University of Twente Student Theses


Root-Cause Analysis of Interfered Current Transformer Due to Pulsed Currents

Bolzonella, L. (2022) Root-Cause Analysis of Interfered Current Transformer Due to Pulsed Currents.

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Abstract:With the widespread use in recent years of non-linear loads that draw pulsed currents with large di/dt, crest factor and amplitude, an increase in EMI was detected on meters, resulting in power metering deviations. In particular, the type of sensor determines the overall deviations: Rogowski coil sensing resulted in errors up to 400%, Hall sensors negative deviations up to -10%, and current transformer in deviations between -10% and 8%. Generally, this resulted in large over-billing of costumers by the hands of utility companies. In this paper the source and implications of the metering interference are analysed for pulsed currents using current transformer sensing. It was noted that pulsed current metering using current transformer incurs in two issues: firstly, the large DC components of the pulse does not induce a secondary current in the transformer, and secondly, the magnetization behavior of the core results in an exponential response. Additionally, the primary pulse width determined the asymmetric behaviour in secondary response, and the small value of load cause a large time constant, and therefore large settling times. Together, these issues result in erroneous current waveform measurements. Finally, the correlation between firing angle and error magnitude and sign is analysed, correlating positive deviations for firing angles above 90 degrees, negative below 90 degrees, and minimal absolute error around 90 degrees. Overall, this research shows the unsuitability of current transformer metering for pulsed currents, as well as the need of additional testing, even for energy meters compliant with current EMI test standards, which will help ensure fair and precise billing of customers by the utilities.
Item Type:Essay (Bachelor)
Faculty:EEMCS: Electrical Engineering, Mathematics and Computer Science
Subject:33 physics, 53 electrotechnology
Programme:Electrical Engineering BSc (56953)
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