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October 29, 1937

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Mechanical And Electrical Engineering On Tyneside

In our last issue we dealt with the works of C. A. Parsons and Co., Ltd., and Pyrotenax, Ltd., which we recently visited. Below we give particulars of other works in the same district.

A. Reyrolle and Co., Ltd.

On June 14, 1886, now over 50 years ago, the late Mr. A. C. Reyrolle established a small switchgear workshop in London; and it is from that beginning that the present works of A. Reyrolle and Co., Ltd., have developed, with all their well-known and world-wide activities. In 1901, when the business was incorporated as a limited company, Mr. Reyrolle removed it to two or three single-storey buildings in Hebburn-on-Tyne. The area of the original site, on a small part of which these stood, was 5½ acres ; but extensions have gone on from time to time until the present total of between 78 and 79 acres has been reached. Very adequate canteens are provided, with electrically-operated kitchens, and many sports clubs are run by a sports management committee. The workshops and offices are of the most up-to-date kind in lay-out, lighting, ventilation, and heating, and the machine tools and other equipment are modern throughout.

Reyrolle and Co. are general manufacturing electrical engineers, specialising in switchgear of all kinds for all purposes. In addition to switchgear and ancillary apparatus for power stations, substations, mines, industrial works, and domestic installations, Reyrolle manufacture protective systems, cable sealing chambers and dividing boxes, electrical accessories, and other products that their specialised experience particularly fits them to turn out.

J. H. Holmes and Co., Ltd., now incorporated with Reyrolle, have their works adjoining the Reyrolle Hebburn New Town Works, and specialise in the building of electric motors and dynamos. The original firm of J. H. Holmes and Co. was established in 1883, and it is interesting and appropriate to recall that in 1884 the late Mr. J. H. Holmes invented the quick-break switch. Their first dynamo was made in 1885, and the earliest portion of their factory was built in Newcastle-on-Tyne in 1887. The firm was reorganised in its present form in 1928, and in 1930 the works and foundry were transferred to their present site.

An important step was taken at the beginning of 1934 in the formation of the Parolle Electrical Plant Co., Ltd., which associated C. A. Parsons and Co., Ltd., of Newcastle-on-Tyne. with the Reyrolle organisation, and therefore with that of Holmes also, so that it has become possible to supply from one source on the North-East Coast complete power station and sub-station main and auxiliary equipment.

Reyrolle and Co., instituted the manufacture of insulating; materials on Tyneside; this was a new industry for the district, and their interest in it was merged in the work of The Bushing Co., Ltd., which was formed in association with another well-known electrical engineering undertaking.

Since our last visit in 1933 the ground area covered by workshops and offices has increased by 41 per cent, and the total floor area by 71 per cent. In 1936 a large up-to-date shop with an area, of 34,000 sq. ft. was erected to provide suitable accommodation for the assembly of airbreak switchgear and the erection of control boards and distribution gear, and this shop is now being doubled in size. The enamelling section of this shop is a large airy building laid out in the most up-to-date manner, with spraying booths and ovens fitted with a conveyor for the continuous stoving of enamelled articles.

A new relay shop, put into commission early this year, enabled the assembly and testing of the various types of relays to be brought under one roof. The lay-out of this shop is of interest, in the provision of exceptional lighting, ample working room, arrangements for progressive assembly, and its own detail store. The test room, through which all relays pass and where they have their settings adjusted, is sectionalised for the various types, and vibration during testing is eliminated since the annexe containing the machines is insulated from the main test room. There is also in this department a soundproof chamber in which relays are tested to ensure silence of operation.

The use of bakelite for moulded insulators and to replace metal-parts grows continually, and a new shop is under construction to keep up with the demand. A store 12,000 sq. ft. in area for the sole purpose of receiving and storing castings became imperative. Castings on arrival by road or rail are checked, inspected and rust-proofed, before being stacked for issue to the machine shop.

The continued demand for metal-clad switchgear has made it necessary to provide considerable extensions to the machine shops. The existing New Town Works machine shop, with its stores and inspection department, covers 240,000 sq. ft., and machine shop No. 2, now under construction, covers an additional 57,760 sq. ft. All these extensions have necessitated the provision of greater heating plant, and the boiler houses at both works have been doubled; in addition, at the Hebburn works a large fuel store is being laid out with a new scraper plant for the handling of the coal used in the boilers.

