As part of the curriculum for ELEC 399, and as per the requirements of the Department of Electrical Engineering at the University of Victoria, we found ourselves with the opportunity to collaborate on a technical project focusing on any given area within the realm of electrical engineering. The focus of our project is the automated de-icing of a bridge with the aid of a control system. Development of our project will be split into three separate stages: research, design, and theoretical implementation.
The Purpose (Mission)
- To create a bridge de-icing system with intentions of increasing road safety during winter months.
- To implement a control system capable of using peripherial I/O to monitor weather conditions, which will control the power system.
- To design a practical power system capable of delivering heating power to the bridge as well as power all instruments and control system devices.
- To research the ability to analyze the ideas of using conductive concrete or resistive elements to de-ice a the surface of a bridge.
Development
Throughout the development of this project, the main aspects divide into three main objectives:
- The Heating System
- The Control System
- The Power System
The Heating System
The heating system refers to the execution of the de-icing process. While researching methods for transferring electrical power to heat we concluded there are two optimal methods: conductive concrete and embedded resistive elements.
Conductive ConcreteTraditionally concrete has used flyash as an additive. A major source of flyash is coal-fired generating stations, where it’s removed from the boiler outlet air using bag-houses or electrostatic precipitators before the air is released up the stack. When the Clean Air Energy Act was passed in 1990, it mandated generating stations to significantly reduce the carbon emissions they release into the air. As a result, the air particulate removal systems at these generating stations began removing flyash with a much higher carbon based content than before. An indirect result of this high carbon content was that it produced highly conductive concrete when it’s used as an additive. Other methods for conductive concrete are to add metal impurities. The specific mix of additives and metal impurities determines the resistivity properties (and therefore the heating properties) of the concrete as well as the workability of the material.
Conductive concrete has been used in applications that are safe for pedestrian use and has been deemed safe for direct contact up to 240V. This application has been designed to use a 208V 600A 3Ph power supply. This gives a maximum power available of 124.8kW (the bridge slabs are single phase but will use the line to line voltage). A rule of thumb for de-icing applications is that a system should deliver between to be effective. For this project, the goal is to achieve a power density of at least 300 W/m^2.
Given the desired power density and the available power supply, the dimensions of a bridge are limited by these parameters to ensure acceptable performance. The average lane width on BC highways is 3.7m. Therefore a typical 2 lane highway bridge over a river would be approximately 8m wide. The bridge size for this design should not exceed 52m to maintain performance requirements, therefore a length of 50m will be focused on.
For even heating across the bridge deck, the heating layer should be broken up into smaller pieces. For simplicity the bridge was split in half so each piece would be 4m wide. The other dimension was fixed at 2m and the slab thickness will be 100mm. This means the bridge deck will be composed of 50 slabs (25 down each side).
Resistive elementsWhile researching information on the implementation of embedded resistive elements we found a Danish company that manufactures the sort of elements that we would require for our project. The company is called SAN Electro Heat, and the datasheet for the heating element provided by the manufacturer was used.
In order to maximize efficiency, we found that it would be best to employ a matrix-style configuration when implementing a system of resistive elements. This conclusion was made due to the following two reasons;The small length of the elements limits the size of the area that can be heated at any given instant and employing a “modular” approach to heating the bridge allows us to reduce the amount of power that is consumed while heating.
The Control System
The control system will consist of a microcontroller with humidity and temperature sensors.. The microcontroller will most likely be a PIC MCU from Microchip. This chip will allow input/output communication between peripheral sensors and external connections.
The idea of the control system is to sense via humidity and temperature when conditions that result in the formation of ice are met. To prevent the formation of ice on the bridge, the controller will activate the heating system via a relay or other isolated device. Temperature sensors will be embedded in the heating system to provide feedback to the control system, preventing excessive temperature on the bridge deck. The control system will deactivate the heating system when the temperature of the bridge passes a certain value, or the temperature/humidity sensors deem that there is no longer viable conditions for the formation of ice.
The Power System
The scope of the power system is to deliver the heating power to the bridge as well as power all instruments and control system devices. Initially, alternative power sources were considered such as solar and geothermal systems, however it was determined the load would be much too large and grid power was needed. For this system a standard distribution voltage of 4160V was assumed. Should the grid voltage be different, the primary voltage of the main transformer would need to be modified accordingly.
The 3 phase heating power from the transformer secondary will be connected to the bridge slabs through (25) 30A rated contactors (2 slabs per contactor). Single phase 120V power will be provided for the micro controller power supply, infrared camera power supply, and contactor control circuits. To meet these requirements the transformer ratings must be 150kVA 4160V-208/120V Delta-Wye.
Deliverables
The major deliverables for the project include, but are not limited to:
- Schematic/Implementation diagrams for the Control System
- Schematic diagrams for the Power System
- Method explinations for each stage of the overall system
- Bill of Materials
- Cost Analysis
- Final Report
- Project Website (ie this one)
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Project Constraints
This project, like any project as a considerable amount of contraints. Due the limited span of 4 months, while also taking a full course load this project had a large time contraint. Due to this it was hard for us to oversee each and every minor concern during the projects development. Thus this project will cover the major safety, practical and environmental concerts that are generally dealt with during the development of a product of this magnitude.