7.  Tensile Load Test - The element of time plays an important role in characterizing the mechanical properties on many polymer  materials, particularly plastics and elastomers. Both plastics and elastomers share some of the features of a viscous fluid where stress is proportional to strain rate but independent of the strain itself, that is, they are viscoelastic. Thus, it becomes important to be concerned about how long the material must sustain load, how fast it is loaded, and how far it is compressed or elongated. It is important to recognize that these factors should be of concern and that standard material test methods often have to be modified to reflect this concern. 

Three samples shall be subjected to a tensile load that shall be increased rapidly but smoothly from zero to 75% of specified mechanical load (SML) and then gradually be increased to the SML in a time between 30 and 90 seconds. If 100% of the SML is reached in less than 90 seconds. The test is passed if on failure occurs. The load shall then be increased until the insulator fails. The historical failure loads shall justify the manufacturer choice of SML

 

 

8.  Torsional Load Test - Three insulators shall be tested to 50 Nm and release. The toraional load shall be applied to the test specimen through a torque member so constructed that the test specimen is not subjected to any cantilever stress. Failure of any one insulator after torsion to meet the dye penetration test shall constitute failure to meet the requirements of this recommendation.

 

9.  Working Cantilever Load Test - Three insulators shall be tested. Gradually load the insulator to 1.1 times its working cantilever load rating at a temperature of 20 C + 10K and hold for 96 hours.

The load shall be applied to the insulator as described in the definition of the cantilever load. After

removal of the load; cut each insulator 90 to the axis of the core and about 50 mm from the base end fitting; cut the base end fitting longitudinally into two halves in the plane of the previously applied cantilever load. The test is regarded as passed if the threads of the base are reusable and each fiberglass rod has no delaminations, and no crack.

 

10.  Thermal Mechanical Test - No non-ceramic material is completely resistant to heat. Time and temperature have their aging effects. Heat resistance is usually measured as change in tensile strength, elongation and hardness. Low-temperature properties indicate a stiffening range and brittle point. With some materials crystallization occurs, at which time the material is brittle and will fracture easily.

Three insulators shall be loaded at ambient temperature to at least 5% of the SML for 1-minute.

During this time, the length of the insulators shall be measured. This will be the reference length. The insulators  shall  then be submitted to thermal variation from  -35C  to  + 50C (ANSI)  and  -50C  to  + 50C (CEA) while under a permanent mechanical load of 0.5 SML for 96 hours. The time at each temperature shall be at least 8 hours per cycle. At the end of thermal cycling, the insulators shall be allowed to reach ambient temperature and the length shall again be measured using the same load as for the reference length. The increase in each insulator!ˉs length shall be no more than 2mm. It is also required that, described in section 3.

 

11. Flammability Test - This test is intended to check the shed housing material for ignition and  

self-extinguishing properties. The test shall be performed according to IEC Publication 707, method FV. The test is passed if the test specimen belongs to category FVO of IEC Publication 707.

 

12. Low Frequency Dry Flashover Test - Three insulators shall be tested. The initial applied voltage may be quickly raised to approximately 75% of the expected average dry flashover voltage value. The continued rate of voltage increase shall be such that the time to flashover will be not less than 5 seconds nor more than  30 seconds after 75% of the flashover value is reached. The dry flashover voltage value of a test specimen shall be the arithmetical mean of not less than five individual flashover taken consecutively. 

Failure of the dry flashover value of any one of the  three insulators to equal or exceed 95% of the rated dry flashover value shall constitute failure to meet the requirements. 

 

13 . Low Frequency Wet Flashover Test - Three insulators shall be tested and voltage application at not less than 1 minute after the final adjustment of the spray, the applied voltage may be raised quickly to approximately 75% of the expected average wet flashover voltage value. The continued rate of voltage increase shall be such that the time to flashover will be not less than 5 seconds nor more than 30 seconds after 75% of the wet flashover voltage value is reached. The wet flashover voltage value of a test specimen shall be the arithmetical mean of not less than five individual flashover taken consecutively. Failure of the flashover value of any one of the three insulators to equal or exceed 90% of the rated wet flashover value shall constitute failure to meet the requirements.

 

14.  Critical Impulse Flashover Test - Three insulators shall be tested under dry conditions only and with a 1.2 X 50-microsecond wave. Failure of the positive or negative critical impulse flashover value of any one of the three insulators to equal or exceed 92% of the rated critical impulse flashover value, whichever is lower, shall constitute failure to meet the requirements. 

 

15.  Radio-Influence Voltage Test - Three insulators shall be tested. All hardware associated with the test circuit shall be relatively free of radio influence at a voltage 10% higher than the voltage at which the tests are to be performed. The wave shape of the applied voltage shall be a sine wave of acceptable commercial standards in accordance with ANSI/IEEE 4-1978. Tests shall be conducted under atmospheric conditions prevailing at the time and place of test, but it is recommended that tests 3 be avoided when the vapor pressure exceeds 0.6 inch of mercury (2.02 X 10  Pascal). Since the effects of humidity and air density upon the radio-influence voltage are not definitely known, no correction factors are recommended for either at the present time. However, it is recommended for that barometric pressure and dry and wet-bulb thermometer readings are recorded so that if suitable correction factors should be determined, they could be applied to previous measurements. The specified voltage shall be applied to the test specimen, and the radio-influence voltage shall be measure in microvolts at the specified radio frequency. It is considered impractical to read radio-influence test voltage that is less than 10 microvolts. Failure of one or more insulators to meet the requirements shall constitute failure.

 

16. Galvanizing Test - Five pieces representative of each type of galvanized hardware used with the insulators shall be tested. Five to ten measurements shall be uniformly and randomly distributed over the entire surface and the average thickness value of each individual specimen and the average of the entire sample shall equal or exceed 78 to 86 mm. If the average of one specimen, or if the average of the entire sample, fails to comply with the values, ten additional pieces of the same type of hardware shall be selected at random and tested. Failure of the retest sample to comply with the minimum thickness criteria shall constitute failure of the lot to meet the requirements of this recommendation.