The Bookpointindia

About the BookAbout the AuthorTable of Contents

Although many textbooks cover the topic of transformers as required of the curriculum, engineers after graduation generally learn about the practical applications of transformers either by trial and error or under the guidance of senior experienced engineers. The need for practical usage information is generally felt in power system utilities by professionals, budding consultants, electrical contractors, and to a larger extent by manufacturers too. This book fulfils the need of a handbook and provides a complete solution to the practical aspects of power transformers—construction, erection, and maintenance—to augment curriculum learning and make budding engineers ready for the field.

Key features:

Basic functions of transformers; information on core, windings, design, types of winding interconnections, connections in practice, tap operations, changing methods with on-load and off-load tap changers

Procedure and precautions to be observed in transportation, erection and commissioning of power transformers at site; pre-commissioning tests; checklist for commissioning power transformers

Maintenance aspects including that of external accessories; use of oil in transformers; various tests to be conducted; reclamation process using filters; oil handling systems; troubleshooting and remedial measures

Various protection schemes; the use of auto transformers in grid network; operation of transformers—loading, tap and parallel operation, emergency operation

Inferences from practical phenomenon: magnetic balance tests, observations made on voltages during Horn Gap fuse failures, sheared-delta connection; two-phasing phenomenon

Measures for enhancing performance by design

Case studies along with their analyses

H Kailasaraman, former Executive Engineer, Tamil Nadu Electricity Board, holds an ME degree in electrical engineering with specialisation in power systems. He has four decades of experience working in various areas on EHT transmission lines, grid network, substations and transmission and distribution network, as well as twelve years of teaching experience at the Transmission and Distribution Training Institute of the Tamil Nadu Electricity Board. He is presently a guest faculty at the institute. He is a member of the Institution of Engineers.

Power and Distribution Transformers: Theory, Conventional

Features and Design

Basic Functions of a Power Transformer
1. Introduction
2. Purpose of a Power Transformer
3. Main Parts of a Transformer
4. Transformer Action under No Load
5. Transformer Action under Load
6. Relations of Ratios
7. Losses in Power Transformers
8. Efficiency of Power Transformers
9. Calculation of Efficiency at Any Load
10. Equivalent Circuit Representation
11. Accounting for Parameters on One Side
12. Parameters Referred to as Percentage Values
13. Parameters in Percentages for Three-phase Transformers
14. Use of Parameters for Voltage Regulation and Power Loss: Sample Calculation
Magnetic Core
1. Core Formation
2. Types of cores
3. Formation of Core-Type Magnetic Circuit
4. Formation of Limb
5. Formation of the Yoke Section
6. Core Clamping
7. Earthing of Transformer Core
8. Basic Core Dimensions
Windings
1. Introduction
2. Position of Windings
3. Coil Notations and Numbering
4. Design Consideration of Windings
5. Winding Direction
6. Types of Windings
7. Winding Insulations

Winding Coil Interconnections
1. Connections in Practice
2. Delta Connection in the Primary
3. Star Connection in the Secondary
4. Characteristics of Delta/Star Combination and Vector Group
5. Interchangeable Vector Group for 41DY11
6. Zigzag or Interconnected Star
7. Coil Connection for Double Ratio Transformer
Tappings and Tap Changers
1. Voltage Control by Tappings
2. Method of Tappings
3. Effect of Tapping on Impedance of Winding
4. Off-load Tap Changers
5. On-load Tap Changers (OLTC)
6. Mechanism for On-load Tap Changers

Transportation, Erection and Commissioning of Power Transformers

Transport, Erection and Commissioning
1. Introduction
2. Low-Weight Transformers
3. Handling of Heavy-weight Transformers
4. Transporting the Transformer
5. Dismantling of Accessories
6. Loading Transformer on Trucks
7. Precautions to be Taken in Transportation
8. Unloading the Transformer on the Plinth
9. Assembly after Erection
10. Hot Oil Circulation
11. Pre-commissioning Test
12. Checklist for Commissioning of Power Transformers
Pre-commissioning Test on Power Transformers
1. Introduction
2. List of Pre-commissioning Tests
3. Ratio Test
4. Short Circuit Test
5. Open Circuit Test
6. DC Resistance test
7. Vector Group Test
8. Phasing-Out Test
9. Insulation Resistance Test
10. Other Tests Conducted

3. Maintenance of Power Transformers

3.1 External Accessories of a Transformer

Introduction
Main Tank with Flow Valves and Top Cover
Cooling system
Conservator
Breather
Oil Level Indicators
Temperature Measuring Systems
Bushings
Buchholz Relay
Explosion Vent
Pressure Relief Valve
Equiliser Pipe Arrangement
Air Release Cock or Plug

Use of Oil in Transformers
1. Introduction
2. Standards for New Unused Oil
3. Use of Transformer Oil
4. Possible Contamination of Oil
5. Oil Test for Contamination and Interpretation
6. Analysis of Gas in Transformer Oil
7. Reclamation of Oil Using Filters
Maintenance of Power Transformers and Improvement of IR Values
1. Maintenance of Oil Handling Systems
2. Testing of Oil Samples
3. Measurement of Insulation Resistance Values (IR Values)
4. Improvement of IR value
Troubleshooting Power and Distribution Transformers

Operation of Power Transformers

Protection Schemes for Power Transformers and Their Operation
1. Introduction
2. Types of Protection
3. Differential Protection
4. Overcurrent Protection
5. Buchholz Protection for Isolating Faulty Transformers
6. Protection from Over-temperature (Thermal)
7. Protection from Excessive Pressure or Turbulence
8. Protection from High Voltage, High Frequency Surges and Lightning
Auto transformer and Its Usage in Power Systems
1. Introduction
2. Principle and Economic Considerations
3. Usage of Autos in Power Systems
4. Use of Tertiary Windings in Autos
Operation of Transformers in Substation
1. Introduction
2. Nameplate Details
3. Loading Operation
4. Tap Operation
5. Parallel Operation of Transformers
6. Emergency Operation of Transformers

5. Inferences from Observed Phenomena and Some Case Studies

Inferences from the Transformer Phenomena

5.1.1Magnetic Balance Test

5.1.2 Observation on LT Voltage for HV Side Fuse Failure

Delta lead cut off: Inference and observation on LT side
Two-Phasing Inference

Case Studies on Power Transformer
Case Studies on Defects in Distribution Transformers
Conclusion Drawn from Case Studies
Performance Enhancement by Design of Distribution Transformers for Field Working Condition