Brief analysis on how to improve the power factor of county-level power grid
With the development of the economy and the increasing demand for power, in modern power companies, a large number of inductive devices with different sizes are connected to the power system. In addition to active power, the transmission power of the telephone network requires reactive power. The power factor is an extremely important factor that determines the economic benefit of the power generation and supply system. It directly reflects the distribution of active power and reactive power in the system. For the power supply and power system, the load not only requires a high load rate, but also A high power factor is required.
According to the "Technical Guidelines for Power System Voltage and Reactive Power" 5.9, the power factor of power users should meet the following requirements: high-voltage power supply industrial users and high-voltage power supply power users equipped with load-adjusting voltage devices, the power factor is above 0.90 , Bulk and agricultural electricity, power factor is above 0.80.
Our bureau is located at the end of Nanyang Power Grid, and the load types are mostly mine, chemical industry and rural power. According to the statistical analysis of our bureau in 2008, the power factor of Tongbai Power Grid is only 0.85 on average. Although it can meet the needs of agricultural power, it is obviously unable to meet the requirements for industrial users with high voltage power supply. There is still a big gap between the first-class power supply companies. It is well known that reactive power compensation equipment provides the necessary reactive power to improve the power factor of the system, reduce energy consumption, and improve the quality of the grid voltage.
1. Reason analysis
In order to cooperate with our bureau to create a “first-class†power supply enterprise and meet the standards and requirements of first-class county power supply companies for power grid hardware, our bureau has successively built or rebuilt 12 substations as integrated automation stations, meeting the requirements of unattended substations . All equipment achieves the "five remote" function, dispatching can realize remote operation of substation equipment, various data can realize real-time telemetry, and dispatch automation has successfully passed the acceptance of provincial dispatch automation. The plan of the situation and the successful organization and implementation of the set goals laid a solid foundation.
Before the comprehensive self-reform was carried out in our bureau, the real-time performance of the substation's reactive voltage regulation switching capacitor was poor, and the substation personnel mainly implemented the switching capacitor manually according to the displayed voltage. Because the load is affected by the load fluctuations during the period, the voltage offset of the power grid increases, which requires greater real-time adjustment. However, the automatic control of the reactive power balance of most substations is not perfect, and the degree of automation is poor. It is impossible to adjust the reactive voltage in real time, resulting in a low power factor. According to comprehensive analysis, the main reasons for the low power factor of the power grid are:
1. The substation is not equipped with a power factor meter or the power factor meter is inaccurate;
2. There is no corresponding prompt signal when the voltage is too high or too low;
3. The method of compensating reactive power is only to switch the capacitor back and forth, and the capacitor switching is not reasonably arranged according to many factors such as the change of load flow, bus voltage, active power, reactive power and power factor;
4 Personnel monitor the voltage changes in real time with poor timeliness.
Second, formulate a plan
The essence of improving the power factor problem is to reduce the reactive power requirements of electrical equipment. In order to minimize the transmission loss of reactive power and improve the efficiency of transmission and distribution equipment, the configuration of reactive power compensation equipment should be combined with overall balance and local balance, combined with centralized compensation and decentralized compensation, and loss reduction and voltage regulation Combining the principles to achieve on-site compensation and on-site balance. The power factor scheduling of each substation should be mastered at any time. According to the "Voltage Reactive Technical Guideline" and the principle of tiered on-site balancing of reactive power, the reactive power compensation capacity configuration should reach 10% -30% of the main transformer capacity. If the power supply voltage exceeds the specified range, it will also have a great impact on the power factor. When the personnel notice the voltage is unqualified, take voltage regulation measures, and implement the capacitor switching, the voltage has often been operating in the unqualified range for a period of time, and cannot be achieved. For dynamic reactive power regulation, the bus voltage of each station should be controlled within the qualified range, and the power factor and reactive power should be combined to switch the capacitor back and forth to solve the problem of over-compensation and under-compensation. At the same time, for the 10KV line capacitors, we require all relevant departments to invest in order to meet the requirements of reactive power compensation on the spot.
