Pipe’s history
High-voltage cable lines (from 1 kV up to 500 kV) are most often laid in the ground. Such lines are at risk of damage at intersections with highways, railways, hot water pipes, and other lines. In these dangerous areas, cables are placed not directly into the ground, but in protective pipes. Just 10 years ago, pipes made of asbestos or steel were widely used for these purposes, but gradually they were replaced by others, among which are known:
- Pipes made of recycled materials (waste, garbage)
- Polyethylene pipes (PE 80, PE 100, PE-RT)
- Polypropylene pipes (PP)
- Polyvinyl chloride (PVC) pipes
It is believed that the advantage of all these pipes (1)-(4) is that they are not afraid of an aggressive environment, are not subject to corrosion, are not brittle, do not heat up from eddy currents. However, pipes (1)-(4) have significant drawbacks.
The temperature of modern cables with insulation made of cross-linked polyethylene (XLPE) or ethylene propylene rubber (EPR) in a long-term normal mode can reach 90-110 C, and in case of overloads and short circuits — even more. Among (1)-(4), only pipes (4) have the ability to withstand the specified temperatures for a long time, i.e., throughout the entire service life, maintain their mechanical strength necessary to protect the cable. As for pipes (1)-(3), their use for laying cables is dangerous, since such pipes may deform over time under the influence of ground pressure and high cable temperature, preventing the cable from being removed from the pipe for repair or replacement with a new one.
Unfortunately, PVC pipes (4) are non-flexible and can only be connected using a socket connection — all this significantly limits the scope of using this type of pipe. That is why a new generation of pipes has appeared — ProtectorFlex.
Polymer pipes ProtectorFlex
ProtectorFlex pipes are flexible, can be hermetically connected to each other by butt welding, are non-flammable (which is important in case of a short circuit in the cable), are not afraid of mechanical impact and aggressive environment. It is important that all these properties of the pipe are preserved for at least 50 years in conditions of high temperature of the laid cable (90-110 C).
High flexibility and susceptibility to butt welding allow these pipes to be laid by all known methods, including routes of any length with a large number of turns.
It is important that ProtectorFlex polymer pipes do not require filling the route with concrete, which is widely used in a number of countries as a way to prevent deformation of the pipes used there. Therefore, the ProtectorFlex accelerates and reduces the cost of construction, as well as simplifies the possibility of opening the route in any of its places if cable repairs are required there for some reason.
Laying methods
The first pipes were placed in the ground in an open way, i.e. at the bottom of the trench. However, over the past 5-10 years, the method of horizontal directional drilling (HDD) has been actively developing, which allows to significantly reduce the amount of excavation work and reduce the construction time of the line.
Currently, with the help of ProtectorFlex polymer pipes and the HDD method, it is possible to create in a short time monolithic continuous pipe sections of the route with a length of up to 500-800 meters and a depth of up to 15-20 meters. Obviously, this would not be possible with PVC pipes (4), since they are not flexible and are connected to each other only by a socket (bell), which will detach when trying to tighten the pipes into the drilling channel.
Connection methods
ProtectorFlex polymer pipes can be connected to each other either by butt welding, or by thermo-couplers. Both methods allow you to create an extended sealed monolithic pipe channel for cable.
When laying in a trench, the connection of pipes can be performed in any of these ways. When laying by the HDD method, only butt welding is allowed.
Ends protection
ProtectorFlex pipes have retained all their properties for at least 50 years and provide the possibility of removing the cable from the pipe in order to repair or replace it. To prevent pipe silting during its lifetime, the pipes should be sealed.
The sealing of the ProtectorFlex pipes is carried out with special seals, and the use of mounting foam is not allowed. In addition, a protective funnel is installed at each end of the pipe, which protects the cable sheath from the impact of the pipe edge both during cable pulling and during subsequent operation of the line.
Classification
ProtectorFlex pipes have the following parameters:
- Diameters from 50 to 630 mm
- Wall thickness from 2 to 80 mm
- Annular stiffness number SN from 4 to 256 kN/m2
- Maximum pulling force from 2 to 3000 kN
- Long-term operating temperatures from 90 to 110 C
- The length of each pipe up to 13 m (in bays — up to 200 m)
ProtectorFlex pipes are equipped with a Cable Fault Locating system (CFL).
CFL — what does it mean?
The cable design must have an outer sheath that prevents water from entering the cable and its insulation. It is very important that when installing the cable and its subsequent operation, this sheath retains its integrity (tightness).
To control the tightness of the sheath, it is checked both immediately after laying the cable as part of acceptance tests, and then periodically during operation.
All known types of pipes (1)-(4) isolate the cable from the ground, i.e. even if there is significant cable outer sheath damage, such a cable line will successfully pass the sheath tests and will be mistakenly recognized as serviceable. CFL-pipes have been developed to solve this problem.
CFL-pipes are the only polymer pipes in the world for laying high-voltage cable lines that do not prevent the test current flowing from the damaged cable through the pipe into the surrounding ground. This allows you:
- Objective tests of the cable sheath and detecting the facts of sheath damage (during standard tests with DC voltage up to 10 kV)
- Quick locating of these damages along the cable route using standard search methods (bridge, step voltage, etc.)