, VICTORIAN INSTITUTE OF ENGINEERS :
rate of flow will be found to be expressible by a general law, at times he has thought that he has glimpsed it, but hitherto he has been unable to crystallise it."
We would direct his attention to papers in the proceedings of the Inst. C.E., London, by Dr. Stanton.
Mr. J. A. SMITH said that Dr. Stanton had not dealt with -the question of air in relation to surface condensation in any form, nor had he enunciated any general law connecting the matters re- ferred to in his (the speaker's) paper. Did Mr. Weymouth affirm -that he had?
'Mr. WEYMOUTH said not all of them, but that did not matter.
Mr SMITH thought otherwise. As the hour was late (9.5o), end as Mr. Weymouth's contribution was in written form, he thought that, in justice to the subject, he should have an opportunity of
perusing it at leisure before replying.
In reply to Mr. Higgins, the paper must speak for itself, but it might be pointed out that each of those who had contributed to the discussion had dealt with one phase of the subject only; the greater -portion of the paper was not referred to.
The PRESIDENT said the discussion would stand adjourned until the next meeting. (Refer to page 29.)
PAPER.
NOTES DESCRIPTIVE OF THE ELECTRIC SUPPLY STATION 'OF THE MELBOURNE CITY COUNCIL.*
By MR H. R. HARPER, City Electrical -Engineer.
In connection with the proposed visit of the Victorian Institute of Engineers to the Electric Supply Station of the Melbourne City Council, a few notes on the history and development of the under- taking may not be amiss.
In 1894 the City Council started the lighting of the streets by means of electricity, generated at the present Supply Station in Spencer-street. The scheme at that time contemplated only public lighting, that is to say, streets and markets, and a sum of £8o,000 -was spent on buildings, generating plant, aerial lines and lamps for
this purpose.
About three years later further expenditure to the extent of about }3o,000 was .incurred in installing plant for supplying current for
• Issued in advance in anticipation of Visit (see page 27).
MELBOURNE CITY ELECTRIC INSTALLATION. 19 private lighting. The demand for such was so promising that the City Council decided to take into their own hands the supply of all electricity within the city area, and with that in view steps were taken to purchase the properties of the companies holding statutory rights in this area. The purchase was completed about the end of 1900, but as the Council was not in a position to generate the whole of the current required, it purchased its requirements in bulk from the companies at the boundary of the city.
In the meantime a new continuous current system was installed and put into operation, in connection with which underground mains were laid in the central portion of the city, to which the companies' late consumers and the .Council's were transferred.
Owing to the supply voltage adopted being 23o, whereas the old supply was at too volts, nearly the whole of the consumers' installa-
tions had to be re-wired before the transfer could be made. The in- stallation of this new system and underground mains, which was com- pleted by the end of 1901, brought the capital expenditure of the undertaking up to about £325,000, and the increase of business due to the purchase of the companies' undertakings increased the annual revenue at a. jump from about (30,000 to £6o,000. At the present time the capital expended stands at £380,000.
STREET LIGHTING.
The system in use at the present time for the lighting of the streets is that known as the Thomson Houston direct-current series system. At the time of its adoption this was the universal system in the United States of America for the purpose of street lighting, but owing to the rapid strides that have taken place in the construction o! electrical machinery, this system is looked upon as being quite obsolete, and, so far as the generating plant is concerned, very inefficient.
The generating plant consists of 24 arc dynamos, divided into four groups, rope and belt driven by four compound condensing horizontal engines, each of 300 i.h.p. Each dynamo is capable of supplying 5o arc lamps, consuming about 35o watts each. This plant, aggregating 1200 h.p., covers a floor space of about 11,200 square feet. It is proposed, in the conversion of the outside area, to eventually instal about 4000 h.p. in turbines in about one-third of the space occupied by the present plant.
E. H. P.
The combined efficiency of the plant'. H P is not very striking, being not higher than about 6o per cent. The steam consumption of the engines, including pumps, taken at about 4 load, is about 44.9 lbs. per kilowatt hour, with a vacuum of about 22/ inches.
