| With the rapid economic growth of our country, the electric power demand is becoming higher and higher. Although the steps of power source construction speed up in recent years, the transmission capability of power grid is still prominently insufficient because of the imbalanced distribution of the production and consumption of the electric power,and the lagging behind of the power grid development compared with that of power source. Thermal capacity of transmission lines has been limited to a fixed (static) rate in case of the overheating problem when line load increases. But the operating experience shows that the limit value conservatively permits safe operation only under worst weather conditions (such as windless under high temperature). So it makes real time rating system possible using the real-time monitor of weather conditions and a complete series of line parameters. A data sampling terminal for dynamic line rating (DLR) system has particularly been introduced through this dissertation. The DLR system can achieve dynamical evaluation of the transmission capacity by measuring the actual weather condition related to line rating such as the wind speed, wind direction, ambient temperature and radiation temperature, and monitoring the real-time conductor tension, using this terminal based on MCU C8051F040.Firstly, the background and the significance of the dynamic line rating are introduced. We consider it technically and commercially feasible according to the result of the feasibility analysis. Obviously it can bring a huge economic benefit and a pleasant marketing prospect. Simultaneously the research status of dynamic line rating at home and abroad has been analyzed. At present most of the monitoring systems are based on the conductor temperature measurement in China. In this paper, a new DLR method is introduced. The conductor temperature is calculated by conductor tension and weather parameters which are sampled real-time. Then the transmission capacity is calculated by the conductor temperature and other parameters to forecast the line rating. In addition, we have illustrated the processing flow of the DLR system, and have elaborated the conductor tension– sag model based on the tension measurement. Also we have introduced two methods for conductor temperature calculation and two models for transmission capacity calculation. Nowadays heat balance equation is used to calculate the thermal rating for the conductor. Two mathematical models are introduced: weather model and conductor temperature model, which are calculated according to the IEEE 738 standard and the method in“Electric power engineering design handbook-primary power system”. Then the more conservative transmission capacity will be adopted. We have chosen mathematical models according to the differences between the conductor temperature and ambient temperature. We have found that the conductor temperature model precision is more accurate than that of weather model when conductor temperature is higher than ambient temperature, then the choice is conductor temperature model. In other situations the weather model will be chosen.The data sampling terminal of the DLR system is introduced in both hardware and software aspects, including the system structure, the hardware diagram and the software design flow of main functions, etc. Main function modules involve the microprocessor, the data acquisition, the data FLASH storage, the data wireless GPRS/GSM transmission, the real-time clock system and the communication with the power management system module, and so on. Finally, some effective measures have been taken to solve the EMC anti-interference problems. The equipment has already past the related EMC tests. At present the DLR system has entered the test run phase, and has been prepared to be put into operation in transmission lines in Guangzhou. The results of test run indicate that the performance of the system is in good condition, which meets the design requests. |
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