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MAINLY concerned with the often costly and elementary mistakes occurring in some of the new generation of light rapid transit schemes the author believes that most stem from an ignorance of practical knowledge and experience from earlier generations of tramway and light tramway engineers. In this critique Dr. Hirsh, a North American traction engineer with a lifetime of experience in traction equipment takes an overview of some aspects of MER operation. |
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Having followed the adventures of the MER for many years, and also having managed to visit the Island many times, (despite the 7,000 mile round trip,) it might be appropriate to focus on some aspects of the past, present and future technical difficulties arising in terms of traction engineering, with the aim of hopefully providing some solutions. Editor and space providing these comments could be expanded to cover rolling equipment, fixed equipment, and infrastructural facilities. This section deals solely with motor and drive gear equipment. The present situation is that traction motor and equipment failure are increasing to the point where the limited maintenance and repair staff in their equally limited facilities, may be unable to keep pace. This is not a new situation for the MER for the same situation arose on the Snaefell Mountain Railway branch in the 1960-70 period, though for very different reasons. In this case, the 1895 motors were of an antique design, which almost certainly would not have justified deep renovation. The same basis does not, repeat does not, apply to the bulk of the equipment on the Douglas-Ramsey line. . The current situation is puzzling, as there seems to be ideas afoot to procure "replacement" motors of unknown sort for no necessarily good reasons. If the example of the Snaefell cares (where 4x 25 hp motors were replaced by 4x61hp units of such unsuitability that new trucks had to be built to accommodate them, and the cars are now only driven on series motoring points) is anything to go by, the experience may not be an altogether happy one. Obviously the Mickey Mouse engineers of the London Transport Board, who appear to have been culpably responsible for the Snaefell junket, are unlikely to be involved in any way again. Similarly it is unclear from this distance, if British Railways has any technical staff in the light of the APT debacle and the more recent experience earlier this year of equipment failures by the hundreds caused, not by the snow that arrived, but by culpably incompetent engineering. The critique that follows may help the MER to solve its own problems without recourse to generic experts. Many of the breakdowns now taking place are happening because the present traction motor equipments are being required to perform under conditions that are themselves damaging and which were probably not encountered until the last ten years or so. A half or two thirds of the weight of a traditional axle-hung motor rests directly upon the axle shaft, and if the wheel set is driving through poor quality track work, the motor will receive a thorough hammering; apart direct impact vibratory and percussive damage, there is also inconsistent commutation. Secondly the MER has some problems with the disposition of its sub-stations and feeder network, and very serious problems with the return circuit, since many of the track joints are not bonded. As a result the motors are required to struggle along for as long as they can under widely varying track voltage conditions, with resultant heating and overheating of windings. Traction motor design usually ensures a dust-free seal for the commutator, access or breech doors in the motor case, and the airflow arrangements through a motor are provided in such a way that the ingress of dust is minimised or eliminated. It is therefore surprising that the practice, evidentially of many years standing, to run many of the traction motors without the commutator covers clamped into place, has been allowed to continue. The response to queries elicited the explanation that by leaving the covers off moisture in the windings is allowed to escape. But if, and it is some if, an effective way of drying-out motors after storage in less than ideal conditions through the lengthy winter periods, then why are the covers not put back into position as soon as the procedure is deemed to be complete? Otherwise the moisture would get back inside, if the theory holds water at all. Far worse is that what else can get in with the cover off: the axle-hung or even frame mounted motor is splashed by rainwater snow and streetwash at other times breathing ferrous oxide particles swept of the head of the rails by the wheels, and doused by iron filings from the brake blocks. The cast iron brake shoes used by the MER probably have a new weight of around 21 lbs each and around 10 lbs when worn out, and removed for scrapping. Somewhere in between a double-truck car will have converted nearly 90lbs of cast iron into iron filings. A proportion of this must enter the motor under these circumstances, causing leakage, flashover and physical damage by the abrasive particles that reach wearing surfaces in contact. And iron filings of this nature can constitute a series risk of fire if ignited by a spark or flashover. Those brush yokes all examined closely had a coating of iron filings and the build-up in more than one indicated that internal cleanliness does not seem to be maintained by regularly swilling out the motor cases with compressed air nozzles and brushes. It is not clear if the brush box springs are regularly gauged but it seems unlikely. On one occasion the youth technician in attendance appeared to be sharpening the business end of a carbon brush, not even with the mandatory glass paper but with a piece of emery. Once a brush is bedded into its commutator, it ought to be left there until a replacement is necessary. If the business end of a carbon is being chewed, then attention is needed to either commutator surface or the brush holders. From further observation it appears that pinions fitted to traction motors are not thoroughly heated first (with oil or water), but are simply knocked into position and the nut run up tightly. No matter how tight the nut is drawn up, it is unlikely that loose pinions can be avoided. There also seems to be a fairly large discrepancy in rheostat groups' values, presumably through defective ribbons being bridged rather than replaced at once. Whilst he foregoing factors would themselves ensure that traction motors would not and could not be expected to achieve much mileage between breakdowns, even less may be being produced by the addition of other factors. On one occasion it appeared to take the combined efforts of four fully grown men to push a trailer, during the process of shunting the car round the trailer at Douglas. Instead of the unit being declared unserviceable, it was loaded and set sail, and it should come as no surprise that flashover occurred a matter of four or five hundred feet from the starting point. The crew of the next car to arrive tried to push their trailer but gave up and ran their motor through both crossovers instead. It is essential that every effort be made to ensure that tractive resistance is kept to a minimum. It is equally necessary to ensure that staff do not insist in running defective units. With any multiple-motor traction equipment efforts are customarily