Partial discharge is an ever-present risk, especially in high-voltage (HV) and medium-voltage (MV) electrical systems. In electrical asset management and equipment health monitoring, Partial Discharge is considered an ongoing risk, which means reliable partial discharge testing is essential for detecting insulation defects in HV and MV equipment before they develop into serious problems.

PD testing identifies small electrical discharges that occur within or around damaged insulation in high-voltage equipment, indicating underlying issues such as insulation weaknesses, voids, cracks, or other defects in equipment such as transformers, switchgear, and cables. With regular testing and timely corrective measures, maintenance teams can address these anomalies early, reduce the risk of unexpected failures, and improve equipment safety and reliability.

As technology continues to advance, new and more reliable ways of detecting and managing partial discharge (PD) are emerging. Conventional PD detection methods are increasingly being complemented by more integrated approaches giving a more broader view of insulation conditions. One such approach is multi-channel PD testing, which captures and compares PD signals from multiple sensors or channels simultaneously. 

Multi-channel PD testing is most useful when noise separation, multi-phase comparison, simultaneous monitoring or accurate defect location is required. Multi-channel PD testing is an advanced method of detecting and monitoring partial discharge activity which distinguish PD signals from electrical noise, compare activity across phases, and locate potential faults more accurately. 

Choosing the right PD testing method should be an uncompromising step to ensure accurate assessment of insulation conditions and identify potential defects before they lead to equipment failure. Reliable testing helps maintenance teams make informed decisions, plan timely interventions, and extend the service life of electrical assets. It also supports a safer working environment by reducing the risk of unexpected electrical failures, equipment damage, and operational hazards, helping protect both assets and personnel. 

 What Is Multi-Channel Partial Discharge Testing?

Multi-channel partial discharge (PD) testing is a diagnostic technique that collects electrical signals from multiple measurement channels connected to different sensing or decoupling points on high-voltage equipment. 

Conventional methods for improving noisy partial discharge (PD) data include filtering and gating, or single-channel PD testing which help reduce unwanted signals and make PD activity easier to identify. Single-channel PD testing is a PD method with one sensor or measurement channel to detect and analyse electrical discharge pulses in high-voltage equipment. It evaluates signal characteristics such as pulse magnitude, phase position, and repetition rate to identify potential insulation defects.

Single-channel PD testing captures and analyses signals through one measurement channel at a time, while multi-channel PD testing records signals from multiple sensors or measurement points simultaneously. Synchronous measurements allow these signals to be captured on a common time basis, enabling the comparison of correlated PD pulses across channels. 

Multi-channel PD testing offers a more comprehensive approach by capturing signals from multiple channels simultaneously and comparing their characteristics. This helps distinguish genuine PD activity from electrical noise, improving the reliability of measurement results and supporting more accurate insulation condition assessment. 

Multi-channel PD testing uses synchronous signal analysis to distinguish partial discharge (PD) activity from electrical noise and identify different discharge sources. One approach is the Three-Phase Amplitude Relationship Diagram (3PARD) method, which compares the amplitude relationships of simultaneously captured signals across three channels. Since PD pulses originating from different locations produce distinct signal patterns, this comparison helps separate individual discharge sources from background noise.

Another technique, the Three-Center-Frequency Relation Diagram (3CFRD), compares the frequency characteristics of signals to distinguish different PD sources and noise. These methods can improve the accuracy of PD assessment in high-voltage equipment, including three-phase systems such as power transformers, as well as single-phase transformers, voltage transformers (VTs), and current transformers (CTs).

In simple terms, Phase-Resolved Partial Discharge (PRPD) and Three-Phase Amplitude Relationship Diagram (3PARD) are techniques used to analyse partial discharge (PD) signals and help identify insulation defects. In multi-channel PD testing, PRPD helps interpret discharge patterns, while 3PARD uses correlated signals across channels to improve PD source separation. 

• Phase-Resolved Partial Discharge (PRPD) analysis: Maps PD pulse activity against the phase angle of the applied AC voltage, along with pulse magnitude and occurrence. The resulting patterns help assess discharge behaviour and identify possible insulation defects.
• 3PARD analysis: Compares the amplitudes of synchronously measured PD signals from three channels. By examining the relationships between these signals, it helps distinguish different PD sources and separate genuine discharge activity from electrical noise.

When Should You Choose Multi-Channel PD Testing?

Multi-channel PD testing is a flexible technique to check insulation conditions in different types of high-voltage equipment.  Partial discharge activity is not always a one-point issue; it can affect multiple points within an electrical asset. In reality, when each phase is tested separately, changes in operating conditions or background noise between measurements can make the results less consistent and harder to compare accurately.