Comparing these results with those obtained from modern plant, such as the Allen-Crompton 75o k.w. unit described later on, shows what considerable strides have been made in the construction of electrical generating plant during the last 15 years or so. What this improvement has meant in coal economy, and reduced generating
costs, is shown by the greatly reduced selling price of electricity during this period. The lamps supplied by this plant amount to 797 arcs and 85o incandescents.
These arc lamps take about 350 watts each, and give a maximum candle power of about 630. In the candle power curve given below, it will be seen that there is a rapid falling away of the candle power between the angles of 25° and 43° from the horizontal. This is due to the heavy frosting of the lower half of the globes.
A number of the Thomson Houston arcs in the centre of the city are now being replaced by about 135 "Excello " flame arc lamps.
The latter, which are being supplied by Korting and Mathieson, of Germany, will be mounted on steel columns.and brackets, manufac-
FIG. I. FIG. 2.
tured by the Mannesmann Tube Co. The flame lamps will each take about 410 watts, and will burn nine lamps in series across the 460-volt outer conductors of the three-wire direct-current underground system.
This replacement will result in the removal of all overhead wires at present in use for street lighting in this portion of the city. There has been no opportunity yet of measuring carefully the candle power of these flame lamps, but from tests made by the Westminster Testing Laboratory, the maximum c.p. may be expected to be about 1840 c.p.
The candle-power curve obtained from these tests is shown in Fig. 2.
As distinct from the existing arc lamps, which have their carbons perpendicular, and one over the other, the Excello flame lamp is designed with both its carbons side by side, not parallel to each other, but placed like the letter V, the arc being, of course, at the point of convergence. This arrangement eliminates the shadow trouble immediately under the lamp, caused by the negative carbon and its attachments, which is such a noticeable feature with ordinary arcs. On the other hand, this type of flame lamp tends to concentrate its light in a more vertical direction than the ordinary lamp, con- sequently it is necessary to place them at a greater height from the pavement.
MELBOURNE CITY ELECTRIC INSTALLATION. 21 The height adopted in the central portion of the city for the flame lamps, spaced about 8o yards apart, is 25 feet, whereas with the ordinary type of lamp, z0 feet would have been enough. In a few cases where the spacing is greater, the flame lamps will be 35 to 4o feet high, and carried on span wires.
After the conversion of the street lighting in the central portion of the city area and connection to the continuous current system, is completed, the conversion of the remainder of the street lighting will be taken in hand. The latter will be probably supplied with current from alternating current machinery, which will be installed shortly to supply both public and private lighting in the outside portion of the city. These conversions, it is hoped, will be completed within about two years' time, and will throw out of use the whole of the existing Thomson Houston series plant.
ALTERNATING CURRENT SUPPLY.
Reverting to the station plant and to that portion of the under- taking which is concerned more or less with the private supply, it has been already stated that about two years after starting the public supply the Council installed machinery, etc., for the supply of current for private purposes. This consisted of four alternating current dynamos, manufactured by the General Electric Co. of America.
These machines, each of 75 k.w. capacity, generating current at about 2000 volts, were, first of all, belt driven from the countershaft of the arc lighting plant. On the completion of the direct-current plant some four years later, two of these alternators were removed, and connected to two direct-current motors, to obviate the expense of running the countershaft and all its gearing during the daytime for the sake of the small amount of day load.
During the year 1899, owing to the increase of load, an additional unit was installed, consisting of a Johnson and Phillips Izo k.w.
alternator coupled to a Peache high-speed engine. In 1901 the new direct-current system previously referred to was in- stalled, in connection with which large additions were made to the station buildings and plant, and underground mains were laid through- out the area extending from Flinders-street to Lonsdale-street, and from Spencer-street to Spring-street. The 'private consumers of the Council, and those of the companies in the city area were at that time supplied by means of overhead wires, the primaries of which were at 2000 volts, and the secondaries at loo volts. The great bulk of the installations, equivalent to about 29,600 I6-c.p. lamps, were transferred to the new underground mains, the balance, being out- side the area supplied by these mains, were left on the old overhead z000 volt system.
DIRECT CURRENT SUPPLY.
