Modeling Capacitive Low-Power Voltage Transformer Behavior over Temperature and Frequency

Abstract

The use of capacitive dividers (CDs) in medium-voltage (MV) networks started as simple voltage detectors and as rough voltage measurement instruments for protective purposes. Now, with the spread of intelligent electronic devices and renewable energy sources at the distribution level, capacitive dividers are designed and installed to perform accurate voltage measurements. Such a requirement is mandatory when the power quality has to be assessed. Therefore, CDs are currently being used either for power frequency or for high-frequency (supraharmonic- or partial-discharge-level) measurements. In this paper, typical off-the-shelf CDs are studied and modeled to understand how they behave in a wide range of frequencies and when the temperature varies. To this purpose, specific setups and tests have been developed and performed. From the results, it is clear that with proper modeling of CDs, it is possible to exploit them for measuring phenomena in a wide range of frequencies, including the effects due to temperature variations and self-resonances.

A Methodology to Analyze and Evaluate the Uncertainty Propagation due to Temperature and Frequency and Design Optimization for EMC Testing Instrumentation

“…Due to manufacturing procedures and imperfections, the frequency response of inductors, capacitors and resistors is never ideal [5,6]. To take into consideration this effect, the equivalent series inductance (ESL) and the equivalent series resistance (ESR) have been introduced.…”

“…According to the GUM, the uncertainty propagation can be calculated using Equations ( 6) and ( 7) where x 1 , x 2 and x 3 are the input quantities and u(x 1 ), u(x 2 ) and u(x 3 ) are the respective uncertainties and y and u(y) are the measurand with its uncertainty. Independently from the number n of input variables, the uncertainty propagation with MCMs simulation can be generally carried out considering Equation (6). The number of input variables represented in Figure 4 serves only an illustrative purpose [11,12].…”

“…For instance, in Figure 5 the input quantities g X 1 (ξ 1 ), g X 2 (ξ 2 ) and g X 3 (ξ 3 ) are described by their PDF, in this case are Gaussian, triangular and again Gaussian, still Figures 4 and 5 are used as a representative example. Independently from the number n of input variables, the uncertainty propagation with MCMs simulation can be generally carried out considering Equation (6). The number of input variables represented in Figure 4 serves only an illustrative purpose [11,12].…”

“…It is well known how different parameters can affect electrical components, affecting not only their nominal value, but also increasing their degradation over time and consequently reducing their estimated lifetime [1][2][3][4]. Furthermore, frequency has a strong impact on electrical components and parasitic components can give rise to problems that were not considered in the design phase [5][6][7][8][9][10][11].…”

“…The paper is organized as follows: Section 2 provides an overview of the existing studies and works on how to evaluate the influence on the measurand of external factors and method commonly used [1][2][3][4][6][7][8][9][10][11]. Section 3 is dedicated at describing the proposed methodology and the instrument used for its verification.…”