THE COLLIERY GUARDIAN AND JOURNAL OF THE COAL AND IRON TRADES. Vol. CXVI. FRIDAY, DECEMBER 20, 1918. No. 3025. Notes on Three=phase Electric Haulage Equipment. By L. FOKES The simplicity of the ordinary application of three- phase motors to surface or underground haulage plant leaves little to be desired, and, given reasonable attention, such installations are quite as reliable as the steam and compressed air engines which they are gradually replacing. However, simple as this type of haulage equip- ment really is, due consideration must be given, when laying down plant, to the work to be performed and the general conditions under which it will operate, both from the mechanical and the electrical stand- point. The selection of gear should rest ultimately with the colliery staff, and not be left entirely in the hands of the manufacturer to supply equipment which may or may not suit the conditions under which the work will have to be done. In the earlier appli- cations of motor drives to hauling, too little study was devoted to the subject, and it was generally expected that such plant would withstand the same treatment as an engine without sustaining injury. Hence the size of motor was often restricted in order to reduce the initial cost of the equipment, with the conse- quence that results were often unsatisfactory. It does not matter if an engine is brought to a stand- still by an excessive load, but in the case of a motor, either the circuit must be automatically disconnected or the motor will burn out and be destroyed. Hence it has been proved—in many cases at no inconsiderable cost—that to put in a motor which is too small for the work is only to cause needless inconvenience and loss of output, results which rapidly offset any saving which may in the first place have been effected by the installation of the cheaper equipment. After the approximate horse-power of a machine necessary for a given haulage plane has been worked out, a margin of at least 25 per cent, should be allowed for con- tingencies, It is often emphasised that to instal motors which are too large for the work required of them implies unnecessary reduction of the power factor of the power supply. This is good advice when applied to motors which run continuously at full load, and should be strictly adhered to : but in the case of main-and-tail haulages, a considerable part of each shift is taken up by shunting or landing journeys, . besides many other operations which call for reduced speed and frequent stoppages. It is therefore impossible to run at full load for more than a few minutes together, and as the power factor is low both at reduced load and speed, the advantage above referred to cannot be utilised. Besides, where a steep gradient forms merely a small part of a haulage plane, the size of motor must be sufficient, plus a small percentage of overload, to take the full journey up the gradient, and consequently will be more or less working considerably under its rated output at all other times. Of course, it must be recognised that conditions of haulage vary so widely that local circumstances must always be the dtermining factor, but those who appreciate the onerous duties of the average haulage motor, and expect continuity of service with the minimum of breakdowns, understand the necessity of providing an ample reserve of power. These remarks are concerned more particularly with the plant itself, assuming the output has already been decided upon. Haulage Room. Not the least essential condition to the satisfactory operation and maintenance of plant is the haulage room. Too often this is cramped and the head room extremely small, with little or no facilities for lifting heavy machinery. When plant is installed under such conditions it always works at a disadvantage, and, owing to the difficulties of dismantling for varnishing windings, or thorough examinations, those responsible often prefer to allow plant to run as long as it will, and disturb nothing until compelled to by a breakdown. Sufficient room should always be pro- vided for readily removing the rotor or, where th? stator of the motor is in two halves, for removing the top half for examination or repairs. The ventilation of the haulage room is also import- ant, as it enables the heat generated by the motor and regulating resistances to be readily carried off. Motor. The selection of a suitable motor requires some con- sideration. The haulage gear, where possible, should be adapted to the speed of the motor, and not the motor to the haulage gear. The slow speed type of machine for haulages re- quiring, say, 100 horse-power and over, makes an ideal drive when coupled to the haulage drums through a single reduction gear. Of course, the slow speed motor is more expensive, but it is also more reliable in that the weight of the rotor relieves the machine of much vibration, and the wear on bearings, when given ordinary attention, is extremely small, whilst the possibility of getting the rotor down on the stator without ample warning is remote. If the haulage room is such that suitable protection can be afforded, the open type of motor is desirable, owing to the accessibility of the windings for cleaning or varnishing, which can usually be carried out with- out having to dismantle any part of the motor. The bearings on such motors can be supported from the lower part of the machine, and provision made for adjusting the air gap in order to compensate for any slight wear in the bearings. The latter may be of the split type, enabling bearings to be renewed without removing the end shields or otherwise dis- turbing the motor, excepting the removal of the bear- ing covers and the lifting of the rotor sufficiently to take the weight off the bottom half of the bearing for the latter to be rolled over on to the top of the shaft for removal. Slip Rings and Brush Gear. Unlike a motor fitted with short-circuiting and brush-lifting device, as used on constant running machines, a haulage motor always has its slip-rings and brush gear in use. These should always be enclosed on machines working underground, in order to prevent open sparking and to keep people from the danger of coming into accidental contact with them when the motor is running at reduced speed. Fig. 1. Supply. ------- Gy—------- nniii j.... ‘•• I tiiiiu I IlliH r—-..1 Fig. 2. A common practice is to enclose the slip-rings so thoroughly as to prevent their being seen at all until the cover is removed. Should sparking occur between the slip-rings and brushes in