Figure 1 - KPM Penta PD with its 5 sensor technology.
What is Partial Discharge?
PD Definitions according to IEC 60270
“Localized electrical discharge that only partially bridges the insulation between conductors and which can or cannot occur adjacent to a conductor
.
Figure 2: PD explanation as per IEC 60270
Partial discharge, often abbreviated as PD, refers to the localized electrical discharge that occurs within the insulation material of high-voltage electrical equipment. It is a consequence of electrical stress exceeding the dielectric strength of the insulation, leading to the formation of small-scale discharges. These discharges can be repetitive, pulse-like events that, over time, may weaken the insulation system and ultimately lead to catastrophic failure.
In other words, Partial discharges (PD) are small electrical sparks that occur within the insulation of medium and high voltage electrical assets. Each discrete partial discharge is the result of an electrical breakdown of an air pocket within the insulation. These discharges erode insulation and eventually result in insulation failure.
Importance of Understanding Partial Discharge
Understanding partial discharge is crucial for several reasons:
Equipment Reliability
· Partial discharge activity can significantly impact the reliability of high-voltage equipment, including power transformers, circuit breakers, and cables. Early detection and mitigation of PD can extend the lifespan of these assets.
· Partial Discharge Failures are not limited to service-aged equipment. Acceptance testing on newly installed equipment builds reliability right from start. Acceptance Testing can Verify original manufacturers test data and identify damaged insulation that occurred from improper installation, poor design, and/or poor workmanship during or after installation.
· Identify premature failures and capture baseline data to trend asset health over the asset’s life cycle to ensure maximum return on investment.
2. Safety
Partial discharge events may lead to insulation breakdown, which poses safety risks, as it can result in equipment failure, fires, or electrical hazards. Comprehensive knowledge of PD is essential for safety management.
3. Environmental Impact
Failure of high-voltage equipment due to PD can result in environmental damage and economic losses. Minimizing PD is essential for environmental sustainability.
What are Causes of Partial Discharge
Partial discharge occurs due to a combination of factors related to the electrical stress applied to the insulation system and the condition of the insulation material itself. The main causes of PD include:
Figure 3 : Partial Discharge treeing process. Image Source internet
a) Insulation Impurities
Even minor impurities within the insulation material can create weak points where partial discharge may initiate. These impurities can be contaminants or gas-filled voids.
b) Voltage Stress
High electrical stress levels, such as overvoltage conditions or voltage transients, can lead to partial discharge. When the electric field strength exceeds the dielectric strength of the insulation, discharge occurs.
c) Insulation Aging
Over time, insulation materials may degrade, reducing their ability to withstand electrical stress. Aging can result from thermal, mechanical, and environmental factors.
d) Mechanical Stress
Mechanical disturbances in the equipment, such as vibrations or movement, can lead to localized stress concentrations, promoting partial discharge.
e) Thermal Stress
Fluctuations in temperature can affect the dielectric properties of insulation materials. These thermal stresses can lead to partial discharge, especially in areas of insulation weakness.
What is the Significance of Partial Discharge Measurement ?
Partial discharge testing is one of the best method for detecting insulation failure in the most initial stages while the other common methods like IR detection / visual inspection happens at the end cycle of the insulation failure, by that time insulation has already deteriorated. The timely detection and treatment of PD activity can save insulation from failure in very initial stage.
Figure 4 - PD activity is the most reliable detection method in the early stage of insulation failure ( * Image Source Internet )
Partial discharge is a significant concern in high-voltage systems for several reasons:
1) Equipment Degradation
Repetitive partial discharge events gradually degrade the insulation material, leading to a reduction in its dielectric strength and ultimately equipment failure.
2) Safety Hazards
Insulation breakdown caused by PD can result in electrical accidents, fires, and equipment failures, posing significant safety risks.
3) Environmental Impact
Equipment failures due to PD can lead to environmental damage and financial losses. Preventing PD is critical for sustainability.
4) Cost Implications
The cost of repairing or replacing high-voltage equipment affected by partial discharge can be substantial. Detecting and mitigating PD in its early stages can save significant costs.
Partial Discharge Testing results can help to predict future performance and reliability of critical assets, including:
· Cables, splices, and terminations
· Power transformers and bushings
· Switchgear
· Motors and generators
Comments