Reactive Power Compensation Planning for Rural Power Grid

1 Importance and tasks of reactive power compensation planning Reactive power, like active power , is an indispensable part of ensuring the power quality and safe operation of the power system. However, excessive reactive power transmission in the power grid will not only limit the active power transmission capacity of the power line, but also increase the power loss and voltage drop of the power grid, directly affecting the safe and economic operation of the power grid. Therefore, long-distance cross-regional transmission of reactive power should be avoided as much as possible. Developed countries such as the United States, Britain, and Japan all advocate that the power grid basically does not transmit reactive power, and its reactive power shortage is mainly solved by "on-site compensation". For a long time, due to the lack of attention paid by the power supply department to the reactive power planning and construction of rural power grids, the coordinated development of active power and reactive power has been affected, resulting in a large reactive power shortage in the power grid. The serious shortage of reactive power has also caused many disadvantages to the operation of rural power grids: (1) The power factor of the power grid is generally low; (2) The voltage quality is poor and the qualified rate is low; (3) The efficiency of power generation and supply equipment is low and the power line loss rate is high; (4) It affects the economic benefits of power supply enterprises. In order to change the above problems existing in the rural power grid, in addition to doing a good job in the planning and construction of active power in the rural power grid, it is also necessary to do a good job in reactive power balance and reactive compensation planning, reasonably arrange reactive power sources to meet the needs of the region or department, and continuously improve the safe and economical operation level of the rural power grid. The tasks of reactive power compensation planning in the rural power grid are: determine the compensation target to be achieved; calculate the compensation capacity; and select a compensation plan suitable for the region. 2 Determination of reactive power compensation capacity There are many ways to determine the compensation capacity, which are generally the following: (1) Determine according to the compensation standard; (2) Determine according to the annual calculation of expenditure factors. Here we only introduce the method of determining the compensation capacity according to the compensation standard. The determination method is: first calculate the actual power factor of the power purchase point, and then calculate the reactive compensation capacity according to the relevant formula based on the target power factor to be achieved. 2.1 Calculation of power factor The power factor of the power grid or user actually reflects the proportion of reactive power transmitted by the network or the amount of reactive power taken by the user. In order to avoid excessive reactive power transmission in the power grid, China's power industry has clear regulations on the power factors of different power users. Any power user who fails to reach the specified power factor must be fined according to the power factor reward and punishment method stipulated by the state, so as to mobilize the enthusiasm of users for reactive power compensation. At the same time, the former Ministry of Electric Power also has specific regulations on the power factors of power grids of different voltage levels. For the power purchase points of the rural power grid, active and reactive power meters are generally installed. If the active power measured within the measured time t is AP and the reactive power is AQ, the actual power factor can be calculated as follows: 2.2 Determination of compensation capacity After determining the actual power factor of each power purchase point of the rural power grid, the compensation capacity can be calculated according to the target power factor to be achieved by compensation. When determining the reactive power compensation capacity, the following requirements should be considered: (1) to meet the needs of load growth; (2) to have sufficient spare capacity; (3) to take into account the commissioning rate. Therefore, the reactive power to be compensated can be calculated as follows: Where Kz is the load growth factor, which can be 1.05; Ppj is the average active power of the maximum load month at the power purchase point; φ1, φ2 are the power factor angles before and after compensation; Kb is the reactive compensation reserve factor, which can be 1.2; Σ% is the commissioning rate, which can be 80% . 3 Selection of reactive compensation equipment There are many reactive compensation equipment in the power grid. For the rural power grid, since its load is relatively dispersed, the compensation capacity required at a single location is relatively small. Therefore, the general principle should be to use phase-shifting capacitors as the main equipment . Because of its simple equipment, flexible capacity combination, easy installation and maintenance, low loss, and low unit investment, it has been widely used in reactive compensation of power grids (especially rural power grids). 4 Configuration of reactive compensation equipment The configuration of reactive compensation equipment includes two aspects: (1) determining the compensation method and compensation location; (2) allocating the total reactive compensation capacity. Therefore, in addition to studying the structural characteristics of the network itself and the distribution of reactive power sources, it is also necessary to make a basic analysis of the reactive power composition of the network and clarify the reactive power flow distribution in order to make a reasonable reactive layout. The reactive compensation of the rural power grid is mainly to reduce losses, and it is advisable to adopt a compensation method that is mainly decentralized compensation and supplemented by centralized compensation. Because the line loss of the distribution network of the rural power grid accounts for about 70% of the total loss of the entire network, only in this way can the line loss of the rural power grid be effectively reduced. The compensation location should be determined in accordance with the principle of "tiered compensation, local balance", so as to achieve the overall balance of the reactive power of the rural power grid, while satisfying the reactive power balance of each substation and each distribution line of each substation, so as to achieve the purpose of improving the quality of electric energy and reducing losses. The total reactive power compensation capacity is allocated in the rural power grid according to the principle of equal network loss slight increase rate to achieve the goal of minimizing line loss. The coordination equation for the optimal allocation of the total compensation capacity among the compensation points is: where ΔPΣ is the total active power loss of the rural power grid; Qci (i = 1, 2, ..., n) is the optimal reactive power compensation capacity installed at compensation point i; Qc is the total reactive power compensation capacity of the rural power grid.

References :

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