Multi-channel PD testing is particularly useful in hard-to-access locations, electrically noisy environments, and equipment with complex geometries. It is also valuable for critical electrical assets that demand continuous PD monitoring to track insulation conditions and identify potential defects at an early stage. 

By capturing and comparing signals from multiple measurement points, PD fault detection is significantly improved, distinguishing discharge activity from electrical noise, and providing a better look into potential insulation defects. This makes it useful in several applications, like for instance for on-site inspections in noisy environments and initial commissioning checks.

• Testing in High-Noise Environments: Multi-channel PD testing can be very effective during on-site inspections where electrical interference makes signal interpretation difficult. Techniques such as 3PARD compare pulse amplitudes across synchronised channels to separate genuine discharge activity from external noise.
•  Monitoring Multi-Phase and Complex Equipment: Simultaneous measurements over multiple phases or sensing points give a clearer picture of discharge patterns in equipment such as power transformers, cables, and gas-insulated switchgear (GIS). With that, comparing the captured signals would become easy, allowing the maintenance team to assess discharge behaviour across different locations.
• Identifying the Location of Defects: Multi-channel electrical or acoustic measurements can help estimate the source of a discharge by comparing signal arrival times or characteristics at different sensors. Depending on the equipment and measurement setup, this can support defect localisation in transformers and high-voltage cables.
•  Factory Acceptance Testing (FAT) and Commissioning: Multi-channel PD measurements can be reliable in assessing insulation condition before equipment is delivered or after installation. The results give a reference baseline that can be compared with future measurements to identify changes in PD activity.
• Continuous Online PD Monitoring: Permanently installed multi-channel monitoring systems can track discharge activity in critical electrical assets during operation. This is particularly beneficial for monitoring and comparing trends over time, helping maintenance teams have a broader understanding of developing insulation problems and plan necessary actions before defects progress.

What Are the Main Benefits of Multi-Channel PD Testing?

• Better Noise Discrimination: Multi-Channel PD testing compares signals across multiple channels. It distinguishes PD from any interference or electrical noise and supports reliable measurements.

• Simultaneous Multi-Point Measurement: Captures signals from multiple locations and monitors several phases simultaneously, enabling direct signal comparison. As a result, technicians get a broader insight into PD activity.

1. Improved Fault Identification and Location: Compares pulse magnitude and arrival time, distinguishing different discharge sources. It also guides further inspection and corrective action.
2. More Reliable Condition Assessment: Supports informed maintenance decisions by combining data from multiple measurement points. This provides a comprehensive view of insulation, helping identify potential insulation defects.
3. Better Baseline and Trending Data: Tracks PD changes for proactive maintenance planning and sets baseline PD measurements

Multi-Channel vs Single-Channel PD Testing

Which Equipment Can Benefit From Multi-Channel PD Testing? 

Multi-channel partial discharge (PD) testing and monitoring systems from IPEC are designed for synchronised, simultaneous measurements across multiple points or phases. This approach helps assess insulation conditions, distinguish genuine PD activity from electrical interference, and identify potential defects in critical electrical assets.

1. Medium- and High-Voltage Switchgear (AIS/GIS)

Multi-channel PD testing is useful for both air-insulated switchgear (AIS) and gas-insulated switchgear (GIS), where insulation defects can develop in different compartments and connection points. Systems such as IPEC's ASM, which supports up to 128 channels, can monitor multiple locations using Transient Earth Voltage (TEV) and ultra-high-frequency (UHF) sensors. Comparing synchronised signals helps identify discharge patterns and distinguish genuine PD activity from external interference, supporting more reliable insulation assessment.

2. High-Voltage and Medium-Voltage Power Cables

Power cables, joints, and terminations can develop insulation defects due to ageing, electrical stress, or installation issues. Multi-channel PD testing uses high-frequency current transformers (HFCTs) at suitable measurement points to capture and compare discharge signals. With appropriate sensor placement and analysis, the measurements can help identify PD activity and estimate its location along the cable. This is particularly valuable when investigating long cable runs and assessing the condition of cable accessories.

3. Power Transformers and High-Voltage Bushings

Power transformers and their high-voltage bushings require reliable insulation monitoring to maintain safe and continuous operation. Multi-channel testing enables synchronised measurements from different phases or monitoring points, helping engineers compare discharge activity and investigate possible insulation defects.

Analysing signal characteristics can assist in distinguishing between different discharge sources, including corona activity and internal insulation defects. The results support condition assessment and help maintenance teams determine whether further investigation is necessary.

4. Rotating Machines (Motors and Generators)

High-voltage motors and generators can experience insulation deterioration due to electrical, thermal, and mechanical stresses during operation. Multi-channel PD monitoring uses HFCTs or suitable embedded sensors to capture discharge activity from different measurement points, including stator winding circuits where the installation permits.

