Studies On Over-voltage Protection And Insulation Coordination Standard

Medium voltage distribution network is a large network that distributes electric energy directly to electricity consumers. Therefore, increasingly importance has been attached to its security and reliability. Because of its complex network structure and low-level insulation, voltage that functions normally will not cause serious damage to equipment. However, overvoltage appears in this system for various reasons. The overvoltage can cause some accidents, such as insulation breakdown, equipment damage and line tripping and so on. Therefore, the analysis of overvoltage and principles of insulation coordination is of great significance to improve the security and reliability of electric supply.This paper has established a variety of instantaneous over-voltage field-circuit analysis models for some common over-voltage. Then the paper does numerical analyses of these models. Using the data from over-voltage monitoring system, such information of over-voltage as waveform, amplitude and duration has been fixed. By means of laboratory tests and simulation analyses using ATPDraw, some practical protection measures have been put forward to deal with some common over-voltage.This paper analyzes the insulation coordination problems in Mv distribution network by conventional methods. On the basis of studies on the protection performance and electrical characteristics of MOA, this paper does research from these three fields: power frequency voltage, switching over-voltage and lightning overvoltage. The paper studies various insulation coordination, such as the insulation coordination between protectors and protected devices, the insulation coordination among protected devices, the insulation coordination between overhead lines and substations, the insulation coordination between internal and external insulation of electrical equipment as well as the insulation coordination among various external insulation. Then the paper puts forward some principles of insulation coordination for Mv distribution network.At present, Mv distribution voltage in China mainly uses the 10kV voltage grade. While 10kV distribution system has some disadvantages, such as supply radius inadequacy, huge network loss and poor power quality and so on. Meanwhile it is also difficult to meet the need of high-load supply. In order to respond to the national strategic requirement of energy saving and emission abatement, upgrade the supply capacity and adaptability of distribution network, reduce distribution network loss and electricity costs as well as reduce resources occupied by electricity facility, the paper first makes reference to voltage hierarchical sequence and experience in upgrading urban grid in some foreign countries. Then it proposes principles of optimizing the voltage grade and voltage promotion transformation of Mv distribution network. Therefore it solves the problem of selecting voltage grade of higher medium voltage. By comparing and analyzing examples from view of economy and technique, the paper proves the accuracy of distribution network optimization and voltage promotion transformation of the present distribution network.