The new generating plant installed consisted of 4-350 k.w. and I-200 k.w. direct-current dynamos, manufactured by Thomas Parker, of Wolverhampton, direct coupled to Bellis high-speed engines work- ing in conjunction with surface condensers. The large dynamos are
VICTORIAN INSTITUTE OF ENGINEERS :
4-pole machines, with shunt-wound fields, and have Eickemeyer wound armatures. The smaller dynamo is a 2-pole machine. They generate current at voltages varying from 460 to 520, depending on the load on the station, and the consequent rise in busbar voltage to overcome the drop in pressure in the mains, and to maintain a constant voltage of 46o at the feeding points of the network.
The engines are of the vertical enclosed 3-crank type, each crank being driven by compound cylinders in tandem, making in all six cylinders to each engine. The speed is 84o revolutions per minute.
The multitude of cylinders is certainly a disadvantage in this type, involving greater expense in upkeep without any compensation in economy of running; in fact, such an engine can have little better efficiency than three small tandem engines of one-third the capacity of the whole engine, and its steam consumption is correspondingly greater than an engine with, say, two or three cylinders side by side.
At the time these engines were installed it was, however, the fashion amongst makers of high-speed engines to build them in this manner.
Needless to say, this type does not, as a rule, figure in manufacturers' recent catalogues. It has entirely given way to the more efficient engine with cylinders side by side.
Recent tests on the engine in question show that the steam con- sumption, at about full load, is about 33 lbs. per k.w. hour, when working with steam superheated slightly, and a vacuum of about 24 inches. As the above plant was fully loaded shortly after its in- stallation, an extension was made in 1905 by the installing of a 75o k.w. Crompton dynamo, direct coupled to a rroo i.h.p. Allen engine. This dynamo has 12 poles, is also shunt wound, and corres- ponds in other details with the other direct-current dynamos previously installed. The engine is a triple expansion, provided with three cylinders arranged side by side, and runs at 275 revolutions per minute. At the official trials the following results were obtained : —
Load. full.
Steam pressure in pipes lbs. sq. in. 160 160 160 160 in steam chest lbs. sq. in. 46 86 124 150 Superheat in degrees ... ... nil nil 3 5 Vacuum at 1. p. cylinder inches 27 _ 23 23
Load in kilowatts 187 375 562 750
Indicated H.P.... 358.7 6221 838.88 1146
Efficiency per cent. 69.2 81 90 87.7
Steam consumption lbs. ... ... 27.6 22.2 20.2 191 Speed, revolutions per minute ... 278 277 276 275
To meet the still increasing demand, a duplicate of the above 75o k.w. set is now being erected, which will be in running order in time for the winter load, making the total capacity of the station
*The low vacuum obtained in these tests was due to a smaller condenser being used than that belonging to the engine.
MELBOURNE CITY ELECTRIC INSTALLATION. 23 plant about 3928 k.w. The maximum demand on the plant during last winter was close on 2000 k.w., of which 35o k.w. was for public lighting.
CONDENSING PLANT.
In regard to condensing plant; surface condensers are used throughout, the circulating water for which is pumped up from the River Yarra by means of motor-driven centrifugal pumps installed at the river-side. There are three pumps, one capable of delivering 70,000 gallons per hour, driven by a 3o h.p. motor, the other two being capable of delivering 140,000 gallons each per hour, and driven by 6o h.p. motors. The starting of the motors is performed by large Sturtevant automatic starting switches, which are controlled by the switchboard attendant at the Supply Station, half-a-mile away. Be- yond a daily inspection for oiling and cleaning purposes, there is no other attendance required.
The water is delivered to the station through a 2-ft. main, the total head on the pumps being about 4o feet. For the purpose required, the motor-driven centrifugal pump, if running at or near full load, is admirable, as it so readily responds to the fluctuating re- quirements of the station, and maintains a constant head. At the station there are four sets of motor-driven Edwards air-pumps, one for the old street-lighting plant, two for the Bellis engines, and one for the large Allen engine. The power absorbed in pumping the circulating water and driving the air-pumps works out at about 4 per cent. and per cent, of the total output of the station respectively.
The condenser attached to the large Allen engine has a feature which may be of interest, in that a higher vacuum is obtained than with the ordinary arrangement. Some of the condensed water is re- tained in the condenser, the lower tubes of which are therefore sub- merged, so that the condensed water is deprived of some of its heat, and leaves the condenser at practically the same temperature as, or even below, that of the discharged circulating water, thus improving the vacuum. By this arrangement a constant flow of water into the pump at the lowest possible temperature is insured, and the air inlet, being taken into the pumps by 'a separate pipe, always has a free passage.
