COMSOL 6.4 - Partial Discharge Inside Solid Dielectrics

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Partial Discharge Inside Solid Dielectrics

The electrical insulation strength of gases is generally much lower than that of solid dielectrics. As a result, small voids, cracks, or imperfections within solid insulation can give rise to localized electrical discharges, commonly referred to as partial discharges (PDs). Although these discharges do not bridge the entire insulation system, they can gradually degrade the material, leading to long-term insulation failure. For this reason, partial discharge detection and analysis are widely used in high-voltage engineering as a diagnostic tool for assessing insulation condition.

This model simulates partial discharges in a spherical air void embedded within a solid dielectric subjected to a 50 Hz AC power frequency. The formulation includes detailed charge transport processes for electrons and ions, fully coupled with electrostatics. Surface charge accumulation at the gas–solid interface is also treated self-consistently, as it plays a key role in the development and quenching of the discharge.

The simulation outputs the Phase-Resolved Partial Discharge (PRPD) pattern, which provides insight into the timing, magnitude, and polarity of discharges relative to the applied voltage cycle. These results can be compared directly with experimental measurements, offering a valuable tool for studying the mechanisms of partial discharge initiation and progression in solid insulation systems.

Model Definition

The Electric Discharge interface is used to simulate the partial discharge. The built-in charge transport model is used:

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e, p, n denote electrons, positive ions, and negative ions

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ni is the number density of the charge carrier (SI unit: 1/m3)

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E is the electric field (SI unit: V/m)

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zi denotes the carrier charge (SI unit: 1)

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μi denotes the carrier mobility (SI unit: m2/(V·s))

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wi is the drift velocity in the electric field (SI unit: m/s)

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Di is the diffusion coefficient (SI unit: m2/s)

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Ri is the reaction rate (SI unit: 1/(m3·s))

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α is the ionization coefficient (SI unit: 1/m)

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η is the attachment coefficient (SI unit: 1/m)

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βep is the electron–ion recombination coefficient (SI unit: m3/s)

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βpn is the ion–ion recombination coefficient (SI unit: m3/s)

The above transport equations are fully coupled with Poisson’s equation through the electric field and the space charge:

where e is the elementary charge.

The Gas–Solid interface is modeled with the dedicated Dielectric Interface, Surface Transport feature described in the Electric Discharge Module User’s Guide.

Results and Discussion

Figure 1 shows the PRPD measured by discharge current as a function of phase angle. Figure 2 shows the surface charge density at the void-solid interface as a function of direction angle for several time instants.

Figure 1: The partial discharge current as a function phase angle.

Figure 2: The distribution of surface charge density at the void-solid interface.

Figure 3: The distribution of electric field at different phase angles.

Electric_Discharge_Module/Partial_Discharges/partial_discharge

Modeling Instructions

From the menu, choose .

In the window, click

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In the window, click

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In the tree, select > .

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In the tree, select > .

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Rectangle 1 (r1)

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Global Definitions

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In the table, enter the following settings:


Name	Expression	Value	Description
V0	12[kV]	12000 V
f	50[Hz]	50 Hz
t	0[s]	0 s
Va	V0sin(2pift)	0 V

Add Material from Library

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Air [Kang et al. 2003] (mat1)

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Electric Discharge (edis)

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Enable the isotropic diffusion stabilization.

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In the V0 text field, type Va.

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Step 2: Time Dependent

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Global Variable Probe 2 (var2)

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In the table, enter the following settings:


Expression	Unit	Description
Va	kV	Applied voltage

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In the text field, type 2*pi*f*t.

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In the field, type deg.

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Surface Charge Density

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Surface Charge Density

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2D Plot Group 3

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Solution Array 1

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Solution Array 1

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Solution Array 1

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button in the toolbar.

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