VA-TEK Engineering Relay testing standards do not compete with each other; they divide the work. IEC 60255-1 defines how a device is type-tested, IEEE C37.233 defines how a protection scheme is tested, NETA ATS and MTS define what a field contractor checks, and DL/T 995 defines what a Chinese utility accepts at commissioning and in service. A test plan that cites one standard for every item is usually wrong in at least one layer.
Key takeaways
- Four layers: application, method, field practice, and product conformance. Each answers a different question.
- Three criterion forms: a fixed limit, a manufacturer’s declared value, or a manufacturer-recommended tolerance. They cannot be substituted for one another.
- Traceability: every field test item should point to a field clause, a method clause, and a product document.
The four layers of relay testing standards
| Layer | Question it answers | China | International / North America |
|---|---|---|---|
| Application | Which protection functions are required, and to what performance? | GB/T 14285-2023 | IEEE C37.233-2023 (scheme application) |
| Method | How is the test performed? | GB/T 7261-2016 | IEC 60255-1:2022 |
| Field | What is tested on site, how often, and against what acceptance criterion? | DL/T 995-2016, GB/T 50976-2014 | NETA ATS-2025 / MTS-2023 |
| Product and conformance | Is the device itself compliant, and can it interoperate? | GB/T 14598 series, GB/T 7261 communication clauses | IEC 60255 function family, IEEE C37.90.x |
The layers are linked by reference, not by substitution. The method layer supplies the procedure, the field layer supplies the acceptance criterion, and the product layer supplies the declared characteristic limits. A defensible test plan can name the source of every item and every pass/fail threshold.
What each standard actually answers
China: GB/T 7261, DL/T 995 and GB/T 50976
GB/T 7261-2016 is the test-method library. It describes how to measure operating values, timing, insulation, environmental performance and electromagnetic compatibility. The 2026 edition has been published with effect from 2027-02-01; until then the 2016 edition remains the working reference.
DL/T 995-2016 is the field procedure. Its 2016 edition organizes commissioning and maintenance into 19 inspection items, from pre-test preparation and CT/VT circuit checks through setting verification, whole-scheme trip tests and commissioning under load. It also fixes inspection intervals and gives numeric acceptance criteria, such as insulation resistance above 10 MĪ© at acceptance, PT secondary voltage drop no more than 3% of rated voltage, and a trip-coil voltage of at least 90% of rated during a whole-scheme test.
GB/T 50976-2014 covers installation acceptance: documentation, panel workmanship, secondary cabling, DC and AC circuits, circuit-breaker control circuits, pilot channels, and the sequence from installation check to energization. It connects to DL/T 995 at the whole-scheme trip test and the on-load check.
IEC: IEC 60255-1 and the function family
IEC 60255-1:2022 is a general requirements and test-method standard. Its central idea is the declared value: the manufacturer states the error limit under reference conditions, and the test verifies that the device stays within that declaration. Clause 6.5.2.1 requires the declared error to be taken from a preferred number series, and clause 6.5.3 requires the manufacturer to declare the variation caused by temperature, auxiliary supply, harmonics, frequency and other influences.
The function-specific parts of IEC 60255 add characteristic tests for distance, differential, overcurrent, frequency and other protection types. They define test points and characteristic behaviour, not field maintenance intervals.
IEEE: C37.233-2023
IEEE C37.233-2023 is a system-level guide. It recommends a bottom-up approach: prove the component, then the interconnected scheme, then the overall protection system. It covers generators, lines, transformers, capacitors, special protection schemes and end-to-end testing, and it is organized by scheme type rather than by device menu.
NETA: ATS-2025 and MTS-2023
NETA’s Acceptance Testing Specifications apply to new equipment; the Maintenance Testing Specifications apply to in-service equipment. Chapter 7.9 covers protective relays: electromechanical and solid-state devices in 7.9.1, microprocessor relays in 7.9.2. The criteria are expressed as “within the manufacturer’s recommended tolerance.” NETA does not publish a universal pickup or timing percentage, and it does not set a single maintenance interval for every relay.
Why the criteria cannot be mixed
Reference conditions differ. IEC 60255-1 declares accuracy at defined temperature, humidity, auxiliary supply and frequency. A field measurement taken at another condition includes variation that the declaration does not. DL/T 995 writes its field criteria for operating conditions, so a direct comparison of the two numbers is not valid.
