A review on wind turbine transformers

Comparative Analysis of the Results of Diagnostic Measurements with an Internal Inspection of Oil-Filled Power Transformers

“…The proper selection of a diagnostic procedure and correct interpretation of the results obtained from different types of measurements are valid, no matter the place of the transformer installation [3][4][5][6][7][8][9][10][11][12][13][14]. In the case of wind and solar farms, appropriate procedures become even more important due to the accumulation of stresses that affect stresses result, among others, from a high variability of loads, frequent de-energizing of transformers, environmental impact (lightning, large daily fluctuations in ambient temperature, and sea climate), and requirements to stay operational during significant voltage dips [15]. The analyses carried out have indicated that transformer failures might occur mainly in the insulation system of the transformer, transformer windings, bushings, and on-load tap changers (OLTC).…”

Techno-economic evaluation of five-level nested neutral point clamped converter topology for transformer-less connection of high-power wind energy conversion systems

“…Environmental factors such as ambient temperature, humidity, and the average wind speed in the vicinity have been identified as the main cause of failure in the power converter of a WECS [2]. Based on previous reliability studies, the electrical subsystem of the WECS was identified to have a high percentage of failure, mainly caused by the variable nature of wind [4][5][6][7]. The wind turbine (WT) transformer was identified as one of the least reliable and costly components of the electrical subsystem, as shown in Figure 1 [7][8][9].…”

“…It is, therefore, vital to ascertain the major causes of failure of WT transformers in a WECS. The main factors responsible for the frequent failure of WT transformers were identified as the variable nature of wind, utilisation of conventional power transformers, and compliance to grid codes [5,6]. The variable nature of wind gives a low loading factor of WT transformer (20 -35%), which results in significant core losses [5,6], and results in multiple loading cycles in the transformer, thereby increasing its aging rate [5,6].…”

“…The main factors responsible for the frequent failure of WT transformers were identified as the variable nature of wind, utilisation of conventional power transformers, and compliance to grid codes [5,6]. The variable nature of wind gives a low loading factor of WT transformer (20 -35%), which results in significant core losses [5,6], and results in multiple loading cycles in the transformer, thereby increasing its aging rate [5,6]. A sudden reduction in the grid voltage caused by voltage unbalance results in an inrush of current in the transformer, which increases the electrical and thermal stress on its windings [5].…”

“…The variable nature of wind gives a low loading factor of WT transformer (20 -35%), which results in significant core losses [5,6], and results in multiple loading cycles in the transformer, thereby increasing its aging rate [5,6]. A sudden reduction in the grid voltage caused by voltage unbalance results in an inrush of current in the transformer, which increases the electrical and thermal stress on its windings [5]. These causes of failure can, however, be minimised by eliminating the WT transformer from the WECS [5][6][7][8][9][10][11].…”