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Power Circuit Breaker Theory And Design By Flurscheim C.h.

The aim has been to provide an up-to-date analysis of the theoretical and practical problems involved in circuit breaker design. Circuit breakers present very special design problems because of the wide mixture of experience required.

power circuit breaker theory and design by flurscheim c.h.

Designers need to have an understanding of the parameters of power systems in which circuit breakers have a duty; of the physics of the arc produced during the interrupting process; of electrical engineering which is concerned with the insulation co-ordination and design problems; of mechanical engineering on which the performance and reliability of the operation of the circuit breaker depend; and of the need to meet cost-effective criteria.

Perhaps because of the wide range of techniques involved, there has until now been very little co-ordinated information available in a form suitable for use at universities and for providing subsequent guidance for postgraduate purposes; and for engineers who are concerned with design, system engineering or the use of circuit-breakers, who may need to have, in varying degrees, an understanding of the design problems involved in circuit breakers.

The approach in editing this book has been to invite eminent engineers concerned with circuit breakers to write chapters in areas that are of special interest to them. It has therefore been planned with chapters covering defined subjects. All of the authors are, or have recently been, occupying senior positions in the power circuit breaker industry.

C.H. Flurscheim, BA, FEng, FIEEE, FIMechE, FIEE, the editor and part-author of this volume, read mechanical sciences at Trinity College, Cambridge. He went to the Metropolitan-Vickers Electrical Co. as a graduate apprentice in 1927 and afterwards joined the staff of the Switchgear Engineering Department. During the war he was responsible for the development of a series of electrical components for aircraft, including under-carriage systems and miniature circuit breakers.In 1949 he was appointed chief engineer of the Switchgear Department, and in 1957 chief electrical engineer of the Metropolitan-Vickers Co., of which he was made a director in 1958. After the reorganisation of the company he became director of engineering of the Power Group and later director of Engineering of the AEI company.Mr Flurscheim has read many papers before the IEE and other technical institutions. He served as Chairman of the IEE Power Division in 1964-65.Apart from his lifelong interest in switchgear, he was, when younger, interested in automobile engineering, and designed one of the first fully automatic gearboxes for motor cars in 1933.

Dr. Charles Flurscheim's early interest in aircraft and mechanical engineering shaped his subsequent pioneering career. A graduate of Cambridge University and a college apprentice at the Metropolitan Vickers company, Flurscheim became an accomplished specialist in electronic switchgear and circuit breaker operations. During the second world war, Flurscheim designed vital electrical systems which increased British military aircraft safety. Subsequently he contributed to electrical and nuclear power station research. His high-voltage circuit breakers are used in power stations throughout the world.

Then in 1932 Metropolitan Vickers were training the Russians to design turbines, and we had a force of engineers there teaching and erecting turbines. I was then asked if I would go to Moscow to teach design of circuit breakers. This was in the days of Stalin, and I did not wish to go to Russia with him in charge, so asked for a salary Metropolitan Vickers would not accept. Fortunately this worked, for shortly after this Stalin needed something to distract attention from widespread troubles, and they invented suitable crimes and put all of our engineers in prison. It took the British government six months to extract them, and they were never the same again.

A couple of months later, instead of sending me to Russia to teach I was asked if I would go to General Electric, U.S.A. to learn how to design these circuit breakers. General Electric at that time had some financial interest in Metropolitan Vickers (instead of Westinghouse) and International General Electric ran a fellowship scheme whereby they paid for one engineer a year to go to General Electric and work there at their expense. I was selected, so in 1932 I went to Schenectady and to the General Electric circuit breaker factory in Philadelphia. The boss there was an outstanding engineer, David Chandler Prince, with a very intellectual wife. They decided they would train me; firstly on engineering, and secondly to be a bit more civilized!

Yes, the Depression was at that time. GE was working "part-time." The engineers were paid about two-thirds of their salary, but they still came in for the whole week. They were very loyal to the firm. I remember we worked thirty-six hours non-stop on some power station tests. I worked with two young engineers, Ed Poitras and Gene Bochne, who were quite outstanding in their abilities as electrical engineers. They understood the theory of all these designs much better than I did and it was a real education to work in this atmosphere. At the end of the year I went back to Metropolitan Vickers. My contract was to go to GE for a year but I had to come back to Metropolitan Vickers, so I returned to them.

