Active shielding solution
A common example is an Israel Electric Corporation (IEC) Ltd. Ultra-High Voltage transmission line, installed next to a residential or office building where people are continuously present, creating a level of magnetic field that is higher than permitted by the authorized authorities (in Israel - the Ministry of Environmental Protection).
How does the active shielding system work?
The active shielding system consists of an electrical circuit that creates an opposite magnetic field to the one we wish to reduce, thereby ensuring that at the relevant area, magnetic field levels are continuously decreased to the defined target levels.
The system is comprised of one or more electrical loop/s installed on poles that are either perpendicular to the ground, on bars protruding from the structure, and/or partially or fully concealed in the ground, in parallel and adjacent to the alignment of the treated area, normally in the medium between the treated area and the source of the magnetic field.
The test point in the treated area will be defined and installed in such a way that at any given moment the magnetic field is tested and according to the result the strength of the magnetic field produced by the system is adjusted, so that overall the magnetic field levels at the treated area are continuously and optimally reduced to meet target values at all times.
At any given moment, the Client is able to view the measured values and even download and save the data.
System Purpose
Active magnetic shielding systems are primarily used to reduce the magnetic fields from power lines owned by electric companies. The system is effective for both extra-high-voltage and high-voltage lines, whether overhead or below ground.
In most cases, the magnetic field can be reduced to a low level within a defined area of the project site.
While passive shielding (such as metal plates) is typically used to reduce fields from infrastructure inside the building/project or for individual rooms, active shielding is usually the only practical solution for reducing magnetic fields from power lines at the building or site level.
This alternative provides a solution for mitigating magnetic fields from power lines when no other viable options are available or when other alternatives are too costly or would require unusually long timelines (several years).
Active shielding can be used for workstations near a high-voltage line with asymmetry between the circuits.
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This refers to the impact of the magnetic field generated by a power corridor in the absence of an active shielding system.
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This refers to magnetic fields after the implementation of an active shielding system solution for the buildings in the center.
System Design Process:
The design process consists of two main stages:
Design—This stage involves the entire process of review, design, and preparation of specifications for implementation and execution.
Execution—This stage covers the installation process of the system, supervision, adjustments, and final testing.
Stage 1 – Feasibility Study
The feasibility study for the active shielding system is the first and essential step before proceeding further.
The study will be conducted after receiving electrical infrastructure data from the electric utility company, or the line owner in the case of energy-intensive industries, along with preparing an initial impact assessment report.
This stage takes approximately one month.
Additionally, an expert inspector will conduct a visit, carry out a comprehensive EM survey, including sampling of several other important parameters related to the magnetic field levels, and, at times, continuously monitor data over a period of several days to reach a final conclusion regarding the feasibility of the active system’s success.
Stage 2 – Initial Design
After the feasibility study is completed, we move on to the next phase: initial design.
At this stage, we will explore several design alternatives for positioning the active system.
The goal is to generate a few options—typically 3-4 design alternatives.
The differences between alternatives will relate to how the system is constructed, such as placing poles in front of the building, on the roof, or integrating the system within the structure, or installing an underground system, etc.
Each alternative will have its pros and cons, and we will aim to advance the most effective and practical option for implementation.
These alternatives will be presented to the developer, architect, and project manager. Ultimately, a selected option will be chosen for further detailed planning.
This stage takes about two to three months.
At the end of this stage, it is usually possible to proceed with obtaining an environmental permit from the regulator (if required), with the condition that the detailed design is completed and integrated into the architectural plan.
Stage 3 – Detailed Design
Once the selected alternative is decided, we proceed to detailed design.
For the chosen alternative, a full specification of the infrastructure layout will be prepared, including details for poles, excavations, piping, control cabinet placement, and any other relevant components required for the system’s installation.
In some cases, structural approval may be required for specific parts of the design (e.g., for pole installation).
The detailed design phase will take approximately three to four months, depending on the complexity of the design.
Stage 4 – Execution
The execution stage consists of two main components:
Infrastructure Installation—This includes the system's infrastructure (layout, poles, excavation, and connection to the control room).
Construction of the Electronic System—This involves installing the monitoring and control units.
Upon completing the installation, adjustments will be made based on the project's progress until optimal performance is achieved.
Afterward, the configuration will be finalized, and a final test will be conducted.
This refers to the predicted magnetic flux density in a building section without an active shielding system.
This refers to the predicted magnetic flux density in a building section with an active shielding system.
System Characterization Process
For every active shielding system, the key challenge to achieving optimal performance lies in the intelligent design of the cable loop network that generates the opposing field. This design, as outlined in the previous stages, is highly complex and entirely tailor-made for each project.
While the specialized equipment/system components are important, they are secondary compared to the design and layout of the entire system and the loops in particular. Active shielding systems are designed using computer models, which allow for a precise prediction of the expected outcomes. This also provides the flexibility to "experiment" with the system’s structure and find the most optimal locations for cables and poles in the final construction. The initial characterization, as mentioned, is the most important step in achieving maximum reduction.
At this stage, dozens of possible models may be examined before narrowing down to the most practical alternatives for implementation.
Principle of System Operation
One can think of a magnetic field as a force with both magnitude and direction. When it encounters an equal force in the exact opposite direction, the forces cancel out, and the net force becomes zero. This is the basic principle of active cancellation, where fundamental physical principles are applied to solve real-world problems. However, in reality, the implementation is much more complex, as the magnetic field strength often changes across a given area, and the (invisible) lines of magnetic flux that form the magnetic field are often at awkward angles to the ground plane.
For example, if the angle of our opposing field does not align with the angle of the field we want to cancel, it won’t matter how much current flows through the system—the desired result will not be achieved. In such cases, it may not be possible to install an effective active shielding system.
System Components
Active shielding systems consist of a network of cable loops (usually outside the building) and a control system that includes electronic equipment and sensors inside the building.
The system monitors the magnetic field within the project area and generates the required current through the external cable network to create the opposing field. This process operates continuously, adjusting for changes in the electrical current on the line and modifying the opposing field accordingly. As a result, our systems can handle high magnetic field levels and peak load times on the grid.
Additionally, the system can send status updates and alerts.
In some cases, the external cable network may be buried underground, hidden from view. In other cases, above-ground components such as poles and cables are required. We aim to integrate the system components seamlessly into the surrounding environment and architectural style of the site to ensure they remain unobtrusive.
In Conclusion
An active shielding system for radiation is a unique solution designed for each case in a precise and optimal way.
Not every case will have a solution through an active shielding system, but in many cases, this solution can be prioritized over other alternatives. In most instances, an active shielding system will be the only realistic solution.
The predicted magnetic flux density in the building section.
