Transformer Diagnostics

Bijan Ghayour, P.E.

Course Outline

This 6-hour course is intended to establish recommended practice as well as to give general advice and guidance in testing and diagnostics of oil-filled power transformers to establish their condition, identify problems, and provide potential remedies. This course applies to oil-filled power transformers (500 kVA and larger).

Guidance and recommendations herein are based on industry standards and experience in existing facilities. However, equipment and situations vary greatly, and sound engineering and management judgment must be exercised when applying these diagnostics. All available information must be considered (e.g., manufacturer's and transformer experts' recommendations, unusual operating conditions, personal experience with the equipment, etc.) in conjunction with this course.

The course materials are based entirely on the Unified States Department of the Interior, Facilities Instructions, Standards, and Techniques Volume 3-31.

This course includes a multiple-choice quiz at the end, which is designed to enhance the understanding of course materials.

Learning Objective

The purpose of this course is to provide guidance for the operating and maintenance engineers in inspection, testing, and diagnostics of power transformers and associated equipment.

At the conclusion of the course the student will be familiar with the:

• Transformer diagnostics and transformer maintenance;
• Transformer diagnostics and power plant rehabilitation;
• Dissolved gas analysis;
• Transformer diagnosis using individual and total dissolved key gas concentrations;
• Diagnosing a transformer problem using dissolved gas analysis and the Duvall triangle;
• Origin of the Duvall triangle;
• How to use the Duval triangle;
• Oil physical/chemical tests;
• Transformer oil tests that should be performed annually;
• Dielectric strength test;
• Interfacial tension (IFT) test;
• Acid number;
• Oil power factor test;
• Moisture test;
• Transformer age;
• Insulation power factor test;
• capacitance tests;
• Excitation current test;
• Bushing tests;
• Percent impedance/leakage reactance test;
• Sweep frequency response analysis tests;
• Visual inspection;
• Infrared temperature analysis;
• Corona scope scan;
• Ultrasonic and sonic fault detection;
• Vibration analyses;
• Turns ratio test;
• DC winding resistance measurement;
• Core insulation resistance and inadvertent core ground test;
• Estimate of paper deterioration (online);
• Estimate of paper deterioration (offline during internal inspection);
• Transformer operating history; and
• Transformer diagnostics/condition assessment summary.
  

Intended Audience

This course is intended for electrical engineers and maintenance personnel involved in the service, maintenance, and upgrade of power transformers.

Benefit to Attendees

Power transformers are key components in the power train at various power plants and are appropriate for analysis under a risk assessment program. Transformer failure can have a significant economic impact due to long lead times in procurement, manufacturing, and installation in addition to high equipment cost.

Determining the existing condition of power transformers is an essential step in analyzing the risk of failure. This course provides a process for arriving at a Transformer Condition Index. This condition index may be used as an input to the risk-and-economic analysis computer models where it is used to adjust transformer life expectancy curves. The output of the economic analysis is a set of alternative scenarios, including costs and benefits, intended for management decisions on replacement or rehabilitation.

Course Introduction

Determining transformer condition is useful in itself for making short-term decisions regarding operation and maintenance. Assessing transformer condition through diagnostic techniques is also important for conducting asset management studies for transformer replacement. Transformer condition is an important input to an engineering and economic model used to determine the most cost-effective alternative for power train rehabilitation (i.e., continued operation, refurbishment, or replacement). A methodology has been developed to use information derived from the diagnostics described in this course for rehabilitation purposes.

Guidance and recommendations herein are based on industry standards and experience in existing facilities. However, equipment and situations vary greatly, and sound engineering and management judgment must be exercised when applying these diagnostics. All available information must be considered (e.g., manufacturer's and transformer experts' recommendations, unusual operating conditions, personal experience with the equipment, etc.) in conjunction with this course.

This course addresses specific testing and diagnostic techniques and tools used to assess the condition of oil-filled power transformers. These processes are often above and beyond routine maintenance work completed on a regular basis to keep the transformer operational.

PDH course E212 Transformer Maintenance, contains some diagnostic information.
In some cases, that information is repeated or amplified here for completeness and clarity. This course and PDH E212 course should be used jointly to provide the full range of transformer maintenance, testing, and diagnostics needed to extend the life of power transformers.

Course Content

This course contains specific examples, with practical emphasis on the inspection, testing, diagnosis of possible problems, and criteria for upgrading of power transformers.

You are required to study volume 3-31, Transformer Diagnostics, published by the Unites States Department of the Interior, Bureau of Reclamation.

Transformer Diagnostics (PDF 1.2MB)

(For an electronic copy of FIST 3-31 go to www.usbr.gov/power/data/fist/fist3_31/fist3_31.pdf)

Please click on the above underlined hypertext to view, download or print the document for your study. Because of the large file size, we recommend that you first save the file to your computer by right clicking the mouse and choosing "Save Target As ...", and then open the file in Adobe Acrobat Reader. If you still experience any difficulty in downloading or opening this file, you may need to close some applications or reboot your computer to free up some memory.

The following contains the outline of volume 5-1, Personal Protective Grounding for Electric Power Facilities and Power Lines, published by the Unites States Department of the Interior, Bureau of Reclamation:

Transformer Diagnostics (PDF 1.2MB)

Table of Contents

1. Introduction
2. Reference Documents
3. Transformer Diagnostics and Transformer Maintenance
4. Transformer Diagnostics and Powerplant Rehabilitation
5. Dissolved Gas Analysis
6. Oil Physical/Chemical Tests
7. Age
8. Doble Tests on Insulation.
9. Visual Inspection
10. Infrared Temperature Analysis
11. Corona Scope Scan
12. Ultrasonic and Sonic Fault Detection
13. Vibration Analyses
14. Turns Ratio Test
15. DC Winding Resistance Measurement
16. Core Insulation Resistance and Inadvertent Core Ground Test
17. Estimate of Paper Deterioration (Online)
18. Estimate of Paper Deterioration (Offline During Internal Inspection)
19. Internal inspections
20. Transformer Borescope
21. Transformer Operating History
22. Transformer Diagnostics/Condition Assessment Summary

Quiz

Once you finish studying the above course content, you need to take a quiz to obtain the PDH credits.

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DISCLAIMER: The materials contained in the online course are not intended as a representation or warranty on the part of PDH Center or any other person/organization named herein. The materials are for general information only. They are not a substitute for competent professional advice. Application of this information to a specific project should be reviewed by a registered architect and/or professional engineer/surveyor. Anyone making use of the information set forth herein does so at their own risk and assumes any and all resulting liability arising therefrom.

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