Breakthrough for Rogowski coils (LPCTs) in medium voltage switchgear: benefits, standardization, and challenges in protection and testing applications

Key benefits include compact size, low weight, and ease of installation, reducing space requirements and commissioning effort. LPCTs provide low-energy voltage signals instead of secondary currents, reducing open-circuit risks. Their air-core construction eliminates magnetic saturation and provides excellent linearity over a wide range, often beyond protection class

Derivative LPCTs also introduce specific challenges. The Rogowski output voltage is proportional to the time derivative of the primary current, which places requirements on the relay measurement chain and on relay testing, even if protection function logic can be simpler due to the absence of CT saturation effects. The relay must withstand high transient voltages

(high di/dt) and perform stable integration to reconstruct the primary current under transient or distorted conditions. Testing must reproduce the intended primary current and the corresponding derivative sensor voltage behavior; a practical approach is presented to generate

Rogowski-equivalent input voltages from primary current test definitions.

Low Power Instrument Transformers (LPITs) also support IEC 61850 process bus architectures. Their low-level analogue outputs suit stand-alone merging units (IEC 61869-13), which digitize measurements and transmit sampled values to protection IEDs (Intelligent

Electronic Devices) using IEC 61869-9 profiles. IEC standardization under TC 38, notably the

IEC 61869 series (including parts 10 and 11), provides a framework for specification, testing, and interoperability. The paper concludes by summarizing the main implications for protection and testing of relays connected to Rogowski LPCTs.