Distribution of Ground Fault Currents Along Transmission Lines -- An Improved Algorithm
The calculation of fault current distribution between ground wires and ground is important for the operation of modern power systems. A new method is presented based on an approach whereby the current distribution is solved through the computation of driving-point impedances. The method is applied to three phase systems with mutual couplings between conductors (phase and ground, respectively) included. Currents computed by this method and methods published in recent literature are compared and are found in good agreement. Results show that the method is more efficient in terms of CPU time and memory space.
Zero-Sequence Current Distribution Along Transmission Lines
The zero-sequence current distribution among ground wires and the ground-return path of overhead transmission lines is subject to change in the vicinity of a ground fault and the feeding point. This paper introduces the concepts used in connection with the end-effect phenomena of transmission lines and describes the necessity for solving the end-effect current distribution. After dealing with the influential factors and basic assumptions, it describes a new calculation method which can be extended to develop generalized equations. The procedures to be followed in the case of ground faults supplied from either one or both sides are detailed. A summary of field tests is also included. The deviations between the measured and the computed values are found to be less than 15 percent. Several cases were studied to investigate the effect of factors, such as ground-wire material, tower-footing resistance, soil resistivity, and distance between feeding point and fault.
Effects of reservoir volume on performance of pulse tube cooler.
A pulse tube cooler has the advantages of long-life and low-vibration over conventional cryocoolers such as G-M and Stirling coolers because of the absence of moving parts at low temperature. On the other hand, the combination of a reservoir and orifice is indispensable to optimize the performance of pulse tube coolers. In order to make the pulse tube cooler compact for practical applications, the volume of reservoir should be minimized. This paper analyzes the effects of the reservoir volume on the thermodynamic performance of various components in a simple orifice and a double-inlet pulse tube cooler by combining a linearized model with a thermodynamic analysis. Expressions of entropy production for those components are presented. The results show that the reservoir volume has a significant influence on the entropy production in the various components when the reservoir to pulse tube volume ratio is smaller than about 5. The ratio is important to determine the minimum reservoir volume for a pulse tube cooler. Optimum settings for a double-inlet pulse tube cooler are also discussed.