110 kv substation design paper

110 kV substation access system optimization and improvement Abstract: Through the analysis of the original 110 kV substation access system, put forward the improvement plan. The implementation of the improvement program, can be obtained to enhance the reliability of power supply within the enterprise. Key words: substation; system mode; improvement 0 Preface Nanchang Changli Iron and Steel Company Limited (referred to as NSC) has two 110 kV substations, with a total transformer capacity of 221?6?15 MVA, of which the first transformer is 90 MVA and the second transformer is 131?6?15 MVA. The two substations have double "T" access. The two substations have double "T" access to 110 kV Changgang Ⅰ line and 110 kV Changgang Ⅱ line, and through these two lines, they are connected to 220 kV Changdong substation of Nanchang Power Supply Company (Figure 1). During the normal production of NSC, the total power load of the first and second transformers is 130~150MVA. 1 Defects of the original access system of 110 kV substation The power supply of iron and steel enterprises is characterized by high demand for electricity and high reliability of power supply, and NSC is no exception. Due to the objective conditions, the first and second transformers can only be connected to the power system grid with double lines, which causes great inconvenience to the operation and management of the internal power grid of NSC. 1) Nanchang Power Supply Company's 220 kV Changdong substation is the only power source of NSC, whether the substation can achieve stable operation and reliable power supply is very critical for NSC. If the 110 kV busbar of this substation fails, NSC will suffer huge loss of power failure. 2) The designed maximum load capacity of 110 kV Changgang Ⅰ line and Ⅱ line is 80MVA and 100MVA respectively, and these two lines can't carry all the loads of normal production of NSC (i.e., they don't satisfy the n-1 operation condition). If either line fails or is scheduled for power outage and maintenance, the first and second transformers will be forced to operate at reduced load. 3) Due to the limitation of line load capacity, the first and second transformers have to change the operation mode of 110 kV system by means of load limitation, no matter under normal condition or accident condition. This will not only cause short-term interruption of power supply to some customers, but also prolong the outage time of the customers in case of an accident, thus expanding the impact of the accident. (4) NSC's "11th Five-Year Plan" needs to add 120~150MVA of power load, due to the existence of power points and receiving channels are few, receiving channel transmission capacity is weak and other problems can not be solved by itself, 110 kV substation's original way of accessing the system does not have the conditions for power capacity increase, and it is impossible to meet the requirements of the "11th Five-Year Development Plan" of the NSC. The original access system of 110 kV substation does not have the conditions for power capacity increase, and cannot meet the new power demand of NSC during the period of "Eleventh Five-Year Development Plan". Maintaining the original access system of 110 kV substation of NSC is not conducive to the stability and smooth running of the internal power grid of the company, nor is it conducive to the sustained development of the company, and it must be optimized and improved by taking appropriate opportunities. 2 110 kV substation access system optimization and improvement plan According to NSC's 2007 technical reform project plan, in June 2007, the construction of NSC's three variables (referred to as three variables) project. The purpose of the construction of the three transformers is not only to solve the problem of new electricity consumption in the "11th Five-Year Plan" period, but also to solve the problem of poor reliability of the 110 kV substation's original access system mode of receiving electricity. After many communications and exchanges between NSC and Provincial Electric Power Design Institute and Municipal Power Supply Company, it was finally agreed that the three-variable project (including one-variable and two-variable) would be designed according to the following requirements for the access system: 1) the three-variable new double circuit line will be connected to 220 kV Guantian Substation of Nanchang Power Supply Company, and the line will satisfy the operation conditions of N-1; 2) the two-variable new double circuit line will be connected to 220 kV Guantian Substation of Nanchang Power Supply Company, and the line will Meet n-1 operation conditions; 3) the first transformer to maintain the original double circuit line (110 kV Changgang Ⅰ line and 110 kV Changgang Ⅱ line) into the Nanchang Power Supply Company 220 kV Changdong substation, the line to meet the n-1 operation conditions; 4) a new 35 kV liaison line between the first, second and third transformer to form the substations to supply each other with security loads of the electric power corridor (Fig. 2a, Fig. 2b, Fig. 2c). 3 The effect after the implementation of the improved scheme At present, the three-variable project has entered the final stage of the project, and after the completion and operation, the access system of 110 kV substations of NSC will be formed: three 110 kV substations will be fed from the two 220 kV substations of Nanchang Power Supply Company; each 110 kV substation will have a double circuit of feeder lines that meet the operation conditions of n-1; and a new power channel will be built between three 110 kV substations to provide security loads to each other (Fig. 2a, Fig. 2b, Fig. 2c). Each 110 kV substation has a double circuit with n-1 operation conditions; the three 110 kV substations are connected by a new 35 kV contact line to provide security power to each other. From NSC's point of view, such an access system design is relatively reasonable, and can significantly improve the comfort and reliability of receiving power. 