Line loss is the general term of the active energy, reactive power and voltage loss generated by the power transmission (usually called the active power loss in the habit). The line loss of power grid can be divided into technical line loss and management line loss according to the nature. Technical line loss is also called theoretical line loss, which is the general term of the power loss of each element in the power grid. The main contents include constant loss and variable loss. The technical line loss can be predicted by theoretical calculation, and the target of reduction can be achieved by adopting technical measures. The technical measures to reduce the loss of power grid include the measures to increase certain investment to carry out technical transformation of power network and measures that need not increase investment but only improve the operation mode of power grid. For example, the power distribution in the network is improved, the operation mode is reasonably arranged, the operation parameters are adjusted, the load balance is adjusted, the maintenance is arranged reasonably, the original power grid is upgraded, the network structure is simplified, and the cross section of the conductor is reasonably selected.

To reduce the technical line loss of rural power network, we can strengthen the following technical measures.

1. improve the reactive power distribution in the network, and think about the method to improve the power factor cos φ

At the same time, the distribution of reactive power is reasonable. Arrange to reduce the long-distance transmission of reactive power according to the principle of nearby. The reactive power compensation device is added to improve the power factor of the load. The power loss can be greatly reduced by reasonably configuring the reactive power compensation device, changing the distribution of reactive power flow, reducing the active power loss and voltage loss, reducing the reactive power sent by the generator and the reactive power transmitted through the lines and transformers, so as to greatly reduce the line loss, improve the voltage quality, improve the transmission capacity of the line and transformer, and reduce the reactive power delivered, so the power grid loss will be significantly reduced .

To realize reactive power compensation can not only improve the voltage quality, but also play a significant role in improving the economic performance of power grid operation. It is necessary to optimize the operation mode according to the loss of the network under various operation modes, and reasonably adjust and use the compensation equipment to improve the power factor. When the power grid is compensated, the reactive power compensation capacity and the distribution of compensation capacity are reasonably selected according to the distribution of reactive load and reactive power in the grid, so as to further reduce the loss of the grid.

In the actual compensation process, the selection of capacitor capacity is a very important problem. If the capacity we choose is too small, it will not play a good compensation role; if the capacity is too large, the phase of the current in the power supply circuit will be ahead of the voltage, and the over compensation will be generated, leading to the rise of the secondary voltage of the transformer, which leads to the increase of the loss of the power line and capacitor itself. When selecting the compensation capacitance of the substation, it should be considered in combination with the distribution of reactive power flow in the network and the reactive power compensation level of the distribution line users. Since the substation generally has two transformers and two secondary side wiring, it can be divided into two sections. In order to adapt to the transformer operation and the convenience of the secondary side section operation and maintenance, the compensation capacitor group is easy to install two groups, and its capacity is generally energy-sharing The average reactive load (near the normal reactive load of main transformer) and light load (close to the no-load operation of main transformer) are generally determined as 10% ~ 20% of the main transformer capacity.

Reactive compensation is the most common and effective energy saving technology measure in daily operation, and reactive power decentralized compensation can realize the local balance of reactive power. It is of great significance to reduce the loss of power supply line, improve the power supply capacity of distribution network and improve the voltage quality. Therefore, the reactive power compensation technology should be promoted in the construction and transformation of distribution network.

2. reasonable arrangement of operation mode

2.1 realize the economic operation of power system and power network

The economic operation of power system is mainly to determine the optimal combination of units and to distribute the load economically. At this time, the economy of the whole system is considered, and the line loss is not the decisive factor. Therefore, under the premise of economic distribution of active load, it is an effective measure to reduce line loss to realize the economic operation of power network and its equipment. The economic operation of substation is mainly to determine the best combination mode and the optimal load rate.

2.2 select reasonable operation voltage for power network

The operating voltage of the power network has an effect on the no-load loss of each element in the power network. Generally, in the 35kV and above power supply network, the operation voltage can be increased by 1%, and the loss can be reduced by about 1.2%. To improve the voltage level of the power grid is to do a good job of reactive power balance of the whole network, including improving the voltage of generator port, improving the power factor of users, and adopting reactive power compensation device. Install the transformer at the load center point and adjust the tap of the transformer under the premise of reactive power balance.

In 10kV agricultural distribution network, the no-load loss accounts for about 50% - 80% of the total loss, especially in the late night, because of the low load and the greater proportion of the no-load loss, the voltage operation should be properly reduced according to the requirements of the user for voltage offset.

For low voltage power grid, its no-load loss is very small, so it is advisable to improve the operating voltage. In the operation of power grid, a large number of on-load voltage regulating equipment can adjust the operation voltage of the power grid reasonably under different load conditions.

2.3 adjust load curve and balance three-phase load

The load peak valley difference is large, and the down line loss is large in the same power supply. When the three-phase load of transformer is unbalanced, especially the low voltage network, it not only affects the safe operation of transformer but also increases the line loss. The regulation stipulates that the current unbalance at the outlet of distribution transformer is generally required to be no more than 10%, the unbalance of the main line and the first end of the branch line is not more than 20%, and the current of the neutral line shall not exceed 25% of the rated current. This is because in the distribution system, some phase current is small, some of which is close to or even exceeds the rated current. In this case, it will not only affect the safety and economy of the transformer Operation, affecting the quality of power supply, and will make the line loss multiplied, the greater the imbalance of three-phase current, the more active power loss, so it is necessary to regularly carry out three-phase load measurement and adjustment work, so that the transformer three-phase current strive to balance. Because of the three-phase imbalance often occurs in distribution lines, if the imbalance is large, it not only increases the loss on the phase line and the middle line, but also endangers the safe operation of the distribution transformer. For the load with large peak valley difference, double circuit power supply mode should be adopted, while for the unbalanced load of three phases, the main means is to adjust the load.

2.4 reasonable selection of conductor section

The energy loss of the line is proportional to the resistance, and the energy loss can be reduced by increasing the cross section of the wire. But the increase of the cross-section of the conductor, the investment in the construction of the line also increases. The selection of conductor shall first consider the voltage drop without end (10kV is allowed to be 5%, low voltage is allowed to be 7%), and the economic current density shall be considered, and the specification of the conductor shall be determined based on the heating conditions and mechanical strength.

conclusion

In a word, the economic operation of the power grid is an effective way to reduce the cost of power supply. It is very important to choose reasonable measures to reduce network loss. In addition to taking various practical measures, the power grid loss management workers need to choose the appropriate measures according to the actual needs of the power grid, so as to achieve higher social and economic benefits.