Analysis of the influence of the hottest three-pha

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The influence of three-phase unbalanced load on the low-voltage line loss rate

after the rural low-voltage power transformation, the low-voltage electrical structure has undergone great changes, and the weak links of the electrical structure have been basically solved. The power supply capacity of the low-voltage power has been greatly enhanced, the voltage quality has been significantly improved, and the low-voltage line loss rate in most distribution stations has been reduced to less than 11%, but so far, there are individual distribution stations with high line loss rate due to three-phase unbalanced load and other reasons, It has caused great difficulties and losses to power supply management enterprises, especially the electrician Group of grass-roots power supply stations. The following is an analysis and discussion of these situations in October this year

I. cause analysis

during the agricultural transformation in previous years, a series of loss reduction technical measures were taken for the distribution station area, such as increasing the number of distribution transformers, adding and transforming distribution panels, placing distribution transformers in the load center, shortening the power supply radius, increasing the wire diameter, building and transforming low-voltage lines, and setting up new household lines, which also achieved good results. However, the line loss rate of some stations is still very high. In view of the reasons, we have made a serious field investigation and analysis, and found that some stations adopt single-phase two-wire system and two-phase three wire system for power supply. Even if the three-phase four wire system is used for power supply, the three-phase load current is unbalanced due to the large difference of each phase current. From the theoretical and practical analysis, it will also cause the line loss to increase

II. Theoretical analysis

low voltage distribution transformers have a wide range and many quantities. If the three-phase load is unbalanced during operation, losses will be increased on the circuit and distribution transformers. Therefore, the main way to reduce power loss is to measure the three-phase load current of the outlet side of the distribution transformer and some main lines frequently during operation and balance the three-phase load current

assuming that the three-phase unbalanced current of a low-voltage line is IU, IV, I, the report W is automatically formed, and the neutral line current is in. If the neutral line resistance is twice the phase line resistance and the phase line resistance is r, the active loss of this line is

Δ P1=(I2UR+I2VR+I2WR+2I2NR) × (1)

when the three-phase load current is balanced, the current of each phase is (iu+iv+iw)/3, and the neutral line current is zero. At this time, the active loss of the line is

Δ P2=■2R × (2)

the power loss caused by the increase of three-phase unbalanced load current is

Δ P adapt to climate change in Xinjiang= Δ P1- Δ P2=■(I2U+I2V+I2W-I2UI2V-I2VI2W+I2WI2U+3I2N)R × (3)

similarly, when the three-phase load current is unbalanced, the transformer itself also increases the loss, which can be calculated by the load current before and after balance. It can be seen that the greater the three-phase unbalanced load current, the greater the loss increase

the unbalance rate of three-phase load current is calculated according to the following formula

k= ■ × 100 (4)

generally, the unbalance rate of three-phase load current at the outlet of distribution transformer is not greater than 10%, and the unbalance rate of three-phase current at the beginning of low-voltage trunk line and main branch line is not greater than 20%. It can be seen that if it is unbalanced, the line loss may increase several times. It is understood that at present, rural single-phase load has become the main aspect of power load. Although rural low-voltage lines are mostly three-phase four wire, many do not pay attention to the balanced distribution of single-phase load to three-phase circuits, and there are a certain number of single-phase two-wire, three-phase three wire power supply. According to the average calculation of general conditions, it is estimated that the line loss of single-phase load may increase by 2 ~ 4 times. Therefore, it can be seen that adjusting the power consumption of three-phase load balance is the main link of loss reduction

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