| Low voltage (LV) distribution networks are at the end of distribution networks andare directly connected to users. With the high-speed development of economy, powerconsumption increases substantially so that the construct and transform of LVdistribution networks can’t follow the speed of load growth. As the key factor of LVnetwork development, LV distribution network planning plays a vital role. In this thesis,several aspects about LV distribution network planning are researched into.Based on the idea of line segments, an improved loss coefficient method is putforward for an LV feeder with a non-lumped load distribution, in order to reduce thepower and voltage loss errors (up to20%). The validity of the improved method isdemonstrated by numerical examples.Considering that different guidelines have huge difference of distributioncapcity-load ratio values, parameters of distribution capcity-load ratio formula areanalyzed, and the difference causes are found out, and the value ranges of distributioncapacity-load ratio are obtained with regional characteristics being considered. Based ona distribution capacity-load ratio, the size and number of distribution transformer aredetermined. Through a comparative analysis, the distribution transformer planningprinciple of load center siting, small capacity, short radius, close arrangement isdescribed.Considering the minimum annual cost, an economic current density formula for LVthree-phase four wire systems is obtained; each parameter in the formula is analyzed,and an LV line economic current density of domestic characteristics is determined.Based on the economic current density value, distribution transformer LV line planningis conducted, the relationship among the distribution capacity, number of LV lines andLV wire cross-section is derived with the distribution transformer and LV line beingeconomically loaded, and the corresponding query table is developed. With the help ofthe table, the number of LV line and the wire cross-section can be choosed. Finally theselected conductor cross-section is checked, by using mechanical strength and allowablemaximum current.In order to solve the problem that the same maximum allowable length of an LVline is used, LV line power supply length is obtained with an allowable voltage loss rateor power loss rate by the loss coefficient formula, and the corresponding query table is established.Finally, based on the above research, new ideas and processes are proposed for theLV distribution network planning, and numerical examples show: with the powerdemands during planning periods being satisfied, the proposed method can substantiallyreduce the LV distribution network reform projects and enhance the investment benefit,and the proposed method is practical and operable. |
