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sequence commutating poles com- bined with compensating winding-- the commutating poles giving the re- actance voltage necessary for com- mutation and the compensating wind- ing, compensating for armature reac- tion--have been adopted by many firms. But even better commutation can be secured by a compensating winding alone, in which the ampere- turns of the compensating winding exceed the ampere-turns of the arma- ture to such an extent as to give a commutating field in the gap between the pole-pieces. Such compensating winding is gen- erally chiefly concentrated on the pole- pieces, and is made with from 2 to 2% times the number of ampere-turns of the armature, in order both to com- pensate for leakage and to give a good commutating field, and since this meth- od of compensating has no iron com- mutating pole, it has the advantage that there is no self-induction to cause time lag at sudden changes of load, and, as the field of the gap between the poles is entirely in air it instantly responds to changes of current in the compensating winding, and thus the sparking found when there is a sud- den change of load with commutating poles is avoided, and the risk of a flash-over largely reduced. Also since there is no iron to become saturated, the commutating field is al- ways strictly proportional to the load, and thus the trouble due to saturation causing sparking at some loads and not at others is avoided. This advantage is especially prominent where the dy- namo is required to give varying volt- ages and to commutate at any of them without outside adjustment of the com- pensating windings by diverters or otherwise. The adoption of these devices has made it possible to make turbo dyna- mos of large size, and now as much as 1,500 kw. is put into a single armature, whereas before such compensating de- vices were adopted 500 kw. was the maximum, and even then the commu- tation was anything but satisfactory. STANDARD PATTERN. In turbo alternators there is practi- cally now--except for small sizes and low voltages--one standard pattern-- that is, a revolving field rotating inside a stator. In the stator there is little variation in design, except in regard to the ventilating arrangements, which have to be very ample on account of the comparatively large quantity of heat to be removed from a small vol- ume, _ One point which has received great attention in recent years is the staying (Of the end windings of such alterna- THE Marine REVIEW tors, it having been found that, ow- ing to their great length, when a "short" took place the stresses on the winding were such as to break the in- sulation and cause disaster. The amount of these forces has been vastly more than was ever anticipated, and if the windings are not thoroughly stay- ed, such movements may be set up as to cause disaster. In the rotors there are two prominent types, the barrel and the salient pole, and much dis- cussion has ensued as to the advantages of the one or the other. After consider- able experience of both, on the whole I may say that at present I prefer the salient pole type. Ample ventilation is much easier to provide for, and im- provements made in protecting and supporting the field coils of this type of rotor have resulted.in a design giv- ing great reliability with the maximum use of the space available. One im- provement has: been enclosing every coil in a tight sheath of sheet steel, so that any movement which may take place due to centrifugal force is be- tween the steel sheath and the body of the rotor, and thus the insulation is protected from any rubbing which might cause it to be cut through and, consequently, break down. Voltage regulation of alternators is also of considerable importance, as Oow- ing to the inductive load required by induction motors there is a heavy de- magnetizing effect on the rotor, and consequent drop of voltage when the load rises. Several methods have been proposed for compounding alternators, most of them requiring a separate commutator or moving contacts alter- ing the resistance of the exciter or main windings, but a method of com- pounding alternators has recently been brought out, which is being largely used with good results. In this ap- paratus the current supplied by the ma- chine is made to act on the exciter field system in such a way as to re- duce the leakage, artificially increased in the first instance, and so raise the voltage of the exciter, and increase the excitation of the alternator, so that any desired amount of compound- ing required can be obtained. This arrangement has been recently de- cribed in a paper before the Institution of Electrical Engineers. TURBO BLOWERS. -- The other applications of the steam turbine, such as driving air compress- ors and pumping water, have also been largely extended during the last few years, and especially prominent 7 this direction has been the application of turbo blowers to blast furnace work, some having been recently installed for as much as 50,000 cu. ft. of air per 17 minute at 10 to 15 Ib. pressure. In this connection it may be mentioned that a very usual size, which is for about 20,000 cu. ft. weighs about 25 tons, and that an ordinary reciproca- ting blower of equal capacity weighs about 450 tons or about 18 times as much as the turbo blower. In many parts of the country recip- rocating engines are running non-con- densing, and it has now been found that the exhaust steam from them is of great value. Such exhaust steam cannot be practically utilized by re- ciprocating engines on account of the huge size and volume of the cylinders required, but it is quite otherwise with the steam turbine, where the large vol- umes of the low presure steam are exactly what are required for the highest economy. These considera- tions have led to the introduction of exhaust steam turbines, taking steam at atmospheric pressure and exhaust- ing into a condenser. When it is remembered that there is as much power in the steam from atmospheric pressure down to 27% in. as there is from 150 Ib. down to atmospheric pressure, it is easily seen that the power of a non-condensing plant can be doubled by the addition of an exhaust steam turbine and con- denser, and in cases where there is not a supply of cooling water, im- provements in cooling towers have enabled them to be put up both cheaply and well. | In this connection the use of inter- mittent supplies of exhaust steam, such as that obtained from engines running intermittently, as in rolling mills or winding engines at collieries, has received a great impetus by the utilization of thermal accumulators, in which the intermittent supply of steam is alternately condensed and re-evaporated, so that a constant flow is obtained for use in the exhaust | steam turbine. And yet another refinement has been introduced by the use of mixed pressure turbines, in which there is a low pressure part sufficiently large to give full power when working with exhaust steam, and if the, supply of this fails, a high pressure part is brought automatically into action, using steam direct from the boilers, and thus there is economical running, -whether the reciprocating engines sup- plying the exhaust steam are working or not. THE QUESTION OF VACUUM. In all turbines the question of vacuum is a very important one, and various improvements have been made in condensers to enable higher vacua