Dry-type transformer partial discharge test acceptance needs a defined measurement, an applicable test procedure and an agreed acceptance criterion. A picocoulomb value by itself does not establish that two offers were evaluated on the same basis. Before ordering, ask the supplier to connect the proposed PD result to the transformer configuration, voltage-time programme, measuring arrangement and treatment of interference. The project engineer should approve that basis before the factory acceptance test.
This guide is for EPC engineers and procurement teams buying dry-type power transformers for IEC-specified industrial projects. It addresses comparison and acceptance of PD evidence, not instructions for performing high-voltage tests.
What does the pC value actually describe?
A charge-based PD result describes apparent charge in a specified test circuit. It is not a direct measurement of the charge at the internal discharge site. Partial discharge is a local electrical discharge that bridges only part of the insulation between conductors.
The IEC 60270:2025 preview defines apparent charge by the equivalent instrument response to a charge introduced at the test object's terminals. Picocoulombs, abbreviated pC, are a common reporting unit. This distinction matters when a purchasing team is tempted to rank transformers simply by the smallest number in a brochure.
For bid review, first ask what was measured and under which conditions. Treat a lower advertised result as a question to investigate, rather than an automatic technical advantage. Do not convert a PD reading into a service-life promise.
Separate the transformer requirement from the measurement method
Identify both the product standard and the PD measurement standard in the acceptance schedule. They serve different purposes.
IEC 60076-11:2018 covers dry-type power transformers within its stated scope: highest voltage for equipment up to 72.5 kV, with at least one winding operating above 1.1 kV, subject to specified exclusions. Its IEC listing includes the March 2019 corrigendum and July 2020 interpretation sheet. Do not assume that every product called a dry-type transformer falls within this scope.
IEC 60270:2025, edition 4, addresses charge-based PD measurement, including measuring circuits, calibration and interference. It replaces the 2000 edition and its 2015 amendment. Its scope includes AC test voltages up to 500 Hz and DC testing.
Ask the responsible engineer to resolve the editions and destination requirements applicable to the contract. Record the relevant acceptance clause and any approved project additions. This article does not prescribe a universal pC limit, test voltage or duration; obtain those requirements from the applicable full standards and approved specification.
Dry-type transformer partial discharge report checklist
Ask for a PD-specific evidence schedule before the supplier issues the final test report. The following is a proposed buyer checklist, not a reproduction of mandatory IEC report fields.
| Report context | Question for the supplier |
|---|---|
| Tested assembly | Which transformer, winding connections, terminals and accessories were included in the assessment? |
| Voltage-time record | At which voltage, frequency and point in the agreed programme was each result recorded? |
| Measurement arrangement | What circuit, instrument settings and measurement bandwidth support the reported apparent-charge value? |
| Calibration evidence | Which records cover the instruments and the measuring arrangement used for this test? |
| Interference and sensitivity | What background disturbance was recorded, and how was its effect on interpreting the result assessed? |
| Decision basis | Which criterion was applied, what deviations occurred, and who reviewed the conclusion? |
Request enough detail for the designated reviewer to understand the result. If information sits in a separate procedure or calibration record, ask for its reference and revision. Keep the PD review focused on measurement validity; use the test-report traceability guide for the separate document-control question of unit identity and drawing revision.
Handle three common comparison gaps
Resolve a mismatch in the evidence before deciding which result is better. These examples illustrate procurement review, not pass/fail decisions.
- One offer shows a pC value; another shows an acoustic indication. Ask each supplier to identify the detection method and intended use. IEC 60270 distinguishes its charge-based electrical measurement from other detection methods. Have the engineer confirm what evidence satisfies the specified acceptance test.
- Two reports state different test conditions. Request a side-by-side explanation against the approved procedure. Do not silently treat readings taken at different points in a voltage programme as equivalent.
- A low result is reported with unclear background information. Ask the laboratory to explain sensitivity and interference treatment. Do not subtract a background figure yourself or infer “zero PD” from an unreadable or incomplete record.
If the explanation is incomplete, leave the affected acceptance item open. Agree who may request further assessment or a retest, how the revised evidence will be reviewed, and whether the issue affects the contractual release milestone. A procurement reviewer should not improvise a new test procedure to settle the question.
Put the acceptance requirement into the RFQ
Ask the quotation to complete this statement: product standard and edition; measurement standard and edition; acceptance clause; voltage-time procedure reference; required report records; witness scope; and approving party. Keep unresolved entries visible. A statement such as “PD test included” should not close the review until those details are agreed.
Use the technical-document review page to organize the requested evidence. Confirm which records can be supplied for the proposed transformer before relying on them as an approval deliverable.
Frequently asked questions
Can a PD result establish the transformer's remaining service life?
No service-life conclusion should be drawn from the reported pC value alone. Ask a qualified specialist to define what the test evidence supports and what additional assessment would be needed for a condition or life evaluation.
Does a calibration certificate replace the test-arrangement record?
Request both forms of evidence where the agreed procedure requires them. Ask the laboratory to explain which document addresses instrument calibration and which demonstrates the measuring arrangement used for the reported test.
Should inception and extinction voltages be requested?
Ask the project engineer whether those measurements belong in the required test scope. If requested, specify the method and reporting basis before quotation; do not assume that every PD report includes them.
Does witnessing the test settle every acceptance question?
No. Define what the witness will review and what records must follow. Attendance should support the agreed inspection plan, while the authorised reviewer still checks the recorded procedure, results and outstanding exceptions.
Can the buyer repeat the factory PD test on site?
Any site testing needs a separately approved plan and qualified high-voltage personnel. Do not reproduce factory connections, voltage settings or test sequences from a blog or a supplier report.
Define the PD requirement in your HEAKOR enquiry
For a HEAKOR dry-type transformer enquiry, provide the destination, phase, kVA, winding voltages, frequency and installation conditions. Add the required standards and editions, PD acceptance basis, report requirements and any witness requirement. Mark unresolved technical items clearly.
Submit Your Project Specification to establish the proposed equipment and document scope. PD testing arrangements, reporting availability and any performance commitment require confirmation for that specific proposal.