An interesting product of A. Reyrolle and Co., Ltd., is class M switchgear, intended primarily for main power stations. New panels are generally similar in over-all design to class M switchgear first installed in a number of large power stations nearly 20 years ago, but improvements in fundamental parts, and hence in performance, have been introduced to keep pace with the increasingly stringent demands of modern service. The panel is of the duplicate bus-bar type, with oil-immersed bus-bar selectors, and all the insulation, as well as all the contacts, are immersed in oil or compound. The circuit breaker is of the vertical draw-out type, the lifting being done by means of a crane. The cable and bus-bar isolating switches, the current transformers, and the voltage transformers are in tanks capable of being lowered quickly for the purpose of inspection and maintenance. Phase separation is complete throughout, and hence any faults in the switch house are to earth only. The circuit breaker is solenoid-operated and capable of closing on maximum fault conditions, and has been short circuit tested up to 2,000,000 k.v.a. at 33,000 volts. Compensators are provided to prevent any tendency to reclose owing to possible tank pressure. The contact mechanism has recently been modernised by the addition of turbulator arc-control devices, with resultant diminution of arcing time and increased life of contacts and oil. The turbulators are fixed by breech-block mountings, introduced by Reyrolle for the purpose of affording quick and easy means of removal for inspection of contacts and maintenance. The bus-bar casings and cross connections are made of non-magnetic cast iron, which has a high melting point in case of fire. Interlocks are provided to guard against any incorrect sequence of operation, and it is not possible to expose any conductor unless it is dead and earthed.

When closing manually a low-voltage heavy-duty oil circuit breaker on a fault, the electromagnetic forces on the plunger bar are sometimes such that the operator may have great difficulty in getting the breaker closed, or, even if he is physically able to close it, he may hesitate in doing so, and fail to close smartly and definitely. Under these conditions the arc may persist until the trip coil operates and allows the circuit breaker to open ; and the arcing time may be such that dangerously high tank pressures result, with possible danger to the operator. In addition, the operator's arm is subjected to shock from the handle trying to reverse its direction.

In order to overcome these difficulties, an impact-trip device has been developed, consisting of a spring fitted in the handle gear between the operating handle and the holding toggle, and initially compressed so that when the operator closes the circuit breaker under normal circuit conditions, the spring is not deflected. When it is closed on a fault, however, the spring is compressed further, and trips out the circuit breaker ; and since the mechanism is of the trip-free type, the handle moves to the "on" position and the operator's arm is not subjected to any appreciable mechanical shock. The more important advantage, however, is that the arcing time is considerably reduced, and the operation is made perfectly safe.

A circuit breaker with manually operated closing mechanism ought usually to be operated without any hesitation on the part of the operator, and as rapidly as possible, particularly over the later portion of the closing operation when the contacts are actually making circuit. To avoid difficulties arising in such ways with hand operation of heavy-duty oil circuit breakers, a quick-make mechanism has been developed for class C switchgear. It takes the form of a spring-operated device added to existing handle gear. The mechanism is interlocked to prevent inadvertent operation, and also to prevent damage of the operator under all conditions. The spring is of the compression type, and is charged by means of a lever operated on the ratchet principle, it being impossible to release the spring for closing the circuit breaker unless the ratcheting handle is in the down position after having completely charged the spring. A dashpot is provided to prevent damage of the mechanism when the spring is released under trip-free conditions. Auxiliary switches are provided for remote indication and other requirements. The mechanism is such that it can be tripped electrically from a remote point, and thus the necessity of entering the switch chamber during the closing operation may be avoided. Further, it can, if required, be arranged for charging by means of a shaft through a wall between the operator and the switchgear, and under these conditions the switch chamber need not be entered except for inspection.

The pole-mounted oil circuit breaker with auto-reclose mechanism has been developed in response to the demand for an automatically reclosing switch where no secondary supply is available for the purpose. The circuit breaker is of the ordinary two-break type closed through a trip-free mechanism, and it may be tripped either by series trip coils mounted with their mechanism in oil or by current transformers mounted in the compound-filled top plate. It can be provided with bushings at each side for open type connections or cable boxes for cable connections, and the settings of the over-current device can, if required, be adjusted from the outside, without lowering the tank : but tank-lowering mechanism can be supplied if required. The circuit breaker is closed by means of a weight suspended from a chain passing over a chain wheel, which drives a cam and closes the switch. When the circuit breaker trips out, the escapement type time-lag device allows the weight to fall and reclose the breaker at any predetermined interval from 10 to 60 sec.

