Detection of Frazil Ice at Water Intakes at Träbena Power Station
Frazil ice is a phenomenon that takes place in cold regions when the water of rivers, lakes or oceans is cooled under 0ºC. Several times during winter, frazil ice can appear at river Ätran, where Träbena hydropower plant is held by the company Wetterstad Consulting AB. Frazil ice particles contained in the flowing water are extremely sticky and adhere to any object placed in the water. Trash racks are used by the power plant at the water intakes to prevent any strange object to go into the turbines. However, frazil ice particles stick to the trash racks creating an ice blockage that interrupts the water inflow. In this situation, the power plant has to stop the production even for several months, due to the lack of water that reaches the turbines. In order to solve this problem, the company has installed a heating system on the trash racks that prevent the adhesion of frazil ice particles. This system is manually operated, and it is turned on or off based on the experience and predictions of the company. This heating system is very power consuming and every time it is turned on unnecessarily the company loses money. An automatic frazil ice detection system that turns on the heating system when needed is to be created. For that, several options have been analysed, and finally a capacitor-based sensor has been developed as a solution. The sensor consist of two steel plates coated with semi-transparent polycarbonate submerged underwater parallel placed in the space between the trash racks’ bars, forming this way a parallel plate capacitor. The capacitance of a capacitor depends exclusively on its geometry and the dielectric material between the plates. Hence when the water temperature is low enough, frazil ice particles stick to the plates of the capacitor and its capacitance will vary indicating that the accretion of frazil ice may block the water inflow. This variation is registered and a signal is send to the heating system to start operating. This way, the heating system is completely automated; no human intervention is needed at all.
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