Publication: Western Electrician
Chicago, IL, United States
Wagner Alternating Apparatus.
For years the Wagner Electric Manufacturing company of St. Louis has been identified in the closest manner with the development of electrical apparatus. Starting in a conservative way, this concern has kept continually increasing its plant until it now occupies one of the finest factories in the United States for the production of its varied product. As the alternating apparatus branch of this company's business, however, is the one through which it is best known, the accompanying cuts are of interest in that they present a good idea of the variety of types of the company's product.
With reference to self-starting single-phase alternating current power motors, the Wagner company states that pressure is being constantly brought to bear on owners of stations to induce them to throw away their single-phase apparatus and install instead polyphase apparatus. The assertion is made that no alternating current central station can be made to pay until a day load is secured, and that with single-phase apparatus, such a day load cannot possibly be secured, for the very simple.reason that "there are no commercially successful single-phase alternating current power motors." Such an assertion, the Wagner company claims, is now a flat contradiction of fact, for it has had in operation for many months, undergoing the most severe tests to which power motors are ever subjected, single-phase, self-starting induction motors. The principle of the motor is extremely simple, there being a primary and a secondary element, bearing the same relation to each other as the primary and secondary coils of a static transformer. The primary constitutes the stationary element corresponding to the field of a direct current motor. The secondary is the movable element, corresponding to the direct current "armature." This secondary is constructed to operate in a double way. For starting, it is thrown in series with the primary by means of carbon brushes running on a commutator. With this connection the operation of the motor is in every essential feature exactly that of a series direct current motor. On attaining the running speed the connections are simply changed, the commutator, in the operation of changing, being completely short-circuited and the carbon brushes lifted off. The motor then runs as a non-synchronous induction motor. These motors are not affected by switching at the station, nor is their operation interfered with by the interrupted electromotive force on the line. As they are induction motors, they do not run in synchronism with the generator at the station and do not experience the unfavorable condition of what is known as getting out of step with the generator.
They further will not slow down and stop when a heavier load than normal is applied, as is the case with the synchronous motor, but when the excess load is discontinued will pull up to normal and continue the same as before. An illustration of the motor is presented herewith. Fig. 1 shows the general mechanical design. The very rapid rise of the efficiency curve on light loads is a significant feature. Not less noticeable and noteworthy is the high efficiency maintained up to the point of 50 per cent. overload. This small drop in speed with increased loads is a further point of superiority, while the high power factor at all loads is a characteristic unprecedented in motors of this capacity. It is possible to pull up from rest double the rated load of the motor with a current only exceeding the load current by 50 per cent. The motor very quickly runs up to the load-service speed, and operates under any and all loads with smoothness and quietness. Another feature which will prove most attractive to the central station man is that there are no pulsations of current with this motor. The motor is also absolutely unaffected by, momentary interruptions in the current supply or a sudden change in frequency or voltage, resulting from necessary station switching.
The frequencies generally found in single-phase stations are 16,000 and 7,206 alternations per minute. This design of motor is guaranteed to operate with equal effectiveness on either.
One of the needs in alternating current central station equipment has been a reliable dead-beat, wide-scale, indicating switchboard instrument. This company has developed a line of indicating voltmeters, ammeters and wattmeters which it claims meet every requirement. These instruments are a radical departure in design, both mechanically and electrically. The moving parts are carried on a vertical shaft, the lower point of which runs in a jewel bearing. This point is at all times immersed in oil, and, accordingly, friction is reduced to a minimum. The deflecting force is so very great that every point on the scale has a positive differential value, and successive deflections, with the same deflecting force, are absolutely the same. Furthermore, the inductive error is eliminated, voltmeters, for example, reading practically the same on direct curent as on alternating current of 16,000 alternations. Finally, every scale is accurately plotted by independent calibration, and as there are no parts the constant of which is subject to change, indications are permanently reliable.
In the Wagner instruments. Figs. 2, 3 and 4; the oscillating of the indicating needles has been wholly eliminated by floating all the moving parts in a light, colorless, odorless oil, a couple of small aluminum vanes serving to afford a dashpot action by which needles are held stationary against any passing, instantaneous disturbance, and at once brought to rest on throwing over. That the instruments are economical in operation is apparent from the statement that the voltmeter consumes but seven watts on 110 volts pressure.
Admirable provision has been made for illumination of the scales; the lamps, two in number for each instrument, are eight candle power, 50 volts each, connected two in series and mounted on a special bracket which holds them in the necessary position. The body of the instrument, which extends through the board, is highly japanned in black. The front cover is of polished brass. Provision is made to keep all dust out of the instrument. The oil is carried in the cup forming the rear portion of the body. The cover to this portion is removable, affording easy inspection and filling of cup with oil. The ammeter is identical in general appearance with the wattmeter and voltmeter, but the principle employed is somewhat different. In instruments up to 100 amperes capacity the entire current of the circuit is sent through the instrument coil. Above 100 amperes use is made of a series transformer, the primary of which is cut in oh the bus-bar. In the voltmeter movement use is made of the dynamometer principle. The scale, being one of 67 degrees arc, is almost absolutely uniform throughout the range. Scales can be plotted to any value desired, from zero to the maximum called for, or from any specific point to the maximum. The maximum pressure of operation is 150 volts. Above that point step-down transformers are furnished.
In the wattmeter the dynamometer principle is again employed. The pressure coil is connected to the 100 volt ends of a step-down transformer. The series