J & P Transformer Book

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The historical basis of the book continues to highlight British experience, but these changes in the thirteenth edition together with updates of IEC reference Standards documentation and inclusion for the first time of IEEE reference Standards, provide a more universal flavor to the volume and a recognition that the transformer industry and market is truly global in scale. The book was last updated in by Martin J.

Heathcote, and in preparing this edition, Mr. Heathcote has continued to draw on his contacts and experience in both the manufacturing and user arenas to provide relevance and value to the industry. Upon graduating from the University of Sheffield in Electrical Power Engineering, his career began immediately with the Transformer Division of Ferranti Limited, where his training led to a position as a transformer designer.

After successfully working on designs up to kV, Mr. Subsequently, since he has provided consulting services specializing in power transformers, primarily working for utilities. Transformer talent is at a premium today, and all aspects of the power industry are suffering a diminishing of the supply of knowledgeable and experienced engineers. Manufacturers still retain highly capable transformer expertise, but their depth of engineering manpower resources is sometimes reduced — perhaps mistakenly - by market economics.

Utilities have difficulty retaining young engineers in the field long enough to develop expert status, and in many cases transformer engineering is outsourced. From my perspective, maintaining appropriate power systems and equipment expertise is necessary for a utility to support the reliability, availability, and quality of service goals demanded by energy consumers now and into the future.

As a result, there is a drive in the industry to capture knowledge and experience before it is lost. While familiar with the stature of the book when Mr. I will enjoy reviewing it often as my career in this interesting field continues, and I trust you will find it a useful addition to your technical library. The design and manufacture of transformers is not cutting edge technology, and compared with many fields of engineering, progress is slow and change is gradual.

It is also true that in many branches of the industry the book has become well known and widely respected, and many owners will not consider replacing their trusted old edition. Indeed, many transformer engineers swear by copies handed down to them from older colleagues. After all, transformers are expected to have long lives so that many that are currently in service could have been designed 20 or 30 years ago using practices that have long been considered out of date.

True, but the industry does change and the Twelfth edition certainly did appear at a time of great change. Electricity supply privatisation in the UK was beginning to have a significant impact on procurement strategy; the single European market was becoming well established, and its effects strongly felt.

There have been many mergers in the industry; many well known and well respected manufacturers in Europe and the USA have disappeared. The result is that the industry has become truly an international one, national standards are disappearing and international standards, in particular those of the IEC, are becoming dominant.

The impression is that the change has been appreciated by readers. The Twelfth edition was, however, written from a UK viewpoint, and with UK experience and practices in mind. This Thirteenth edition has aimed to be less parochial and recognize that, practices may differ in different parts of the world; that there is often more than one way of resolving a problem; and the way that is familiar might not necessarily be the only way.

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That view has been acknowledged primarily by reducing the references to British Standards with which a high proportion of readers will not be familiar, and replacing these with European and International Standards. Though less extensive than the work involved in the production of the previous, Twelfth, edition, there is still a large amount of effort involved, which would certainly not have been possible without their help.

Because the main substance of the Twelfth edition remains and because, without that the Thirteenth edition would have come to nothing, a great debt of gratitude is still owed to all the friends who assisted in its preparation; these include W. Jim Stevens who read every word of the Twelfth edition and provided invaluable criticism and comment; to Professor Denis Allan, FEng, from whom much help and guidance was received; to Dr. Grateful thanks are also offered to many organisations who freely provided assistance, as well as data, diagrams and photographs which enabled the chapters to be so generously illustrated.

In the relatively short time since the Twelfth edition was produced a significant number of the above have disappeared or been absorbed into larger groupings. Finally, despite the extensive revision involved in the production of the Twelfth and Thirteenth editions, some of the work of the original authors, H. Morgan Lacey, the late S. Stigant, the late A. Franklin and D.

Franklin, remains; notably much of the sections on transformer testing, transformer protection, magnetising inrush, parallel operation, and third harmonic voltages and currents, and for this due acknowledgement must be given. Appendix 6: A symmetrical component study of earth faults in transformers in parallel. Appendix 7: The use of finite-element analysis in the calculation of leakage flux and dielectric stress distributions.

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Appendix 8: List of national and international standards relating to power transformers. The invention of the power transformer towards the end of the nineteenth century made possible the development of the modern constant voltage AC supply system, with power stations often located many miles from centres of electrical load. Before that, in the early days of public electricity supplies, these were DC systems with the source of generation, of necessity, close to the point of loading.

Pioneers of the electricity supply industry were quick to recognise the benefits of a device which could take the high current relatively low voltage output of an electrical generator and transform this to a voltage level which would enable it to be transmitted in a cable of practical dimensions to consumers who, at that time, might be a mile or more away and could do this with an efficiency which, by the standards of the time, was nothing less than phenomenal.

Todays transmission and distribution systems are, of course, vastly more extensive and greatly dependent on transformers which themselves are very much more efficient than those of a century ago; from the enormous generator transformers such as the one illustrated in Fig. For a reasonable understanding of the subject it is necessary to make a brief review of transformer theory together with the basic formulae and simple phasor diagrams.

