. Electrical world. een developed for field rheostatsfor shunt dynamos and motors by Mr. Krause and others. Onaccount of limited space, we cannot attempt to detail all of thesemethods, but would refer to the excellent book, Die Gleichstrom-maschine, by E. Arnold, Vol. II, where they are lucidly described. The Design of Motor Starting Rheostats. By M.\x Freimark. The article of Mr. Arthur H. Ford in your issue of January 9 leadsme to submit a similar and well-known method for designing motor-starting rheostats. Assuming that the object is to make the starting current,always equal to the normal
. Electrical world. een developed for field rheostatsfor shunt dynamos and motors by Mr. Krause and others. Onaccount of limited space, we cannot attempt to detail all of thesemethods, but would refer to the excellent book, Die Gleichstrom-maschine, by E. Arnold, Vol. II, where they are lucidly described. The Design of Motor Starting Rheostats. By M.\x Freimark. The article of Mr. Arthur H. Ford in your issue of January 9 leadsme to submit a similar and well-known method for designing motor-starting rheostats. Assuming that the object is to make the starting current,always equal to the normal current i, is =: i. If, in this case, R isthe entire resistance of the armature, connections and starter, Ethe line (see Fig. i), then we have the equation: E E If e is the motor , r = the resistance of the motor, then E — e E — e = i R, or Ij =^ , Rs being the starter resistance, Rs + r Rs + r — Rm„vhen one section {Rm,, ) is cut stated by Mr. Ford, there will be a continual increase and. FIGS. I .^ND 2. decrease of the current between i^ and t^, as is to be seen from Fig. 2. The ratio of these extreme currents may be / Rs + r R R — R, h Rs + r — R,„„ n being the number of sections. ^i = r -^ Rm^; r^ = r + R,„^ + R,„„; r,, = >? + /?„,, + /?,„, -f . . + R„, ,^„_| + R,„^^ = R = — = —, etc. Rn-v 1 = • • ?/ r^ = / r^ ^ r . ^- as r^ ^ A . r; . . ?« = ^ ? r,,.^ = That is to say, the resistance must increase geometrically with ? R When is ^= i then a = f = per cent, loss, since£ = is R, . E := i . r,i r is R .^s now n = logy the number n of sections is fixed by the March 12, 1904. ELECTRICAL WORLD and ENGINEER. S2I allowed drop of pressure in the armature. The following table gives some usual values of 0. and n, and showsthe influence of ^ the ratio of i,, and t^: The conditions are shown I I cally in Fig. 2, where A ft 5 4 B = C D = y. QS= r„ ; R S = r„ 1-35
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectelectri, bookyear1883
