Discussion and practice of low voltage line loss m

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discussion and practice of rural low-voltage line loss management

(I) problems in rural low-voltage line loss management

generally speaking, if the outgoing lines of rural 35kV substations are chaotic, there are many circuitous lines, the transmission radius is too large, the lines operate with ultra economic current or even ultra safe current, there are many high energy consuming transformers, insufficient reactive power compensation, and poor voltage quality, Will lead to a large line loss rate, such as aerospace, ordnance and many other important industries. But there are also some common problems, such as:

1, matching problem. Due to the wide, scattered and small number of rural users, there are many lines with over supply radius, the space distance of the lines is too long, there are many circuitous and "neck" power supply lines, the load points on the distribution lines are scattered, the distribution and transformation power supply points are far away from the power load center, and the selection of conductor section does not match the load, etc

2. Equipment problems. The power supply equipment is old and worn out. High energy consumption distribution transformers and electrical equipment are still in use, some conductors are worn, the wire diameter is small, the wire section is small, the carrying capacity is large, and the line loss reduction is serious

3. Operation problems of distribution transformer. The capacity of distribution transformer does not match the actual power load, and the phenomenon of "big horse pulling small car" is common

4. Measurement problems. The loss caused by the electric energy metering device, the unqualified metering accuracy or the low terminal voltage cause the phenomenon of slow wood-based panel universal testing machine

5. Management problems. Users' illegal use of electricity and power theft losses, error losses in meter reading and verification, and negligence in the use and replacement management of users' meters are easy to cause power loss. In rural temporary seasons, the management of telegraph installation is not strict, and there are electricity consumption without meters and other unknown losses

6. Reactive power compensation. Most 10kV distribution transformers and below are not equipped with compensation devices, resulting in serious reactive power loss and uneconomical power operation

(II) measures for loss reduction and energy saving

1. From the perspective of the technical measures of saving energy and paying attention to the connecting line of the controller on the electronic universal experimental machine at the same time, through the adoption of new products, new technologies and technological transformation, the electric energy meters and mutual inductors should be calibrated and rotated regularly in strict accordance with the procedures, especially the metering meters of large users should be strengthened. The new electronic watt hour meter is preferred, which not only makes the measurement more accurate, but also reduces its own loss

2. Optimize the power supply mode, transform the circuitous line, and the transformer should be close to the load center to minimize the no-load transformer. Determine the best location of the load center to reduce or avoid the phenomenon of power supply beyond the power supply radius. The general requirements for the power supply radius of rural lines are: 400V lines are not greater than 0.5km, 10kV lines are not greater than 15km, 35kV lines are not greater than 40km, and 110kV lines are not greater than 150km

3. Install reactive power compensation equipment to improve power factor and reduce reactive power transmission. The voltage supplied by the power system to the load changes with the change of the active and reactive power transmitted by the line. When the line transmits a certain amount of active power and the starting voltage remains unchanged, for example, the more reactive power transmitted, the greater the voltage loss of the line and the higher the line loss rate; When the power factor is increased, the reactive power absorbed by the load to the system will be reduced, the voltage loss of the line will be reduced accordingly, and the line loss rate will be reduced. If possible, install capacitors for reactive power compensation

4. Adjust the number and capacity of transmission and distribution transformers in time according to load changes to improve the utilization rate of transformers. The cross-sectional area of the power supply line is selected according to the density of the economic current. Both economy and safety should be considered in the selection of conductors. If the conductor section is too large, the line loss is too small, but it will increase the line investment; The wire cross-section is too small, and the line loss is too large, which can not meet the power supply needs of today's development, and the safety factor is also small. In practical work, when the load rate is 50% - 70%, the distribution transformer is in an economic operation state, with high efficiency and low loss. To avoid long-term "big horse pulling small car" or frequent overload operation of distribution transformer, the capacity of distribution transformer should be adjusted in time or the power supply of parent-child distribution transformer should be adopted. Sometimes, due to seasons, load changes and other reasons, the power load flow changes greatly, resulting in an increase in line loss. At this time, pay attention to seasonal load fluctuations and switch transformers and capacitors in time. When necessary, install the sub bus transformer for seasonal loads. Two transformers can be installed according to the maximum load and the minimum load respectively. Put the large capacity transformer into operation when the load is large and the small capacity transformer into operation when the load is light. The installation of the sub bus transformer has obvious effect on reducing the loss of some loads. The transformers put into operation due to seasonal changes shall be shut down in time

5. By improving meters at all levels and carrying out regional electricity analysis, problems can be found in time. The metering circuit shall be dedicated and shall not be shared with protection, measurement, negative control and other circuits, and any load and device shall not be connected in series or in parallel. The transformation ratio of current transformer should be selected so that the actual load current is about 2/3 of its primary rated value, not too large or too small. Pay attention to the load on the secondary side of the current transformer. The secondary wiring of the current transformer should be connected with copper wire, and it is forbidden to connect with aluminum wire, so as to avoid oxidation and the meter will not go

6. Reduce the level of transmission and distribution, that is, reduce the times of voltage transformation and improve the level of transmission voltage

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