, so degrading insulation can be found and addressed before it causes an outage.
To detect insulation defects early and prevent failures.
Transformers, GIS, AIS, HV cables, motors.
Testing during operation to monitor live discharges.
Defects in insulation, voids, sharp edges, contamination.
No, it is a non-destructive test.
Using coupling capacitors, sensors, and analyzers.
IEC 60270, IS 6209, IEEE 400.
Depend on equipment type and manufacturer guidelines.
PD Testing is commonly performed on:
Power Transformers
Cables & Terminations
Switchgear (Indoor & Outdoor)
Generator Stator Windings
Motors & Rotating Machines
Bushings, CTs, PTs, GIS, and HV connections
Before commissioning new electrical equipment
During routine preventive maintenance cycles
After lightning strikes or overvoltage events
When unusual noise, heat, or insulation deterioration is observed
Before insurance inspections or electrical audits
After long idle periods or extended service life
Partial discharge is a small electrical discharge that occurs within insulation voids or defects under high electric stress. Unlike a full breakdown, it doesn’t immediately short the system but gradually damages insulation over time.
Even small PD activity slowly erodes insulation material. Left unchecked, this erosion can lead to complete insulation failure — resulting in outages, fires, property damage, or equipment replacement costs.
We use advanced instruments such as PD detectors, acoustic sensors, and high-frequency measurement tools that capture electromagnetic and acoustic signals produced by partial discharges.
Yes. PD testing is non-destructive and performed under controlled conditions without harming your electrical equipment.
Testing can sometimes be done online while equipment is energized (for certain assets like transformers under load), but offline testing may require planned shutdown for detailed evaluation.
Elion’s partial discharge testing follows IEC 60270, the international standard for high-voltage partial discharge measurement techniques.
Yes — online PD testing is performed while equipment stays in service. Offline testing requires planned downtime and is used for more detailed diagnostic work.
Corona discharge, surface discharge, and internal discharge — see the “Types of Partial Discharge” section above for details on each.
This depends on asset criticality and age; many facilities include PD testing as part of an annual or biennial condition-monitoring programme, with more frequent testing for aging or high-value assets.
Elion provides a severity assessment and recommendations — ranging from continued monitoring for low-severity findings to repair or replacement guidance for high-severity discharges.
Transformers, switchgear, power cables, and other high-voltage insulated equipment.
No — it is a non-invasive measurement technique and does not affect equipment operation or condition.
A report with PD levels, discharge location and type, severity assessment, and actionable recommendations for follow-up.
Cost depends on the number and type of assets, voltage class, and whether testing is online or offline — request a fixed-fee quote with your asset list.