Low voltage load forecasting planning and design

Three-phase load access method selection

According to the regulations, the load of the three-phase transformer should be balanced, and the neutral current cannot exceed 25% of the rated current of the low-voltage side. If this ratio is exceeded, the loss of the neutral energy will increase, and it will easily lead to neutrality. The position of the point moves, so the network planning and power load must grasp the balanced design of the three-phase load. The key to the three-phase load balancing design is the load access mode. Under normal circumstances, each load point adopts the three-phase introduction mode and adjusts the load balance, and any one of the neutral currents is zero. The three-phase line current is low, it is not difficult to calculate, in this comparison of line loss and other ways of loss, this kind of connection mode line loss is the lowest, the voltage quality is also the best.

The impact of three-phase load imbalance

If the three-phase load is unbalanced, a “zero drift voltage” will be generated, resulting in distortion of the output voltage in the three stages of A, B, and C. Some of the three-phase voltages are greater than 220V, and some of the three-phase voltages are lower than 220V. Low, affect the normal use of the user's load. First of all, its impact has caused direct economic losses to the company. When the three-phase load is unbalanced, a small load will affect the production capacity of the distribution transformer of the equipment and increase the low-voltage line loss. When the three-phase load is seriously out of balance, due to serious distortion of the three-phase voltage, the load of the small-sized three-phase voltage is maximized, so that a serious accident will occur in the load phase line, including household appliances such as lighting, color TVs, and refrigerators. As a result, the use of the distribution transformer is not properly protected and there is a danger of destruction. According to the relevant provisions of the "Measurement Measures for Household Appliances Damage to Residents," not only should the power users be compensated accordingly, but the power bureau also bears the cost of repairing the distribution transformers; secondly, it affects the power supply reliability of the power customers. The commitments made by the department to users cannot be fulfilled and the customers cannot satisfy the electric power service. Therefore, the three-phase load imbalance is a great harm, which not only causes the economic losses of the electric power companies, but also affects the electric power enterprises in the people’s hearts to some extent. image of. The following measures shall be adopted for the three-phase load imbalance: (1) Investigation of the customer's load situation in order to find out the corresponding low-user business expansion, planning and designing the line well, and careful and meticulous work reports for the power users to connect and install, fully consider Three-phase wire load balancing problems may occur; (2) the selection of the neutral section should be selected with the same phase; strengthen equipment inspection line inspection, do a good job of daily operations and management and maintenance, to prevent the occurrence of neutral breakage (3) Voltage monitoring should be installed at the exit of each transformer. Observe and analyze the balance of three-phase voltages, especially the peak load, to adjust the three-phase load balance load as much as possible.

Make load forecasting and reasonably select transformer capacity

The power load of lighting, agriculture, and rural enterprises that may increase the existing load within five years will be predicted based on the existing load, and plans will be made in advance to reasonably determine the number of transformers and power supply capacity. The choice of transformer capacity: (1) The main transformer for industrial use, based on a planned load of 1.3 times the transformer kVA. For the lighting, commercial, industrial and other comprehensive application of transformer capacity, fully take into account the situation when the electrical equipment is started at the same time, according to the actual peak load 1.35 times, optional kilovolt-ampere transformers. (2) For transformers dedicated to lighting, select the total kilowatts of the transformer based on the sum of the lighting. At the same time, in light of the local development situation, the actual load rate after the peak of growth of the distribution transformer station area after five years is predicted based on the average growth of the local electricity load in the past few years. (3) Combining with the outline of the development plan of the local government, reasonably determine the capacity of the transformer.

According to the load center method, reasonable selection of distribution transformer location

Combine the low-voltage rectifier circuit, according to the load plan, place the transformer in the load center as much as possible. The distribution transformer extends from the low voltage to each load point as an exit, but the power supply radius is not more than 500m. It should also be taken into account that the transformer should be located high on the ground, easily accessible from high and low voltage lines, and placed away from residential areas. The line voltage drop of the voltage is reduced, thereby improving the final voltage. The voltage after the transformation is maintained above 210V.

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