Determination of stator temperature profile using distributed sensing

The aging of generators is intimately associated with the hotspot temperature of the stator windings groundwall insulation. Common resistive thermal detectors (RTD) installed in the machine are well suited to monitor temperature changes and trends during normal operation, as long as temperature distribution is uniform, but are blind to some hotspots. Moreover, the relationship between the RTD temperature and the one of the copper conductor depends on the operating condition, the machine design and its cooling system so a simple rule of ten degree of difference is not always valid. When generators are operated close to their limit, it is essential to determine as precisely as possible the exact hotspot temperature to prevent any life reduction of the equipment. To optimize generation without any life reduction, Hydro-Quebec Research institute IREQ has been developing over the past decade a generator model that includes finite element modeling of electromagnetism, thermal, mechanical and fluid dynamics of the cooling air. This model relies on experimental data from the field to validate calculation. One of the main sensors use to validate thermal simulation is an optic fiber installed in the stator core´s vent ducts. This sensor is use for distributed temperature sensing (DTS) measurement. This paper presents the comparison of the thermal model calculations, the DTS measurements and other sensors used to measure temperature in five case studies on actual generators.