A Complete Portable Partial Discharge (PD) Measurement and Diagnostic System

A portable partial discharge (PD) measurement and diagnostic system is used to detect, measure, record, and analyze partial discharge activity in high-voltage electrical insulation systems.

Partial discharge occurs when a localized electrical discharge partially bridges the insulation between conductors. It may be associated with insulation voids, surface defects, electrical treeing, contamination, poor connections, or other local electric-field problems.

PD measurement is used in factory testing, commissioning, maintenance, and insulation condition assessment. It can help engineers identify abnormal discharge activity and investigate potential insulation defects before they develop into more serious failures.

A complete portable system may combine a PD measuring instrument, coupling devices or sensors, signal acquisition and analysis software, connecting cables, calibration accessories, and application-specific interfaces. The exact configuration depends on the test object and measurement method.

For conventional charge-based measurement, IEC 60270:2025 covers partial discharge measurement techniques, measuring circuits, calibration, test procedures, and related instrumentation requirements. Other detection methods may require different procedures and equipment.

A portable PD diagnostic system is more than a measuring instrument. It needs compatible sensors or coupling devices, signal connections, and software appropriate for the application.

Not every system includes every component. For example, conventional electrical PD measurement and high-frequency or electromagnetic detection may use different sensors, signal-processing methods, and calibration procedures. Confirm the supplied configuration against the intended test application.

3.1 Partial Discharge Measurement

A PD measurement system detects discharge-related signals and quantifies the measured activity using the parameters supported by its measurement method.

For conventional charge-based testing, apparent charge is commonly expressed in picocoulombs (pC). It represents the charge that would produce an equivalent instrument response when injected into the specified test circuit; it is not a direct measurement of the actual charge at the internal defect.

Depending on the system, measurement results may include:

Apparent charge magnitude

Pulse count or repetition rate

Discharge activity over time

Phase-resolved partial discharge (PRPD) patterns during AC testing

Test voltage and discharge inception or extinction behavior, where supported

These parameters help engineers characterize PD activity, compare test results, and identify changes that may require further investigation.

3.2 Phase-Resolved Partial Discharge (PRPD) Analysis

PRPD analysis displays discharge pulses in relation to the phase angle of the applied AC test voltage. The resulting pattern can help engineers compare discharge behavior and investigate possible sources.

PRPD patterns may provide clues about internal discharges, surface discharges, or corona-related activity. However, patterns can overlap, and external interference can resemble genuine PD. A pattern should not be used alone to make a definitive diagnosis; engineers should also consider the test setup, background noise, sensor arrangement, and other evidence.

3.3 Noise Identification and Interference Rejection

Field measurements may be affected by radio-frequency interference, switching activity, grounding problems, and other electrical noise. A portable diagnostic system may provide filtering, pulse separation, noise mapping, or multi-channel comparison, depending on its design.

Useful features to evaluate include:

Background-noise monitoring

Adjustable measurement bandwidth or filtering

Pulse waveform or phase-pattern display

Multi-channel acquisition, if required

Data recording for post-test analysis

Noise rejection should not be treated as proof that every remaining pulse originates from the test object. The measurement circuit and test environment must also be checked.

3.4 Trend Recording and Diagnostic Reporting

Software can help engineers record measurements, compare test runs, and document changes in discharge activity. Depending on the instrument, reports may include test voltage, apparent charge, pulse activity, PRPD patterns, instrument settings, and measurement notes.

A trend can be useful when measurements are taken under comparable conditions. However, results from different test methods, sensor configurations, bandwidths, or voltage levels may not be directly comparable.

• Power transformers

PD measurement can support factory acceptance testing and specified insulation diagnostics. The measurement arrangement may use a coupling capacitor or a suitable bushing connection, depending on the transformer and test circuit.

• GIS and switchgear

PD-related measurements can help investigate insulation defects in gas-insulated switchgear and other high-voltage assemblies. The appropriate electrical, UHF, acoustic, or other detection method depends on the equipment and diagnostic objective.

• Power cables and accessories

PD testing may be used to assess cable insulation, joints, and terminations during specified commissioning or diagnostic procedures. The system must be compatible with the cable test method and sensor arrangement.

• Bushings and other HV components

PD measurement can support insulation evaluation of bushings, insulators, and other components when an appropriate test circuit and measurement method are available.

Portable measurement systems and permanently installed online monitoring systems serve different operational needs.

Portable equipment can be suitable for teams that test different assets at multiple locations. Online systems may be more appropriate where ongoing monitoring of critical equipment is required. Some maintenance programs use both approaches.

For a complete portable PD system, the applicable standard depends on the measurement technique and the equipment under test.

IEC 60270:2025: Covers charge-based PD measurement, including measurement circuits, calibration, test procedures, and relevant instrument requirements.

IEC TS 62478: Provides guidance on PD measurements using electromagnetic and acoustic methods, including higher-frequency approaches. The applicable method and requirements should be confirmed for the specific test object.

A system described as "IEC 60270 compatible" should be checked against the required measurement configuration and calibration procedure. The label alone does not establish that every included sensor or diagnostic function meets every applicable requirement.

Before purchasing a system, identify the assets to be tested, the required measurement method, and the expected field conditions.

Selection tip: Do not compare systems only by their lowest stated pC value. Sensitivity depends on the measurement circuit, test object, bandwidth, noise environment, and calibration arrangement. Ask suppliers to explain how the stated performance was established.

Step 1 - Define the test requirements

Identify the asset, applicable procedure, measurement method, test voltage, and acceptance criteria.

Step 2 - Connect the measurement system

Install the appropriate coupling device or sensors, check grounding and connections, and configure the acquisition channels.

Step 3 - Verify calibration and background noise

Follow the applicable calibration procedure and assess the background noise before interpreting test-object signals.

Step 4 - Acquire and analyze PD data

Record discharge activity under the specified test conditions and use supported plots or diagnostic tools to assess the results.

Step 5 - Review and report

Document the test voltage, measurement configuration, calibration details, background noise, results, and any limitations affecting interpretation.

High-voltage PD testing must be performed by qualified personnel using appropriate isolation, grounding, interlocks, and discharge procedures. Follow the equipment manual and site safety requirements throughout the test.

A complete portable partial discharge measurement and diagnostic system helps engineers measure and analyze PD activity in high-voltage insulation systems. A suitable configuration may combine a measuring instrument, sensors or coupling devices, calibration accessories, signal cables, and diagnostic software.

The best system depends on the test object, required measurement method, noise environment, measurement performance, and reporting needs. Confirm these requirements before selecting a product, and use calibrated measurement arrangements and qualified personnel to ensure meaningful results.

Goldhome provides high-voltage electrical testing equipment solutions for power utilities, manufacturers, testing laboratories, and electrical service contractors.

Website: www.goldhomehipot.com

Contact: +86 18971538425