made to ensure that wheel diameters are kept within fairly close limits usually around half an inch, so that the effort required from each motor from a group is roughly similar. Yet one car of the 5-9 class had at one stage one set of wheels that must have been three inches larger than all the others on the same car. Quite apart from the strain on the motors, one wonders what effect this derangement must have had on brake and suspension performance. Lastly there was the light hearted suggestion from two of the platform crews that one MER car featured a mixed-bag of plain and roller-bearing armature shafts, but this suggestion can be safely laid to rest in the fairy tales of Manx folklore. To summarise therefore the incidence of traction motor breakdown is not primarily due to age and condition. The fact that most of these units continue to perform under these circumstances says a good deal for the excellence of their original design and manufacture. Breakdowns now occur because the units are being required to produce an unattainable level of performance in an increasingly difficult environment. By seeking new motors, the effects of problems are being tackled, not the problems themselves. So what, therefore are the obvious options available? The first and most economic option is to eliminate as far as is possible the factors that are responsible for the present level of damage and breakdown. To this could be added a programme of uprating and improvement. All of the MER's current traction motors represent the early years of traction technology and were designed and produced during a period of intense and rapid development. It might be said that by the late 1930's orthodox technology reached a zenith with lightweight, high-speed, high-efficiency motors. Motors supplied to the MER between 1902 and 1906 could be said to represent raw underdeveloped designs, and both the SEHC (Witting Eborall) and GE (USA) units might well prove to be capable of considerable development. Most of these were somewhat crudely converted to roller-bearing armature shafts about 12 years ago but no attempt was made to reassess the entire machine design with a view to upgrading and modernising. It should present no difficulty to an experienced traction engineer to devise a development scheme involving new field and armature windings (for half line voltage operations in series pairs) together with communicating pole and four-brush yoke gear with improved brush holders. Such a programme would be fairly costly but would produce machines of vastly improved horsepower rating, reliability, efficiency and very low maintenance obligation. The trails and testing of the first pair of prototypes would be beyond local facilities but there is at least one British university technical school, which has a sufficient grasp of what they are doing to be entrusted with this stage of the work. To this ought to be added the use of helical and resilient gearwheels. The helical traction gear became popular about 75 years ago, and widely superseded the straight-toothed spur gearing still in use on the MER. Straight toothed gears may be cheap in first cost but wear rapidly, require relatively frequent replacement and are extremely noisy. The motor nose suspension of the SEHC motors in the Brill trucks (and probably the Brush ones too) badly needs revision preferably by means of a compact resilient chevron rubber assembly; it would seem that the SEHC motors were not regarded by J G Brill as a standard equipment option and the neatness of the GE.60 suspension in the same trucks on cars 32-33 should be noted For the purposes of comparative study, other options may be explored. The abortive RTTS scheme for the MER included a plan to produce a suitable standard motor with locally produced welded steel box frames and other components brought in as original equipment as required. This is by no means an impractical option even now, although rather than use an adapted Metrovick design (as seemed to be the case with RTTS) it might be more appropriate to use a developed version of the GE.60 as the basis. A good deal more of the new and maintenance work could at one time have been carried out by the MER but another of the mysteries is the fact that although the works staff is said to include apprentice painters, traction apprentices (the most important of all) they no longer exist it seems. At the time of the 1957 nationalisation, one of the very important reasons put forward for the Railway's retention was the vocational training obligation inherent to the MER and in particularly armature winding. This, like cable jointing was and remains an internationally marketable skill. Coming back to where we came in, the last option is to try to seek out a suitable batch of suitable motors at a suitable price on the second hand market. This is by no means an easy answer. The potential field is not wide; in fact it is literally narrowed by the three-foot gauge of the track, which leaves about two feet eight and a half inches between the backs of the wheel bosses, to accommodate the motor and its gearwheel. There were never that many standard production traction motors built for such a narrow gauge and from memory only the GE.53 (usually 45hp for meter gauge), the GE.58 (usually 37hp for meter gauge), the GE.59 (usually 25hp and supplied in large numbers to Lisbon), the GE.60 (as on MER 32-33) and the GE.61 (usually 42hp for gauges of twenty-four inches upwards.) were prominent. In later years, the GE subsidiary in Britain, AEI produced the Metrovick MV 109 (usually 35hp but later developed to 50hp) and the MV115 (usually 45hp and again supplied to Lisbon in limited numbers). There were others too, but demand and production was limited. Certainly there is no known source today of suitable standard motors manufactured in sufficient number to provide new units at a reasonable cost to suit this track gauge. The option of using frame or even body-mounted motors might be considered, and might equally be rejected. The foregoing will provide and indication of the problems that confront the MER management. For the MER to have survived intact, as it is, to this day and age is something of a miracle, and credit must be given to those responsible for its existence. The trolley cars and the technology in use have now survived for far longer than a man's average life expectancy and have covered a period of between three and four working generations. In this context it is inevitable that the reasons why certain things were done in a certain way, may very well have come to be forgotten in the day-to-day routine of actually running and maintaining the equipment. Therefore the reasons for this critique, which are in no way to be considered critical, are self-evident. The technical expertise is still there, and any who doubt this might recall that a short time ago, as reported in MANX TRANSPORT REVIEW, the decision was taken to convert to the American OB carbon slipper trolley-head, which itself will save its own cost in the first year of operation, as events may have already proved. ("Unfortunately this scheme was not pursed" AMG) It might very well be that these units had been adopted almost nationwide in the US by the late 1930's and spread into almost universal use throughout the world, but it is worth remembering that no British electric tramway apparently even bothered to try it at any time in the ensuing half century. So full marks to the MER.
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