Abstract
Most power transformers operating in a power system possess oil-paper insulation. A serious defect of this type of insulation, which is associated with long operation time, is an increase in the moisture content. Moisture introduces a number of threats to proper operation of the transformer, e.g., ignition of partial discharges (PDs). Due to the varying temperature of the insulation system during the unit’s normal operation, a dynamic change (migration of water) takes place, precipitating the oil-paper system from a state of hydrodynamic equilibrium. This causes the PDs to be variable in time, and they may intensify or extinguish. Studies on model objects have been conducted to determine the conditions (temperature, humidity, time) that will have an impact on the ignition and intensity of the observed phenomenon of PDs. The conclusions of this study will have a practical application in the evaluation of measurements conducted in the field, especially in relation to the registration of an online PD monitoring system.
Highlights
The last few years have brought a clear shift in the strategy of network asset management, including large power transformers
The overall aging of the transformer population, manifesting itself, e.g., in an increase in the average moisture content [1], and the more often occurring catastrophic failures have forced the introduction of new regulations and recommendations for the operation and diagnosis of strategic importance devices to ensure a continuity of energy supply
In the case of very dry insulation (0.4%), changes in temperature insulation did not lead to ignition of partial discharges (PDs)
Summary
The last few years have brought a clear shift in the strategy of network asset management, including large power transformers. The overall aging of the transformer population, manifesting itself, e.g., in an increase in the average moisture content [1], and the more often occurring catastrophic failures have forced the introduction of new regulations and recommendations for the operation and diagnosis of strategic importance devices to ensure a continuity of energy supply. The growing demands of insurance companies concerning an aged network infrastructure, and burdened with a high risk of failure, have forced operators to change the current policy. Currently, an alternative to periodic diagnosis is more often the use of a transformer monitoring in the short-term (e.g., weekly monitoring of partial discharge (PD)) or continuous mode (the measurement system is installed permanently). It should be noted that continuous monitoring systems very well fit into the strategy that assumes resignation from manned substations in the near future to those that are fully automated and remotely managed
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