Comparing these signals helps assess insulation behaviour and identify changes that may indicate developing problems. Online monitoring can also track PD trends during normal operation, reducing the need for repeated offline testing.

How Is a Multi-Channel PD Test Performed?

Step 1: Set the Testing Requirements

Identify the equipment subject to the inspection and ensure clarity on the purpose of the test by considering its operating conditions, criticality, and suspected insulation issues.

Step 2: Select Suitable PD Sensors

Choose appropriate sensors and coupling methods based on the equipment type and testing requirements. These may include HFCT, TEV, UHF, or other suitable multiple PD sensors.

Step 3: Connect the Measurement Channels

Install the sensors at appropriate measurement points and connect them to the multi-channel PD monitoring system. Ensure each channel captures the required signals accurately.

Step 4: Synchronise the Channels

Configure the measurement channels to capture signals on a common time basis. Synchronisation lets pulses detected at different points be compared reliably.

Step 5: Acquire PD Signals Simultaneously

Record signals from all connected channels during the same measurement period. This is particularly useful for using correlated data to analyse discharge activity across different locations or phases.

Step 6: Distinguish PD Signals from Noise

Analyse the captured signals to find genuine discharge activity and minimise external interference. Techniques such as 3PARD can help separate PD sources from noise.

Step 7: Analyse Signal Patterns

Examine phase-resolved patterns, pulse amplitudes, timing, and frequency characteristics. These features help assess discharge behaviour and distinguish between potential sources.

Step 8: Identify Potential Defect Locations

Compare signal characteristics across channels to investigate the likely origin of discharge activity. The measurement setup allows signal timing and propagation patterns to help estimate defect locations.

Step 9: Evaluate the Results

Compare the findings with available standard measurements, past trends, and assessment criteria to determine the significance or the intensity of the detected PD activity.

Step 10: Report Findings and Recommend Action

Document and record the measurements, identified discharge patterns, and potential insulation concerns. Recommend further investigation, corrective maintenance, or continued monitoring based on the results.

When Is Multi-Channel PD Testing Not Necessary?

Multi-channel PD testing is not essential for every insulation assessment. Simple diagnostic tasks or controlled tests may be adequate, which are done using a single-channel setup, particularly when noise interference is low and the test objective is clearly defined.

The choice of testing method should depend on the equipment being assessed, the testing environment, the level of electrical noise, and the diagnostic requirements. Multi-channel testing becomes more valuable when simultaneous measurements, noise discrimination, or identifying multiple discharge sources is necessary.

Key Factors to Consider Before Choosing Multi-Channel PD Testing

Choosing the right multi-channel PD testing setup needs careful consideration of several factors, for instance, the technical and operational elements. These factors are essential to determine the appropriate measurement configuration, improve accuracy, and ensure reliable PD assessment. The following are some of the key factors to check before choosing this technique:

• Asset type and voltage level: Consider equipment design and voltage ratings.
• Number of phases/measurement points: Identify all required measurement locations.
• Background noise: Assess noise levels before testing.
• Required fault-location accuracy: Determine the desired location precision.
• Offline vs. online testing: Select the appropriate testing approach.
• Accessibility of measurement points: Evaluate access to connection points.
• Required sensitivity and diagnostic resolution: Define the required detection sensitivity.
• Applicable testing standards: Follow relevant industry testing standards.
• Criticality of the asset: Prioritise assets based on operational importance.

Need Multi-Channel Partial Discharge Testing in UAE?

Reliable high-voltage asset assessment demands accurate PD measurements, effective diagnostics, and proper interpretation of test results. Our multi-channel partial discharge testing services help identify potential insulation defects, assess discharge activity, and provide valuable insights into the condition of critical electrical assets. By combining advanced testing technologies with technical expertise, we support informed maintenance decisions and improved asset reliability.
Technomax is a trusted condition monitoring service provider, backed by decades of technical expertise and industry experience across the GCC. Serving a wide range of renowned industrial sectors, we combine advanced technologies, modern diagnostic techniques and specialised engineering knowledge to address complex asset reliability challenges.

With expertise in condition monitoring, partial discharge (PD) detection, vibration analysis, thermography and other specialised diagnostic services, Technomax helps industries assess equipment health, identify potential faults early and make informed maintenance decisions, focusing on predictive maintenance and proactive asset management to support improved equipment performance, reduced unplanned downtime and long-term operational reliability.

Contact us for professional Partial Discharge Testing and PD Diagnostic Services in the UAE. Our team can help assess your high-voltage equipment and identify potential insulation-related issues before they affect operational reliability.