Dielectric Loss Calculation for XLPE Insulated Single Core Copper Cable

Dielectric loss calculation means the calculation of electromagnetic energy loss as inherent dissipation of dielectric material. 

Dielectric loss is represented as tan δ, widely known as the loss angle or loss tangent.

An example to calculate Dielectric Loss for 132 kV XLPE single-core copper conductor cable:

The above formula shows that the calculated dielectric loss for the mentioned cable is 0.38 watts per meter. The parameters used to calculate this value are shown.

Rated voltage 132 kV, so, phase to earth voltage is 76.2 kV or 76,200 volt (132/sq root 3);

Insulation thickness 18 mm (outer diameter – inner diameter)/2 or (74.5-38.5)/2;

The value of the loss angle tan δ depends on the type of material.

What Is XLPE?

XLPE is the short form of Cross-Linked Polyethylene (XLPE) is modified three-dimensional molecular structure of polyethylene that is manufactured from polyethylene plastic to improve some specific properties like heat deformation, smokeless during fire, abrasion, cand ontinuous work at 90 deg. and the highest 250 deg. centigrade temperature and so on.  

Basic molecular differences between LDPE, HDPE, and XLPE are shown in the figure. In modern cable engineering technology, XLPE provides an advantage for use as insulation.

Why Happen Dielectric Loss in XLPE?

If you look carefully at the XLPE molecular structure in the figure, you will find some open ended brunches. The main branches are strongly bonded to each other and form a three-dimensional strong structure, but one end opened brunch comparatively weakly bonded. When this material is placed in a high electromagnetic field, these weak branches vibrate continuously and lose energy, which is known as Dielectric Loss.

What Is Dielectric Loss?

A definition for Dielectric Loss is very difficult to find an easy and understandable to all. Most of the definitions are specialized and not recognizable to a non-technical or general person. That is why we are here today with this article to define the Dielectric Loss.

First of all, let us see some definitions of Dielectric Loss that are used today:

1> Dielectric Loss is defined as the inherent dissipation of electromagnetic energy as heat in dielectric materials, which is represented as Loss-angle or Loss-tangent tan δ.

2> Dielectric Loss is an energy loss in dielectric materials as heat dissipation due to cycle of current in a period of time. In alternating current system dielectric materials charged in first by one direction and then discharge and re-charged by opposite direction of current flow, this repetition system causes of unproductive heat generation which define as Dielectric Loss.

 

What are dielectric materials?

Dielectric material is such a kind of insulator material that can be polarized when applied an electric field to it. So, dielectric material having a polarization property. That means when dielectric material placed in an electric field it’s electric charge get aliened and attempt to flow but not flows. Dielectric materials are mainly use in capacitor for their dielectric property.

Dielectric material is a poor electrical conductor used as an insulator for an electrical system. Porcelain, Plastics, Glass, Mica, and the oxides of various metals are used as insulators. In electrical cable, PVC, HDPE, MDPE, LDPE, LLDPE, XLPE, EPR, etc. are used as insulation.

What is the Dielectric Strength?

Simply we can explain the dielectric strength of an insulating material that the material can withstand in their insulating property in which maximum electric field. Other way, how much strength can take a dielectric material without any breakdown.

Dielectric strength not same for all materials, to understand the comparison of dielectric strength in various materials find the table.

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What is the difference between an insulator and a dielectric?

The material used as an insulator for its electrical insulating or obstructing property; on the other hand, dielectric is used for electric charge holding or storing property. A common example of an insulator is the outer jacket of an electrical cable, and a dielectric is the insulating material in a capacitor.

Comparison of Dielectric Strength
Material	Dielectric strength (kV/inch)
Vacuum	20
Air	20 to 75
Porcelain	40 to 200
Paraffin Wax	200 to 300
Transformer Oil	400
Bakelite	300 to 550
Rubber	450 to 700
Shellac	900
Paper	1250
Teflon	1500
Glass	2000 to 3000
Mica	5000