Research On Fault Characteristics And Protection Criteria Of Half-wavelength AC Transmission Line

In recent years,with the continuous economic development of the society,the electricity consumption is increasing.Ultra-long-distance and ultra-high-power electric energy transmission technology has gradually become one of the important directions of electric power development.The research of half-wavelength AC transmission technology has increasingly higher economic significance and practical value.The problem of line protection is one of the key problems that need to be solved in the practical application of half-wavelength transmission technology.Therefore,it is necessary to study the protection scheme of half-wavelength AC transmission lines.The Bergeron current differential protection itself will not be affected by the capacitive current,and it is widely used in ultra-high voltage transmission lines and UHV transmission lines.In this paper,the applicability of Bergeron current differential protection in half-wavelength lines is studied,and a specific protection scheme is proposed.First of all,this paper points out the main problems of conventional Bergeron current differential protection when applied to half-wavelength lines.Conventional Bergeron current differential protection generally selects the end or midpoint of the line as the reference point.When the half-wavelength line is in normal operation and out-of-zone faults,the actual value of the Bergeron differential current is not zero.When selecting the end of the line as a reference point to protect the line,if there is a fault in the middle section of the line,especially at the midpoint,the Bergeron differential current will be small,and there may be probl ems in distinguishing the middle section of the line,out-of-area faults,and normal operating conditions.When the midpoint of the line is selected as the reference point,there is still the problem that the full length of the line cannot be protected.This paper attempts to study the operating characteristics and fault characteristics of half-wavelength lines,and find the characteristic quantities that can effectively distinguish the normal operation of the line,the faults outside the area,and the faults in the middle section of the line.By adding auxiliary criteria on the basis of conventional Bergeron current differential protection,a new comprehensive protection scheme for half-wavelength lines is formed.There will be a significant difference in the voltage amplitude of the faulted phase terminal in the case of a fault outside the line area and a fault at the midpoint of the line.According to this characteristic of the terminal voltage,it is theoretically possible to distinguish the faults outside the half-wavelength line from the faults at the middle section of the line,especially at the midpoint of the line.Based on the above characteristics of terminal voltage,this paper proposes a new comprehensive protection scheme for half-wavelength lines.The auxiliary criterion of terminal voltage is formed according to the characteristics of the amplitude of the line terminal voltage.By combining the terminal voltage auxiliary criterion and the Bergeron differential current criterion with different high and low sensitivity,it is possible to isolate the fault outside the zone,protect the full length of the line,and realize the fault phase selection.It is verified by simulation that the scheme can achieve the ideal protection effect.When there is a fault in the half-wavelength line,the protection operates reliably and correctly identifies the fault phase;when there is a fault outside the area or in normal operation,the protection does not operate reliably.