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# What is the Dielectric Estimation (Tan Delta) of a Transformer and What is the Test Purpose and Method?

##### What is Tan Delta (dielectric loss) Test?

Since transformer oil is used in circuit breakers, cables and switches, it is also necessary to test the conditioning of the oil. This is because it strengthens the dielectric properties of the oil and hence the Tan Delta Test is used to know the condition of the oil in the transformer. The complementary angle of the included angle (power factor angle Φ) between the current phase and the voltage phaser flowing in the dielectric under the action of the alternating electric field is called the dielectric loss angle δ. Under the action of the alternating electric field, the charge accumulated in the dielectric has two components:

(1) Active power. One is the power consumed for heating, also known as the in-phase component;

(2) Reactive power, also known as out-of-phase component. The ratio of the out-of-phase component to the in-phase component is called the dielectric loss tangent tanδ. tanδ=1/WCR (where W is the angular frequency of the alternating electric field, C is the dielectric capacitance, R is the loss resistance). The dielectric loss tangent is a dimensionless physical quantity.

##### What is the Purpose of Tan Delta (dielectric loss) Test?

The main purpose of the tan delta test is to ensure that the transformer operates safely and reliably. It gives the result of the insulation behavior of the windings by calculating the spread factor and capacitance values.

With the tan delta test method, the loss factor and capacitance values ​​at the required frequency level can be easily known. Thus, any aging factor can be detected earlier and the relevant action can be taken.

The dielectric loss of the transformer generally refers to the magnetic dielectric loss. It mainly consists of two parts: one part is hysteresis loss and the other part is eddy current loss.

Hysteresis Loss: In a transformer, hysteresis loss occurs due to magnetization saturation in the core of the transformer. Magnetic materials in the core eventually become magnetically saturated when placed in a strong magnetic field, such as the magnetic field created by an AC current.

Eddy Current: Eddy currents are currents that circulate in conductors like swirling eddies (an eddy) in a flow. They are induced by alternating magnetic fields and flow in closed loops perpendicular to the magnetic field plane.