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Home / Technical Articles / Power Transformer Capacitance and Dissipation Factor Test
Figure 1 - Capacitance and Dissipation Factor Test connection diagram
Figure 1 – Capacitance and Dissipation Factor Test connection diagram

Transformer insulation system

The capacitance and dissipation factor test is an AC low voltage maintenance test and is very similar to the power factor test.

The test as it is termed, measures the capacitance and dissipation factor (or loss factor) of the transformer insulation system. This test may be required to be performed during the acceptance testing stage to establish a baseline reading for future test comparison.

While the transformer preparation is identical to the power factor test procedure, there is no requiremnts to make connection changes once the initial test set connections are made. High-voltage winding and low-voltage winding test set connection changes are made through a selector switch provided on the test set.

Winding capacitance and dissipation factor test values are obtained by balancing a null meter for each variable at every the measured variable selector switch positions.

Capacitance and Dissipation Factor Test Set
MEGGER Semi-Automatic Capacitance and Dissipation Factor Test Set (Direct readout of capacitance, dissipation factor and watts dissipated)

Capacitance and Dissipation Factor Test Procedure

(Two winding dry-type transformer)

Step 1.

Isolate the equipment, apply working grounds to all incoming and outgoing cables and disconnect all incoming and outgoing cables from the transformer bushing terminals. Disconnected cables should have sufficient clearance from the switchgear terminals greater that the phase spacing distance.

Use nylon rope to hold cable away from incoming and outgoing terminals as required.

Step 2.

Isolate the neutral bushing connection if applicable from the transformer grounding bar.

Step 3.

Short-circuit all high voltage bushing terminals together.

Step 4.

Short-circuit all low voltage bushing terminals and the neutral bushing terminal together.

Step 5.

Connect the capacitance and dissipation factor test set. Refer to Figure 1 above.

Step 6.

Record the capacitance and dissipation factor values once the null meter is balance for both phasing position. Record values for the five test-variable selector switch position.

Power Transformer Testing – Measuring capacitance and power factor or dissipation factor

The condition of the bushings and the overall insulation of power transformers can be investigated by measuring the capacitance and dissipation factor, also known as the tangent delta, or power factor. Aging and decomposition of the insulation, or the ingress of water, increases the losses and thus more energy is turned into heat in the insulation.

The level of this dissipation is expressed by the dissipation factor or power factor.

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Reference: Substation Commissioning Course – Raymond Lee, Technical Trainer

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Edvard Csanyi

Electrical engineer, programmer and founder of EEP. Highly specialized for design of LV/MV switchgears and LV high power busbar trunking (<6300A) in power substations, commercial buildings and industry facilities. Professional in AutoCAD programming.


  1. Eng. Omar
    Apr 28, 2020

    Many greeting Sir ;
    Thank you so much for your efforts and very helpful information regarding electrical transformers , We have Tan Delta 4300 test device , and power transformer 63MVA , 132/33/11 Kv , Yyd . And when we connect CH cable pf the device to the Neutral of 132KV side , the test device give us alarm and did not complete the test .But when we shorted phase A,B and C with the neutral of 132Kv side and connect CH of the device to the short wire ,the test is done correctly . Why we are cannot test by connect CH to the neutral directly ? knowing that we are doing this testing way by connect to the neutral of the Star side of transformer directly when we use Megger to test the insulation resistance of the transformer . With my best regards .

    Aug 26, 2019

    Well explained. Thank you so much.

  3. Electrical concepts
    Jul 08, 2019

    Very Nice article. Well explained and the transformer must be get tested for tan delta test for reliable operation.

  4. Abg Nizam
    Nov 14, 2018

    What to do if the DF of Transformer is critically high say 5%?

    Please advise.

  5. Ubaid
    Apr 03, 2018

    what is the acceptable range of values of Capacitance and Dissipation factor of Power Transformer (132KV) voltage level?

    Dec 20, 2017

    Working with power sector

  7. Narsimhulu Nayini
    Jul 27, 2017

    Join me into this group

  8. Ghulam Hyder
    Dec 21, 2016

    Please tell the what actually the CNDF equipment is giving the test equipment to get the results? For-example in megger the Megger device is giving the voltage to winding to get the results in Ohms so here what CNDF device is sending to transformer to get the results? or say internal theory of CNDF device ?

  9. Enrique Galindo Ibarra
    Nov 22, 2016

    Good evening

    If I doesn´t connect the shortcircuit between H1, H2, H3 and H0. How many is the tan delta value compared as when I shortcircuit them? Is it lower, because I excited less winding?

  10. Adnan Munir
    May 21, 2016

    Dear Edvard,
    Kindly tell me what is the Specific value of capacitance 7 dissipation factor of Power Transformer.
    Kindly reply to me above given E-mail Address.
    me waiting your best response.

    Thanks & regard,

    Adnan Munir

  11. Jimi Jaspar Kispotta
    Apr 01, 2016

    I have a query regarding the Insulation Power factor test results . There are various design of transformers which are available now for dry type and liquid type. Is there a base line which says that the IPF values for the dry type and liquid type should be (_) this value irrespective of the design of the transformer.
    Or can we also get different values for same (e.g liquid type ) but different design transformer ( say e.g pad mounted or substation transformer )


  12. Pravin
    Jul 13, 2015

    Hello Edward,

    Glad to know about your experience in Busbar Trunking Systems. We are manufacturers of Busways (Sandwich <6300Amp) and would like to get in touch with you for some work which might be of your interest. Would it be possible for you to share your email id ? Regard Pravin ([email protected])

  13. salimkhan
    Jul 27, 2014

    thank u sir plz can give me your face book ID i will be great full i have a lot of questions to ask

  14. vipin
    Feb 20, 2014

    send me power system book pdf please on my mail [email protected]

    • Edvard
      Feb 20, 2014

      Dear Vipin, feel free to use search box on the top.

  15. Brian Sussex
    Jan 22, 2014

    By chance will you have a segment on transformer doble testing??

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