Selection Standard for High Voltage Transmission Line Insulators

Importance of reliability assessment and reasonable selection for insulators

As an important component of the transmission lines, insulators are divided into porcelain insulators, synthetic insulators and the newly developed glass fiber reinforced plastic insulator. The reliability assessment and reasonable selection for composite insulators is directly related to the safe operation of the transmission line, what type of insulator is more suitable for high voltage transmission line in oil field power system? Evaluation of the insulators should follow the following criteria:

1. Life cycle of insulators
The products maintain its performance not being lower than the factory standard minimum useful life under the standard conditions of use, which is "life cycle". This indicator reflects not only the safe use of the insulators, and can also reflect the economic investment in transmission lines. Our country has tracked and made comparison test for the electrical and mechanical performance of fiberglass insulators and porcelain insulators that have run 5 to 30 years. The results showed that the life of the glass insulator depends on the metal accessories and the life of the polymer insulators depends on the insulation. The life cycle of the FRP insulator is up to 40 years, and the average life cycle of porcelain insulators is only 15 to 25 years, which can greatly extend its life cycle except it adopts advanced manufacturing technology; synthetic insulators has gone through three generations of "development, but so far the average life cycle is only 7 years judging by the analysis for the test and running results worldwide.

2. Failure rate of insulators
The ratio between the annual running failure insulator quantity and the total number of the running insulators is called the annual failure rate. The average failure rate for domestic glass steel insulators within their life cycle is (1 ~~ 4) ×; The failure rate of porcelain insulator, except individual joint venture enterprise products may reduce, is one or two magnitude higher than glass insulators; The failure rate for suspension insulators is difficult to predict, because its life cycle cannot be predicted, the formulation of synthetic materials and manufacturing process cannot be completely set.

3. Failure detection rate
The detection rate can be detected after the insulator failure is a more important factor on the line safe operation than the failure rate itself. The detection rate depends on the insulator failure manifestations and the reasons for failure. The manifestation of glass fiber reinforced plastic insulator failure is "automatically broken" and "zero value break". In addition, the failure of porcelain insulator and synthetic insulator is the aging of materials and the degree of aging is a function of time. Aging is hidden, so it brings great difficulties for detection, resulting in very low detection rate; the synthetic insulators are virtually impossible to detect.

4．Accident rate
The ratio between the annual insulator fault line trip times and running insulator number is known as annual accident rate. The line trip caused by the insulator off the string, the pollution flashover, zero values, and other reasons is one of the most serious accidents of the overhead transmission line. The impact of widespread and prolonged power outage oil transmission lines is extremely serious.

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