Current Transformer Testing (CT)

I wrote an article for the NETA World magazine in 2004 that covers several different manual techniques for Current Transformer Testing that should help even the most experienced technicians.  Here’s a summary of the current transformer testing paper.

Back to the Basics – Current Transformer Testing (CT) 

As test equipment becomes more sophisticated with better features and accuracy, we risk turning our field personnel into test set operators instead of skilled field service technicians. A test set operator connects the leads, pushes the buttons, and records the results; hoping the numbers he records are good. A test technician connects the leads, pushes the buttons, and records the results. However, the test technician understands what the test set was doing while all the lights were flashing, and why. The technician can also evaluate the results and determine if a re-test is necessary with different connections or substitute external equipment for tests when the test equipment malfunctions. The purpose of this article is to help a test set operator understand the tests they perform, and hopefully add or re-enforce a test technique to the test technician’s repertoire.

 Table of Contents

• Description of operation (Page 1)
• 1.0 Visual and Mechanical Inspections (Page 2)
  • 1. Compare equipment nameplate data with drawings and specifications (Page 3)
    • a) Accuracy (Page 3)
    • b) CT Class (Page 4)
    • c) Burden (Page 5)
  • 2. Inspect physical and mechanical condition (Page 8)
  • 3. Verify correct connection of transformers with system requirements (Page 8)
  • 4. Verify that adequate clearances exist between primary and secondary circuit wiring. (Page 10)
  • 6. Verify that all required grounding and shorting connections provide contact. (Page 10)
• 2.0 Electrical Tests – Current Transformers (Page 10)
  • 1. Perform insulation-resistance tests (Page 10)
  • 3. Perform a polarity test of each current transformer (Page 12)
  • 4. Perform a ratio-verification test (Page 23)
  • 5. Perform an excitation test (Page 24)
  • 6. Measure current circuit burdens (Page 27)

You can download the complete Current Transformer Testing article as I submitted it with the link below.

Back to the Basics – Current Transformer (CT) Testing

This article will be the basis of an upcoming book and I welcome any corrections or suggestions you may have.  I am also looking for pictures of different kinds of CTs.  I am also looking for BAD test results along with a description of what you found.  I have thousands of good CT results but have only one bad CT result so far.  You will receive a free copy of the book and credit if we use your submission.