Testing arc resistance

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Several other related properties appertaining to tracking, arc resistance, and surface discharge resistance have standardized test methods [29-32]. These procedures arc cither very specialized or else controversial and are not likely to be of general interest. For this reason, no detail is given a discussion of arc resistance test methods will be found in the paper by Mathes [3.3]. 

The arc resistance of an insulator may be defined as the time in seconds that an arc may play across the surface without burning a conducting path. A schematic of an arc-resistance test is shown in Figure 3.55. 

Sequence of 1-min current steps in arc resistance test according to ASTM D 495-73... 

The dry-arc resistance test measures the ability of a material to withstand the discharge across its surface of an initially intermittent and then continuous high voltage, low current arc. 

Figure 4-3. (a) Typical setup for arc resistance test. (Courtesy of Bayer Corporation.) (b) Commercially available arc resistance tester. (Courtesy of CEAST U.S.A. Inc.)... 

Attempts have been made to develop true, high-current arc resistance tests. A standardized German test employs carbon electrodes with 5 A at short circuit and 250-V dc (open circuit). The test is so severe that it destroys most organic materials and is useful only for inorganic materials. A United Kingdom test uses the test geometry of a small circuit breaker with a plastic arc chute. This practical approach evaluates plastics under actual operating conditions. However, the results depend on the size and shape of the arc chute standardization is difficult. 

Arc Resistance Tests performed to determine the resistance of a polymer compound to electric arcs such as appear in high voltage switch-gear and in circuit breakers. 

Electrical Resistance—Conductivity. Most fillers are composed of nonconducting substances that should, therefore, provide electrical resistance properties comparable to the plastics in which they are used. However, some fillers contain adsorbed water or other conductive species that can gready reduce their electrical resistance. Standard tests for electrical resistance of filled plastics include dielectric strength, dielectric constant, arc resistance, and d-c resistance. 

This test shows the ability of a material to resist the action of an arc of high voltage and low current close to the surface of the insulation in tending to form a conducting path therein. The arc resistance data are of relative value only for distinguishing materials of nearly identical composition, such as for quality control, development, or identification. 

The arc resistance of a polymer is the length of time for which we can apply an electrical discharge to its surface before it breaks down and begins to conduct electricity. Breakdotvn typically takes the form of conductive carbonaceous tracks that are caused by oxidation due to locally high temperatures. Polymers -with lowpolarity typically fare better in this test than polar polymers. Arc resistance is reduced by dirt, moisture, and other surface contaminants. 

The arc resistance (ASTM-D495) is a measure of the ability of the polymer to resist the action of a high-voltage arc on the surface of the polymer. The results of this test may be used to classify materials in the laboratory. 

ASTMD495, Test Methodfor High-Voltage, Low-Current, Dy Arc Resistance of S olid Electrical Insulation, Vol. 8.01, ASTM, Philadelphia, Pa., 1989. 

Additives such as antioxidants can cause staining of any surface that comes in contact with or near to the polymer material. The problem is mostly found with rubber or flexible cellular seals and is an important consideration in such consumer products as cars and kitchen appliances. The compounder has to achieve adequate environmental resistance without an unacceptable degree of staining. No staining would be ideal, but in practice some staining may have to be tolerated. To ensure that levels arc acceptable, tests to produce and measure staining arc often included in specifications. 

ASTM Method D495, Standard method of test for high voltage, low current arc resistance of solid electrical insulating materials. 

Fire resistance is the ability to prevent the passage of flame heat, smoke, and lire gases in a defined (often developed) fire environment. Polymer products arc rarely required to meet fire resistance requirements on their own, although they may be used in composite systems. Fire resistance tests of a similar nature are specified in many countries and by the ISO. 

ASTM D 495-73 (reapproved 1979) is devoted to the measurement of high-voltage, low-current, dry arc resistance of solid electrical insulations. The test is intended to simulate conditions in alternating circuits operating at high voltage but at currents limited to tens of milliamperes. The arc resistance is the total elapsed time of operation of the test until failure occurs. Types of failure may be ... 

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