Electromagnetic Transient Analysis and Novel Protective Relaying Techniques for Power Transformers

Xiangning Lin, Jing Ma, Qing Tian, Hanli Weng

• Publisher: Wiley-IEEE Press
• Year: 2014
• ISBN:
  9781118653852
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Power Resources
• Index: Technology & Engineering

An advanced level examination of the latest developments in power transformer protection

This book addresses the technical challenges of transformer malfunction analysis as well as protection. One of the current research directions is the malfunction mechanism analysis due to nonlinearity of transformer core and comprehensive countermeasures on improving the performance of transformer differential protection. Here, the authors summarize their research outcomes and present a set of recent research advances in the electromagnetic transient analysis, the application on power transformer protections, and present a more systematic investigation and review in this field. This research area is still progressing, especially with the fast development of Smart Grid. This book is an important addition to the literature and will enhance significant advancement in research. It is a good reference book for researchers in power transformer protection research and a good text book for graduate and undergraduate students in electrical engineering.

Chapter headings include: Transformer differential protection principle and existing problem analysis; Malfunction mechanism analysis due to nonlinearity of transformer core; Novel analysis tools on operating characteristics of Transformer differential protection; Novel magnetizing inrush identification schemes; Comprehensive countermeasures on improving the performance of transformer differential protection

• An advanced level examination of the latest developments in power transformer protection
• Presents a new and systematic view of power transformer protection, enabling readers to design new models and consider fresher design approaches
• Offers a set of approaches to optimize the power system from a microeconomic point of view

Chapter 1
Principles of Transformer Differential Protection and Existing Problem Analysis

1.1 Introduction

With the development of the electric power industry, large capacity power transformers are more and more widely applied in power systems. As the heart of the whole power system, the performance of the transformer directly affects the continuous and stable operation of the whole power system. In particular, once a modern transformer of large capacity, high voltage, high cost and complicated structure is destroyed by a fault, a series of problems will emerge, such as wide-ranging impact, difficult and lengthy maintenance, and great economic loss. Statistics show that during the years 2001–2005, the average correct operating rate of transformers 220 kV and above is only up to 79.97%, far below the correct operating rate of line protection (more than 99%).

Differential protection is one of the foremost protection schemes used in the power transformer. The theoretical foundation of differential protection is Kirchhoff's current law (KCL), which is applied successfully in the protection of transmission lines and generators. However, there are many problems when it is necessary to identify transformer internal faults under various complicated operation conditions [1]. From the perspective of an electric circuit, the transformer's primary and secondary windings cannot be treated as the same node, with the voltage on each side being unequal. Besides, the two sides are not physically linked. In terms of basic principle, transformer differential protection is based on the balance of the steady magnetic circuit. However, this balance will be destroyed during the transient process and can only be rebuilt after the transient process is finished. Therefore, many unfavourable factors need to be taken into account in the implementation of transformer differential protection:

• Matching and error of the current transformer (CT) ratio.
• Transformer tap change.
• Transfer error of the CT increases during the transient process of the external fault current.
• Single-phase earth fault on the transformer's high voltage side via high resistance.
• Inter-turn short circuit with outgoing current.
• The magnetizing inrush.

With respect to the scenarios listed above, solutions to the first five mainly rely on the features of the differential protection. The tripping resulting from the inrush current needs to be blocked for the purpose of preventing mal-operation. In this section, various problems in current differential protection principles and inrush current blocking schemes are firstly studied and discussed. Then, some novel principles for transformer main pr...

Table of contents

• Cover
• Title Page
• Copyright
• About the Authors
• Preface
• Chapter 1: Principles of Transformer Differential Protection and Existing Problem Analysis
• Chapter 2: Malfunction Mechanism Analysis due to Nonlinearity of Transformer Core
• Chapter 3: Novel Analysis Tools on Operating Characteristics of Transformer Differential Protection
• Chapter 4: Novel Magnetizing Inrush Identification Schemes
• Chapter 5: Comprehensive Countermeasures for Improving the Performance of Transformer Differential Protection
• Index
• End User License Agreement