Chapter 3-3-3 Insulators

Article 248. Suspended Insulators

1.Insulators used at special points

Insulators (multi-stage insulators or special insulators) shall be used at branch points, etc. of overhead power lines with voltage up 1kVto. The neutral conductor shall be connected to insulators.

Suitable post-type insulators are permitted to be used at transpositions or near arresters, circuit breakers or disconnectors of overhead power lines with not less than 110kV.

As for poles with appropriate insulated composite arms, it is not necessary to use insulators.

As for overhead power lines with voltage up to35kV, both post-type insulators and suspensiontype insulators are permitted to be used.

2. Number of suspension insulator bowl

(1) Suspension-type insulator bowls of overhead power lines with voltage up to 35kV

The number of suspension-type insulator bowls at one insulator string of overhead power lines with voltage from 6kV to 35kV shall be selected as below (creepage distance of each bowlshall not be not less than 250mm.).

-Up to 10kV: 1 bowl

-From 15kV to 22kV: 2 bowls

-35kV: 3 bowls

The number of suspension-type insulator bowls at one insulator string and post-type insulators are permitted to be selected independent of altitude of the lines.

The requirements for suspension-type insulator bowls of overhead power lines with voltage of 15kV and directly grounded neutral shall be selected as those for the lines with voltage10kV and isolated neutral.

(2) Suspension-type insulator bowls of overhead power lines with voltage from 110kV to 500kV

The number of suspension-type insulator bowls at one insulator string of overhead power lines with voltage from 110kV to 500kV at altitude up to 1,000m shall be calculated by the following formula. Calculated number shall be rounded up to the nearest integer.

n= d UDmax

n: Number of suspension-type insulator bowls at one insulator string d : Selective creepage distance (mm/kV)

-12.7mm /kV: Very light polluted environment

-16mm/kV: Light polluted environment

-20mm/kV: Medium polluted environment

-25mm/kV: Heavy polluted environment

-31mm/kV:Very heavy polluted environment

U max : Maximum operating voltage (kV)

D : Creepage distance of one suspension-type insulator bowl of the specification (mm)

When a type of suspension insulators are selected for each insulator string with creepage distance longer than 2.3 times of designed creepage distance of insulator string in normal operating

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voltage condition, the bowls of insulators shallbe added according to the calculated creepage distance. For polymers insulator, thecreepage distance shall be selected to the same length of one of ceramic insulators or glass insulators. Requirement in details shall refer to IEC 60815-3- 2008/3.

3.Additional requirements for the insulation hanging bowl

(1)The number of all types of suspension-type insulator bowls at each strain insulator string of overhead power lines with voltage up to 110kV and 500kV shall be one bowl more than these in support insulator string., The number of suspension-type insulator bowls in each strain insulator string of overhead power lines with voltage of 220kV and these in support insulator string are the same.

(2)For the polewith the height over 40min the large cross span,they shall beinstalled with

additional bowls of suspended insulators in each insulator string

- One insulator on overhead power lines equipped with lightning arresters at the crossing section.

-One insulator for every additional 10m to the height of 40m poles with lightning conductors. e.g. A40m pole: X insulators

A50m pole: X + 1 insulator A60m pole: X + 2 insulators

(3)For overhead power lines with voltage up to110kV traversing areas at altitude exceeding 1000m to 2,500m and overhead power lines with voltage from220kV to 500kV traversing areas at the altitude exceeding 1,000m to 2,000m, the number of suspensiontypeinsulator bowls in insulator string shall be added to one more than the number shown in item 3-(1) and 3-(2) in this article.

For overhead power lines traversing the area (near industrial enterprises, coastal areas, etc) which is severely polluted, the number and type of insulator shall be selected base onthe actual conditions.

Article 249. Mechanical Strength of Insulators

1.Safety coefficient of insulator with voltage up to 1kV

Mechanical safety coefficient (the ratio of breaking stress to maximum standard load acting on insulator) of insulators shall not be less than 2.5.

Mechanical safety coefficient of feet of insulators and hooks shall not be less than 2.0.