The rewinding of the weight and the tripping of the breaker are both done by one rod down the side of the pole. This rod is normally padlocked, and rewinding is brought about by removing the padlock and pulling the rod down until it reaches the stop, resetting it to its previous position and repadlocking.

The new electrical testing and research laboratory buildings are at present being built at the southern end of the Hebburn works on a site near the existing laboratory, and facilities for further extension are available, which will increase the laboratory area from 4,860 sq. ft. to 13,800 so. ft. Bay 1 is primarily designed for heavy-current work, such as heat tests, and heavy current development work in connection with protective systems. The five 6-volt 1,000 amp. heavy current testing transformers and the 50-cycle artificial pilot at present in the old laboratory will be transferred to this bay, and other transformers and equipment will be added as they are required. The effective test areas will be increased from 810 sq. ft. to 2,070 sq. ft. A silence chamber is provided at one end for tests of insulators and the like when absolute quiet is necessary. This chamber has been specially designed in conjunction with experts on soundproofing. Double doors are provided, and there is a special soundproof trapdoor in the roof through which heavy equipment can be lowered by means of an overhead crane.

Bay 2 is primarily designed to house an impulse generator with its auxiliary equipment, a cathode ray measuring device, and a large tank for oil to be used in testing. The impulse generator, which is of the well-known Marx circuit type, is designed for 1,500,000 volts. A one-metre sphere gap will be erected alongside of the oil tank. The oil tank is being placed in a pit, and has required special consideration in design, the top being kept large (24 ft. in diameter) to restrict surface flashover, whereas the bottom is reduced where possible in order to save oil.

Bay 3 is divided up into five enclosures equipped principally for various types of insulation testing.

The existing electrical laboratory was built in 1924, and was at that time one of the most modern in Great Britain. During succeeding years, many additions and modifications have been made, culminating in the extensions described above.

The chemical and physical laboratories occupy 2,000 sq. ft. The chemical laboratory is essentially engaged in research into new-materials, and in the chemical testing of materials already in use to see that they comply with the purchasing specifications, while the physical laboratory enables physical characteristics to he investigated. The removal of apparatus to the new laboratory will give more space for chemical and physical work in future. The same building contains rooms occupied by the works photographic section.

The Hebburn Short-circuit Testing Station.

It is recognised as essential that all electrical equipment for use in mines should be tested for flameproofness by a recognised authority, such as the Mines Department, whose testing station is at Buxton. A certificate issued by such an authority is a guarantee that the equipment has passed the most stringent tests to prove that any flame inside the enclosure will not ignite external explosive gases. This safeguard is of paramount importance, but it is equally important that users should be certain that all circuit-breakers installed have been tested to prove their ability to perform satisfactorily under the severest conditions of operation. To install an electric motor without the knowledge backed by test that it will deliver its rated horse-power is unthinkable, but it is still common for users to install switchgear without any assurance that it will perform satisfactorily at the ratings stated on the nameplate.

The duty of a circuit-breaker, apart from normal-load switching, is to isolate automatically and rapidly, by the opening of its contacts, any excess current due to an overload or short circuit. It may also be closed on a circuit in which a fault exists. Ratings are assigned to a circuit-breaker stating the currents it is capable of making and breaking at a stated voltage, and a circuit-breaker should never be installed to protect a circuit in which the available short-circuit currents are greater than the assigned ratings. The available short-circuit currents depend upon the amount of generating plant connected to the system, and the impedance of the circuit or circuits between such generating plant and the position of the fault.

The effect of a fault-current passing through a circuit-breaker is twofold. First, it produces heat in the conductors and contacts and subjects them to mechanical stress, both heat and stress varying with the square of the current. The maximum current occurs during the first cycle of short circuit. Thus the heating and the mechanical stress are greatest when the circuit-breaker is closed on a short circuit. If the maximum current exceeds the making capacity of the circuit-breaker, the contacts may weld, and the current-carrying parts and the mechanism may be distorted. Secondly, when the contacts open an arc is formed, the heat of which, acting on the oil used as an insulating medium, generates gas and a rise of pressure occurs in the enclosure. The volume of gas generated varies with the amount of current in the arc and the time the circuit-breaker takes to extinguish the arc. This time varies with the voltage of the circuit and the efficiency of the circuit breaker. In an inefficient circuit-breaker, the arc duration may be prolonged and pressures set up that may distort the enclosure (and so render a mining type circuit-breaker non-flameproof), or even under extreme conditions cause total destruction. Since such destruction may be accompanied by an explosion and emission of flame, it is essential that all circuit-breakers should be tested to ensure satisfactory operation when making, carrying, and breaking short circuits.

