A fast time–frequency transform based differential relaying scheme for UPFC based double-circuit transmission line

This paper presents a new differential relaying scheme for a mutually coupled, double circuit transmission line in presence of Unified Power Flow Controller (UPFC) in the line. The process starts at retrieving the three phase current signals at both ends of the transmission line synchronously and processing it though the time–frequency transform such as Fast Discrete S-Transform to derive the spectral energy content of the current signals. The differential spectral energy of current signals (difference between the spectral energy of the current signal at the sending and receiving ends, respectively) of the respective phases of transmission line is used to register the fault pattern. The proposed approach includes fault detection and classification along with identification of the fault section with respect to UPFC location in one of the double-circuit transmission line. The extensive test results indicate that the proposed differential relaying scheme is highly reliable in registering fault patterns in UPFC based transmission line including wide variations in operating parameters of the power network.     

China’s electricity transmission and distribution tariff mechanism based on sustainable development

In order to guarantee the rapid sustainable development of the social economy, the power grid will make large investments in the construction of smart grids, the renewable energy network, the construction of long-distance transmission grid channels as well as the technology and service innovation of the power grid. According to the electricity transmission and distribution tariff accounting mechanism of costs and benefits, the power grid investment needs to be recycled by the transmission and distribution tariff. However, at present, the low electricity transmission and distribution tariff in China, which is based on the difference between the electricity sales price and the average purchase price, cannot guarantee the return of investment and the sustainable development of the power grid. Based on the current situation of China’s power grid construction and electricity transmission and distribution tariff, this paper proposes that the new investments in the power grid can be divided into technical innovation investments, environmentally friendly investments, service promotion investments and other kinds of investments, according to their functions. Then, four electricity transmission and distribution tariff and power grid investment linkage models are built and example analysis undertaken, respectively, which are the timely linkage model, static linkage model, ladder linkage model, in which the electricity tariff space changes by a fixed absolute value annually and ladder linkage model in which the electricity tariff space changes by a fixed proportion value annually. The results reveal that the ladder linkage model in which the electricity tariff space changes by a fixed absolute value annually can guarantee relatively smooth changes in the electricity tariff, and is suitable for the actual situation of China’s power market. The transmission and distribution electricity tariff and power grid investment linkage models based on sustainable development built in this paper are beneficial for promoting the reforms of the electricity transmission and distribution tariff in China and guiding the establishment of a scientific electricity tariff mechanism.     

Effect of the variation of the charge distribution along multi-overhead transmission lines’ conductors on the calculation method of ground surface electric field

This paper presents a new methodology to calculate the ground surface electric field, produced by overhead transmission lines (OHTLs), taking into account the effect of the variation of the charge distributions along the conductors of multi-overhead transmission lines. In this paper, the effects of the conductors sag, the presence of the tower, replacing the sub-conductors of each phase with an equivalent conductor, the presence of the ground wires, and the presence of another overhead transmission line (OHTL) circuit on the electric charge distribution along the OHTL conductors and hence on the calculation of the ground surface electric fields are extensively studied. The suggested technique is verified by comparing its results with a measurement by the other. The suggested technique is based on both the Charge Simulation Method (CSM) and the Image Method (IM).