The tolerance language differs. DL/T 995 gives fixed limits or setting-sheet values. IEC 60255-1 gives a manufacturer’s declaration. NETA gives a manufacturer’s recommended tolerance. The same measured error can pass one form and fail another, not because the relay changed but because the question changed.
Severity sources differ. GB/T 7261 takes immunity severity from the product standard. IEEE C37.90.x sets its own levels. IEC 60255-26 assigns levels by port and application zone. Quoting an EMC level without its source is meaningless.
A worked example: 220 kV line commissioning
| Test item | Field basis | Method basis | Product basis |
|---|---|---|---|
| Secondary-circuit insulation | DL/T 995 5.3.2.4 (above 10 MĪ© at acceptance) | GB/T 7261, insulation test clauses | Device technical specification |
| Dielectric strength | DL/T 995 5.3.2.4 | GB/T 7261, dielectric test clauses | Type-test report |
| Setting verification | DL/T 995 5.3.4 | GB/T 7261 operating-value and timing methods | Manufacturer declaration |
| Pilot channel | DL/T 995 6.3 | Channel test procedure | Channel equipment specification |
| Whole-scheme trip test | DL/T 995 5.3.7 | Scheme test procedure | Panel and breaker documentation |
The table shows why a single blanket citation is technically inaccurate. GB/T 7261 does not provide field acceptance criteria, and DL/T 995 does not provide type-test methods. Reviewers should ask for this traceability table before they review the prose of a test plan.
How to select the standard set for a project
| Project context | Primary field standard | Method reference | Typical acceptance form |
|---|---|---|---|
| Chinese utility substation | DL/T 995-2016; GB/T 50976-2014 for installation | GB/T 7261-2016 | Fixed limits and setting-sheet values |
| IEC-market OEM factory test | Contract and manufacturer procedure | IEC 60255-1:2022 plus function part | Declared value and declared variation |
| North American utility or service contractor | NETA ATS-2025 or MTS-2023, plus owner specification | IEEE C37.233-2023 for scheme testing | Manufacturer-recommended tolerance |
| Export project with mixed specifications | Owner’s field standard | IEC 60255 or IEEE C37.233, as specified | State the form explicitly in the report |
Frequently asked questions
Which standard should a relay test report cite?
Cite the field standard that defines the acceptance criterion, then the method standard used to measure it, then the product document that supplies declared limits. A report that lists only one standard cannot show where each pass/fail threshold came from.
Is NETA mandatory?
NETA specifications are widely used in North America and in contractor qualifications, but they are not a law. Their force comes from the owner’s specification or the contract. Where a project names NETA, its “manufacturer’s recommended tolerance” wording governs the acceptance decision.
Can DL/T 995 be used outside China?
It can be used by agreement, particularly on Chinese-financed or Chinese-built projects. It is written around Chinese field practice and setting-sheet control, so the contract should state which clauses apply and which local standards take precedence.
Does IEC 60255-1 define field test intervals?
No. IEC 60255-1 defines type-test methods and declared performance. Maintenance intervals come from the owner’s policy, the field standard, or the manufacturer’s guidance, not from the general requirements standard.
Where VA-TEK test sets fit
The VAE-430 provides 3Ć0ā40 A AC and 4Ć0ā120 V AC, with 8 binary inputs and 4 binary outputs, for three-phase relay and scheme testing. The VAE-660 adds six current and six voltage channels, 6Ć0ā30 A AC and 1Ć0ā180 A at 1000 VA in single-phase mode, for differential and busbar schemes that need more current sources at once. Both are described on the secondary test instruments page. The full range is listed on the relay test set hub.
For the field procedure that applies these standards, see the protective relay testing guide and the commissioning checklist. For interval selection, read how often protection relays should be tested.
Free whitepaper: the standards, test items and test-set requirements discussed in this article are consolidated in Relay Protection Testing: Standards, Test Items and Test-Set Requirements — a 29-page PDF, free to download without registration.
Standards and references
- IEC 60255-1:2022, Measuring relays and protection equipment – Part 1: Common requirements. IEC Webstore: webstore.iec.ch.
- IEEE C37.233-2023, Guide for Power System Protection Testing. IEEE Standards: standards.ieee.org.
- NETA ATS-2025 and MTS-2023, Chapter 7.9. NETA: netaworld.org.
- DL/T 995-2016, Testing regulations for relaying protection and security automatic equipment; GB/T 7261-2016; GB/T 50976-2014.
