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

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. 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 (

  2. 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

  3. vipin
    Feb 20, 2014

    send me power system book pdf please on my mail

    • Edvard
      Feb 20, 2014

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

  4. Brian Sussex
    Jan 22, 2014

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

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