part 1:

 

Tests normally performed on an composite insulator/silicone rubber insulator/polymer insulator by the manufacturer and the user are described below:

 

1. Water Penetration Test - Various materials absorb varying amounts of water that may affect the polymeric materials on different ways. Electrical properties change most noticeably with moisture absorption. In particular, the dielectric strength of materials varies greatly with absorbed water and materials that absorption. In particular, the dielectric strength of materials varies greatly with absorbed water, and materials varies greatly with absorbed water, and materials that absorb almost no water are favored for electrical insulation. Mechanical properties are also deteriorated by moisture to some extent.  Water penetration test is intended to determine the insulator resistance to moisture.

Three samples of the insulator shall be kept immersed in boiling tap water, having 0.1% by weight of NaC1, for 100 hours. At the end of this period, the insulators shall remain in the vessel until the water cools to approximately 50C. This temperature shall be maintained until the verification tests start.

The verification tests consist of the sequence of tests described in 1.1 through 1.3 and shall be completed within 48 hours. These tests are described as followed:

1.1  Visual Examination - The housing shall be inspected visually. No cracks and no sign of dissolving or crumbling are permitted.

1.2  Steep Front Impulse Voltage Test - An impulse voltage with a front steepness of at least 1000 kV/ms shall be applied to each test section. Each test section shall be stressed with 25 impulses of positive and 25 impulses of negative polarity in accordance with ANSI standard and 10 impulses of positive and 10 impulses of negative polarity in accordance with CEA standard. Each impulse shall cause an external flashover of the test section. No puncture shall occur.

1.3.  Power Frequency Voltage Test - Each test specimen shall be individually subjected to 80% of its average flashover  voltage as determined by averaging five flashover voltage on each of the three test specimens. The flashover voltage shall be corrected to standard

conditions. The flashover voltage shall be reached within 1 minute by increasing the voltage linearly from zero. The voltage shall be maintained for 30 minutes. No puncture shall occur and the temperature of the shank measured immediately after the test shall not be more than C 20 above ambient.    

1.4.  Hardness Test - The hardness of two sheds of each insulator shall be measured in accordance with ASTM D2240. The hardness must not change from the pre-boiled specimen by more than 20%.

 

2.  Aging and Accelerated Weathering Test - Outdoor weathering is a natural phenomenon which affects all materials to some extent. Outdoor weathering includes the effects of varying temperature, humidity, rain, wind, impurities in the atmosphere, and the heat and ultraviolet rays of the sun. Under such conditions, the surface of an insulating material may be permanently changed. Physically by roughening and cracking and chemically by the loss of soluble components and by the reactions of the salts, acids, and other impurities deposited on the surface. Surfaces become hydrophilic and water penetrates more easily into the volume of the material.

Three samples of the weathershed material shall be tested for 1000 hours by one of the following test methods, except that test without water is not permitted. Surface defects such as cracks and blisters are not permitted.

Carbon Arc Methods: ASTM D750, D1499, or G23. 

Cenon Arc   Methods: ASTM G26, or D2565.

Fluorescent UV Methods: ASTM G53.

 

3.  Dry Penetration Test - Three 10-mm long cross sections of the insulator shall be tested for

porosity by performing a dye penetration test. The samples shall be placed upright on a layer of steel or glass balls in a 1% alcohol solution of fuchsin dye. The time taken for the dye to rise through the samples shall be longer than 15 minutes.

 

4.  Water Diffusion Test - Six samples, 30 mm shall be cut from the insulator 90 degree to the axis of the core with a diamond-coated circular saw blade under cool running water. The cut surfaces shall be smoothed with a 180-grit abrasive cloth. The cut ends shall be clean and parallel. The removal of the housing is optional. 

The test specimens shall be boiled in deionized water with 0.1% by weight NaC1 in a glass container for 100 hours. After boiling, the samples shall be removed from the salt water and placed into tap water for at least 15 minutes. The samples shall be then placed between two plane brass electrodes and a voltage increasing at a rate of 1 kV per second shall be applied. With the applied voltage reaching a value of 12 kV and remained for 1 minute, there should be no puncture or surface flashover. The current during the whole test shall not exceed 1 mA r.m.s.

 

5.  Power Arc Test - Three insulators having any one design of end fittings shall be tested for power are endurance while tensioned horizontally at 3000 lb. An arc shall be initiated across the insulator by means of a copper shorting fuse wire. The arc shall burn 15 to 30 cycles and its current magnitude is determined by ampere-time product (I X t) equal to a minimum of 150 kA cycles. Each insulator is only acceptable if there is no exposure of the core, no mechanical separation of the insulator, and no cracks in the housing.

 

6.  Tracking and Erosion Test - The long -term performance of a polymer material used in electrical insulation design is directly related to the leakage current and the dry-band discharges that develop in service. Service experience has shown that the amplitude and frequency of dry-band discharges on electrical insulation are not dependent on design alone but also dependent on the surface properties of the polymer material used.

For many years, tracking chamber methods had been proven to be very reliable in providing enough data on expected performance for a particular model insulator under severe contaminated conditions.

Tracking chambers can be classified in term of the process of wetting the sample into three groups namely salt-fog chambers, tracking wheel chambers and drizzle chambers. The tracking wheel test method imposes wet and dry cycles on a stressed surface of specimens in order to simulate the formation of dry-band arcing as it is experienced on service. It is designed to evaluate insulator shapes and/or materials for outdoor applications. Surface degradation in outdoor applications of either erosion or tracking takes place only in association with arcing over dry bands, which developed during or immediately after precipitation. The surface damage, erosion, or carbonization results from the heat of the arc, and this damage accumulates until the surface between the electrodes can no longer sustain the applied voltage. As this mechanism is the same as occurs in service, correlation with experience has been good.

Three insulators shall be tested for resistance to tracking on a tracking wheel chamber. At the end of test, there shall be no significant signs of erosion and tracking. Each individual insulator shall not suffer more than two flashover provided no damage occurs to the surface of the insulator.