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{{Language_sel|LANG=ger|ARTIKEL=Elektrische Durchschlagfestigkeit}}
{{PSM_Infobox}}
Electrical strength, Electrical breakdown strength or Electrical breakdown resistance
__FORCETOC__

==General principles and definition==

Electrical strength is the electric field strength at which the conductivity of an insulator increases by several orders of magnitude.

A polymeric insulation material cannot withstand the influence of a high voltage indefinitely. At a certain voltage or after a certain time after the application of a high voltage, it irreversibly loses its insulating properties. This is associated with structural damage to the [[Plastics|plastic]]. If the voltage applied to a test [[Specimen | specimen]] is continuously increased, the current flow increases proportionally at first, then non-linearly, and finally increases extremely sharply when a certain voltage is reached.

This voltage is called the breakdown voltage ''U''d. The conductivity increases by many orders of magnitude, and the [[Plastics|plastic]] loses its insulating properties under spark and light arc formation. This behaviour is called electrical breakdown. An analogous phenomenon is observed when a sufficiently high voltage is applied to the test [[Specimen | specimen]] for a sufficiently long time [1, 2].

==Fundamentals of electrical breakdown==

The mechanism of electrical breakdown in solid dielectrics is still poorly understood theoretically. Generally, two stages of electrical breakdown are distinguished. The breakdown-prepared stage, in which the plastic loses its electrical strength, and the stage in which the plastic is destroyed and breakdown is completed [3, 4]. Furthermore, depending on the mechanism, three basic forms of electrical breakdown can be distinguished:

* the purely electrical breakdown (field breakdown, internal breakdown),
* thermal breakdown and
* long-term breakdown (partial charge-induced breakdown, electrical ageing).

==Determination of the electrical strength==

For testing, the insulation material is clamped between two electrodes to which an electrical voltage is applied. During the test, the applied voltage is continuously increased until the electrical strength is reached [5, 6]. During this process, the test specimen heats up only slightly between the electrodes due to the short test time. The rapidly increasing electric field strength changes the structure of the insulator shortly before the breakdown by forming a more or less branched breakdown channel system, resulting in irreversible damage to the material, which enables the breakdown.

Electrical strength is a material-specific property. In addition to the [[Polymers & Structure | chemical structure]] of the [[Plastics|plastic]], it is strongly dependent on the thickness of the test [[Specimen|specimen]], the type of voltage stress and the ambient conditions.

==Electrical strength as a material parameter==

The [[Material Parameter | material parameter]] that characterises the behaviour of a polymeric insulating material with regard to electrical voltage stresses is the electrical breakdown strength ''E''d

{|
|-
|width="20px"|
|width="500px" | <math>E_d\,=\,\frac{U_d}{d}</math>,
|}

where ''d'' is the smallest distance between the electrodes and is also referred to as the impact distance. The electrical strength is not a material constant. In addition to the [[Polymers & Structure|chemical structure]] of the plastic, it is strongly dependent on the thickness of the test specimen, the way in which the stress is applied and the ambient conditions such as temperature and humidity. It represents the electrical field strength at which the conductivity of an insulating material increases by several orders of magnitude.

==Characteristic values of electrical strength for plastics==

As an example, short-time values of the electrical strength for selected [[Plastics|plastics]] are compiled in the table.

