The Electrical Transmission and Distribution Reference Book, popularly known as the TD Book, is a standard reference for utility engineers, and many colleges have adopted it as a basic textbook. Since its first appearance as a Westinghouse Electric Company publication, three generations of power engineers have used this book, both as a core technical reference and as a tutorial on the finer points of power delivery system design and operation. ABB Inc. has published the fifth edition. This edition not only continues the traditional, practical focus of the TD Books creators, but has added RD activities focused on meeting the needs of the 21st century with new equipment, designs, and technology.