Characterization of Voltage Instrument Transformers Under Nonsinusoidal Conditions Based on the Best Linear Approximation

Abstract

Voltage instrument transformers are usually tested at the rated frequency. In order to assess their performance in measuring harmonic components, typically, the frequency response function (FRF) is evaluated. Therefore, this conventional characterization does not consider nonlinear effects that may have a nonnegligible impact on the accuracy, especially when the transducer under test is represented by an inductive voltage transformer (VT). In this paper, a simple procedure for the characterization of voltage instrument transformers is presented. The method is based on the concept of best linear approximation of a nonlinear system. It requires applying a class of excitation signals that resembles the typical voltage waveforms found in power systems. Results consist of the FRF that permits the best linear compensation of the transducer response, and sample variances that allow quantifying the impact of noise and nonlinearities on the accuracy. The method is presented and explained by means of numerical simulations. After that, it has been applied to the characterization of a conventional inductive VT. Experimental results show how the accuracy of the transducer under test is heavily degraded by nonlinear phenomena when low-order voltage harmonics are considered.

Best Linear Approximation of Nonlinear Continuous-Time Systems Subject to Process Noise and Operating in Feedback

“…Using the BLA one can easily check the validity of the linear framework in practical applications such as, for example, operational amplifiers [7], industrial robots [5], bit-errorrate measurements in telecommunication [9], characterization of lithium ion batteries [10], control of a medical X-ray system [6], voltage instrument transformers [11], and current transformers [12]. In addition, the dependence of the BLA on the excitation power spectrum also provides some guidance for nonlinear model selection [13], [14].…”

Calibration Procedure to Test the Effects of Multiple Influence Quantities on Low-Power Voltage Transformers

“…As for the calibration, several studies are found in literature for ITs and the research is evolving and continuing every day [8][9][10][11][12][13]. In particular, among the studies, three different ways of tackling ITs' accuracy are distinguished (but not limited to them): (i) the use of compensating techniques to solve the ITs' nonlinearities; (ii) assessment of the ITs' behavior when working at off-nominal conditions; and (iii) studies based on preliminary characterization at rated conditions.…”

Toward the Standardization of Limits to Offset and Noise in Electronic Instrument Transformers

“…As a matter of fact, the accuracy evaluation is a critical task for all kind of electrical assets. For example, a new way of expressing uncertainty in voltage transformers (VTs) was presented by the authors of [9], while characterization and compensation techniques for their evaluation were presented by the authors of [10][11][12] (when the VT was working under non-sinusoidal condition in [10] and in a wide frequency range in [11]). An equivalent effort has been dedicated to current transformers (CTs) by the authors of [13][14][15][16][17][18].…”