. Railway and locomotive engineering : a practical journal of railway motive power and rolling stock . with i-1- when the load is taken away, withvoltage still applied. The motor will>peed up as the load comes off, witha drop in current, as less and less dif-ference between the impressed voltageand counter is required to pro-duce the necessary torque; also thefield is weakening, which increases thespeed. The motor will, if the load isremoved, race and be destroyed. Thusseries motors should not be fitted witha belt, but with a positive drive, unlesssome automatic feature is installed
. Railway and locomotive engineering : a practical journal of railway motive power and rolling stock . with i-1- when the load is taken away, withvoltage still applied. The motor will>peed up as the load comes off, witha drop in current, as less and less dif-ference between the impressed voltageand counter is required to pro-duce the necessary torque; also thefield is weakening, which increases thespeed. The motor will, if the load isremoved, race and be destroyed. Thusseries motors should not be fitted witha belt, but with a positive drive, unlesssome automatic feature is installed tocut off the power, in case the beltshould slip off or break. The shunt motor is so called becausethe field takes, or shunts its current,from the line independent of the cur-rent in the armature. In other words,the current passing through the arma-ture does not pass through the diagrammatic sketch is shown in , and referring to Fig. 4 connectionsare shown, so that the motor will op-erate as a shunt instead of a series mo-tor. From these diagrams it is readily Series Connections+ ». Shunt Connections nzn i—1 FIG. 4. THE STAR SHOWING SERIES AND SHUNT WINDING. the load. The series motor will alwaysgive the same torque for the samevalue of armature current (which alsopasses through the field) independentof the voltage impressed at the termi-nals of the motor, as torque is equal tothe armature current times the fieldstrength. With lower voltage the mo-tor will, of course, run slower, becausethere is less back to series motors are used for elec-tric locomotives on railway work, asthey are required in these cases to startup against a heavy load and in railroadpractice saving of power consumptionis a very important item. Moreover,the automatic variable speed character-istic of the motor is an advantage. Byregulating the voltage to the motor asslow speed as desirable can be ob-tained. Series motors are also u = edfor cranes, hoists and for steel ro
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