Cables in Metal Pipes

This feature can calculate the effects of cables in metal pipes, including induction and heating of metal pipes.

Introduction

The presence of cables inside a magnetic pipe causes eddy current losses and hysteresis losses in that pipe. In some cases, these losses lead to a significant reduction in the ampacity of cables

Example of a Model with a Metal Pipe

Start by adding a metal pipe. You can use one of the pipes in the component library or create a custom pipe in the component designer. A third option is to add a metal pipe by creating a “custom item”.

There is considerable variation in the physical properties of steel and stainless steel, and these properties should be adjusted for each pipe or casing to ensure more accurate simulations.

Once the desired design is set, run the simulation to view the losses in the pipes in the results:

The graphs below illustrate the difference in magnetic field strength when using a 163/4.5 mm steel pipe compared to a 160 mm PVC pipe. At ground level, the magnetic field is reduced from 9.0 μT to 1.2 μT when a steel pipe is used.

Pipe-in-Pipe

The user should be aware that the limitation for pipe-in-pipe calculations also applies if a pipe is placed inside a metal pipe. The heat distribution in the outer pipe layer is calculated without convection.

In summary, this means that the heat in area ‘1’ is calculated using air convection based on the verified formula developed by SINTEF. However, air convection is not considered in area ‘2,’ resulting in a conservative estimate for this region. The larger the size of area ‘2,’ the more conservative the estimate becomes.

Steel Pipe Around a Single Conductor

A metal pipe surrounding a single conductor will trap a significant portion of the magnetic field, leading to increased eddy currents and higher temperatures. This, in turn, greatly reduces the cable’s ampacity.

Circulating Current Losses

No circulating current losses are considered for magnetic pipes, as the pipe is buried in the ground, where the potential 0V is assumed.

Default Material Values

Since the physical properties of steel and stainless steel can vary significantly, it’s important to adjust the values for each pipe or casing to achieve more accurate simulations.

Default metal values can be found here

Verification

The verification of this feature is found here