Investigation of high voltage stator winding vibrations in full-scale slot model

This paper presents an approach to a high voltage stator winding vibration in slots evaluation using a specially designed full-scale slot model. Considerable research and testing has been carried out on vibration affecting both mechanical and electrical operation conditions of the winding bars in slots. The correlation of the operation and testing condition was evaluated by calculation of electromagnetic forces and slot reactances. Different testing coil connection diagrams were used to provide the desired coil current and radial electromagnetic forces, respectively. Vibration magnitude of the coils under test has been measured along slots with different wedging and side packing systems. The effectiveness of different systems has been evaluated and compared. It was confirmed that long term vibration thermocycling loading interaction leads to the start of high intensity slot spark discharge which can cause a groundwall insulation failure prematurely. The improvement of wedging and side tightening system (STS), including at least the spring type elements, has been considered and investigated. Measurements of the slot model teeth vibration are also presented and discussed. The results obtained allowed re-evaluation of the significance of some winding parameters: vertical and circumferential stiffness, proximity of natural and disturbing force frequencies of the bar considered as a beam with oscillating cross-bend; presence of constant spring-effected forces produced by tightening systems; capability of STS to a self-improvement with a temperature, etc