2.Safety coefficient of insulator with voltage exceeding 1kV

Safety coefficient of post-type insulators (the ratio of destructive stress to maximum standard load acting on insulator) and the one of pensionsus-type insulators (the ratio of electro-magnetic strength to maximum standard load acting on insulators) shall not be less than 2.7 in normal operating conditions and not less than 5.0 at annual mean temperature.

Safety coefficient of feet of insulators shall not be less than 2.0 in normal conditions, and not be less than 1.3 in fault conditions.

Safety coefficient of suspension-type insulators of overhead power lines with voltage of220kV in fault conditions shall not be less than 1.8, and that of the one with voltage500kVof in fault conditions shall not be less than 2.0.

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Chapter 3-3-4 Power Line Accessories

Article 250. Accessories

Conductors of overhead power lines shall be fixed to suspension-type insulators by support or anchor locks, and to post-type insulators by dedicated straps or clamps.

It is permitted to use fixed-type and slide-type support locks. Conductors and lighting conductors in large overcrossing span are permitted to be suspended by special pulleys or locks.

Conductors of different phases on the same poles as well as conductors of one phase on different poles are permitted to be fixed by different support locks (fixed-type and slide-type).

Lightning conductors on support poles shall be fixed by fixed support locks. Conductors on anchor poles shall be fixed by support locks.

Conductors and lightning conductors of overhead power lines with voltage not lesshant 110kV shall be fixed by dedicated locks, and it is permitted to be fixed by bolt clamps.

Mechanical safety coefficient (the ratio of destructive mechanical stress to the maximum load acting on accessories) of accessories shall not be less than 2.5 in ormaln operating conditions and not less than 1.7 in fault operating conditions.

The force acting on accessories shall be determined by the contents shown in article258in this Guideline.

Chapter 3-3-5 Overvoltage Protection

Article 251. Atmospheric Overvoltage Protection

1.Protection for overhead power lines with voltage up to 35kV

Overhead power lines with voltage up to35kV are not required to be protected for the whole length of them from lightning by lightning conductors. Poles of the lines shall be earthed in compliance with the requirements in article 554 in Technical RegulationVol.1 and this Guideline.

2.Protection in the substation

Overhead power lines with exceeding1kV in the section where they traverse substations shall be protected against atmospheric overvoltage.

3.Shielding angle (Protection angle)

Lightning conductors shall be installed in compliance with the following requirements.

(1) The shielding angle of single metallic or reinforced concrete poles with one lightningconductor of overhead power lines with voltage exceeding 1kV shall be not more than 30 degrees.

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(2)The shielding angle for the outer edge power conductor arranged horizontally on single metallic pole with two lightning conductors of overhead power lines with voltage exceeding1kV shall not be more than 20 degrees.

(3)The shielding angle for the outer edge power conductor of overhead power lines with voltage exceeding 1kV on reinforced poles with gantry shape shall not be more than 30 degrees.

(4)The distance between two lightning conductors of overhead power lines with voltage exceeding 1kV at the top of a pole shall not be more than 5 times of vertical distance between the power conductor and the lightning conductor.

(5)The value of shielding angle to be designed is permitted to be reduced to not more than the above-mentioned values depending on the lightning days, topography of the area where the overhead power line with voltage exceeding1kV traverse, the height of poles and importance of

the line.

4.Vertical distance between power conductor and lightning conductor

The minimum vertical distance against atmospheric over-voltage protection between power conductor and lightning conductor of overhead power lines with voltage exceeding1kV without consideration of the swing of both conductors due to wind shall not be less than the values shown in the following table.

*Note: If the span-length is in between the above values, interpolation method can be applied.

sectional area not more than 50mm2 shall be earthed by a conductor connected in parallel with the locks.

Article 252. Additional Lightning Conductor Requirements

Lightning conductors of overhead power lines with voltage exceeding1kV shall be earthed at all poles. However, lightning conductors are permitted to be fixed to insulators withthe gap, if inducted electro-magnetic force and current are not more than the permissible values.

When OPGW are arranged in parallel with lightningconductors without optical fiber cables, all lightning conductors shall be earthed at all poles.

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