Influence of Rotor Eccentricity on the Reliability of the Pole Drop Test for Salient Pole Synchronous Machines

Han Ju Kim, Juan De La Morena, Carlos A. Platero, Muhammad Faizan Shaikh, Thotahage Sumadhurie Hansika, Sang Bin Lee

Research output: Contribution to journalArticlepeer-review

5 Citations (Scopus)


The pole drop test is the most common test for detecting inter-turn insulation failure in the rotor field winding of salient pole synchronous machines. Shorted field turns are detected by comparing the voltage drop across each rotor pole with ac voltage applied to the field winding terminals. It is a simple and effective test that is usually performed with the rotor inserted for convenience and high sensitivity. In this work, the influence of rotor eccentricity on the pole drop test is analyzed. It is shown that anomalies in the airgap can interfere with the pole drop test to cause false positive indications. Alternative test options immune to false indications are also suggested in this letter. The analysis and test options for screening false indications due to eccentricity are verified on 4 and 6 pole, 5, 5.5, and 30 kVA synchronous machines under emulated fault conditions. It is shown that eccentricity interferes with the pole drop test and that testing under dc excitation is immune to eccentricity although the sensitivity is lower, which are not reported elsewhere.

Original languageEnglish
Pages (from-to)2240-2243
Number of pages4
JournalIEEE Transactions on Energy Conversion
Issue number3
Publication statusPublished - 2022 Sept 1

Bibliographical note

Publisher Copyright:
© 1986-2012 IEEE.


  • Off-line testing
  • pole drop test
  • rotor eccentricity
  • rotor field winding
  • salient pole synchronous machine
  • turn insulation failure

ASJC Scopus subject areas

  • Energy Engineering and Power Technology
  • Electrical and Electronic Engineering


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