Detection Technology
What does the PD test result indicate?
time：2025/7/3 source：Wuhan UHV reading：250 time
The PD tester under Wuhan UHV can help many power workers conduct various power tests more conveniently.
What do PD Test Results Indicate? (PD stands for Partial Discharge)
PD (Partial Discharge) test results are key indicators for assessing the insulation health of electrical equipment (such as transformers, cables, GIS switchgear, motors, etc.). They primarily reveal the following information:
1. Presence of Insulation Defects:
This is the core indication. The main purpose of PD testing is to detect whether there are localized, minor weaknesses or defects in the equipment's insulation.
Common defect types include:
Voids/Air bubbles: Tiny air pockets within solid insulation or at interfaces, causing field concentration and discharge.
Floating Potential: Metal components not properly grounded or with loose connections, developing potential differences under the electric field and discharging (e.g., loose shielding rings in transformers).
Sharp Points/Burrs: Protrusions on conductor surfaces causing field distortion, leading to corona discharge.
Surface Discharge: Discharge occurring along the surface of insulation material (e.g., due to pollution or moisture on insulators).
Internal Discharge: Discharge caused by impurities, delamination, or voids within solid or liquid insulation materials.
Poor Contact: Loose or oxidized conductor connections causing increased contact resistance and sparking.
2. Degree of Insulation Deterioration:
Discharge Magnitude (pC): The measured PD amplitude (usually in picocoulombs pC) is a crucial parameter for assessing defect severity. Higher discharge magnitudes generally indicate more severe defects, a higher degree of insulation deterioration, and a greater threat to safe equipment operation. Standards typically specify allowable discharge magnitude limits for different equipment types and voltage levels.
Discharge Phase: The phase angle position within the AC voltage cycle where PD pulses occur (e.g., near voltage peaks or zero crossings) helps identify the discharge type (e.g., internal discharge, surface discharge, corona discharge).
Discharge Pattern: Using phase-resolved partial discharge (PRPD) patterns or 3D plots, discharge patterns can be identified (e.g., "rabbit-ear" patterns often represent internal discharge). Different patterns correspond to different typical defect types and deterioration mechanisms.
3.Approximate Location of Defect:
By combining multiple sensors (e.g., electrical methods with acoustic or UHF methods) or using time-of-flight location techniques, the approximate physical location of the PD source can be determined (e.g., in which winding or region of a transformer; in which section of a cable). This is critical for subsequent maintenance decisions.
4.Nature of Defect (Preliminary Assessment):
As mentioned, the phase distribution, pattern, frequency characteristics, and location information of the discharges help engineers make a preliminary assessment of the defect's nature (e.g., void, floating potential, surface discharge, or other types).
5.Equipment Operational Risk:
The presence of PD signifies a weak point in the insulation system.
Sustained PD accelerates the deterioration of insulation materials (electrical erosion, chemical decomposition, carbonization), potentially leading to catastrophic insulation failure, causing equipment breakdown, power outages, or even safety incidents.
Test results (especially discharge magnitude, pattern, and trend) are key evidence for assessing the current operational risk and predicting remaining life of the equipment.
6.Trend of Development:
Regular PD testing (condition monitoring) allows tracking changes in PD activity. If the discharge magnitude, number of discharges, or activity area significantly increases, even if absolute values are still below limits, it indicates the insulation defect is rapidly worsening, requiring high vigilance and prompt action. Trend analysis often provides a more accurate reflection of the equipment's true state than a single measurement.
In summary, PD test results indicate:
Does the equipment's insulation system have localized defects? (Yes/No)
Where is the defect approximately located? (General area)
What type might the defect be? (Void, floating, surface, etc.)
How severe is the defect? (Discharge magnitude)
What is the degree of insulation deterioration? (Comprehensive judgment based on magnitude, pattern, etc.)
What is the current operational risk level of the equipment? (Is it close to failure?)
Is the defect stable, developing, or worsening? (Comparison with historical data or standard limits)
Copyright description: all articles, pictures, video and other materials on this site belong to wuhan huatian power automation co., LTD. For use, please contact us; Permission to reprint articles, pictures, video and other materials please quote "from: huatian power".
How do you identify partial discharge? | 2025/7/4 | reading273time How do you perform a primary injection test? | 2025/7/3 | reading232time return