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Partial Discharge (PD) can occur in almost any electrical insulation system, especially where the electric stress exceeds the insulation strength locally without entirely bridging the electrodes. Usually, PD occurs inside insulation voids, cracks, air gaps, or on contaminated insulation systems in high-voltage equipment such as transformers, motors, generators, switchgear, cables and GIS (gas-insulated substations) systems.

PD may look minute in the beginning, but continuous PD activity gradually weakens the insulation material through heat, chemical reactions and erosion. Eventually, the insulation collapses, leading to fire risks, equipment damage and more. The following are the common locations of PD activity:

• In insulation mediums (Air, Oil, Solid, GIS).
• Voltage classes ranging from 3 kV up to 769 kV and higher.
• In both indoor and outdoor metal-enclosed switchgear panels.
• Found in indoor as well as outdoor insulators.
• In power and distribution transformers.
• In transformer cable termination boxes.
• SF6 gas-insulated, oil-insulated, and air-insulated equipment systems.
• In medium-voltage (MV) and high-voltage (HV) cable systems.

Partial Discharge can occur in different ways, largely depending on the location and condition of the insulation system. The most common types of PD include:

• Internal PD occurring inside air voids, cracks inside power cables, motors etc.
• Surface PD due to moisture, dirt or soiling in bushings, insulators and cable terminations.
• Corona discharge occurring in the air around high-voltage conductors is commonly seen in overhead transmission lines and HV connectors.
• PD in cable joints and transformer insulation systems is subject to uneven electrical stress between insulation layers.
• PD in GIS if contaminants or defects are present.
• In rotating machines like motors and generators, insulation in the winding is prone to PD.

Partial Discharge analysis is done by studying minute electrical discharges that happen inside or on the surface of insulation. PD Pulses, their magnitude, phase position, frequency and pattern are thoroughly analysed; the main goal is to see if the insulation inside the equipment is healthy or if there is a defect developing.

The PD signal is captured, amplified, digitised and processed using filters. In modern Partial Discharge (PD) measurement systems, the PD signal is first amplified using a pre-amplifier, which is then converted into digital mode through an analog-to-digital converter. After digitising, the signal is processed using digital filters, digital detection methods and computer-based analysis.

As most of the PD processing is done digitally, the data received will be accurate and likely repeatable. Unlike traditional analog systems, digital systems are less prone to changes in time, temperature, or component ageing.

The analysis mainly aims at checking the following points:

• PD Magnitude, showing the strength of discharge.
• Phase Position to know the type of defect by checking the point at which PD occurs.
• PD Pattern aids in diagnosis, where PD charges are plotted as a pattern.
• Repetition Rate, showing the frequency of PD activity. A high repetition rate indicates insulation deterioration.
• Trends Over Time, increasing PD level shows insulation weakening.
• Noise Separation to avoid false readings from other sources.

Generally, PD measuring is done by connecting an appropriate PD sensor or coupling device to the electrical equipment. At first, a test voltage is applied, and any small discharge pulses produced inside or on the surface of the insulation are detected. These advanced vibration sensors and tools record and analyse the readings to understand the condition of the insulation. The following are the steps involved:

By analysing these results, the condition of the insulation can be assessed and early defects can be identified before major failure occurs, making it effective in tackling PD issues.

Detecting Partial Discharge (PD) in medium and high voltage electrical equipment can be tricky and requires careful attention. To make this process easier and avoid interrupting the power supply, the best approach is to use advanced sensors and tools that can capture signals at various frequencies. This combination of technology helps ensure that no PD pulses are missed, leading to more accurate detection. By using these tools, we can improve the safety and reliability of electrical systems.

• Ultrasonic System
• TEV
• UHF
• HFCT/RFCT

AssetConditionMonitoring’s Integrated Partial Discharge Testing and Monitoring Solutions are a suite of advanced tools, combining online and offline testing as well as periodic and continuous electrical assets health monitoring. AssetConditionMonitoring.com adopts strategic and effective ways to customise a PD system that suits your needs. We offers the following comprehensive services, which you can choose from:

• Online PD Testing
• Continuous Online Monitoring
• Remote PD testing
• Handheld-compact sensors
• Periodic PD testing
• Ultrasound Analysis
• Offline PD testing
• Tan Delta
• Very Low Frequency (VLF)

AssetConditionMonitoring.com offers advanced online and offline Partial Discharge Testing solutions, incorporating the latest tools and technologies for accurate electrical inspection and monitoring and to spot even minor PD activity in your electrical assets. Our expert technicians provide partial discharge monitoring, ensuring local support from installation to ongoing technical assistance specific to your needs.

Reach out to us and explore our comprehensive partial discharge Monitoring services to protect your electrical infrastructure. We provide expert assistance in condition monitoring services, insulation resistance testing, PD testing. Our PD testing showcase: