2064 IEEE TRANSACTIONS ON POWER DELIVERY, VOL. 21, NO. 4, OCTOBER 2006 Novel Sensor System for Leakage Current Detection on Insulator Strings of Overhead Transmission Lines Eduardo Fontana, Sérgio Campello Oliveira, Fernando José do Monte de Melo Cavalcanti, Renato Bandeira Lima, Joaquim F. Martins-Filho, and Elio Meneses-Pacheco Abstract—We report the development of a measurement system capable of monitoring and characterizing the main features of the leakage current flowing on a polluted insulator string of a high-voltage transmission line. The system comprises a fiber-optic sensor, directly connected to one insulator of the string, that emits a sample of the leakage current waveform to a processing module via an optical link. A capacitive sensor connected to the processing module allows recording the relative humidity of the outer environment. At the present stage, six measurement units have been deployed on CHESF’s electrical transmission system in the Northeast of Brazil, and studies are underway to further correlate the degree of environmental pollution with humidity and leakage current activities on high-voltage insulator strings. Index Terms—Flashover, insulators, leakage current, op- tical-fiber transducers, power transmission lines. I. INTRODUCTION W HEN insulator strings of overhead transmission lines are exposed to polluted environments under high humidity, their insulation capacity is reduced due to the coexistence of, partially conductive, wet and dry regions on the insulator’s sur- face. This leads initially to partial discharges whose rate and severity can grow to generate a full line-to-ground discharge known as a flashover [1]. The partial discharges are caused by salt contaminants or by non-soluble substances on the insu- lator’s surface in the presence of humidity. Many techniques have been proposed in the literature to mea- sure the quantity of pollutants deposited on an insulator’s sur- face, such as, measurement of equivalent salt deposit density (ESDD), determination of non-soluble deposit density (NSDD), and measurement of surface resistance (SR) [2]–[5]. These tech- niques require bringing the insulators from the field to the lab- oratory for measurement of the quantity of surface pollutants. One of the most promising techniques for online measure- ments is the monitoring of leakage current flowing on the in- sulator’s surface itself. For measurement of this parameter re- searchers frequently use current transformers [6]–[9], shunt re- sistors [10]–[13] and filters [14] to discriminate the conduction Manuscript received July 21, 2005; revised December 15, 2005. This work was supported by Companhia Hidro Elétrica do São Francisco (CHESF) under Contract CT - I - 92.2002.0960.00. Paper no. TPWRD-00427–2005. E. Fontana, S. C. Oliveira, R. B. Lima, J. F. Martins-Filho, and E. Meneses-Pacheco are with Grupo de Fotônica, Dep. de Eletrônica e Sis- temas, Universidade Federal de Pernambuco, Recife PE 50.740-530, Brazil (e-mail: fontana@ufpe.br; scampello@ufpe.br; rbandeirinha@hotmail.com; jfmf@ufpe.br; meneses@ufpe.br). F. J. M. M. Cavalcanti is with Companhia Hidro Elétrica do São Francisco, Recife PE 50.761-901, Brazil (e-mail: ferrnandj@chesf.gov.br). Digital Object Identifier 10.1109/TPWRD.2006.877099 current from high-frequency signal components associated with partial discharges. Because these methods are carried out in the electrical domain they are subjected to electromagnetic interfer- ence generated by the distinct high voltage phases of the trans- mission line. Other major problem associated with these mea- surements is the risk of electrical discharge when performed on a high voltage line. Youssef and colleagues [15] have recently proposed a system that uses an antenna to capture the electro- magnetic radiation associated with the partial discharges gen- erated along with the leakage current. This system will not be damaged by a flashover occurrence, but it has not been tested on the field yet, where the electromagnetic interference generated by corona and other effects on the high-voltage conductors is expected to be large. In order to predict the imminence of flashover based on infor- mation collected from leakage current it is possible to analyze a few attributes of the signal such as the odd harmonics [7], the pattern [15], or the peak amplitude and rate [2]. These attributes are employed on laboratory tests for the definition of a criterion of flashover prediction but the great complexity of the real world situation makes it practically impossible to reproduce the con- ditions found on the field [2]. In this paper, we report the development of an optical moni- toring system that stores information on relevant parameters as- sociated with the leakage current. Optical sensing of the leakage current and optical transmission of the waveform signal to a pro- cessing module eliminates the effects of electromagnetic inter- ference. The system is simple to install and only a low-cost, re- placeable, fiber-optic sensing head will damage if a flashover occurs. Environmental humidity is measured by a capacitive sensor connected to the system’s processing module and simul- taneous use of this parameter with information obtained from the leakage current attributes, can be used to infer the degree of pollution on high-voltage insulator strings. At the present stage six measurement units are currently de- ployed on CHESF’s transmission line system across three states of the Northeast of Brazil to further correlate the degree of en- vironmental pollution with humidity and leakage current activ- ities on high-voltage insulator strings, as described in detail in the following sections. II. SYSTEM DESCRIPTION The system is composed of two distinct parts: a fiber-optic sensing head and a microprocessor controlled detection and data storage module, interconnected through an optical-fiber link, as illustrated in Fig. 1. The fiber-optic sensor has two elec- tric terminals that are connected to the two terminals of the insulator string nearest to the ground side of the transmission 0885-8977/$20.00 © 2006 IEEE Authorized licensed use limited to: Universidad Federal de Pernambuco. Downloaded on April 27,2010 at 02:58:55 UTC from IEEE Xplore. Restrictions apply.