Elektrizitätswerk Venedig

Allgemeines

FirmennameElektrizitätswerk Venedig
OrtssitzVenedig
Art des UnternehmensElektrizitätswerk
Quellenangaben[Hedges: Continental electric light stations (1892) 13]




Unternehmensgeschichte

Zeit Ereignis
1890 Erbaut




Produkte

Produkt ab Bem. bis Bem. Kommentar
Elektrizität          




Betriebene Dampfmaschinen

Bezeichnung Bauzeit Hersteller
Dampfmaschinen um 1890 Franco Tosi




Allgemeines

ZEIT1892
THEMABeschreibung
TEXTThis installation has been selected as an example of the Zipemowsky-Déri-Bláthy alternating system, not on account of its size, as it is in that respect inferior to those at Rome and Leghorn, but its construction was undertaken in the face of many difficulties, which have been overcome, and its operation has been attended with great success.
Venice, as everyone knows, is a city peculiar to itself. Every yard of ground on the group of islands, which can hardly be called terra firma, is built over, and it was only by pulling down a palace, dating from the sixteenth century, that a site for the central station was obtained. The foundations of the buildings are on piles; in fact,
the greater part of the wedge-shaped piece of ground on which they stand is filched from the adjoining canal, which at one time was not confined to the regular channel it is now. Great care was bestowed on the foundations of the engines and dynamos; a strong wooden framework is first securely attached to the piles, and about three feet
of concrete is run over the whole, a rubble foundation securing an even bearing on the earth beneath. The machinery rests on a mass of brickwork, which is altogether isolated from the outside walls. The electrical equipment at present is as follows: Four complete sets of direct-coupled engines, alternating-current dynamos and exciter, each group capable of a maximum output of 80.000 watts - 40 amperes at 2000 volts; the speed of the combined plant is fixed at 250 revolutions per minute, and at full work each group is said to maintain 1500 lamps of sixteen candles. The dynamo is of the well-known Ganz type, in which the external armature is fixed, and is composed of twenty
bobbins having cores of laminated wrought-iron connected in series. The revolving armature has twenty bobbins, also divided into two circuits of ten each; the number of alternations is 5000 per minute. This low number of changes of polarity is always adopted by Messrs. Ganz for every type of alternating machine, and is said to be advantageous, in spite of the increasing weight and size of converters which it necessitates. The exciter is of the Gramme type, and furnishes 4000 watts at the same low speed of 250 revolutions per minute. Messrs. Ganz do not make arrangements with this type of plant for withdrawal of the armature of the alternating machine, which was noticeable in those at the older Rome installation; they also find the heating of the coils to be much reduced by increasing the air space between the magnets and bobbins, which is at Venice about 20 millimetres. The steady working of the plant is mainly due to the low speed and to the method adopted for coupling to the engine shaft, which obviates any strain due to bad alignment of the two shafts. The number of sets of plant will be increased to seven, which with one spare set will enable 9300 lamps to be run at once ; at present about 5600 are worked, which is not a bad result, as the erection of the station was only commenced The steam engines are vertical compound tandem, condensing, by Tosi, Legnano; the high-pressure cylinder is 325 millimetres diameter, and the low-pressure 475. The valves are of the piston type, and are arranged so that the expansion can be varied. In outward appearance the engine resembles the ordinary kind, the lagging being carried upwards from the low-pressure cylinder. The compounding in this way, although common enough on board ship, has not been extensively adopted for electric light installations. The manifest advantages a vertical has over a horizontal engine, besides its regularity of piston speed, are that less floor space is required, and compactness is secured without sacrifice of economy; these engines have been guaranteed to give a horse-power hour with 19 lbs. of steam, the working pressure being 120 lbs. on the square inch. Although, on account of the abundance of water, the exhaust steam is condensed, separate pipes are fitted for free exhaust, in the event of a breakdown of the separate engine which works the air pumps. The boilers are an Italian adaptation of the well-known Babcock-Wilcox type. The difference is chiefly in the way in which the ends of the water tubes are connected, in order to allow good circulation and stop the priming which the American boiler is not always free from, especially if the feed water is not good ; and it certainly is not at Venice, as, in spite of all regulations to the contrary, the canals are the receptacle for the house drainage, which the small amount of tide is powerless to remove. The system of working is very simple. Groups or units of plant are added as the demand increases. All the machines are coupled in parallel, both the alternators and their exciters; it would not be safe, however, to switch a spare machine on to the circuit of one heavily loaded. Recourse is had to an artificial resistance, which is
usually a bank of lamps; these can be added until the load of the two machines is equal, and their running together assured. The E.M.F. of the primary circuit is kept constant by the method of adding or diminishing resistances in the field magnet circuit of the exciting dynamos, which are of the shunt type. For large variations the regulation is effected by hand, but for small variations by means of the Bláthy rheostat - an apparatus which, by means of a solenoid, causes a number of wires to gradually enter a cup filled with mercury. The object in view is not to maintain the E.M.F. constant at the terminals of the primary current in the station, but at the transformers. To bring a separate wire back from each transformer in order to measure the fall in E.M,F. would be impracticable, apart from the cost of the wire, so that a special arrangement had to be designed, which controls the pressure at the transformers and keeps it constant. The primary circuit passes through two special converters; one of which is the equalizer, and the other the reducer, which serves to work the automatic rheostat and also permits an ordinary voltmeter to be employed. The method of distribution is, as a rule in Italy, by aerial cables, which are run along the fronts of the houses ; but underground cables have also been employed for some time, and have carried the full pressure of 2000 volts without any break-down. The concentric cable usually employed is similar to that which has been recently laid down for the London Electric Company by Messrs. Siemens. The output, weight, and duty of the standard sizes of converters is given by Messrs. The converters are installed either in the cellars, or - as in Venice, where this would be impracticable - they are often carried on brackets fixed to the outside wall
of the houses. The branches are taken from the mains by means of a porcelain connector, which also contains the switches and cutouts. Insulated cables are always used, except at the connectors, where bare copper facilitates the jointing up. This plan has worked exceedingly well at Venice, and is preferred to casing or lead-encased cables, on account of the dampness of the walls. The current is supplied by meter, on the Bláthy system, which gives the amount
consumed either in ampere hours or watt hours. It is said to work with one-tenth of an ampere.
QUELLE[Hedges: Continental electric light stations (1892) 13]