Health Index, Risk and Remaining Lifetime Estimation of Power Transformers

Abstract

A new method for systematically estimating health index, probability of breakdown and remaining life for power transformers is presented. The method combines three basic models; a physical winding degradation model, a health index model based on condition monitoring data combined with expert judgement, and a statistics-based end-of-life model. The statisticsbased model uses data from a database of scrapped transformers under development in Norway. Combining the first two models with the statistics-based model, an individual and conditiondependent probability of breakdown is obtained. From this, the expected remaining life is calculated. Finally, the stochasticity of the method is utilized for optimization of maintenance and replacement. The method hence provides key decision support for transformer managers, enabling them to identify transformers in poor condition, and to follow-up and prioritize transformers for maintenance and replacement. The proposed method has been implemented in a transformer asset management tool for Norwegian utilities. The usefulness of the method is illustrated by applying it to selected transformers from one of these utilities. Finally, important limitations, uncertainties and further improvements are discussed.

Non-Contact High Voltage Measurement in the Online Partial Discharge Monitoring System

“…It is enough to do this for at least one measuring point because this relation is linear, as shown in Section 6. Knowing the maximum values of the voltages U 1 and U 2 , as well as the parameters of the measuring system, i.e., the elements included in the impedance Z 2 , the value of the coupling capacitance C 1 can be determined using Equation (5), which results from the transformation of Equations ( 1) and (2). It is assumed that the impedance Z 1 is purely capacitive.…”

“…Unfortunately, a common problem in most countries is that a significant part of these transformers either exceed the lifetime predicted by manufacturers (estimated at about 30-35 years) or are close to this limit. Numerous reports and statistical analyses indicate more and more frequently occurring transformer failures [1][2][3]. These failures not only cause electrical power cuts but can also lead to oil leaks and fires (environmental contamination) and damage to high voltage (HV) devices associated with them at a substation or power plant.…”

On-Line Partial Discharge Monitoring System for Power Transformers Based on the Simultaneous Detection of High Frequency, Ultra-High Frequency, and Acoustic Emission Signals

“…Their reliable operation ensures continuity of electrical energy supply and stability of the power energy system. A serious global problem is a high share of power transformers, for which the designed lifetime (usually estimated at 30-35 years) expired [1][2][3]. However, considering the high cost of purchase, transportation, and insurance as well as very long delivery time (even over a year), power transformers are not, at the moment of expiring their lifetime, immediately replaced with new ones.…”

Reliable Estimation for Health Index of Transformer Oil Based on Novel Combined Predictive Maintenance Techniques

“…On the other side, different approaches of diagnosis and monitoring are used, based on a wide variety of thermal, mechanical, electrical, and optical effects. These approaches provide information on aging, allowing the state assessment, and recommend measures to improve the quality of the insulation and lifetime assessment [23,24]. One of these approaches is the health index, whose evaluation is based on different factors [23,25].…”

“…These approaches provide information on aging, allowing the state assessment, and recommend measures to improve the quality of the insulation and lifetime assessment [23,24]. One of these approaches is the health index, whose evaluation is based on different factors [23,25]. These factors include dielectric strength measurement, DGA, turns ratio, leakage reactance, winding resistance, and degree of polymerization for paper insulation.…”