High-frequency characteristics of low power instrument transformers (LPITs)

Advancements in semiconductor technology have led to the development of power converters with increased switching frequencies, which is integral part of Distributed Energy Resources (DERs). Those high switching frequencies introduce new challenges and vulnerabilities that can impact grid stability. To maintain a reliable power system, grid operators must adapt continuous grid visibility with critical insights into potential reliability threats, enabling a proactive approach to grid management. Reliable operation of medium-voltage (MV) grids depends on accurately measuring disturbances, which necessitates enhanced instrument transformer performance, including improved accuracy across a broader frequency range. This study explores the performance of LPITs for high-frequency measurements in MV grids, with a focus on their ability to capture high frequency phenomena such as lightning impulse. The experimental setup used an impulse generator to produce standard and chopped lightning impulses, with measurements compared between Haefely HV divider and LPIT under test. The LPIT accurately reproduced both full and chopped waveforms, as validated by time-domain and frequency-domain analyses, showing strong agreement with the reference signal up to 1 MHz and a deviation of less than 3 dB. Furthermore, Polarity reversal testing, involving sequences of positive and negative chopped impulses, shows high coherence between reference and LPIT measurements. Results highlight LPIT based on capacitive voltage divider suitability for high-frequency testing and its potential role in enhancing grid monitoring systems.