Analysis of reactive power compensation scheme - Power Circuit - Circuit Diagram

### How to Achieve Reactive Power Compensation The principle of localized balance must be applied to ensure real-time equilibrium between the total output of reactive power (inclusive of reactive power compensation) and the total reactive power (inclusive of total reactive power losses). Although the Wangkui Bureau has implemented centralized compensation at substations, this discussion focuses solely on reactive power compensation for 10kV lines, distribution transformers, and motors. #### Reactive Power Compensation for 10kV Distribution Lines: The Wangkui Bureau has installed one or two high-voltage reactive power compensation devices on each 10kV distribution line, with the compensation capacity limited to approximately 10% of the total capacity of the line's distribution transformers. With a total distribution capacity of 40,500 kVA, the reactive compensation capacity is around 4,000 kvar, costing roughly 550,000 yuan. Typically, one compensation device should be placed at 2/3 the length of the line from its starting point. If two devices are installed, the first should be positioned at 2/5 the line's length from the start, and the second at 4/5, each having half the total compensation capacity. Practical considerations such as ease of operation, maintenance, and repair should also be taken into account. #### Reactive Power Compensation for Distribution Transformers: Most rural power grids experience significant fluctuations in day-and-night loads. Many villages use electricity primarily for residential purposes, leaving transformers lightly loaded or idle for extended periods. Transformer losses include both active and reactive components, with reactive losses comprising no-load excitation and magnetic flux leakage losses. Studies indicate that reactive losses account for about 60% of the total distribution network losses. To effectively compensate for these reactive losses and reduce power factor lagging, light voltage issues, and costs, static reactive power compensation is recommended for distribution transformers with capacities below 200 kVA, set at approximately 5% of the distribution capacity. This compensation device should be installed at the low-voltage outlet of the transformer and switched off simultaneously with the transformer. For transformers above 200 kVA, automatic tracking compensation devices should be utilized. #### Reactive Power Compensation for Motors: Motors with a high commissioning rate of 7.5 kW and above are ideal candidates for reactive power compensation. However, care must be taken to avoid over-compensation, which can lead to resonant overvoltage and damage the motor. Therefore, the motor's no-load power factor should be compensated close to unity. Since the motor’s reactive load is minimal at no-load, even after compensation, the fully loaded motor's power factor remains lagging, preventing overcompensation. Low-voltage capacitors should be connected in parallel with the motor to directly compensate for its reactive losses. For motors with less mechanical inertia, such as fans, the compensation capacity (Qc) can be estimated using the formula Qc ≈ 0.9Qo, where Qo represents the motor's no-load reactive power. The no-load current can often be obtained from the manufacturer; otherwise, it can be approximated using Ie = 2Ie(1 - cosφ). For motors with high mechanical inertia, such as pumps, the compensation capacity can be estimated as Qc = (1.3~1.5) Qo. Centralized compensation in workshops and factories can be determined using the formula Qc = Pm(tgφ1 - tgφ2), where Pm is the average active power at peak load, and tgφ1 and tgφ2 represent the tangents of the power factor angles before and after compensation, respectively. Reactive power compensation for motors primarily benefits the user, so the cost should be borne by the consumer. ### Economic Benefits Analysis #### Economic Benefits of Distribution Transformer Reactive Power Compensation: After implementing reactive power compensation, not only do we reduce the losses in power distribution equipment, but we also lower the high and low voltage distribution currents, reducing the line loss rate. Additionally, the copper losses in the main transformer and the wire losses in the upper transmission lines are decreased. To simplify calculations, the economic equivalent of reactive power compensation can be used to estimate the benefits. Each 1 kvar of compensation capacitors installed is equivalent to reducing active losses by 0.15 kW. Based on the actual conditions in Wangkui County, a value of 0.1 was used. With a required reactive power compensation capacity of 2,500 kvar, annual power losses could be reduced by 1.7 million kWh. At a unit price of 0.3 yuan/kWh, this results in an annual income of 500,000 yuan. #### Economic Benefits of 10kV Distribution Line Reactive Power Compensation: The total reactive power compensation capacity for the 10kV distribution line is about 4,000 kvar. Using a reactive economic equivalent of 0.06 and assuming the compensation equipment operates for 6 hours daily, the annual power loss reduction is 500,000 kWh. At 0.3 yuan/kWh, this yields an annual profit of 150,000 yuan. #### Economic Benefits of the Compensation Equipment Itself: After installation, the power consumed by the compensation equipment can be calculated using the formula A = Qc·tgφ. Assuming a 160,000 kWh annual power consumption and a unit price of 0.3 yuan/kWh, there is an annual loss of 50,000 yuan. In summary, the total investment in reactive power compensation is approximately 1 million yuan, yielding an annual return of 600,000 yuan. The entire investment can be recouped within two years. ### Conclusion Implementing reasonable reactive power compensation with minimal investment, rapid results, high returns, and practicality is indeed an effective way to reduce line losses and enhance power quality.

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