Insulator selection and verification

1. Insulator selection

Ceramic crossarms or pin insulators are available for 3 to 10KV lines. The tensile rod is a combination of a suspension insulator or a suspension insulator and a butterfly insulator. Suspension insulators are generally used for voltage lines of 35KV and above. The 35KV linear tower can also be used with porcelain cross arm. When selecting the number of insulators per string of suspended insulator strings for 35KV and above, it is generally considered that no wet flashover occurs under operating voltage, no flashing occurs under internal overvoltage or the probability of flashing is limited to a reasonable degree. It should not be less than the number of pieces specified in the Regulations.

The number of insulators per string of linear towers is generally selected as: 35KV, 2-3; 110KV, 6-7; 220KV, 12-13.

The number of tensile insulator strings on the tensile tower should be one more than the same insulator on the linear tower. In areas above 1000m above sea level, the number of insulators increases by 1% for every 100m increase.

In areas with more serious pollution, synthetic suspension insulators can also be used. This type of insulator is expressed in letters and represents the rated voltage and rated mechanical damage load in fractional data.

2. Insulator mechanical strength check

The mechanical strength of the insulator is verified by a safety factor (formerly known as the safety factor), which is expressed by:

(1)

In the formula, K-safety factor, needle and butterfly normal operation take 2.5; suspension insulators take 2.0 for normal operation, 1.3 for disconnection, and 3.0 and 2.0 for porcelain cross-arms respectively;

T-insulator mechanical strength value, for the porcelain crossarm and the pin insulator for its bending failure load, for the butterfly insulator to destroy its load;

For the suspension insulator, its 1h electromechanical test load;

Tmax—the maximum load of the insulator (N).

Suspended insulator string during normal operation :

Tensile insulator string or suspension insulator string when disconnected

Where gmax—maximum specific load [N/(m·mm2)]

S-wire cross section (mm2);

- the vertical gear distance (m) of the maximum specific load;

σ—The maximum operating stress (ice, wind, or low temperature) of the wire for the tensile insulator string and the wire breakage stress (Mpa) for the suspended insulator string.

In addition, according to the maximum vertical load (usually ice coating) of the suspended insulator string under certain meteorological conditions, the allowable vertical span of the insulator string is obtained, and then converted into the vertical span value under the meteorological condition of the positioning template, and finally The mechanical strength critical curve of the insulator string is suspended for verification.