Transmission line protection zone

Protection zones, i.e. protective corridors are designated alongside the route of overhead power lines as required by law. The regulations require that no structures be built within such corridors, no inflammable and explosive substances stored and no hop fields planted; trees and other vegetation within such corridors should reach no higher than 3 metres above ground level. Meeting the requirements concerning protection zones is vital because of potential conductor sag; the extent of such sagging varies according to conductor temperature which can pose a potential risk to the surrounding environment. Conductor temperature varies according to weather conditions (air temperature, humidity etc.) and conductor loading (with an increase in load, conductor temperature rises and sagging increases). Standards covering the minimum distance between trees or vegetation and live line elements (energised conductors) are set at 4 metres for 220kV lines and 5 metres for 400kV lines. This distance is required in order to avoid the risk of direct contact between live conductors and trees or other vegetation which might cause short-circuiting and, potentially, fire.

The width of the protection zone along overhead power lines as measured from the outer conductor varies according to voltage level:

• above 1kV to 35kV.................. 7 metres
• above 35kV to 110kV............. 12 metres 
• above 110kV to 220kV........... 15 metres
• above 220kV to 440kV........... 20 metres
• above 440kV......................... 30 metres

For underground power lines, the width of the protection zone as measured from each of the outer cables is:

• up to 110kV............................ 1 metre
• more than 110kV.................... 3 metres

Within the protection zone of an underground power line, earthwork without a special permit is prohibited as are the building of structures which would make access to the line impossible, the planting of trees and shrubs and the manoeuvring of machinery heavier than 3 tonnes.

The width of the protection zone of a transformer station is 20 metres as measured perpendicularly to a fence or the station wall.

Types of towers used by ČEPS

The transmission system is composed of a number of various elements, each of which performs a specific function. Transmission towers provide support and ensure the physical separation of individual phases within the power line.

The ČEPS backbone transmission system carries 220kV and 400kV high voltage power. Accordingly, transmission towers are higher and stronger than other towers within the national power system. A specific type of tower is selected according to the required tower strength and lifetime, line route, climatic and weather conditions and the respective voltage level. Towers are designed to withstand extreme weather conditions, such as ice coating or violent storms, i.e. wind speeds exceeding 120 km/hour.

The above-ground tower foundation segment usually consists of four concrete cylinders approximately 90 cm in diameter and at least 40 cm in height. Each tower leg is anchored to one of the cylinders. The area covered by the tower’s foundations is approximately 60m², including the mandatory 1m wide protection zone.

Types of towers for download.