IEC 60076-21:2018

Overview

IEC 60076-21:2018 - Power transformers - Part 21: standard requirements, terminology, and test code for step-voltage regulators is an IEC/IEEE dual-logo standard that defines electrical, mechanical and test requirements for liquid‑immersed, single‑ and three‑phase, 50 Hz and 60 Hz step‑voltage regulators. It applies to self‑ and forced‑air cooled distribution, overhead and substation regulators rated up to 1 000 kVA (single‑phase units) or 3 000 kVA (three‑phase units) and smaller, for system voltages up to 34 500 V (minimum 2 400 V), including their associated controls.

Key topics and technical requirements

• Ratings and classification: preferred ratings, cooling classes (self‑cooled and fan‑cooled), taps, nominal and maximum system voltages.
• Construction and marking: tank, bushings, external dielectric clearances, terminal markings and nameplates.
• Control and interfaces: requirements for associated controls and a universal interface between control enclosure and apparatus.
• Short‑circuit and mechanical capability: revised short‑circuit requirements and mechanical demonstration of withstand capability.
• Test code: comprehensive test procedures including ratio, polarity, no‑load and load losses, excitation current, temperature‑rise, dielectric tests (lightning impulse, applied and induced voltage), insulation power factor, and on‑load tap‑changer (OLTC) routine and type tests.
• Acoustics and enclosure integrity: sound pressure emission tests and tank enclosure integrity test procedures.
• Updates and harmonization: updated IEC and IEEE normative references, tables for fan‑cooled ratings, external clearances and sound levels, and alignment with IEEE terminology and practice.

Applications and who uses this standard

IEC 60076-21 is used for:

• Transformer and regulator manufacturers - to design, type‑test and certify step‑voltage regulators compliant with international acceptance criteria.
• Power utilities and grid operators - for procurement specifications, factory acceptance testing (FAT) and site acceptance testing (SAT) of distribution and substation regulators.
• Testing laboratories and inspection bodies - to perform standardized dielectric, thermal, acoustic and mechanical tests.
• Consultants, specifiers and regulators - to reference standardized ratings, safety clearances and interface requirements in project documents.

Practical benefits include consistent performance verification, interoperability of control interfaces, verified short‑circuit and acoustic performance, and clear guidance for selection and installation of step‑voltage regulators.

Related standards

• IEC 60076 series (power transformer standards)
• IEEE Std C57.15 (this edition aligns IEC/IEEE practices and supersedes earlier versions)

Keywords: step‑voltage regulators, voltage regulators, on‑load tap‑changer, IEC 60076‑21, transformer test code.