BOILER-HOUSE PLANT.
For the generation of steam there are at present installed ro water-tube boilers, and two more are in course of being erected.
Four 6f these, which were installed in 1894 with the street-lighting plant, are situated in the new boiler-house. These are the only ones not fitted with superheaters. They are hand-fired, and have each a heat- ing surface of 2823 square feet. When the new direct-current system was installed, four large Babcock and Wilcox boilers, each having 4020' square feet heating surface, were installed in a new boiler house. For a couple of years these boilers were hand-fired, but subsequently chain-grate stokers were substituted. In the same boiler-house are installed
two Stirling boiiers with chain-grate stokers, each boiler having 323o square feet heating surface. Two additional Babcock nd Wilcox boilers and stokers have been recently erected, and are al- most in complete working order. They are of the same size as the other boilers of the same make in this boiler-house.
Owing to the accommodation for coal on the floor becoming less each year on account of extension of plant, a steel bunker was erected overhead, capable of holding about 55o tons. A bucket conveyor elevates the coal from the receiving hopper to the overhead bunkers at the rate of about 22 tons per hour. The buckets overlap one another, so that on the return journey through the basement, ashes can be pushed into the conveyor without any special filling arrange- ments. The bunker and conveyor were supplied by Graham, Morton and Co., of Leeds. The coal is introduced into the hoppers of the stokers by means of travelling overhead self=registering. weighing machines of the Ingrey type. On each side of the boiler-house there are installed two batteries of Green's fuel economisers, the total number of tubes being 96o.
The introduction of chain-grate stokers soon made it evident that a careful analysis of the flue gases was necessary, as the coal con- sumption showed, a marked increase following their adoption. With the aid of an Orsat-Linge apparatus, samples of the gases were ob, tamed and tested. As is well known, the gases of combustion consist principally of oxygen, carbon monoxide, carbon dioxide and nitrogen in varying quantities, depending on the effectiveness of combustion.
There is always about 8o per cent. of nitrogen present, associated with other rarer gases in small quantities. If the combustion of fuel has been good, there should be no carbon monoxide, from 14 to 19 per cent. of carbon dioxide, and from r to 6 per cent. of oxygen. A larger percentage of free oxygen, attended with a low percentage of 002, indicates that excess air is being allowed to pass. This was the trouble found, and although a view of the top of the chimney-stack showed smokeless combustion, yet it was evident that combustion very far from being perfect was being experienced. Samples taken at this stage with the dampers fairly wide open showed a maximum of 5 per cent of 002, and about 14 per cent of free oxygen. By restricting the boiler damper openings until the draught was no more than of an inch of water at the dampers, the results were improved to the following extent
002, 14 per cent.; O., 5.5 per cent. ;. CO , nil ;
the draught being sufficient to obtain the rated duty from the boilers.
These changes resulted in bringing the efficiency of the boilers from 69 per cent. to 79 per cent. Under these conditions it was found that the chain-grate stokers are not absolutely smokeless, as they are claimed to be, but whatever, smoke there is, is by no means serious from a nuisance point of view.
The coal consumption,which at the initiation of the stokers went as high as 9i lbs. of coal per unit generated, has been reduced by careful supervision on the part of the station staff to about 51- lbs.
The coal used is the slack or small coal from the collieries in the
MELBOURNE CITY ELECTRIC INSTALLATION. 25 Newcastle and Maitland districts, and is of a bituminous nature. Its cost, delivered to the works, is 12s. 5d. per ton. Previous to the use of mechanical stokers, Bulli large coal was used, which at the pres- ent time is about 16s. per ton. The financial result, due to the adop- tion of stokers burning slack coal, has been a drop in the cost of coal per unit generated from .58 pence to .35 pence. When the old street-lighting plant is replaced by more modern plant, these re- sults will be considerably improved.
