Seismic Evaluation and Retrofit of 230-kV Porcelain Transformer Bushings

Abstract

Static and earthquake-simulator testing of two 230-kV, 3000A, Type-U transformer bushings manufactured in the mid 1980s by the General Electric (GE) Company was undertaken to evaluate both the seismic performance of bushings known to be vulnerable to damage from moderate earthquake shaking, and the efficacy of simple retrofit details. Both bushings survived earthquake shaking compatible with the IEEE spectrum for High Level qualification when mounted on a rigid frame. When mounted on a flexible frame, one 230-kV bushing was unable to sustain the High Level qualification shaking without oil leakage and slip of the porcelain units. Two retrofit details utilizing two semicircular ring plates and epoxy filler were prepared by utility representatives with the objective of limiting slip of the UPPER-1 porcelain unit over the gasket connection. The second detail, Ring-2, permitted the 230-kV bushing to sustain substantially larger accelerations and displacements than those of the unretrofitted bushing and eliminated the permanent slip of the UPPER-1 porcelain unit over the gasket connection for extreme earthquake shaking.

Seismic vulnerability assessment of a high voltage disconnect switch

“…), [9]. In the past, the National Italian Electric Authority (ENEL) carried out an experimental campaign on some of these apparatuses, [10], showing their high vulnerability; more recently, in California, a wide analytical and experimental campaign on the seismic response of electrical substation equipment has been performed, in which many aspects, including the fragility curves evaluation of a disconnect switch have been treated, [11,12]. Very recently the hybrid simulation technique has been applied to a disconnect switch for the evaluation of its seismic response, [13,14].…”

Seismic safety of network structures and infrastructures

“…In the literature, four bushing failures modes are reported (Gilani et al 1999a): oil leakage at the connection, due to the vertical slip of the ceramic element; slip of the porcelain units relative to the flange; extrusion of the rubber gasket at the gasket connection; and cracking of the ceramic bushings.…”

Seismic safety evaluation of electric power supply at urban level

“…The switch is modelled with a commercial finite element code, see Figure 3; from tests made on similar components in Italy ( Figure 4) and in the US [26], oil leakage at the connection between the steel and ceramic parts, was recognized as the dominant mode of failure. The ultimate limit state was shear at the steel-ceramic connection.…”