In the diagrams showing the connections of dynamoelectric machines, the heavy coils represent the series winding on the field magnets through which the entire current of the machine passes; the lighter coils represent the shunt winding on the field magnets through which only part of the main current passes. Lamps connected in series. Lamps connected in multiplearc or parallel. Edison three-wire system. DYNAMOS AND MOTORS. MOTOR CIRCUITS. To find the size of wire on stationary motor circuits: 10.8 ohms is the resistance of 1 ft. of commercial copper Under ordinary circumstances, 10% loss from generator to motor is a maximum on stationary motor circuits. EXAMPLE.-What is the size of wire necessary for a circuit on which a 10 H. P. 500-volt motor is running, when the distance between the motor and generator is 2,000 ft. and the loss is 5% ? In the table on page 253, the approximate efficiency of a 10 H. P. motor is given as 85%. c. m. = 10 X 746 X 4,000 X 10.8 = 29,165. In the table on page 238, the nearest size of wire corresponding to this area is No. 6 B. & S. gauge. The approximate weight and resistance per mile of round bare wire when d is the diameter in mils, are, for copper wire, Copper wire is approximately 1 times the weight of an iron wire of the same diameter. In determining the size of wire to be used for inside work, after finding the c. m., always refer to the table on page 238, and see that the wire obtained by the formula is sufficiently large to carry the current; if not, use larger wire, regardless of per-cent. loss. For pole-line construction, never use wire smaller than No. 8 B. & S. gauge. DYNAMO DESIGN. The fundamental principle of dynamo design is expressed by the formula in which E= NCn 108 X 60' electromotive force in volts given by the dynamo; number of lines of force used to magnetize the armature; number of conductors in a bipolar machine, measured all round the outside of the armature (whether in one or more layers), or in a multipolar machine, as measured from a point opposite one north pole to a corresponding point opposite the next succeeding north pole; n = number of revolutions per minute of the armature. For example, a 2-pole dynamo has 2,000,000 lines of force passing from the north pole through the armature to the south pole; there are 200 conductors on the surface of the armature, and the speed is 1,500 rev. per min. The electromotive force generated will then be If a 4-pole dynamo were used, having a 4-circuit armature and 4 sets of brushes, with 1,000,000 lines of force passing through any one pole piece, then the total number would be 2,000,000, because the same lines of force pass into a south pole that emerge from a north pole. With the same armature as above, the number of conductors to be counted is only 100, as taken from one north pole to the next, and the electromotive force is For determining the number of lines of force required in a specific case, the above formula may be reversed, and we have EX 108 X 60 N = |