2　Terms and Symbols

2.1　Terms

2.1.1　Overhead transmission line

An electric line whose conductors are supported above ground，generally by means of insulators and appropriate supports.

2.1.2　Telecommunication line

Various communication lines for electric signals.

2.1.3　Large crossing

Tension sections of lines crossing wide navigable rivers，lakes or straits with large span lengths（above 1000m）or high towers（higher than 100m），where special consideration shall be given to conductor selection or tower design and a fault may severely influence navigation or is extremely difficult to repair.

2.1.4　Light/medium/heavy icing area

A light icing area is an area with design icing thickness of 10mm and below，a medium icing area with 10mm to 20mm，and a heavy icing area with 20mm and above.

2.1.5　Reference wind speed

Wind speed determined by probabilistic method through the mean annual maximum wind speed in 10minutes at 50（30）-year return period at 10m height above flat and open ground.

2.1.6　Rare wind speed，rare ice thickness

Severe winds or icing which did occur according to historical records and significantly exceeded historically recorded frequency curves over the years.

2.1.7　Tension section

Linesection between two strain towers.

2.1.8　Everyday tension

The tension at the lowest point of sag of conductor or earthwirecalculated under annual average temperature.

2.1.9　Equivalent salt deposit density（ESDD）

Amount of sodium chloride（NaCl）that，when dissolved in demineralized water，gives the same volume conductivity as that of the natural deposit removed from a given surface of the insulator divided by the area of this surface，ESDD for short.

2.1.10　Non-soluble deposit density（NSDD）

Amount of non-soluble residue removed from a given surface of the insulator，divided by the area of this surface，NSDD for short.

2.1.11　Weighting foundation

A foundation whose uplift stability mainly depends on its weight which shall be larger than the standard value of uplift force.

2.1.12　Reinforced concrete pole

The general name for common reinforced concrete pole，partial prestressed concrete pole and prestressed reinforced concrete pole.

2.1.13　Residential area

Populated areassuch as industrial area，port，wharf，rail station and towns.

2.1.14　Non-residential area

Areas other than residential areas defined in 2.1.13.

2.1.15　Difficult transport area

Areas inaccessible for vehicles and agricultural machinery.

2.1.16　Electrical clearance

Minimum clearance between any live part of a line and grounding parts.

2.1.17　Clearance to ground

Minimum clearance between any live part of a line and ground under specified conditions.

2.1.18　Shielding angle

The angle between the vertical plane through the earthwire and a plane through the earthwire and the conductor to be protected against lightning strokes.

2.1.19　Mining affected area

Areas affected by mining activities.