Protection of power transformers connected to gis against lightning overvoltages

Abstract

During the last ten years Iberdrola Distribución Eléctrica has built a considerable number of high voltagemedium voltage transformer stations in urban areas using high voltage (220 kV and 132 kV) Gas Insulated Substations (GISs). The typical configuration of such GISs is double bar with two transmission line bays, two transformer bays and a coupling bay. Overhead transmission lines and power transformers are connected to the GIS using either insulated cables or Gas Insulated Lines (GILs) of different length. The protection of the power transformers against lightning overvoltages is performed with surge arresters at the connection point of the overhead lines with either the insulated cables or the GILs.

This paper reports an exhaustive study conducted by Iberdrola aimed at assessing the performance of the protective scheme in three configurations in both 132 kV and 220 kV stations:

1. Power transformers are connected to the GIS using GILSs. Overhead lines are connected to the GIS also using GILs. 2. Power transformers are connected to the GIS using insulated cables. Overhead lines are connected to the GIS also using insulated cables. 3. Power transformers are connected to the GIS using insulated cables. Overhead lines are connected to the GIS using GILs. Very detailed models of the stations for electromagnetic transient simulation have been developed using manufacturer data of the GISs, insulated cables, GILs, power transformers and surge arresters.

The study has comprised simulation of a reference case of each configuration and several sensitivity studies with respect to the length of the insulated cables and the GILs.