Power Transformer Condition Monitoring and Diagnosis
Power transformers are a key asset for electricity utilities around the globe. However, aging populations of large power transformers require reliable monitoring and diagnostics techniques to extend the asset's lifetime and minimise the possibility of catastrophic failure. This book describes the most popular power transformer condition monitoring techniques from principles to practice. Topics covered include concepts and challenges in power transformer condition monitoring and diagnosis; dissolved gas analysis, measurements and interpretations; moisture analysis for power transformers; assessing degree of polymerisation value considering thermal ageing and paper moisture; frequency response analysis; monitoring of power transformers by mechanical oscillations; lifecycle management of power transformers in a new energy era; and other topics in power transformer asset management and remnant life. Each chapter covers the fundamentals and theory of the topic, and conveys techniques to measure relevant parameters and assess or interpret the results. Power Transformer Condition Monitoring and Diagnosis is essential reading for researchers in academia and industry involved with power transformer R&D, engineers in utilities working with equipment monitoring techniques, and advanced students in power engineering.
Inspec keywords: oscillations; partial discharges; paper; ageing; power transformer insulation; chemical analysis; condition monitoring
Other keywords: dissolved gas analysis; condition monitoring; mechanical oscillations; moisture analysis; thermal ageing; partial discharges; paper; power transformer
Subjects: Transformers and reactors; Insulation and insulating coatings; Dielectric breakdown and discharges; General electrical engineering topics
- Book DOI: 10.1049/PBPO104E
- Chapter DOI: 10.1049/PBPO104E
- ISBN: 9781785612541
- e-ISBN: 9781785612558
- Page count: 323
- Format: PDF
-
Front Matter
- + Show details - Hide details
-
p.
(1)
-
1 Dissolved gas analysis, measurements and interpretations
- + Show details - Hide details
-
p.
1
–38
(38)
Oil-filled power transformers were first conceived and manufactured in the mid-tolate-1800s. They were (and to this day are) an essential component of the electrical power transmission and distribution infrastructure. Power transformers perform a power conversion function. A transformer takes electrical power of certain voltage and current characteristics through its primary terminals and delivers this power on its secondary terminals with changed voltage and current levels. By increasing voltage, and thus reducing the current level, power transformers minimise losses and enable the economical transmission of electrical power over long distances.
-
2 Partial discharges: keys for condition monitoring and diagnosis of power transformers
- + Show details - Hide details
-
p.
39
–85
(47)
The combination of thermal and electrical stress, in conjunction with the synergic effects of moisture in the insulation, might dramatically reduce the lifetime of a power transformer, which is roughly estimated to be 40 years if properly maintained, meaning that many transformers do not experience any failures before being dismantled. Mechanical stresses during short-circuits can also play a role leading, in the worst case, to the radial buckling of the winding and damage of the connection cables at the bushing terminations. A number of these factors can, in the course of time, give rise to partial discharge (PD) phenomena which can be a cause of failure or a symptom of degradation. PD measurements can be carried out conventionally, following the standards IEC 60270 and IEC 60076. Alternative methods, such as those presented in the IEC TS 62478 standard based on acoustic or ultra-high frequency sensors, have been proposed and might offer better sensitivity, particularly for monitoring purposes, and the capability to locate the PD sources. For all these methods, identification of the PD source is a key to achieve a correct course of action (run, repair and replace).
-
3 Moisture analysis for power transformers
- + Show details - Hide details
-
p.
87
–123
(37)
In this chapter, the problem of moisture in transformer insulation is tackled. The physical processes involved in moisture dynamics are first described, then the different methodologies that can be applied to estimate the value of this variable are explained. Finally, the challenges that lie ahead regarding moisture monitoring are discussed.
-
4 Assessing DP value of a power transformer considering thermal ageing and paper moisture
- + Show details - Hide details
-
p.
125
–142
(18)
Current power transformer (PT) ageing models are approximations to reality based on experimental and theoretical evidence; these models are simplifications of complex interactions inside units, because of that loss-of-life results could be presented in a wide range. In PT decision-making context-investment, replacement or maintenance, this amplitude could lead inadequate actions and, in extreme cases, might compromise technical operation and profitability. Solid insulation failure is the leading cause of end-of-life of PTs, insulation paper is composed by long fibers of cellulose; the average length of these fibers is called degree of polymerization (DP), it is widely accepted that DP value is a good index of PT loss-of-life. Considering the above, this chapter presents a holistic methodology for solid insulation ageing assessing based on all thermal degradation process (oxidation, hydrolysis and pyrolysis) and the influence of paper moisture dynamics. Paper moisture is estimated using as input external variables such as hot-spot temperature, transformer technical data and measurements regarding oil moisture, in order to consider uncertainty in oil moisture growing, arithmetic-Brownian-motion (ABM) algorithms are presented. For illustrating the application of this method, DP value of two units is assessed; available information for this example are hourly profiles of load and ambient temperature and yearly moisture in oil samples for a period over 15 years.
-
5 Frequency response analysis
- + Show details - Hide details
-
p.
143
–210
(68)
Transformers can be treated as a time-invariant system which can be characterized by its response to the Dirac's delta function. This impulse response is completely unique and should remain so over the system life. Therefore, it can be used as a kind of indicator to check if the internal compartments, elements or parameters have physically changed during service life. The system response is the convolution of the system impulse response with the excitation signal. This time-domain response has its equivalent response in the frequency domain. Thus, the frequency response of a time-invariant system should also remain unchanged if system parameters are unchanged. This concept can be utilized to evaluate the mechanical structure integrity as well as diagnosis of transformers and rotating machines. It is called frequency response analysis. This chapter is specifically focused on frequency response measurement and analysis of transformers.
-
6 Monitoring of power transformers by mechanical oscillations
- + Show details - Hide details
-
p.
211
–237
(27)
Condition-based asset management is gaining importance, which leads to a prospering of power transformer monitoring. Different methods, for example the dissolved-gas-analysis and oil-aging evaluation, partial discharge measurements and also frequency response analysis have been established to determine the status of the transformer's electric insulation and windings. The last part of this chapter correlates vibrations to direct current (DC) components running through transformers' grounded star points impacting the magnetic operational status. In addition, vibration measurements are used to estimate the resulting changes of transformer's noise due to DC which gains importance for power transformers and in particular low-noise transformers.
-
7 Lifecycle management of power transformers in a new energy era
- + Show details - Hide details
-
p.
239
–258
(20)
In this chapter, I will discuss some ideas and opinions of what this evolving environment means in terms of power transformer lifecycle management. This text is not meant to be an authoritative or scientifically rigorous treatment of this subject matter but rather merely a thought-provoking exercise for actors and stakeholders involved in planning, designing, building operating and maintaining the transformers and electrical networks of the future.
-
8 Power transformer asset management and remnant life
- + Show details - Hide details
-
p.
259
–293
(35)
The quality of insulation system within power transformer reflects the overall health condition of the asset. A timely and reliable maintenance decision along with the remaining operational life estimation of the asset can be identified through the measurements of some parameters reflecting the degradation rate of the transformer dielectric insulation. However, the process is not always straightforward due to the complexity of the insulation structure and degradation process. This chapter proposes a new fuzzy-logic approach to provide a proper asset management decision and predict the remaining operational life of a power transformer based on some insulating oil tests. The developed fuzzy-logic model is validated through field data collected for various transformers of pre-known health condition and life span. The results show that the proposed model is reliable and can be facilitated to provide a timely asset management decision with less reliance on expert personnel.
-
Back Matter
- + Show details - Hide details
-
p.
(1)