Shielding cable trays

SHIELDING CABLE TRAYS

Ideal for both overhead cable trays and underground power lines, custom-made to comply with the goal requested. Due to their characteristics we always test them before delivering to our clients.

shielding cable trays

 

 

shielding cable trays

A practical example: Shielding underground power lines.

The purpose of the test is to assess the best G-iron configuration in order to reduce the induction generated by 3 conductors in a trefoil position (inter-axle spacing = 200 mm) with current I=870 A (underground long-distance power line) in order to reach the target of a shielded induction no greater than 3 μT when measured 2,500 mm above the bottom of the trench.
First of all, we built a same-scale model (see picture on the next slide) simulating the conductors with aluminum rods (diameter = 50 mm, length = 3000 mm). The rods were connected in a short-circuit on one end with a 3mm-thick Al plate. This setting, requested by the Client, was used to reproduce real-life conditions where the conductors are installed inside plastic tubes (diameter = 200 mm).
The system was powered by a transformer 400/4 Vac, with output current gradually varying from 10A to 2000A.
We determined reference points (marks) at 2,500 mm above the bottom of the trench:

Mark1: perpendicular to the centre of trefoil line
Mark2: 500 mm from the centre
Mark3: 1,000 mm from the centre
Mark4: 1,500 mm from the centre

The induction was measured with EFA 300 measuring system made by Narda STS and a B field probe (both with currently valid calibration certificate).
The connection to the PC is guaranteed by an optical fiber cable. The measuring system is controlled remotely with Narda STS’ EFA Remote software.
Before powering the system and proceeding with the test, we shielded the cables used to power the rods in order to contain the influence of the magnetic flux coming from said cables. For the same reason we also shielded the transformer.

shielding cable trays

shielding scheme

On the side you can see a picture of the complete test set-up with the shielded power cables and the wooden stool for the measuring system, which is connected to the PC via optical fiber.

Prior to starting the test we determined the current levels needed to plot the attenuation graph:
I1=290 A
I2=580 A
I3=870 A value used for the final test.
The current values are checked with an ammeter clamp on one phase.
For each Mark we measured the induction at 3 different current values.

We repeated the measurements with the same parameters used in open space for each shielding configuration in order to compare the shielded induction values for each Mark.

The results of the tests show which shielding configurations are more efficient for a specific project.
Thus, the client can choose the solution that best fits his/her need.

It is obvious that other G-iron combinations could be designed upon request:

we could develop shielding solutions aimed to shield greater current levels or solutions aimed to reach the target level of induction at smaller distances from the source..

G-iron laboratory

Insights and topics.

Magnetic and electromagnetic fields. Analyses and epidemiological studies on several cases.

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