Voltage Endurance Test over two different models of hydrogenerator stator bars due to different overhang configuration

摘要

Non acceptable values of Insulation Resistance and Polarization Index was discovered in one of three hydrogenerators rewound due to the fact that, the stress grading coating had been extended up to physically touch the copper in the bar end instead to has a separation of 20 mm like in the other two previous rewound groups in the same hydro plant. In order to clarify the behaviour of this new winding configuration versus the previous or standard one, a voltage endurance test (VET) was proposed to manufacturer over two equal models: one composed from bars with physical separation between grading coating and copper lug (20 mm) and other one, with physical contact. Also, to can determine the behaviour of insulating blocks/cords especially in the case of adjacent bars of different phases, both models were composed of two bars with the same machine geometry and distances. A number of according tests and inspections were agreed in order to look for differences between both models before, during and after VET.