The New Zealand Railways Magazine, Volume 2, Issue 1 (April 21, 1927)
Electric Traction Development
During the past few years, much has been done in connection with the development of electric traction. Nearly every country is interested at present in railway electrification, and it is interesting to note the various schemes which have been adopted by each.
Standardisation is the principal factor governing electrification of any railway. This is very important in order to secure proper interconnection on the various lines which may, at a later date, be affected and become electrified.
Recently, several countries have embarked on big electrification schemes, and one of the largest of these (it is using the universally adopted voltage of 1,500 direct current) is that of the Midi Railway in France. In view of the magnitude of the development, a few remarks on this particular railway will not be out of place, more especially as it is a similar system to the one already in use by the New Zealand Railways at Otira Tunnel.
Shortly after the War, a commission was set up by the French Government to investigate different railway electrification systems in use in France and abroad with a view to carrying out a 2,000 mile electrification, a work which was to occupy a period of ten years for its completion. The conclusions arrived at by this commission were finally adopted by the Government, and it was decided to use direct current at 1,500 volts with a condition that in special cases 3,000 volts could be used. The method of collecting the current was to be either by overhead or third rail, the locomotives to be designed for both methods of collection. Direct current using 1,500 volts is generally favoured at present by the majority of engineers in various countries, with the exception of America, which has used 11,000 volts single phase very extensively. It is interesting to note the deductions arrived at and the reasons given by the French commission for selecting this particular voltage and current.
Firstly, direct current was considered to be the best means of overcoming inductive interference on low tension circuits. It allowed of less weight and lower cost of direct current locomotives, greater overload capacity, and cheaper maintenance cost of motors. The voltage selected was also considered the maximum permissible for the use of third rail. The main power lines are fed along the railway by 60,000 volt feeders to the various transformer stations by means of overhead wires, the current being then transformed down and converted to 1,500 volts direct, to be sent out on the track.
Two types of convertor are in use on this system. The rotary convertor and mercury rectifier. The typical substation is equipped with 1,500 k.w. sets of two 750 k.w. (750 volt rotaries) operated in series, and it appears from the number of substations already equipped this way that very satisfactory operation can be obtained. The overloads, which the machines are capable of withstanding, are in the vicinity of 200 per cent. without flashing over.
A later development, however, is the introduction of the Brown Boveri Mercury Rectifier producing 1,500 volts direct current. Several of the Midi Railway Substations have already installed groups of 1,200 k.w. capacity rectifiers. The groups consist of a pair of cylinders in parallel connection and fed with 12 phase current produced by special transformers manufactured by the same Company. The efficiency of these stations is very high at all loads and their overload capacity is quite as high as that of a rotary convertor station. These static machines have been brought to such a state of perfection that there is every prospect that they will be adopted fairly extensively for traction work. They are capable of handling very heavy momentary overloads, and there page 45 appears to be no difficulty in maintaining the vacuum in cylinders.
The rectifier presents several distinct advantages over the motor generator and rotary convertor machines, the principal outstanding features being as follows:—
(1) Small space occupied. (2) Small weight. (3) No vibration. (4) Little attendance. (5) Facilities for transport. (6) No foundations or rotary parts. (7) Noiseless running and heavy overload capacity. (8) High efficiency at all loads.
These advantages speak very much in favour of this plant, more especially where several stations have to be installed on a long length of track. The net result would be to obtain a high all round efficiency along the track at all conditions of loading as compared with the other forms of convertor. In addition to this, there would be a considerable saving effected in size of buildings, cost of transport and handling, which are expensive items where a large number of plants are involved.
Quite recently the Berlin Metropolitan Railways decided to install 125 Mercury Rectifiers of various makes on their railways, using 800 volts direct current for the supply. The total output of rectifiers represented was 114,000 k.w. and it is evident that a good impression was made on the German Commission of Engineers by the reliability and performance of this particular plant. The rectifiers are adapted to automatic control in the same way as the rotary convertor or motor generator substations.
Another installation recently put into commission, which is of special interest, is a 3,000 volt railway in Brazil running between Jundiahy and Campinas, a distance of 27 miles, with further extensions now under construction to Rio Claro, making a total length of 83 miles of electrified line. Most of the equipment is of the equipment is of American manufacture, but recently a very large locomotive was supplied by the Metropolitan Vickers Electrical Co., Ltd., having a rating of 2,340 H.P. and weighing 100 tons. It is the largest electric locomotive built so far for passenger service, and a few remarks on its construction will be of interest.