such cases, no warning is given until both slip-rings and brushes become so damaged as to cause a considerable delay, if not a complete shut down for a day or tw’O in order to renew the parts. This may, however, be avoided by making a part of the brush gear enclosure of copper gauze, such as is used in the ordinary miner’s lamp. The parts over which the gauze is placed should be limited in extent for mechanical reasons, but sufficient open- ing should be provided to enable arcing of any kind to be seen from outside without having to remove the enclosure. As regards brushes, it is usual to provide carbon brushes, but a considerable quantity of copper gauze brushes are also in use, although these are not so successful for motors ■which reverse, owing to their liability to buckle if the rings become a little rough. Even the carbon brush leaves much to be desired, as its comparative high resistance often raises the temperature so high during heavy loads as to damage the insulation of the brush gear and slip-rings. This is aggravated by the gear being so confined, which prevents the radiation of heat. In this connection the use of copper morganite brushes has proved very beneficial, as their high con- ductivity greatly reduces the slip-ring temperature at all loads; in fact, these are cases where the tem- perature due to carbon brushes has been sufficient to char the brush gear, but the substitution of copper morganite for the carbon brushes reduces the rise in temperature to practically nil in comparison with the surrounding air, even under heavy load. To quote a case in point, a large machine has been running about five years -with copper morganite brushes without the rings or brushes being disturbed in a single instance, whereas this same machine had its brush gear ruined by the heat generated by carbon brushes before ths change was made. Control Equipment. Figs. 1 and 2 show the general lay-out of a three- phase haulage plant using metallic, resisters in the rotor circuit. In fig. 1 the rotor has two distinct windings, and therefore requires four slip-rings, while in fig. 2 the rotor has a three-phase winding. Isolating Switch. This is indicated in the lower part of each of the figures referred to, and should take the form of an oil switch of the “draw-out” type mounted on a cast iron pillar. The switch should be provided with overload trip coils on two or three phases, depending on whether the neutral point of the supply is insu- lated or earthed. Where only two trips are employed, it is possible to provide a no-voltage release device, but this is not really necessary, since the haulage driver is always at hand when the motor is working, and can bring the controller immediately to the “off” position if the power supply becomes interrupted. An ammeter should always be provided, for by it the driver can tell if the journey leaves the rails, or if any obstruction exists, besides having a check on the performance of the motor itself. : The current transformer for the .ammeter is usually arranged for in the switch, the secondary leads are brought out to enable an exten- sion to be made, and the meter is placed in a con- venient position for the driver. Trifurcating boxes should be provided on the switch pillar to receive the armoured cable coming from the supply, and also that leading to the reversing switch from the pillar. It will usually be found advantageous to employ time limits on the overload trip coils, as there is a tendency, where these are absent, for the switch to “climb the setting.” That is to say, the continual switching “in” and “out,” common to all main-and-tail haulage, causes the trips to slip by degrees until they lose their hold on the switch, and the latter then opens, without any warning, in con- sequence of vibration. When this occurs while run- ning at full speed on a sharp incline, the driver may be taken by surprise and an accident result. The provision made for altering the trip setting on switch gear is usually inside the switch, and cannot be reached without removing the oil tank. This is in- convenient, and the trips should be arranged for adjustment from the outside. Such provision should be fitted with a suitable locked cover, to prevent unauthorised persons interfering with the setting. Reversing Switch. This switch is of great importance, and should be of a most reliable design in order to withstand the onerous duty expected of such switchgear. When a haulage works a district which necessitates a great deal of shunting, the reversing switch may be operated, first in one direction and then in the other, some hundreds of times in a single shift, and as the stator windings of a motor are highly inductive, the arcing at the contacts is of a most destructive nature. Many forms of contacts have been designed in order to reduce the burning, but none will -withstand the wear for long without renewal or filing up. A feature common to all is the provision for both making and breaking the circuit by means of auxiliary contacts which close before, and open after, the main current- carrying contacts, and thus relieve the latter from any arcing effects. Auxiliary contacts of the roller type have given much satisfaction, and are doubtless one of the best forms of contact. They consist of loose roller contacts which continually change their positions as the switch is operated—the arcing being thus distributed over the whole surface of the rollers—and they are able to work for considerable periods without being badly burnt. In all cases, however, auxiliary contacts, what- ever form they may take, should be of such design that they can be readily removed and replaced, and they should also be of such a nature that collieries should not have to depend solely upon obtaining supplies from the makers, but could easily have them made in the electrical repair shop. Much has been learnt during the war of the inconvenience entailed by being compelled to wait for fittings, etc., to be supplied by manufacturers, owing to the difficulty of making them on the premises. In future, when obtaining switch- gear of all descriptions, consideration should be given to the simplicity of parts, since to be self-supporting in cases of emergency is very desirable in colliery work. The continual breaking of the circuit causes a con- siderable accumulation of highly inflammable gas in reversing switches, and it is of great importance to provide ample ventilation, together with means of relieving the pressure in the event of an explosion in the switch tank.