1) Reduction of the impact area of electrical faults. An outage at one 220 kV substation will not cause a simultaneous outage at three 110 kV substations; an outage at one 110 kV line will not cause a total outage at the corresponding 110 kV substation; and even if a total outage occurs at a particular 110 kV substation, the security load can be delivered to the substation via the 35 kV contact line. At the same time, the number of outage contingency plans available increases accordingly. By implementing different contingency plans for power outages, the impact on the company's production caused by the outage of a 110 kV line or a 220 kV substation can be limited to the smallest possible extent. 2) The problem of the inability of NSC's internal power grid to continue to increase the capacity of electricity has been well solved. If we do not take into account the superior 220 kV substation capacity factor, only with the second transformer, the third transformer receiving line design load capacity estimation, the two substations *** have the ability to continue to increase the capacity of 100 MVA, basically can meet the new power demand of NSC in a five-year planning period. After the three transformers are put into operation, we can also consider transferring an eccentric furnace transformer, which has been supplied separately by Nanchang Power Supply Company's 35 kV Luo Steel Line for a long time due to its insufficient power supply capacity, to be supplied by the three transformers. This can not only improve the load rate of the three main transformers, but also reduce the company's electricity costs. 3) If we continue to carry out partial improvement and reconstruction in the first and second transformers, we can also realize the following: (1) reconstruction of the 110 kV busbar switch of the second transformer (replacing the busbar disconnecting switch with a busbar circuit breaker). After the modification, all three 110 kV substations will be able to flexibly change the operation mode of the 110 kV system without affecting the normal power consumption of the customers. (ii) 110 kV self-provisioning devices were installed in the first and second transformers. After completion, the accident response speed of all three 110 kV substations can be synchronized and improved. 4 Problems and countermeasures that must be noted when adopting the new access system 1) How to prevent the formation of a ring network (meaning that the two 220 kV substations of the power system form an electrical ring network in the internal power grid of NSC) operation problems. There are two conditions that must be met if the grid can be operated in a loop. One is to ensure that the stable operation of the power system does not affect; the second is the requirement of monitoring in place, organization, technical measures are complete. As an end-user of the grid, NSC does not have the ability to control the operation of the grid, and if it blindly carries out the operation of the grid, there may be unpredictable and serious consequences. Therefore, the company must strengthen the operation management of 35 kV security lines and 35 kV and 6 kV important users equipped with two independent power sources (such as improving the regulations, implementing the system, and installing electrical and mechanical locking devices in the possible ring network points, etc.) in order to prevent the occurrence of ring network operation. 2) How to prevent small generating units in the internal power grid from non-simultaneous parallel operation with the system power grid. According to national industrial policy and energy law, NSC has built and put into operation two small generators (one gas cogeneration generator and one TRT generator). In the future, a number of integrated energy utilization generators will be built as needed. Under normal conditions, there is no possibility of non-simultaneous paralleling between the small generating units of the internal grid and the system grid, but under special circumstances (e.g., tripping of the 110 kV receiving line, failure of the small generating units of the internal grid to follow the emergency switching, and the absence of voltage-detecting automatic reclosing of the superior substation), non-simultaneous paralleling may occur. The following technical measures must be adopted to prevent the above problems: ① The line reclosing device of the superior substation (110 kV self-provisioning device of the first, second and third transformers) must be utilized for voltage checking and blocking, and the line reclosing device (110 kV self-provisioning device of the first, second and third transformers) shall not be put into operation if the above conditions are not met. ② The small generating units of the internal power grid must be installed with low-voltage low-frequency cut-off devices. 3) How to adjust the power load of the first, second and third transformers of NSC. After the construction and operation of the third transformer, the power load of the three 110 kV substations of NSC must be adjusted. The purpose of load adjustment is twofold: firstly, to allow important users to obtain two independent power sources, so as to improve the reliability of power supply to important users and the flexibility of operation; secondly, to carry out reasonable distribution of loads according to the actual carrying capacity of each 110 kV substation and the trend of the future growth of loads in the station, so as to facilitate the economic operation of the substation and the safety of power supply. Load adjustment must take into full consideration of the structure of the internal power grid and the status quo of power supply, according to the principles of power supply of new projects from three transformers, load transfer near to the substation (load transfer between two and three transformers), load transfer by using the existing lines, etc., and carry out this work in phases and step by step, and strive to make the implementation convenient and the investment most economical. 5 Conclusion The optimization and improvement of the access system of Nangang Company has made the formerly fragile power receiving channel become both strong and smooth. This has played a powerful role in improving the operation quality of the internal power grid and enhancing the ability to guarantee supply. How to adapt to the change of the access system, and further rationalize the company's internal grid structure, so that the grid operation is more stable and the power supply is more reliable, still need to be further studied and explored in the future work.