{| border="1px" style="border-collapse:collapse"
|+ '''Table 1''': Short-time electrical strength values for selected plastics [2, 7, 8] at T = 23 °C
!! style="width:200px; background:#DCDCDC" | Plastic film
!! style="width:133px; background:#DCDCDC" | Thickness ''d'' (μm)
!! style="width:133px; background:#DCDCDC" | ''E''d (kV mm-1)
!! style="width:134px; background:#DCDCDC" | References
|-
|polypropylene (PP)
|style="text-align:center"|40
|style="text-align:center"|200
|style="text-align:center"|[2]
|-
|polyester
|style="text-align:center"|40
|style="text-align:center"|160
|style="text-align:center"|[2]
|-
|poly (vinyl chloride) (PVC)
|style="text-align:center"|40
|style="text-align:center"|150
|style="text-align:center"|[2]
|-
|cellulose – aceto butyrate
|style="text-align:center"|40
|style="text-align:center"|130
|style="text-align:center"|[2]
|-
|cellulose triacetate
|style="text-align:center"|40
|style="text-align:center"|120
|style="text-align:center"|[2]
|-
|PE
|style="text-align:center"|40
|style="text-align:center"|110
|style="text-align:center"|[2]
|-
|PE
|style="text-align:center"|1,000
|style="text-align:center"|40
|style="text-align:center"|[7]
|-
|PET semi-cristalline
|style="text-align:center"|
|style="text-align:center"|30
|style="text-align:center"|[7]
|-
|PET amorphous
|style="text-align:center"|
|style="text-align:center"|250
|style="text-align:center"|[7]
|-
|PA 6
|style="text-align:center"|1000
|style="text-align:center"|15
|style="text-align:center"|[8]
|-
|PBT
|style="text-align:center"|1600
|style="text-align:center"|13
|style="text-align:center"|[8]
|-
|PVDF
|style="text-align:center"|1000
|style="text-align:center"|40
|style="text-align:center"|[8]
|-
|PEEK
|style="text-align:center"|1600
|style="text-align:center"|25
|style="text-align:center"|[8]
|-
|PS
|style="text-align:center"|1600
|style="text-align:center"|43
|style="text-align:center"|[8]
|-
|ABS
|style="text-align:center"|1000
|style="text-align:center"|41
|style="text-align:center"|[8]
|-
|SAN
|style="text-align:center"|1600
|style="text-align:center"|32
|style="text-align:center"|[8]
|-
|PSU
|style="text-align:center"|1000
|style="text-align:center"|30
|style="text-align:center"|[8]
|-
|PES
|style="text-align:center"|1000
|style="text-align:center"|35
|style="text-align:center"|[8]
|-
|PEI
|style="text-align:center"|800
|style="text-align:center"|33
|style="text-align:center"|[8]
|-
|PVC-U
|style="text-align:center"|600
|style="text-align:center"|40
|style="text-align:center"|[8]
|}

==Equipment system for measuring characteristic values==

The electrical parameters electrical breakdown strength and contact resistance are determined with an electric strength tester or a high-impedance resistance measuring device with connected measuring capacitor ('''Fig. 1''').

[[file:Elek_Durchschlagfestigkeit-1.jpg|450px]]
{|
|- valign="top"
|width="50px"|'''Fig. 1''':
|width="600px"|High-voltage tester RMG 15 AC with electrode arrangement and test cage from Cooper Bussmann, Wuppertal
|}

==See also==

* [[Electrical Conductivity | Electrical conductivity]]
* [[Volume Resistance | Volume resistance]]

'''References'''

{|
|-valign="top"
|[1]
|Schönhals, A.: Electrical and Dielectrical Properties. In: [[Grellmann,_Wolfgang|Grellmann, W.]], [[Seidler,_Sabine|Seidler, S.]] (Eds.): Polymer Testing. Carl Hanser Munich (2022) 3rd Edition, pp. 330–368 (ISBN 978-1-56990-806-8; ; e-book ISBN: 978-1-56990-807-5; ePub ISBN: 978-1-56690-808-2; see [[AMK-Büchersammlung | AMK-Library]] under A 22)
|-valign="top"
|[2]
|Carlowitz, B.: Tabellarische Übersicht über die Prüfung von Kunststoffen. Giesel Verlag für Publizität, Isernhagen (1992) (ISBN 978-3-980-29420-1; see [[AMK-Büchersammlung | AMK-Library]] under C 9)
|-valign="top"
|[3]
|Ku, C. C., Liepins, R.: Electrical Properties of Polymers. Carl Hanser Munich Vienna (1987) (ISBN 978-0-521-55219-6)
|-valign="top"
|[4]
|Whitehead, S.: Dielectric Breakdown of Solids. Clarendon Press, Oxford (1953)
|-valign="top"
|[5]
|DIN EN 60243-1 (2014-01): Electric Strength of Isulating Materials – Test Methods – Part 1: Test at Power Frequencies (IEC 60243-1:2013)
|-valign="top"
|[6]
|DIN EN 60243-2 (2014-08): Electric Strength of Isulating Materials – Test Methods – Part 2: Additional Requirements for Tests Using Direct Voltage (identical with VDE 0303-22:2014-08)
|-valign="top"
|[7]
|Bonten, C.: Kunststofftechnik: Einführung und Grundlagen. Carl Hanser Munich Vienna, 2. updated Edition (2016) (ISBN 978-3-446-44674-8) (see [[AMK-Büchersammlung | AMK-Library]] under H 52)
|}

==Weblink==

{|
|-valign="top"
|[8]
|[https://www.kern.de/de/richtwerttabelle https://www.kern.de/de/richtwerttabelle] (access on 20.07.2022)
|}

[[Category:Electrical and Dielectrical Testing]]
[[Category:Film Testing]]

Electrical Strength - Revision history