Measurements of disturbances produced by power electronic devices on EHV overhead lines using Electric Field Sensors

Abstract

It is widely known that more and more power electronic devices are being installed in power systems. The main reasons of this are the increasing number of large variable speed drives connected to medium or high-voltage grids, the installation of devices for voltage control and flicker mitigation such as SVCs, and last but not least the electronic equipment required to integrate renewable energy sources – such as wind farms – to the existing power system. On the other hand, nowadays, in most countries there are severe Power Quality rules that Utilities as well as customers have to comply with. Therefore, even though power electronic devices are installed in networks in order to improve certain issue, it is also necessary to assess carefully the levels of disturbances – mainly harmonics – that they also emit. The traditional procedure to determine the origin of such disturbances is to perform field measurements in all the plants containing power electronic equipment, located near the point in which high levels of disturbances have been detected. Nevertheless, in most cases field engineers find it difficult to have access to the plants belonging to Utilities and also to the different industries settled nearby, which are also likely to emit disturbances. In addition, the task of installing the PQ recorder in the electrical cabinets inside the plant demands a considerable time, as well. With the intention of avoiding all the difficulties that can arise when field engineers are searching for a disturbing load, it was considered a great challenge to design a novel device to make the field work simpler. Such a challenge was based on designing a measuring system capable of recording voltage waveforms with no physical contact with the installations and without the assistance of Utilities personnel. In order to achieve this goal an Electric Field Sensor (EFS) was employed in the design of the measuring system. This paper deals with the results of testing an electric field measurement system – completely designed by the authors – for monitoring voltage Flicker and harmonics in aerial power systems. Some results of field measurements performed in plants containing disturbing loads are shown.