Measurement of the transformer winding resistances
Measurement of the transformer winding resistances (photo credit:

Purpose of the measurement //

The resistance between all pairs of phase terminals of each transformer winding are measured using direct current. Furthermore the corresponding winding temperature is measured.

The measured resistances are needed in connection with the load loss measurement when the load losses are corrected to correspond to the reference temperature. The resistance measurement will also show whether the winding joints are in order and the windings correctly connected.

Apparatus and basic measuring circuit

The measurement is performed by TETTEX 2285 transformer test system.

Tettex 3 Channel Winding Resistance Meter
Tettex 3 Channel Winding Resistance Meter

This device is an automatic winding analyzer, optimized for three phase power and distribution transformer measurements.

Circuit for resistance measurement
Figure 1 – Circuit for resistance measurement


  • T1 – transformer under test,
  • A – Ammeter,
  • U – Voltmeter
  • B – DC supply,
  • Th – Thermometer

The principle of the measurement is as follows:

The voltage drop Udc caused by the direct current Idc an by the resistance RAB, RAC and RBC is measured.The resistances are then calculated from Udc and Idc using correction for the error caused by the internal resistance of the voltage measuring equipment.

The temperature is measured from oil filled thermometer pockets situated in the transformer cover by means of an electronic thermometer connected to the computer.

Test report

The resistance values and the average temperature are calculated. In the report the terminals, between which the resistances are measured, the connection, the tapping position and the average temperature of the windings during the measurement are stated.

Reference: Testing of power transformers – ABB

About Author //


Edvard Csanyi

Edvard - Electrical engineer, programmer and founder of EEP. Highly specialized for design of LV high power busbar trunking (<6300A) in power substations, buildings and industry fascilities. Designing of LV/MV switchgears.Professional in AutoCAD programming and web-design.Present on


  1. Oye
    Apr 06, 2015

    Hi dear Edvard
    I have a big problem while testing a zigzag transformer. I don’t know how to test vector group of zigzag transformer. I know how to normal power transformer like YNd11 or other groups by using Autocad, but I face problem with zigzag transformer. Could you please tell me how to test it? Thank you so much.


  2. kunle
    Apr 05, 2015

    this blog is very cool for knowledge sharing.Good job!

    What are the necessary steps in performing Insulation Testing on a feeder pillar 800Amps 8-ways.
    What parameters are important in calculating the voltage drop across distribution network of (300kVA/11/0.415kV) over a total distribution distance of 1.6km.

  3. Ribhu Gaur
    Mar 24, 2015

    How to find faults and type tests for inverter type 5 wdg transformers. typical ratings is 3,25 MVA , 33/ 0.38 KV each Dy11, Dy11 all 5 wdgs.

  4. Ribhu Gaur
    Mar 24, 2015

    I am M.Tech in Power Systems and a PMP working on Solar & Substations projects interested in Transformer, Breakers, Designing and Project Management articles.

  5. ashok sonawane
    Mar 05, 2015


  6. sourabh jaiswal
    Mar 03, 2015

    This is the best site for me and also for electrical engineers… thank u eep providing knowledge to me… awesome!

  7. Selby
    Feb 22, 2015

    Hi engineers,
    I would like to take your time and tell you my situation maybe dear engineers will assist.
    I am having S1 in electrical engineering ( process instrumentation) and N4 in electrical engineering (power) so I need a company which can train me I’m at Mpumalanga Middelburg.

    Your correspondence is very essential to me. Thanks for the advices in advance.

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