3. Organization and implementation
In the 12 integrated automation substation projects newly built or rebuilt by our bureau, the bus voltages, loop currents, active power, reactive power, reactive power compensation power of the capacitors of each station and the main transformer high, medium, The main data such as low-voltage side power factor are uploaded to the dispatched primary system diagram through optical fiber. All data can be real-time telemetry, fully utilize the "five remote" functions of dispatch automation, and realize remote switching of substation capacitors. The bus voltage of the station is controlled within the qualified range (the allowable deviation value of the 10kv user's voltage is ± 7% of the rated voltage of the system, and the 35kv voltage fluctuation range should not be greater than 10% of the rated voltage of the system). The bus voltage is not qualified for dispatch automation Voice alarm, when the voltage is too high or too low to remind the dispatcher on duty. We reasonably arrange the switching of capacitors (as shown in the table) according to many factors such as load flow changes in substations, bus voltage, active, reactive power and power factor changes, to prevent the occurrence of undercompensation or overcompensation. The main transformer of the substation The economic effect of on-load voltage regulation is firstly established on the basis of reactive power on-site balance of the power grid. Economical voltage regulation effectively achieves reasonable switching of the capacitor bank first, then appropriately adjusts the main transformer tap, and adjusts the transformer tap to achieve power. Factor and voltage balance. Adopt "reverse voltage regulation" method to reasonably adjust the transformer gear. When the load of the power grid is high, adjust the tap position of the on-load voltage regulating switch to increase the bus voltage to about 10.5kV; when the valley is low, reduce the bus voltage to 10.2kV Left and right, so that the voltage fluctuation range can be controlled between 2-5%, not only to ensure the bus voltage, but also to ensure that the 10kV distribution line terminal section and the secondary outlet voltage of the distribution transformer are in the qualified range. The main component of transformer reactive power consumption is its no-load reactive power, which has nothing to do with the load rate. Therefore, in order to improve the power factor of the power system, the transformer should not run without load or be in a low-load operating state for a long time. There are two main transformer substations. Due to the differences in the technical characteristics of the transformers, and the active and reactive losses of the transformers change nonlinearly with the load, after accurate calculations, we will make the transformer economically critical. The operation area is determined, and the dispatching staff pays close attention to the load changes and adjusts the operation mode of the transformer at any time to minimize the loss of the transformer on the power grid. After the above measures, the voltage qualification rate of the 35kV and 10kV busbars is guaranteed, the network loss is reduced, and the power factor of the high-voltage side of the main transformer is about 0.95.
Configuration table of voltage, reactive power and capacitor
No. of grid voltage and reactive power status capacitor switching
1 The voltage and reactive power are qualified, and the stable working area is not adjusted
2 High voltage, reactive power balance strong cut capacitor
3 High voltage, low reactive power, strong cut capacitor
4 Qualified voltage, less reactive power cast capacitor
5 Low voltage, low reactive power and less capacitors
6 The voltage is low, and the reactive power balance cast capacitor.
7 Low voltage, multiple reactive capacitors with reactive power bias
8 Qualified voltage, reactive power bias multi-cut capacitor
9 The voltage is too high, and the reactive power is multi-cut capacitor.
10 If the voltage is too low, cast a capacitor.
11 Excessive voltage cut capacitor
Fourth, the effect check
According to the implementation of the plan from March to December 2009 for nearly a year, the effect is still very significant. According to relevant statistical data, the average power factor of the power grid has been increased from 0.85 to 0.95 to achieve the expected effect. The contribution to Tongbai Power Grid is as follows:
1. Improve equipment utilization.
For the original power supply equipment, under the same active power, due to the increase in power factor, the load current is reduced, so the power supply and distribution equipment such as transformers, switches, and wires that pass power to the load increase the power reserve to meet The need for load growth.
2. Reduce the energy consumption of the system
We calculated: the active power transmitted by the line before and after compensation remains unchanged, and when the power factor is increased from 0.70 to 0.85 to 0.95, it can be obtained that the active loss will be reduced by 20% to 36%. We have tested it on the pilot line. When the power factor of the 10KV line is 0.85, the line current is 40A. When the line power factor reaches 0.95 and the line current is the same value, the line loss is reduced to 0.649 times the original, that is, the loss is One third, the effect is obvious.
3. Improve voltage quality.
The substation bus voltage qualification rate is 100%, and the reasonable compensation for reactive power is conducive to the stability of the voltage at the end of the line and the start of large motors.
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