A power transformer normally consists of a pair of windings, primary and secondary, linked by a magnetic circuit or core. When an alternating voltage is applied to one of these windings, generally by definition the primary, a current will flow which sets up an alternating m. This alternating flux in linking both windings induces an e.

In reality, the current which flows is the transformer magnetising current. In the secondary winding the induced e. If a load is connected to the secondary winding which permits the flow of secondary current, then this current creates a demagnetising m.

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To restore the balance an increased primary current must be drawn from the supply to provide an exactly equivalent m. Since there is no difference between the voltage induced in a single turn whether it is part of either the primary or the secondary winding, then the total voltage induced in each of the windings by the common flux must be proportional to the number of turns.

Thus the well-known relationship is established that:. Hence, the voltage is transformed in proportion to the number of turns in the respective windings and the currents are in inverse proportion and the relationship holds true for both instantaneous and r. This is normally expressed in the form. The above expression holds good for the voltage induced in either primary or secondary windings, and it is only a matter of inserting the correct value of N for the winding under consideration.

Figure 1. Usually in the practical design of transformer, the small drop in voltage due to the flow of the no-load current in the primary winding is neglected. Assumed turns ratio If the voltage is sinusoidal, which, of course, is always assumed, K is 4. For design calculations the designer is more interested in volts per turn and flux density in the core rather than total flux, so the expression can be rewritten in terms of these quantities thus:. It is then an easy matter to determine the number of turns in each winding from the specified voltage of the winding.

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Mention has already been made in the introduction of the fact that the transformation between primary and secondary is not perfect. Firstly, not all of the flux produced by the primary winding links the secondary so the transformer can be said to possess leakage reactance. Early transformer designers saw leakage reactance as a shortcoming of their transformers to be minimised to as great an extent as possible subject to the normal economic constraints.

With the growth in size and complexity of power stations and transmission and distribution systems, leakage reactance — or in practical terms since transformer windings also have resistance — impedance, gradually came to be recognised as a valuable aid in the limitation of fault currents. The normal method of expressing transformer impedance is as a percentage voltage drop in the transformer at full-load current and this reflects the way in which it is seen by system designers.

For example, an impedance of 10 per cent means that the voltage drop at full-load current is 10 per cent of the open-circuit voltage, or, alternatively, neglecting any other impedance in the system, at 10 times full-load current, the voltage drop in the transformer is equal to the total system voltage.

Expressed in symbols this is:.

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J and P Transformer Book, 13th edition by Ray Arnold & Martin Heathcote

Of course, R and X may themselves be expressed as percentage voltage drops, as explained below. Occasionally some transformers are deliberately designed to have impedances as high as More will be said about transformer impedance in the following chapter. The transformer also experiences losses. The magnetising current is required to take the core through the alternating cycles of flux at a rate determined by system frequency. In doing so energy is dissipated.

This is known variously as the core loss, no-load loss or iron loss. The core loss is present whenever the transformer is energised. On open circuit the transformer acts as a single winding of high self-inductance, and the open-circuit power factor averages about 0. The flow of load current in the secondary of the transformer and the m.

The flow of a current in any electrical system, however, also generates loss dependent upon the magnitude of that current and the resistance of the system. Transformer windings are no exception and these give rise to the load loss or copper loss of the transformer. Load loss is present only when the transformer is loaded, since the magnitude of the no-load current is so small as to produce negligible resistive loss in the windings.

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Load loss is proportional to the square of the load current. The total current in the primary circuit is the phasor sum of the primary load current and the no-load current. Ignoring for the moment the question of resistance and leakage reactance voltage drops, the condition for a transformer supplying a non-inductive load is shown in phasor form in Fig. Considering now the voltage drops due to resistance and leakage reactance of the transformer windings it should first be pointed out that, however the individual voltage drops are allocated, the sum total effect is apparent at the secondary terminals.

The resistance drops in the primary and secondary windings are easily separated and determinable for the respective windings.

The reactive voltage drop, which is due to the total flux leakage between the two windings, is strictly not separable into two components, as the line of demarcation between the primary and secondary leakage fluxes cannot be defined. It has therefore become a convention to allocate half the leakage flux to each winding, and similarly to dispose of the reactive voltage drops.

In fact the sum total effect is a reduction in the secondary terminal voltage. The resistance and reactance voltage drops allocated to the primary winding appear on the diagram as additions to the e.

J and P Transformer Book - A Practical Technology of the Power Transformer (13th Edition) - Knovel

Of course, the drops due to primary resistance and leakage reactance are converted to terms of the secondary voltage, that is, the primary voltage drops are divided by the ratio of transformation n , in the case of both step-up and step-down transformers. In other words the percentage voltage drops considered as occurring in either winding remain the same. To transfer primary resistance values R 1 or leakage reactance values X 1 to the secondary side, R 1 and X 1 are divided by the square of the ratio of transformation n in the case of both step-up and step-down transformers.

Voltage drops divided between primary and secondary sides. Voltage drops transferred to secondary side.