Although the use of the Orsat apparatus was very beneficial in pointing out the direction in which combustion could be improved, yet some means of obtaining a continuous record of the state of the flue gases was felt to be necessary. With that in view, an Ados "
CO2 recorder was installed in such a manner that at short notice any boiler could be connected to it, and observations taken continuously, and over any length of period. Space does not permit of a descrip- tion of this apparatus, but it can be observed at the station under working conditions. It has proved invaluable, and its records are now understood and thoroughly appreciated by the firemen.
Before leaving this part of the subject, reference might be made to the coal-testing apparatus, which is often in use for obtaining the calorific value of the fuel. This testing is carried out by means of a
" bomb " calorimeter of the " Mahler " type, consisting of a coal com- pressor, an enamelled " bomb " and the calorimeter proper, with stirring gear and attachments.
SWITCHBOARD, STORAGE BATTERY, ETC.
There are three main switchboards. One is for controlling the arc circuits from the street-lighting plant, and the other is for controlling what remains of the 2000 volts alternating current private supply. A third board, and the most important of all, controls the direct-current supply. To this board the current generated by the Parker and Crompton dynamos is led by cables drawn into earthenware pipes laid in the concrete floor. From this board the current is taken away by underground feeders to various parts of the city. A full description of these boards is impossible in these notes; inspection is necessary.
Behind the direct-current switchboard, and in a separate room, is installed a Tudor accumulator, consisting of 28o cells, capable of maintaining a discharge of 400 amperes during, four hours, or r000 amperes for one hour. The station output has become too great to allow of the full benefits derivable from the installation of such a battery being obtained. During the daytime the direct current output is seldom below 15oo amperes. The battery is, however, useful at times of maximum demand, or when it can assist the generators.
Space does not allow of much reference to . the meter and photometer rooms, in which all the meters for registering the supply at consumers' premises are tested and repaired, and any photo- metrical work carried out. Samples of the various types of meters in use will be shown under working conditions during the visit. In the photometer room will be seen the Simmance-Abady flicker photo- meter, which is the instrument used for all reliable work, and which
VICTORIAN INSTITUTE OF ENGINEERS :
was designed to overcome the difficulty met with in endeavouring to compare the intensities of two lights composed of different coloured rays.
DISTRIBUTION SYSTEM.
Although it will not be possible during the visit to see any portion of the direct-current underground distribution system, a word or two in connection with this branch of the undertaking may be interesting.
The supply cables are laid on what is known as the three-wire prin- ciple. On both sides of all important streets are laid the three wires, the middle one of which is maintained at earth potential. The other two, termed the outers, are each maintained at a pressure of 23o volts between them and the middle wire, one being at 23o volts above each potential, and the other 23o volts below. The whole of the lamps, etc., connected to these three wires are divided as nearly as possible, half between the middle wire and one outer, and half between the other outer and middle wire. If this balance be perfect, no cur- rent returns along the middle wire;. but as this condition is unattain- able, a certain amount of current is always returning to the station, which is controlled by a special machine called a balancer, which is composed of two dynamos running at 230 volts, rigidly coupled to- gether. The main dynamos simply supply current to the outer wires.
To certain points of the network, two-wire feeders are laid straight from the station, which convey the whole of the current generated by the machines. Pilot wires are connected between these feeding points and the main- switchboard, so that the pressure at these points can always he controlled.
All the cables are insulated with specially impregnated paper, and covered by a lead casing. They are laid in troughs made of hard- wood, filled in solid with hot pitch. This protection serves very well for the distributors, but in the case of feeders some other method of laying seems very desirable, which would, in the event of the feeders becoming too small, allow of their being replaced by larger ones. At the present time along Lonsdale-street a system of conduits is being laid, into which it is proposed to draw some additional feeders which are required to meet the increasing demand for current. As spare conduits are being laid in the same trench, further additional feeders may be drawn into them when required, without having to open up the streets. These conduits are made of bituminous fibre, and whefi laid are cemented into one block by being surrounded with concrete.
Altogether about 15,000 yards of this conduit is being used, the number in one trench ranging from four to as many as fourteen.
In conclusion, some figures relative to the present size of the undertaking may be of interest.
The connections for private lighting stand at the equivalent of 56,844 16 c.p. lamps, included in which are 884 private arc lamps.
The power connections stand at 1666 h.p.
The total units generated for the year ended February 28th, 1906, were 5 614,603, and the revenue obtained was over £72,000