The locomotive is designed to run on a 5 ft. 3 in. track and is of the 2-6-0+0-6-2 type, equipped with six motors each wound for 1,500 volts and insulated up to a pressure of 3,000 volts. The motors, each of which is 390 H.P., transmit their power to the axles by means of flexible spur gearing. The main body of the structure is carried on two trucks each having three driving axles and a single guiding axle. The trucks are coupled together by an articulated ball joint, and the body is supported on two pivots which engage in centres suitably placed to give the desired loading on the track. The direct current at 3,000 volts is collected by means of two pantographs which can be raised or lowered by compressed air. Spring control is also provided to allow of any variations in trolley wire height above the rail level. The motors are field controlled and are arranged for re-generation on down grade, a special motor generator being provided for the excitation of fields of the main motors. The control equipment is of the electro-pneumatic type, the master contractors being operated in turn by means of electrically controlled valves. The driver's control consists of a non-automatic drum type, fitted with three handles, viz., accelerating handle, the combined reverse and motor combination handles, and a re-generative handle, which operate three drums fitted on a combined shaft.
A large number of similar control equipments were supplied to the South African Railways, but were 1,200 H.P. each and arranged for multiple unit control. The motors were designed for 1,500 volts to operate with at least two always in series across the line voltage. Regulation of the speed of the train is obtained by grouping the motors by special control apparatus in series and in parallel.
Another big development in railway electrification is the introduction of the automatic substations and supervisory control. The Capetown Suburban Railway in South Africa is a typical installation where remote control is used over a line approximately 30 miles in length. The power is transmitted partly overhead and partly underground by cables carrying 33,000 and 12,000 volts to convertor stations located at definite intervals along the page 46 track. Each convertor station is equipped with automatic control gear for operating the various high tension switches, transformers, and convertor switches, and these, in turn, are dependent on a system of supervisory control from a central point, such as the Power House or Terminal Railway Station.
At the load despatcher's office, the essential apparatus is the despatcher's control board and supervisory cabinet. By means of these boards the “operator” or “load despatcher” has complete control over the whole system, and is able to ascertain whether the various stations are functioning correctly along the line. Any faults occurring in any one station under control by the supervisor are at once made obvious by the dropping of a signal pilot lamp or relay shutter which indicates the exact location of the trouble.
The supervisory control is, undoubtedly, a very ingenious development. It provides for the correct functioning of all switches located in substations along the line, many of which are miles away and cannot be seen by the operator. The selections of apparatus and their operation are governed by a series of three trains of impulses. One will select a substation, another a group of circuit breakers and the operation to be performed, and a third, the required circuit breaker. The first impulse train sent out would be received by all the substations, locking out those not wanted, and the two subsequent trains are received only by the selected station. When a circuit breaker has been selected along the line, an indicating shutter or lamp shows the operator that the correct selection has been made and the operation is allowed to proceed.
Rotary convertors, rectifiers, circuit breakers, and all other control gear which forms part of the substation equipment, may be designed for full automatic control from the “load despatcher's” desk miles away down the track, resulting in a big annual saving in attendants' wages.
New Zealand is already in the happy position of possessing several large hydro-electrical power stations connected throughout the country by extra high tension transmission lines and having bulk supply substations located at all important points for the supply of power. The whole of this system could be utilised to advantage by both the Power Boards and the Railway Department, resulting in an improved load factor and greater economy in operation.
In conclusion, it may be stated that the electrification of railways is gradually assuming big proportions, and the day is not very far distant, when countries like our own will be compelled to consider electric traction, at any rate, for its suburban sections.
Amongst the features of railway construction which have provided subject matter for discussion in various journals lately, the length of station platforms has produced lively controversy.
It is stated that the reason for the long platforms in India is that the lay-out which best suits Indian passengers is one or, at the most, two long platforms, which will accommodate all trains halting at one time, usually four at the large junctions. This lay-out is said to be better for their requirements than several short platforms connected by overbridges or subways.
In New Zealand, Dunedin takes pride of place with a platform length (exclusive of ramps) of 1,485 feet, or only 15 feet short of the London (Victoria) platform