In order to carry out the tests, special testing stations are required capable of reproducing the conditions of short circuit, and therefore including equipment for generating, controlling, and recording short-circuit currents and voltages, and various ancillary equipment for measuring and recording other data connected with the tests — for example, pressure-rises in tanks, distortion of enclosures, and so on. There are three such short-circuit testing stations in Great Britain, erected by switchgear manufacturers, and others are in course of construction.

The Hebburn short-circuit testing station, built by A. Reyrolle and Co., Ltd., in 1929, has been in continuous use since then.

Since our 1933 visit another generator, No. 2, and another test-bay unit, No. 2, have been added. The testing station thus consists of generating plant and two test-bay units, each including workshop facilities for preparing and dismantling apparatus before and after test, accommodation for analysis, a place for conferences, and other similar offices. The output of the testing station cannot be stated in simple figures other than by its initial symmetrical output of 2,000,000 k.v.a. The testing station is at all times operated by a highly trained staff. When doing work for Reyrolle, it operates under the wing of their technical and research department. It is also operated, however, under the associated company known as The British Short Circuit Testing Station, Ltd., who let the testing facilities to anyone in the industry requiring private tests.

The testing station is capable of testing, at voltages from 440 up to 132,000 volts, circuit-breakers of appropriate short-circuit ratings up to 1,500,000 k.v.a. Tests are made in accordance with relevant British standard specifications. No specification has yet been issued for the short-circuit testing of mining switchgear, and until such a specification is available it is the practice at this testing station to test mining and industrial circuit-breakers to the standards laid down by the International Electrotechnical Commission in their specification for alternating current circuit-breakers, which has recently been approved by the national committees as a basis for their own specifications. This specification requires that tests should be made under conditions that ensure the reproduction of the worst service conditions.

Tests are made not only at the rated making capacity and breaking capacity of a circuit-breaker, but also at values ranging from 10 per cent, of these ratings upwards. Further, although in accordance with the specification it is only necessary to test up to the rated making capacity and breaking capacity, tests at higher values are made at Hebburn to ascertain the factor of safety; if this is insufficient for switchgear intended for use under conditions requiring it to be flameproof, it, is the practice to de-rate the switchgear accordingly, for example, a circuit-breaker rated at 25,000 k.v.a. for non-flameproof service may be de-rated to 15,600 k.v.a. for flameproof service.

A certificate of rating is issued by the short-circuit testing station for a circuit-breaker that has passed its tests, and users who purchase equipment having such a certificate may be assured of reliable operation under short-circuit conditions up to the making capacity and breaking capacity ratings specified in the certificate.

The rapid advances made during recent years in the art of electric arc welding have made it a process of great practical importance throughout the engineering industry in all its branches, and in none, perhaps, is this more noticeable than in shipbuilding and ship repairing. In an endeavour to keep ahead of these developments, J. H. Holmes, and Co., Ltd., have specialised in the manufacture of electric arc welding equipments for many years, and have designed them in collaboration with expert welders, so that they embody the knowledge gained from wide experience in welding shops as well as from the large number of sets supplied to shipyards, railway shops, and general engineering works in Great Britain and abroad.

An important feature in the success of Holmes multi-operator welding equipments is the absence of interference between welders, and actual operating experience has shown that even with a two-operator equipment, where the maximum interference might be expected, there is in fact no interference at all.

In addition to multi-operator sets, Holmes manufacture a comprehensive range of single-operator sets suitable for any kind of prime mover, such as an electric motor or an oil engine, with outputs from 150 amp. up to 350 amp. These single-operator equipments have a drooping characteristic, and are self-stabilising with a practically instantaneous voltage recovery.

Although Holmes have given special attention to some specialised products, they continue to manufacture standard motors and generators for the usual industrial purposes, and carry large stocks to enable them to give quick delivery. The smaller sizes in their range of variable speed commutator a.c. motors, developed primarily for the printing trade but suitable, of course, for other industrial purposes, have been re-designed, and one special feature is that they have a small and squat outline, which makes them particularly adaptable for short-centre drives.