In nuclear power plants, electrical cabinets that contain safety related equipment must be structurally stable during a seismic event. In addition, cabinets that are not safety related but could impact safety related equipment must be stable enough not to impact the safety related equipment or adjacent cabinets. In-cabinet response spectra are required to ensure qualification of mounted equipment.
Seismic Qualification of Electrical Cabinet:
This project was performed for a cabinet manufacturer for use in a nuclear power plant. The purpose of the analysis was to determine the structural strength of the cabinet and the cabinet mounting during a seismic event. The qualification of the internal electrical equipment was not part of the analysis. Qualification of some internal equipment, such as relays can be determined via frequency review, but this was not required in this analysis.
The structural elements and sheet metal were modeled in our Finite Element Analysis (FEA) software. The internal equipment was modeled as brick elements with mass of the bricks specified to equal the equipment mass. Because the cabinet was determined to have a natural frequency that indicated that it was not seismically rigid, a dynamic analysis was required using a seismic response spectra.
Our conclusion showed that the lower support cross members would experience stresses that were above the allowable limits. Based on this, we provided a design recommendation to reinforce the support members. In addition, we recommended additional reinforcement around the base anchor bolts to prevent local high stresses. An increase in bolting size was also recommended.
In-Cabinet Response Spectra:
The client required an “in-cabinet” response spectrum at various points within an electrical cabinet for use in the qualification of mounted equipment.
Our solution was to use a Finite Element Analysis (FEA) model in combination with a transient stress analysis with modal superposition of the cabinet. A base time history “acceleration vs time” input was developed from the known base response spectra. From this input, time history output was obtained at the locations of concern. This time history output was converted to response spectra for use by the client.