Dynamic Resistance Measurement for OLTC Condition Assessment

Member companies       
  • ESBI Ireland
  • Liandon The Netherlands
  • Alliander The Netherlands
  • ARCE Spain
  • Gas Natural Spain
  • EAC Cyprus
  • Terna Italy
  • ELIA Belgium
  • MHY Pro Power Malaysia
  • Elektroprenos Bosnia
  • Megger USA, Sweden
  • ONE Nordic  Sweden
  • DV Power Sweden
  • MR - Reinhousen Germany, USA
  • Doble PowerTest UK
  • Omicron Austria
  • Seitz Instruments Switzerland
  • PG&E USA
  • ABB Transformers Sweden
  • ABB Components Sweden
  • STEVO Belgium
  • EGAT Thailand
  • EDF France
  • Siemens Germany, Italy
  • HydroOne Canada
  • Meralco Philippines
  • TEIAS Turkey
  • Aspect Energy Solutions Greece
  • Progress Energy USA
  • Western Power Australia
  • TNB Malaysia
  • Northwestern Energy USA
Resistance types


Reactance types


Dynamic resistance measurement is a DC test (transformer winding resistance) used to verify OLTC by recording the current at high sampling rate while changing the tap position, and presenting it graphically in time.

The group members presently use four instruments: SEITZ , DV-Power, and Megger Programma T1800 for graphing purpose, and Omicron for numeric analysis - and are aware of other products on the market. We invite users of other instruments to join our working group and contribute to the knowledge base.

There are other test methods to provide condition assessment of OLTCs - such as motor torque, infrared, vibration testing, DGA analysis in oil, etc. We will be looking into any correlation between these at a later stage. There is more information  in the literature section.



The Working Group  wants to exchange knowledge and experience, and learn from each other, collect information and improve diagnostic power of this method.
We do NOT want to endorse any product or manufacturer; however, we will, upon finalization of our work, approach manufacturers to implement our suggestions into their products. If you wish to join the WG, please send us an e-mail.



At the first meeting held in Dublin October 2010, participants agreed to collect and analyze information and case studies, and organize workshops to try various methods and procedures to establish better understanding of the test method.

The activities of the working group are defined, and various process variables and issues are outlined... here>>>>


Some of the first papers on this topics were published in 1995-2000. Since then, there was a lot of work and research done. We will be collecting all the literature published and offered on this topic.
List and links to download some of these papers can be found.... here>>>



Data and explanations collected on good and bad OLTC will be presented in "case studies" model, and these will constitute our knowledge base.
To get access to this information click...  here >>>>



The fifth meeting and workshop in Belgrade, Serbia October 28-29, 2013  report>>>

The fourth working group meeting, Paris January 30, 2013 at EDF R&D Clamart  report>>>

The third working group meeting in Stockholm February 15, 2012 report>>>

Our first meeting was held in Dublin during the FORUM 2010, the second meeting with workshop in Madrid on May 16, 2011.
See the report from the workshop  here >>>


NOTE: This is a WG protected web site, a proper credentials are required to access the information and literature.