Non-Contact High Voltage Measurement in the Online Partial Discharge Monitoring System

The article presents an innovative system for non-contact high voltage (HV) measurement, which extends the measurement capabilities of a portable partial discharges (PD) monitoring system intended for diagnostics of power transformers. The proposed method and the developed measuring system are based on the use of a capacitive probe, thanks to which the high voltage measurement is safe (galvanic separation from the objects at ahigh potential). It is also flexible because the voltage ratio of this system can be configured in a wide range by changing the probe’s position. The proposed solution makes the portable PD monitoring system fully autonomous and independent of the substation systems and devices. The article presents both the concept of the non-contact HV measurement system and its practical implementation. The procedure for determining the voltage ratio and measurement uncertainty, which is at an acceptable level of 1–5% in laboratory conditions, was discussed in detail. In addition, the article discusses the digital filtering and wavelet de-noising methods implemented in the software of the monitoring system, which makes it possible to measure the voltage in the presence of strong electromagnetic disturbances occurring at the substation. Finally, the results of field tests carried out on a 250 MVA power transformer are presented, which confirmed the high accuracy of the HV measurement using a capacitive probe and the advantages of this technique.

CALIBRAÇÃO DE SONDA CAPACITIVA EM NITOSSOLO VERMELHO LATOSSÓLICO EUTROFÉRRICO CULTIVADO COM FORRAGEIRAS IRRIGADAS

CALIBRAÇÃO DE SONDA CAPACITIVA EM NITOSSOLO VERMELHO LATOSSÓLICO EUTROFÉRRICO CULTIVADO COM FORRAGEIRAS IRRIGADAS ARTHUR CARNIATO SANCHES1*; DÉBORA PANTOJO DE SOUZA2; FERNANDA LAMEDE FERREIRA DE JESUS3; RODOLFO GUERTAS MAFFEI4; FERNANDO CAMPOS MENDONÇA5 E JOSÉ RICARDO MACEDO PEZZOPANE6 1Professor Doutor, Faculdade de Ciências Agrárias, Universidade Federal da Grande Dourados, Rod. Dourados-Itahum, km 12 – Cidade Universitária, 79804-970, Dourados, MS, Brasil, e-mail: [email protected] 2Doutoranda em Engenharia de Sistemas Agrícolas, Departamento de Engenharia de Biossistemas, ESALQ/USP, Avenida Pádua Dias, 11, 13418-900, Piracicaba, São Paulo, Brasil, e-mail: [email protected] 3Professora Doutora, Departamento de Engenharia Agrícola, Universidade Federal Rural da Amazônia, Campus Tomé-Açu, Rod. PA 140, km 03, 68680-000, Tomé-Açu, PA, Brasil, e-mail: [email protected] 4Graduando em Agronomia, Departamento de Engenharia de Biossistemas, ESALQ/USP, Avenida Pádua Dias, 11, 13418-900, Piracicaba, São Paulo, Brasil, e-mail: [email protected] 5Professor Doutor, Departamento de Engenharia de Biossistemas, ESALQ/USP, Avenida Pádua Dias, 11, 13418-900, Piracicaba, São Paulo, Brasil, e-mail: [email protected] 6Pesquisador, Embrapa Pecuária Sudeste, Rod. Washington Luiz, Km 234 s/nº, 13560-970, São Carlos, SP, Brasil, e-mail: [email protected] 1 RESUMO O conhecimento do teor de água no solo é importante para o manejo adequado da irrigação, pois permite estimar a quantidade necessária de água a ser aplicada no tempo correto. Sensores de capacitância são uma alternativa de quantificação do teor de água do solo (θ, m3 m-3), provendo leituras em profundidade de forma prática e rápida. Uma sonda capacitiva foi calibrada em um Nitossolo vermelho Eutroférrico Latossólico cultivado com forrageiras tropicais na área experimental da ESALQ/USP na cidade de Piracicaba (SP), Brasil. Quatro tubos de acesso foram instalados e, a cada duas semanas, foram coletadas amostras com três repetições para cada nível de profundidade, até o final de oito semanas, partindo do θsaturado. Efetuaram-se leituras com o equipamento para cada 0,1 m de solo até 0,7 m de profundidade, juntamente com a coleta das amostras de solo para a determinação de θ em laboratório. Uma equação de potência foi desenvolvida para cada profundidade estudada, como também para todo o perfil do solo. A curva geral de calibração proposta (SF = 0,256*θatual0,3422), ajustada por análise de regressão, foi significativamente relacionada às medidas do equipamento, com alta correlação (r2 = 0,87) e erro-padrão de 0,022 cm3 cm-3. A calibração para cada profundidade tem mostrado maiores coeficientes de correlação nas profundidades menores, minimizando o erro dasestimativas. A calibração feita no local permitiu melhor acurácia do monitoramento da água no solo e assim, proporcionar um melhor manejo da irrigação. Palavras-chave: sensor, manejo da irrigação, umidade do solo, reflectometria no domínio da frequência. SANCHES, A. C.; DE SOUZA, D. P.; DE JESUS, F. L. F.; MAFFEI, R. G.; MENDONÇA, F. C.; PEZZOPANE, J. R. M. CAPACITIVE PROBE CALIBRATION IN EUTROFERRIC LATOSOL RED NITOSOL CULTIVATED WITH IRRIGATED FORAGES 2 ABSTRACT Knowledge of soil water content is important for proper irrigation management because it allows estimating the required amount of water to be applied at the correct time. Capacitance sensors are an alternative for quantification of soil water content (θ, cm3 cm-3), providing depth readings in a practical and fast way. A capacitive probe was calibrated in a Eutroferric Red Nitosol cultivated with irrigated forages at the experimental area of ESALQ/USP in the city of Piracicaba - SP, Brazil. Four access tubes were installed and every 2 weeks samples were collected with 3 replicates for each depth level, for 8 weeks starting from θsaturated. Readings were taken with the equipment for every 0.1 m of soil up to 0.7 m of depth, together with the collection of soil samples for the determination of θ in laboratory. A power equation was developed for each depth studied as well as for the whole soil profile. The proposed general calibration curve (SF = 0.256*θcurrent0.3422), adjusted by regression analysis, was significantly related to the measurements of the equipment, with high correlation (r2 = 0.87), and standard error of 0.022 cm3 cm-3. The calibration for each depth has shown higher correlation coefficients at lower depths, minimizing the error of estimates. On-site calibration allowed better accuracy of soil water monitoring and, thus, better irrigation management. Keywords: sensor, irrigation management, soil moisture, frequency domain reflectometry.

Low Power Contactless Voltage Sensor for Low Voltage Power Systems

Contactless measurements represent the desirable solution in many contexts, where minimal cabling is required or, in general, cabling is not possible. This paper presents a new contactless voltage sensor for low voltage power systems. It is based on a contactless capacitive probe, which surrounds the power cable. It has two concentric electrodes insulated by a shield. A low power analog conditioning circuit evaluates the power line voltage by measuring the current in one of the capacitances of the probe. All the single stages of the circuit have been designed by using low-power rail-to-rail operational amplifiers, supplied at 3.3 V, in order to minimize the power absorption. The sensor has been characterized in various conditions, with sine waves and distorted signals, varying the frequency and the harmonic distortion. The influence of the current, flowing into the power cable, on the voltage measurement has been evaluated too. It shows a good accuracy (lower than 0.3%) from 100 V to 300 V, with a power consumption less than 5 mW.