No, not at all, and perhaps they supported this exercise as a form of training for me. As a result I became well known, and this may have contributed to my being promoted to be the boss of high voltage circuit breakers. I then spent several years developing high-voltage circuit breakers and doing research on the problems of voltage division on multi-break designs. Normally voltage division is controlled by capacitance, and if the contacts are enclosed in a steel tank full of oil, the capacitance distribution is very uneven, perhaps 85% and 15% on two breaks, so the second break is not much use, and the distribution can be even worse with more breaks. I carried out experiments on our short circuit test plant using cathode ray oscillographs to measure the actual distribution immediately after current zero at interruption. This disclosed that with plain break circuit breakers the post arc currents flowing were sufficient to overbalance the capacitance currents and provide a more or less equal distribution of voltage across all the breaks.

However, with arc control devices the interruption was far more effective, the post arc current was almost zero, and the voltage distribution followed closely that controlled by capacitance. This was used in support of a 66,000 volt single break design, made by one of our engineers, for a London power station, as the theoretical justification of building it with only one break, at a time when competitors' designs had several. Those circuit breakers operated in London for about fifty years. I received the John Hopkinson award from the IEE for my paper on this work. After that my work was largely electromechanical, developing new forms of circuit breakers, some based on Prince's ideas, but applied to British requirements. In these, the oil, instead of being pushed by the arc, was pushed mechanically across the arc. His famous Boulder Dam breaker had eight breaks in an insulation tube, with capacitance voltage control, and a very large spring mechanism which forced the oil across the arc. This breaker operated in three cycles from trip to interruption, on a 287,000 volt circuit. My impulse circuit breakers used compressed air mechanisms which I thought were simpler than the spring designs. When the war came, we were all put on war work...

I developed this, and it operated perfectly, protected by my circuit breakers, with electrical and manual operating time of about six seconds and it weighed less than the hydraulics it replaced. I went on the test flights for this and the pilot was so astonished with the quick retraction he started playing with it, as you could raise and lower while you were flying. The motor was only short-rated because you didn't need a continuous-rated motor for an undercarriage. I thought "Do I stop him doing this, or do I trust my circuit breakers?" I trusted the circuit breakers because I thought it would be disastrous psychologically to tell him he must stop. He went on operating and every now and then the circuit-breaker tripped, then the circuit-breaker would reset and he could continue. This unit worked safely for many years. Following these tests the Air Ministry said, "All right, we'll give you an order, full-scale for the Lincoln Bomber," which was being developed as the successor to the Lancaster, the primary bomber in the war. My design used a ball recirculating screw which is a screw system in which the load is taken by balls, and these recirculate and return themselves into the nut through a spiral circuit. This was invented about 1850, but it requires extreme accuracy to make it work efficiently. Its first successful operation in production appeared about 1939 in the steering gear of a car. I developed the first electrically driven recirculating screw applied to aircraft. It had to extend about three feet and swivel during this movement. I developed the screw thread form and the whole system from zero. It had a motor driven gearbox, and electrically operated brakes to lock the down and retracted positions, and an emergency compressed air operation; it retracted or lowered electrically or in emergency by compressed air in six seconds, had 90% efficiency, and weighed 10% less than the hydraulics system it replaced. The two stage development delayed this too long, and it only completed its type tests as the war ended. Metropolitan Vickers then gave up all its aircraft interests and except for a number of smaller ball screw actuators I had also developed, these never went into production.

I had dealings with customers as a director and earlier when I was designing equipment. The Metropolitan Vickers policy in my department, was that, as I designed the equipment, on important projects I should go out and sell it, because I knew more about it than the sales people did. So I traveled around the world selling circuit breakers - Canada, Australia, India, South Africa, Finland, Spain and of course England and Scotland. I also had dealings with important clients as Director when company policy was involved. I had a particular interest in man-machine relationships. When I was designing my undercarriage for the Lincoln bomber, I was associated with an engineer by the name of Roy Chadwick, who was the designer of the Lancaster and the Lincoln bombers, a brilliant artist as a designer. The Lancaster was designed originally with two Rolls-Royce engines, with twenty-four cylinders each, but these proved to be unreliable. He was told to change it to four twelve-cylinder engines. To change a bomber from two twenty-four-cylinder engines into four twelve-cylinder engines is a major task. The Lancaster came out of this the best bomber in the war. I had an association with this engineer and admired him greatly. Just after the end of the war, he was going on a test flight in one of his bombers and it crashed, and he was killed, and the reason was that the ailerons were connected in reverse, so when the pilot thought he was banking one way, it tilted the other way. This was possible because you could connect the ailerons in reverse, but a thing like that should be designed so that you can't connect it in reverse.


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