Humidity in Power Converters of Wind Turbines—Field Conditions and Their Relation with Failures

Abstract

Power converters in wind turbines exhibit frequent failures, the causes of which have remained unexplained for years. Field-experience based research has revealed that power- and thermal-cycling induced fatigue effects in power electronics do not contribute significantly to the field failures observed. Instead, clear seasonal failure patterns point to environmental influences, in particular to humidity, as a critical stressor and likely driver of converter failure. In addition to the electrical operating conditions, it is therefore important to also identify and characterize the climatic conditions that power converters in wind turbines are exposed to, both as a contribution to root-cause analysis and as a basis for the derivation of suitable test procedures for reliability qualification of components and systems. This paper summarizes the results of field-measurement campaigns in 31 wind turbines of seven different manufacturers spread over three continents. The temperature and humidity conditions inside the converter cabinets are characterized and related to the environmental conditions of the turbines and to their operation. The cabinet-internal climate is found to be subject to pronounced seasonal variations. In addition to the site-specific ambient climatic conditions and the operation of the turbines, the converter cooling concept is identified to significantly influence the climatic conditions inside the power cabinets.

Field‐data‐based reliability analysis of power converters in wind turbines: Assessing the effect of explanatory variables

“…With a negative sign, the effect of liquid cooling is decreasing the failure intensity; therefore, the reliability of liquid-cooled converters is higher than that of air-cooled converters. A potential explanation might be the higher temperature and-as a result of that-lower relative-humidity level encountered in liquid-cooled converters compared with air-cooled converters reported in Fischer et al 11 In the lifetime regression model, the evaluated set of turbines only contains liquid-cooled converters.…”

“…While the first investigation was still limited to a relatively small turbine population with approximately 170 turbines, 30,31 the path of field-experienced-based research has been continued covering increasing numbers of turbines, with previous publications of the authors being. [8][9][10][11]…”

“…This comprehensive research has revealed that fatigue‐induced failures are not among the prevailing causes of the converter failures observed in the field. The results of exploratory statistical analysis based on a large converter‐specific data set covering more than 10000 wind turbines spread over Europe, Asia, Australia, and North and South America, therefore covering different climatic conditions, have revealed strong seasonal failure patterns in different regions and point to environmental influences, in particular to humidity, as a likely driver of converter failures 8–11 …”

“…Within the project CONFAIL, a previous study of one of the authors, root‐cause analysis of power converter failures in wind turbines by means of a field‐experience‐based approach was followed for the first time. While the first investigation was still limited to a relatively small turbine population with approximately 170 turbines, 30,31 the path of field‐experienced‐based research has been continued covering increasing numbers of turbines, with previous publications of the authors being 8–11 …”

“…The results of exploratory statistical analysis based on a large converter-specific data set covering more than 10000 wind turbines spread over Europe, Asia, Australia, and North and South America, therefore covering different climatic conditions, have revealed strong seasonal failure patterns in different regions and point to environmental influences, in particular to humidity, as a likely driver of converter failures. [8][9][10][11] In order to extract further useful insights from field-reliability data, this work presents results of statistical analysis of failure data of power converters. The objective is to assess the effect of design and site conditions on power-converter reliability by means of regression models.…”