The purpose of this work is to determine the applicability of the ZigBee technology to electric motor rotor measurements. Requirements for data transmission, electrical structure and powering of a sensor are discussed. A prototype wireless ZigBee-based torque sensor is built and tested. The results of the tests are analyzed.
Energy harvesting or scavenging from environment is being researched intensively. The main motivation of the research is to develop a maintenance free energy source for ubiquitous electronics, such as wireless sensors or sensor networks. The on-line condition monitoring of electric motors requires also sensors that are installed at the motor. In this case, the energy required by sensors could be harvested from a magnetic field. In this article, current transformer based energy harvesting is considered. A switch-mode power supply utilizing current transformer is designed. It is tested in laboratory with the mains supply and variable speed drive. According to the tests carried out, the current transformer based power sources are a feasible alternative to supply the electronics attached to an electric motor.
Abstract-Small scale or micro scale hydroelectric power production is characterized by high investment costs compared to operation costs. In addition, the repayment time is often long, more than ten years (if not subsidized heavily) which requires that a small-scale hydropower plants can be profitable only if both the investment costs and the running costs are low. The performance and efficiency of a plant is very important because having long repayment time means that the efficiency improvement of one percentage unit often means the ten percentage unit improvement in profit. The most economical way to control the flow is sometimes a two point control where generators are switched on and off depending on high water level used as control variable. The water level cannot be kept constant using this method, but the traditionally used mechanical blade angle adjustment system is too expensive in very small (approximately <100 kW) units. The new method of controlling the upper water level (head) is the use of rotational speed control of turbine, implemented by a four quadrant frequency converter. The efficiency of a 4-quadrant frequency converter is approximately 97 %, which reduces the income compared to the situation where the generators are directly connected to electricity network. However, when the head is kept constant using a frequency converter, it is not required to switch off the generator circuit breakers which have a finite life t im e a n d th e h e a d h e ig h t c a n b e k e p t o p ti m a l in t e r m s o f performance. In this paper, a system structure, a pilot plant installation and example calculations on the feasibility of a frequency converter driven fixed blade hydro power turbine is given.
Abstract. In deregulated electricity markets, the market price of electricity can be used to control power generation in order to obtain maximum revenue. This makes the building of smaller and smaller hydroelectric power stations economically feasible. High price of energy indicates that power demand is high relative to production capacity. Therefore, price-based optimization will enable the production of electricity when it is most needed. In this article, the feasibility of market price based control strategy for a small-scale hydroelectric power station is evaluated. An actual Finnish small-scale hydroelectric power plant is used as the basis for the modeling.
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