Shake table testing of voltage and current transformers designed for the high voltage and extra-high voltage ranges

Two voltage transformers (VTs) and two current transformers (CTs) having different system voltage levels, respectively in the high voltage HV and extra-high voltage EHV ranges, were subjected to shake table tests at the EUCENTRE Foundation laboratories. The four full-scale specimens, provided by the manufacturer company Trench Italia S.r.l., are characterised by a total height ranging from 2.44 m to 4.68 m, and a total mass ranging from 400 kg to 900 kg. One of the main structural differences between the VTs and the CTs concerns the bushing, constituted of a hollow central cylinder and external sheds on the perimeter to ensure adequate surface insulation behaviour. In the two VTs, both the cylinder and the sheds are made of ceramic material, identified as aluminous porcelain C-120. On the other hand, in the two CTs, the bushing is composed of a hollow stiff internal cylinder, made of glass fiber reinforced polymer (GFRP), also called fiberglass, coated externally with high temperature vulcanized (HTV) silicone rubber, the latter being also the material constituting the sheds.

The experimental results were used to calibrate refined 3D numerical models of the transformers, developed in OpenSees. The goal of this project was the derivation of 16 fragility curves for the four instrument transformers in both stand-alone and elevated/supported configurations, also considering two different soil types. Based on the derived curves, one of the voltage transformers is expected to experience light or negligible damage due to earthquake shaking, owing to its high resonance frequencies (and hence stiffness), whilst the remaining three devices may suffer moderate damage under medium to strong shaking intensities; however, their seismic risk is in effect mitigated by the presence of the typically employed supporting column.

This research was funded by the Research Fund for the Italian Electrical System under the contract agreement between Ricerca sul Sistema Energetico—RSE S.p.A. and the Ministry of Economic Development—General Directorate for the Electricity Market, Renewable Energy and Energy Efficiency, Nuclear Energy in compliance with the Decree of 16 April 2018.