CHAPTER XII 

 DIRECT CURRENT RAILWAY MOTORS 



Direct Current Series and Railway Motors 



The principal type of series motor is the railway 

 motor. Other types, however, are built for use with 

 hoists, air compressors, pumps, etc. As all these motors 

 are designed for intermittent service, the test, unless 

 otherwise specified, is a one hour run at full load, with 

 the brushes set on the neutral point. The load must 

 never be taken off a series motor unless the armature 

 circuit is first opened, otherwise the motor will run 

 away. For the same reason a series motor should 

 always be started under load. All running light tests 

 must therefore be made with the field separately excited. 



As the tests on railway motors are very complete 

 and the general method applies to tests on any series 

 motor, those on railway motors will be discussed more 

 or less in detail. Hot and cold resistances must be taken 

 on all railway motors and high potential applied both 

 while the motor is cold and hot. 



GENERAL TESTS consist of sufficient preliminary 

 tests to warrant engineering approval or disapproval 

 for production. It is impossible to definitely define 

 the heading, since the tests may include only a few minor 

 tests, or they may include complete and special tests. 

 For instance, it may be necessary to make slight changes 

 in either the construction or design of a standard motor 

 in order that it may meet special requirements. After 

 these changes have been made, tests are conducted 

 to make sure that the motor will meet such conditions 

 satisfactorily. These tests are included under general 

 tests, and if after completion they are found to be 

 satisfactory, engineering approval is given for the 

 production of the machine in question. 



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