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Transformers – Basics, Maintenance, Diagnostics

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TOC

1. Introduction
2. Introduction to Transformers
2.1 Principle of Operation
2.2 Transformer Action
2.3 Transformer Voltage and Current
2.4 The Magnetic Circuit
2.5 Core Losses
2.6 Copper Losses
2.7 Transformer Rating
2.8 Percent Impedance
2.9 Internal Forces
2.10 Autotransformers
2.11 Instrument Transformers
2.12 Potential Transformers
2.13 Current Transformers
2.14 Transformer Taps
2.15 Transformer Bushings
2.16 Transformer Polarity
2.17 Single-Phase Transformer Connections for Typical Service to Buildings
2.18 Parallel Operation of Single-Phase Transformers for Additional Capacity
2.19 Three-Phase Transformer Connections
2.20 Wye and Delta Connections
2.21 Three-Phase Connections Using Single-Phase Transformers
2.22 Paralleling Three-Phase Transformers
2.23 Methods of Cooling
2.24 Oil-Filled – Self-Cooled Transformers
2.25 Forced-Air and Forced-Oil-Cooled Transformers
2.26 Transformer Oil
2.27 Conservator System
2.28 Oil-Filled, Inert-Gas System
2.29 Indoor Transformers

3. Routine Maintenance
3.1 Introduction to Reclamation Transformers
3.2 Transformer Cooling Methods Introduction
3.3 Dry-Type Transformers
3.3.1 Potential Problems and Remedial Actions for Dry-Type Transformer Cooling Systems
3.4 Liquid-Immersed Transformers
3.4.1. Liquid-Immersed, Air-Cooled
3.4.2 Liquid-Immersed, Air-Cooled/Forced Liquid-Cooled
3.4.3 Liquid-Immersed, Water-Cooled
3.4.4 Liquid-Immersed, Forced Liquid-Cooled
3.4.5 Potential Problems and Remedial Actions for Liquid-Filled Transformer Cooling Systems
3.4.6 Cooling System Inspections

4. Oil-Filled Transformer Inspections
4.1 Transformer Tank
4.2 Top Oil Thermometers
4.3 Winding Temperature Thermometers
4.4 Oil Level Indicators
4.5 Pressure Relief Devices
4.6 Sudden Pressure Relay
4.6.1 Testing Suggestion
4.7 Buchholz Relay (Found Only on Transformers with Conservators)
4.8 Transformer Bushings: Testing and Maintenance of High-Voltage Bushings
4.9 Oil Preservation Sealing Systems
4.10 Auxiliary Tank Sealing System

5. Gaskets
5.1 Sealing (Mating) Surface Preparation
5.2 Cork-Nitrile
5.3 Cork-Neoprene
5.4 Nitrile “NBR”
5.5 Gasket Sizing for Standard Groove Depths
5.6 Rectangular Nitrile Gaskets
5.7 Bolting Sequences to Avoid Sealing Problems

6. Transformer Oils
6.1 Transformer Oil Functions
6.1.1 Dissolved Gas Analysis
6.1.2 Key Gas Method
6.1.3 Sampling Intervals and Recommended Actions
6.1.4 Atmospheric Gases
6.1.5 Dissolved Gas Software
6.1.6 Temperature
6.1.7 Gas Mixing
6.1.8 Gas Solubility
6.1.9 Diagnosing a Transformer Problem Using Dissolved Gas Analysis and the Duval Triangle
6.1.10 Carbon Dioxide/Carbon Monoxide Ratio
6.1.11 Moisture Problems

7. Transformer Oil Tests that Should Be Completed Annually with the Dissolved Gas Analysis
7.1 Dielectric Strength
7.2 Acid Number
7.3 Test for Oxygen Inhibitor
7.4 Power Factor
7.5 Oxygen
7.6 Furans
7.7 Oil Treatment Specification
7.7.1 Taking Oil Samples for DGA

8. Silicone Oil-Filled Transformers
8.1 Background
8.2 Carbon Monoxide in Silicone Transformers
8.3 Comparison of Silicone Oil and Mineral Oil Transformers
8.4 Gas Limits
8.5 Physical Test Limits

9. Transformer Testing
9.1 DC Winding Resistance Measurement
9.2 Core Insulation Resistance and Inadvertent Core Ground Test (Megger)
9.3 Doble Tests on Insulation
9.4 Visual Inspection
9.5 Ultrasonic and Sonic Fault Detection
9.6 Vibration Analysis
9.7 Turns Ratio Test
9.8 Estimate of Paper Deterioration (Online)
9.9 Estimate of Paper Deterioration (Offline During Internal Inspection)
9.10 Transformer Operating History
9.11 Transformer Diagnostics/Condition

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