IEC 62505-3-2:2020

Overview

IEC 62505-3-2:2020 defines particular requirements for current transformers (CTs) used in fixed installations of AC traction systems (railway applications). Applicable to new CTs for indoor or outdoor traction substations, it covers devices operated at the AC line voltages and frequencies specified in IEC 60850. This second edition (2020) replaces the 2009 edition and aligns CT requirements with the IEC 61869 instrument transformer series while adding railway‑specific ratings, detailed test requirements and specified partial discharge voltages.

Key topics and technical requirements

• Scope and service conditions: CTs for traction systems, including low‑voltage types (e.g., ring‑core, cable types) where applicable.
• Ratings and designation: New rating designations added to align with other railway standards (for example IEC 62497).
• Insulation coordination: Rated voltages, impulse and power‑frequency withstand voltages, and insulation requirements adapted for railway overvoltage and earthing practices.
• Design and construction: Requirements for transformer construction, external insulation, nameplates and electromagnetic compatibility (EMC).
• Testing: Detailed test requirements tailored to railway operating conditions, including EMC tests and partial discharge tests with specified voltages and permissible levels (see Table 2 in the standard).
• Operational rules: Guidance for transport, storage, erection, operation and maintenance, plus safety and environmental influence considerations.
• Information and documentation: Required data for enquiries, tenders and orders to ensure correct selection and application.

Practical applications and users

This standard is essential for:

• CT manufacturers designing and certifying current transformers intended for AC traction substations.
• Railway electrical engineers specifying measurement, control and protection CTs for substations, feeders and protection systems.
• System integrators and switchgear designers ensuring compatibility of CTs with protection relays, meters and control equipment.
• Test laboratories and certification bodies performing EMC, partial discharge and dielectric testing to railway operating conditions.
• Procurement and asset managers who need clear technical requirements for tenders and lifecycle maintenance.

Typical applications include metering, fault detection and protection in traction power supply systems (e.g., 15 kV 16.7 Hz, 25 kV 50 Hz systems listed in IEC 60850).

Related standards

• IEC 61869‑1 / IEC 61869‑2 – Instrument transformer general and current transformer requirements (used in conjunction).
• IEC 60850 – Supply voltages of traction systems.
• IEC 62497‑1 – Insulation coordination for railway equipment.
• IEC 62236‑5 – EMC emission and immunity for fixed railway power installations.

Keywords: IEC 62505-3-2, current transformers, AC traction systems, railway applications, partial discharge, insulation coordination, IEC 61869, IEC 60850, CT testing, EMC.