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Properly designed flexible buswork is one item that can increase the probability that a facility will still be operational after an earthquake. During such events, significant dynamic forces may be generated at the equipment terminals due to the push and pull of flexible connections during the motion of equipment. It is therefore important that the forces transmitted be within predetermined limits. This paper presents the results of a study aimed at obtaining sound criteria to appropriately design flexible buswork to account for seismic effects. This study was conducted with non linear finite-element simulations of representative interconnected substation equipment in existing installations, using an experimentally validated conductor model. It presents the resulting design methodology which specifies how to properly establish the required slack in a given flexible buswork configuration, as well as a predetermined level of force to be expected at the equipment terminals. Index Terms--Dynamics, earthquakes, finite-element methods, interconnections, stranded conductors, substations.

Stranded conductors are widely used structural components. Owing to their construction in layers, their bending stiffness may vary according to their tension, curvature and deformation history. Recently, a sound and practical model of variable bending stiffness using the secant stiffness method became available. Based on the same physical assumptions, this paper presents the development of a variable bending stiffness model using the tangent stiffness method and its implementation in a classical finite-element formulation adapted for nonlinear analysis under arbitrary loading. This extends its use to a general finite-element program. Comparisons with static and dynamic tests on short-span substation conductors show that the model computes a representative bending stiffness for such cases and yields adequate predictions of tractions generated at their ends, in both static and dynamic regimes. Index Terms--Cables, dynamics, finite-element methods, interconnections, power transmission lines, stranded conductors, substations.

This paper presents a simple and useful method to estimate the expected displacement at the interconnection point of substation equipment under seismic excitation. Analysis and a survey of qualification reports on standalone equipment revealed that for many types of equipment, the displacement is composed almost entirely of the contribution of the first vibration mode. The generalized single-degree-of-freedom method is therefore recommended to evaluate the displacement, using the first modal-participation factor and the spectral displacement from the required response spectrum. Mean and bound values of this factor were determined and are presented. Shake table tests were performed to investigate the effect of the flexible connection on this factor. It was found that, when sufficient slack is provided, its main effect, on average, is to decrease the standalone modal-participation factor. Index Terms--Dynamics, earthquakes, finite element methods, flexible structures, interconnections, substations.

This paper presents the results of a study aimed at developing alternative flexible-bus geometries in an aim to minimize earthquake effects on interconnected substation equipment. The approach chosen was to develop universal configurations that could be applied between any given pairs of components for a given voltage level and specific ground acceleration. Both dynamic testing and the nonlinear finite-element method were used to achieve this goal. The main product of this study takes the form of tables for each voltage level considered recommending one or more configurations according to the span. Index Terms--Dynamics, earthquakes, finite element methods, interconnections, stranded conductors, substations.

Low-impedance faults are difficult to contain from the point of view of cover retention and tank rupture in pole-type distribution transformers. When evaluating a transformer's containment capabilities, one needs to consider two aspects: the overpressure caused by an arc of given parameters and the pressure withstand of the tank. This paper presents two methods to calculate overpressures as a function of the arc and all of the relevant geometrical parameters: tank diameter, air-space height, and the depth of the arc below the oil. Both methods have been validated with experiments. Results of tests to determine the pressure withstand of typical tanks are presented. It was found that an average value of the overpressure withstand capability is approximately 100 kPa. For a given tank geometry and fault parameters, a current-limiting fuse would be required if the methods proposed here predict an overpressure of more than 100 kPa. Index Terms--Arc discharges, explosions, finite-difference methods, prediction methods, pressure effects, transformers.

When an electric arc is generated in transformer oil, a strong overpressure may rapidly develop in the tank, especially for low-impedance faults. This paper presents the test method and results obtained in a project aimed at assessing the human and environmental risks associated with this type of fault. Limit energy and pressure values were defined in terms of different safety levels. The best method of limiting the energy and pressure at a safety level in the transformer tank during internal faults of greater than 1.7 kA is to protect the transformer with a current limiting fuse. Other ways to increase the mechanical withstand of transformer tanks under such faults are also discussed. Index Terms--Arc discharge, fault current, fuse, protection, safety, test pressure, transformers.

The effects of connections made of flexible conductors must be included in the seismic design of substation equipment. A common practice is to take account of their effects as static loading only, providing sufficient slack to permit the expected relative displacement between interconnected equipment during an earthquake. This paper presents the approach and the results of an experimental study performed to investigate the significance of the dynamic behavior of connections made of flexible conductors under earthquake excitation. It is found that they can be excited in resonance and generate significant forces on the equipment to which they are interconnected, even when sufficient slack is provided. The study shows that the dynamic reactions of connections must be considered for the proper design of substation equipment. A method of establishing the natural frequencies of connections likely to be excited during an earthquake is proposed. Keywords: Connection, interconnection, connecting lead, conductor, cable, substation, earthquake, seismic, resonance.