Direct current traction motors operate in one of the most severe environments of any rotating electrical apparatus. Since the motors are used on transit systems, extremely high reliability is essential. This level of reliability can be increased by testing before the new or rebuilt armatures are installed. In order to test the bar-to-bar and coil insulation at relatively high voltage, either a high frequency or pulsed test must be used. Two approaches to this test have been developed and used by the various manufacturers. The first technique uses a standard current surge generator and pulses a span of bars in series between two probes connected to the commutator. The voltage drop across this span produces the bar-to-bar stress on the system. Insulation faults are detected and located by simultaneously comparing readings across two equal numbers of bars on a dual channel oscilloscope. The second technique uses a high current surge generator and tests a single pair of bars. The higher current level is required because of the lower inductance of a single coil. The advantage of this test is that it more closely approximates the operating condition of the armature. Also, since the voltage is not dropped across a group of bars, a uniform bar-to-bar distribution of voltage need not be assumed. Tests have shown that the voltage distribution using span testing is far from uniform. Location of any insulation fault is also facilitated by testing individual coils. Following the description of two test methods, a comparison of test results is made. The advantages of both techniques are discussed.

Media Info

  • Pagination: p. 65-67

Subject/Index Terms

Filing Info

  • Accession Number: 00316265
  • Record Type: Publication
  • Source Agency: Engineering Index
  • Report/Paper Numbers: IEEE 79CH1510-7-EI Conf Paper
  • Files: TRIS
  • Created Date: Sep 16 1981 12:00AM