IEC 60587 Electrical Insulating Materials for Use in Harsh Environmental Conditions - Test Methods for Evaluating Resistance to Tracking and Corrosion

The standard “IEC 60587 Electrical insulating materials for use in harsh environments - Test methods for evaluating resistance to tracking and abrasion” developed by the International Electrotechnical Commission (IEC) describes two test methods for evaluating electrical insulating materials for use in severe environments at power frequencies (45 Hz to 65 Hz) by evaluating resistance to tracking and abrasion using liquid contaminant and inclined plane samples:

• Method 1: Testing at constant voltage
• Method 2: Testing at gradually increased voltage

The constant voltage test method (Method 1) is the most commonly used method because it requires less continuous monitoring. The test conditions are designed to accelerate the production of effects, but do not reproduce all conditions encountered in service.

For the purposes of this standard, the following terms and definitions apply:

• A trace is a partially conductive path created by local breakdown on the surface of an insulating material.
• Tracking is the gradual formation of conductive paths produced on or within the surface of a solid insulating material due to the combined effects of electrical stress and electrolytic contamination. Tracking is usually caused by surface contamination. The remaining degraded materials do not necessarily remain conductive, especially after cooling.
• Erosion refers to the electrical loss of material due to stray current or electrical discharge.

In the tests, flat samples with a minimum size of 50 × 120 mm2 should be used. The preferred thickness should be 6 mm. Samples with different thicknesses can be used. The thickness should be stated in the test report.

Mechanical processing of test specimens is as shown in the figure given in the standard to allow attachment of electrodes.

Samples should be washed with a suitable solvent (e.g. isopropyl alcohol) to remove residues such as oily residues from preparation and handling. Samples should then be rinsed with distilled water.

Samples used for evaluation by Criterion B shall be marked with reference marks on both long sides 25 mm above the upper edge of the lower electrode. Unless otherwise specified, test samples shall be conditioned for at least 24 hours at a temperature of 23 degrees plus/minus 2 degrees and a relative humidity of 50 percent plus/minus 10 percent. When mounting cleaned and conditioned samples, care shall be taken to ensure that they are free from contamination.

Good wettability of the sample surface with the contaminant is an important prerequisite for this test method. Wettability should be assessed in advance. If the contaminant does not wet the surface, the samples may be slightly abraded. Grinding should be carried out under water with fine alumina or zirconium alumina abrasive until the entire surface is wetted. The samples should be rinsed appropriately with distilled water after grinding. Any grinding or other changes made to the surface should be noted in the test report.

An alternative to grinding is to temporarily increase the flow rate until the surface of the sample is suitably wetted before turning on the test voltage.

The equipment used in the tests consists of electrical apparatus and sample assemblies, each of which optionally contains a mounting support, electrodes, and a filter paper pad to feed the contaminant and a sample.

Since the test will be performed at high voltage, a grounded safety enclosure must be used. The circuit includes:

• A 5 to 0,1 Hz power supply with a sinusoidal voltage with not more than 6 percent total harmonic distortion and a nominal current of at least 45 A for each sample, variable up to approximately 65 kV
• Output voltage to be fixed at plus/minus 5 percent at nominal current
• True RMS voltmeter with 1,5 percent accuracy of reading
• A 10 W resistor with a tolerance of plus/minus 200 percent is in series with each sample on the high voltage side of the power supply.
• An overcurrent delay relay or other device connected in series with each sample that operates when 60 plus/minus 6 mA remains in the high voltage circuit for 3 seconds plus/minus 1 second.

If only one power supply is used for several samples, each should be provided with a circuit breaker or similar device to ensure that failure of a single sample does not result in the test voltage being switched off for all the other samples.

A sample assembly consists of:

• Test specimen optionally with a mounting bracket
• Electrodes with accessories such as screws, washers and nuts
• A stack of filter paper to feed the pollutant
• A montage

All electrodes, fasteners, and metallic mounting elements such as screws associated with the electrodes should be made of stainless steel, preferably type 302 (an 8 percent chromium, 8 percent nickel austenitic alloy).

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