In this book no attempt has been made to discuss the subject of armature winding from theoretical or design stand-points. On the contrary, it is a compilation of practical methods that are used by repairmen and armature winders. In selecting the material a special effort has been made to include as far as possible details of those methods which have been found by actual experience to represent best practice in a repair shop of average size. In this work the writer has drawn from his own experience in repair work, from the experiences of repairmen and armature winders in large and small repair shops and manufacturing plants which have been visited, from descriptions of practical methods and the procedure followed in the solution of special problems as presented by practical men in technical journals.

The title of repairman as used throughout this book is one that a good engineer can bear with pride when he measures up to all its qualifications. Such an engineer is one who in in the majority of cases not only knows what to do in the case of an electrical trouble but just how to proceed to do that particular thing and who seldom guesses without a good percentage of the probabilities of being right in his favor. The main difference between the designer and the repairman is that the former must know what to do while the latter must know how to do it. A capable repairman combines both qualifications through years of experience.

When called upon to locate troubles in motors and generators, electricians and repairmen whose experience in this kind of work has been limited often find themselves wondering just what to do first. It is from just this viewpoint that the information on winding procedure and the hunting and correcting of troubles has been presented. That is, instead of discussing the fundamentals involved in any method of working out a repair problem, the actual problem or job as the case may be is discussed from the "how-to-do-it" standpoint. Then for each individual operation or procedure the applications of fundamental laws and rules are worked out. Considerable repetition of some details of similar methods will therefore be discovered in connection with information covering such procedure as the rewinding of machines of the same class but of different types. This has been considered advisable since a repairman should not be required to study a complete volume when details and information are desired at any one time on the procedure for a particular type of winding for a particular design of machine.

Liberal use has been made of practical data and practices in repair shops so as to combine the good features of a book of methods with handbook information covering these methods. If this book shall help young repairmen to absorb information that can be secured otherwise only through years of experience in handling one job after another, and if the older and more experienced repairmen find it a handy source of reference as a supplement to their own stock of information, then the aim of the author will be accomplished.

When material has been taken from the experiences of engineers and their recommendations on repair methods as published in the technical journals, it has been the aim to give credit to both the author and the journal in the paragraph, or section where the material is used. Special acknowledgment is made to A. H. McIntire, editor of the Electric Journal, for permission to make liberal use of information contained in several articles compiled at his suggestion and published in the Journal. This material has been incorporated in Chapters 3, 8, 9 and 11. To A. M. Dudley, engineer of the industrial division, Westinghouse Electric & Manufacturing Company, the author is also especially grateful for suggestions and for permission to use details of methods which he has developed for reconnecting and testing induction motor windings. This information appears in Chapters 9 and 11. The diagrams at the end of Chapter 11 have been selected from a series of eighty-one devised by Mr. Dudley and shortly to be published in a valuable treatise on "Connecting Induction Motors."



INTRODUCTION

Through the courtesy of the author of this book the writer has had the privilege of reading the proofs. I have found, with great delight, that the treatment of the subjects discussed is not only clear and easily understood but always from the practical man's standpoint. While the book will appeal strongly to practical men engaged in repair shop work, power station work and the maintenance of motors in industrial plants, it will also appeal, in the opinion of the writer, to students of electricity. Since the material presented in this book, which I dare say is unique in its field, has been obtained from actual practical experiences and outlines the practical remedies that have been applied by repairmen in the solving of puzzling problems, it will be of decided assistance to men who are in need of such practical help.

It is an "electrical book of knowledge," for in its pages readers will find answers to practically all armature winding questions and solutions of many of the repair problems that they will meet in practical work. The diagrams are clear and easily followed by the shop man and run in synchronism with the text. Theory with mathematical considerations have been resorted to only in a very few cases so that the reader of the book can make use of the information and understand the discussions of all phases of armature winding even though he may have only a limited knowledge of mathematics.

A book of this kind, in spite of the errors that are bound to creep in, is a very valuable asset to any practical man who de- sires to enlarge his own stock of knowledge by learning how other men in similar positions have solved the many electrical problems that come to the repairman.

The essential physical differences between a complete direct-current and a complete alternating-current armature winding is that the former is wound on the rotating member of the machine while the latter is wound on the stationary member and that the direct-current winding requires a commutator while the alternating-current winding does not. However, since the practical make-up and construction of windings will be discussed later for particular types of direct and alternating-current machines, the general theory of armature windings will likewise be taken up first for direct-current and then for alternating-current machines (see Chapter II).

Action of a Commutator. The emf and current produced in each armature conductor of a direct-current generator is alternating in character. It is the function of the commutator to deliver from the armature winding an electromotive force and current that is unidirectional, that is, such that one terminal will be always of positive polarity and the other of negative polarity. The commutator and its brushes accomplish this by being connected in series between the generator leads and the armature windings so as to reverse (in effect) the connections of the armature coils (connected to the commutator bars) with respect to the machine leads every time the emf and current induced in these coils reverse upon moving out of the influence of one pole into the field of the next adjacent pole. The alternating emf and current generated in the armature winding is thus rectified or commutated into a unidirectional emf and current.

In the case of an alternating-current generator no such rectifying of induced emf and current is necessary so that the coils or elements making up the armature winding can be connected directly together with the resulting terminals of the winding becoming the terminals of the machine.

Types of D.-C. Armature Windings. In general, armature windings are either of the open circuit or the closed circuit type. The latter is used in all modern direct-current machines, while alternating-current machines may have either open or closed windings. In the closed circuit winding of the direct-current machine the end joins up with the beginning or re-enters itself with the commutator tapped to the winding at equally distant points. In the case of open circuit winding of an alternating-current generator wound on the revolving member, the ends terminate in collector rings and the winding is thus open until closed by the brushes of the external circuit. When the winding is on the stator of an alternating-current machine the ends are joined through the load circuit. The following classification of closed circuit or direct-current windings may be made:

Direct-current windings (closed circuit).

1. Lap multiple or parallel.
(a) Single lap.
(b) Multiplex lap.

2. Wave series or two-circuit.
(a) Single wave.
(b) Multiplex wave or series-parallel windings.

Winding Parts and Terms. In formulas for armature windings and in laying out a repair job, certain terms are used which refer to parts of the armature winding, the armature core and details of the arrangement of the former in the slots on the surface of the latter. In what follows these terms are explained. In most cases they are used alike both in windings for direct-current and for alternating-current machines.

Armature Conductor or Inductor. That part of a wire which lies in an armature slot and cuts the magnetic lines of force or field flux as the armature rotates, is called an armature conductor or an inductor.

Winding Element or Section. That part of an armature winding which is connected between two commutator bars is called a winding element. In its simplest form a winding element consists of a coil of one turn of wire or two conductors. An element therefore must have at least two conductors but may consist of more than one turn of wire or even number of conductors.

Armature Coil. When a winding element consists of more than one turn of wire or two conductors, it is usually known as a coil and the winding is a coil winding as distinguished from a bar winding, where the conductors in the armature slots are copper bars.

From a mechanical standpoint an armature winding consists of a number of coils connected to a commutator in the case of a direct-current machine or connected together in the case of an alternating-current machine to form a series orgroup. Each coil may be made up of one turn of wire with each side forming one armature conductor or inductor, or a coil may be made up of several turns of wire or of copper strips. A classification of the different types and uses of armature coils which has been made by R. A. Smart (Electric Journal, Vol. VII, No. 6) is given in the accompanying table.


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