1. Project Goals/Objectives:

The purpose of this research project is to improve the qualification requirements for transformer bushings. This project will focus on the qualification of bushings rated at and above 161kV, since this class of bushings is believed to be the most vulnerable. This project has two main specific objectives:

The integrated qualification requirements summarized in the items above would be submitted for incorporation into the next revision of the IEEE 693 standard in 2002. The project will be conducted in collaboration with Mr. Rulon Fronk who will act as an advising subcontractor for the project.

2. Role of this project in supporting PEER’s mission (vision):

The IEEE 693-1997 standard specifies seismic qualification requirements for transformer bushings that include shaking table tests with the bushing mounted on a rigid test stand, for rated voltages exceeding 161kV. The standard requires the use of ground motions that match a specified response spectrum that is amplified by a factor of 2 to account for amplification resulting from the structure supporting the bushing. Shaking table tests conducted in previous PEER projects have raised questions about the adequacy of qualification requirements currently in use. Except for the amplification factor of 2 given in IEEE 693 for bushing qualification, no guidance is given to the transformer designer on how the bushing support structure should be designed. This project will contribute in elaborating such guidance.

3. Methodology Employed:

The proposed research project will consist of the following three main phases:

Phase 1: Static and Dynamic Testing of Supporting Structures for Transformer Bushings

Manufacturers will be approached to donate a complete supporting structure for transformer bushings above 161kV. The supporting structure will be anchored to a strong floor next to a reaction wall. In order to determine its lateral stiffness, strength and failure mode, the supporting structure will be loaded laterally by a hydraulic actuator anchored between the supporting structure and the reaction wall. The load will be applied at a distance above the top of the supporting structure in order to simulate the eccentric loading provided by the inertia force originating at the center of gravity of the bushing. From the results of these tests, the important sources of flexibility in the bushing support assembly will be identified.

Phase 2: Dynamic Modeling of Supporting Structures for Transformer Bushings

Based on the experimental results obtained in Part 1, a finite element model will be developed to predict the dynamic response of the supporting structure. Using this model, Frequency Response Function (FRF) curves will be constructed for each of these dynamic models in order to determine the Dynamic Amplification Factor (DAF) for a wide range of harmonic base excitation and to determine the range of excitation frequencies resulting in a DAF below 2. Finally, “top of supporting structure” response spectra will be generated under base input motions compliant with the IEEE 693 standard in order to evaluate the effect of the supporting structure on the seismic input at the support of a bushing. Again, various designs will be considered to limit the amplification to a maximum of 2.0.

Phase 3: Shake Table Testing of a Supporting Structure - Transformer Bushing Assembly

For the third phase of the project, the supporting structure tested in Phase 1 of the project will be tested on the uniaxial seismic simulation system at the University of California, San Diego. These tests will provide a unique opportunity to measure the actual DAF provided by the supporting structure at the connecting point of the bushing and to evaluate the accuracy of the dynamic models developed in Phase 3

4. Brief Description of past year’s accomplishments (Year 6) & more detail on expected Year 7 accomplishments:

At the time of writing, the project has been active for less than three months. A 500 kV transformer tank structure has been identified for donation. The finite element modeling of this structure is underway.

5. Other Similar Work Being Conducted Within and Outside PEER and How This Project Differs:

6. Plans for Year 8 if project is expected to be continued:

7. Describe any actual instances where you are aware your results have been used in industry:

8. Expected Milestones & Deliverables:

Because of late start of the project, it is expected that the project will end approximately 3 months after the anticipated end date with a set of design guidelines to transformer designers.