8-A] OPERATION AND LOAD TEST. 265 



pare 20, 21, Exp. 6-A. From the speed and frequency, com- 

 pute the number of poles per phase, 5. 



Note the manner in which the motor is to be connected to the 

 supply circuit and any special provision there may be for starting. 



22. Polyphase Motor. Connect in one line circuit an amme- 

 ter with a range, say, 50 or 100 per cent, in excess of the full-load 

 current. Start the motor in the regular manner, without load, 

 and note the starting current and the current when the motor is 

 running at full speed. Note the change in current as the motor 

 gains speed and as the motor is changed over from the starting 

 to the normal running conditions. Repeat the test with the motor 

 belted to some load (belted, for example, to a generator) and note 

 the current taken to start the motor and note that more time is 

 required to attain full speed. 



A 3-phase motor can be run on any 3~phase circuit, of proper 

 frequency and voltage, irrespective of whether the circuit is star, 

 delta, T or V connected. 



A 2-phase motor with two independent circuits can likewise be 

 operated on any 2-phase circuit. If, however, a 2-phase motor 

 has its circuits brought out to only three terminals, as (b) in 

 Fig. I, Exp. 6-A, it can only be operated on a 3-wire circuit and 

 cannot be operated on a quarter-phase system (as c or d). Con- 

 versely, if the motor is connected as c or d, it cannot be operated 

 on a 3~wire circuit, as b. 



23. Polyphase Motor Started with Secondary Resistance. 

 If a secondary starting resistance is provided, start the motor with 

 this resistance in circuit and cut it out, either gradually or in one 

 step, as the motor attains full speed. Note that the primary cur- 

 rent is increased by cutting out the starting resistance. Unless 

 specially designed for continuous operation, this resistance will 

 overheat if kept long in circuit. 



If a half -voltage supply is available, start the motor, with no 

 load, without the starting resistance, noting that the starting cur- 



