The power system of a certain factory has a total installed capacity of 47,500 kVA, including one 110 kV substation, four 10 kV inter-stations, and four sets of electrolytic rectifiers. It has 22 power transformers and four rectifier transformers, with an annual electricity consumption of over 200 million kWh. The rectifiers account for two-thirds of the total electricity consumption. The rectifiers have a relatively high average power factor of 0.95, but their presence also results in significant harmonic distortion. Other power loads are mainly asynchronous motors with very low average power factors. Compensation is primarily implemented for the low-voltage distribution network. Before compensation, the overall power factor of the power system was only 0.87; after compensation, the power factor can reach over 0.95. I. Main Causes and Countermeasures Affecting Power Factor: (I) The Influence of Asynchronous Motors on Power Factor The vast majority of power loads are generated by asynchronous motors. The air gap between the rotor and stator of an asynchronous motor is the main factor determining the amount of reactive power required. The reactive power consumed by an asynchronous motor consists of two parts: its reactive power under no-load conditions and the increase in reactive power under a certain load. Therefore, to improve the power factor of an asynchronous motor, it is necessary to prevent the motor from operating under no-load conditions and to maximize the load factor. Thus, when selecting an asynchronous motor, attention should be paid to both its mechanical performance and its electrical specifications. The model, specifications, and capacity of the asynchronous motor should be selected rationally to ensure it operates in an economical state. If the motor operates under low load for a long time, it will increase power loss and significantly deteriorate both the power factor and efficiency. Therefore, from the perspective of saving energy and improving the power factor, it is essential to correctly and rationally select the motor capacity. Secondly, it is necessary to improve the maintenance quality of asynchronous motors, because changes in the number of turns in the stator windings and the air gap between the stator and rotor have a significant impact on the reactive power of the asynchronous motor. (II) Impact of Power Transformers on Power Factor The reactive power consumption of power transformers is due to the fact that the transformer transformation process is accomplished by electromagnetic induction, and energy conversion is achieved by the establishment and maintenance of the magnetic field by reactive power. Without reactive power, transformers cannot transform voltage and transmit electrical energy. The main component of reactive power consumption by transformers is their no-load reactive power. To improve the power factor of transformers, it is necessary to reduce their reactive power losses and avoid no-load operation or long-term low-load operation. (III) Impact of Rectifiers on Power Factor For rectifier systems alone, their power factor can reach 0.95. However, because the grid-side current of the rectifier system is not sinusoidal, the rectifier transformer, in addition to drawing fundamental current from the grid, also sends harmonic current to the grid, seriously affecting the operation of parallel capacitors. Minimizing the generation of harmonic components is the fundamental way to eliminate the impact of rectifiers on power factor compensation equipment. The grid-side harmonic components of the rectifier unit are closely related to the equivalent phase number. Increasing the equivalent phase number is an effective measure to suppress harmonic generation. The company's rectifier system has four rectifier transformers. To increase the equivalent phase number, the rectifier transformers are connected in Δ/Δ▽ and Y/Δ▽ configurations, forming a 12-phase rectifier system. The working principle of a single 6-pulse rectifier remains unchanged; only one rectifier transformer uses Y/Δ phase shifting to cancel out the 5th, 7th, 17th, 19th… harmonics. Only the 12K±1st characteristic harmonic is injected into the system. Without increasing equipment, this achieves maximum suppression of harmonic components and reduces their impact on capacitor operation. Measures to improve the power factor: Improving the natural power factor mainly relies on increasing the load rate of transformers and motors, and adjusting the load structure to achieve the optimal power factor. II. Improving the Power Factor with Parallel Phase-Shifting Capacitors Since the company's actual production process does not use synchronous motors, parallel phase-shifting capacitors are used for power factor compensation. (I) Selection of Compensation Method: Based on the installation location of the phase-shifting capacitors in the factory's power supply system, there are three methods: high-voltage centralized compensation, low-voltage group compensation, and low-voltage decentralized compensation. Centralized high-voltage compensation involves installing high-voltage phase-shifting capacitors on the 10kV busbar of the substation. This method only compensates for reactive power on all lines upstream of the 10kV busbar (in the direction of power supply), leaving downstream lines within the plant uncompensated. Therefore, its economic efficiency is lower than the latter two methods. Furthermore, due to the presence of rectifiers in the plant, even with adjustments, harmonic components cannot be completely eliminated. Centralized high-voltage compensation would severely impact the safe operation of the high-voltage capacitors. Distributed low-voltage compensation, also known as individual compensation, involves installing phase-shifting capacitors in various workshops or near electrical equipment. This method compensates for reactive power on all high and low voltage lines upstream of the installation location and the main transformer of the substation, thus offering the largest compensation range and better results. However, this method requires a larger overall investment, and the capacitors are disconnected when the equipment stops operating, resulting in low utilization. Low-voltage group compensation involves installing phase-shifting capacitors on the low-voltage busbar of the workshop substation. This compensation method can compensate for the reactive power of the workshop substation main transformer, the high-voltage distribution lines in the plant, and the upstream power system before the low-voltage busbar of the workshop substation, and its compensation range is relatively large. Because this compensation can reduce the apparent power of the transformer, the transformer capacity can be selected to be smaller, which is more economical. Moreover, it is installed in the low-voltage distribution room of the substation, which is convenient for operation and maintenance. At the same time, due to the existence of harmonic sources, the presence of the workshop transformer also plays a role in isolating and attenuating harmonics. It is conducive to the safe and stable operation of the low-voltage phase-shifting capacitors. Considering the advantages and disadvantages of the above three compensation methods, and based on the actual situation of the plant, the low-voltage group compensation method was selected. (II) Determination of compensation capacity For the workshop substation, the installed capacitive reactive power should be equal to the sum of the capacitive reactive power required to compensate for the load on the busbar where the device is located to improve the power factor and the capacitive reactive power required to compensate for the transformer. The required capacity of the load compensation device Kvar (kilovar) is considered by the following formula: QC1=P(tgφ1-tgφ2) Qc1——Capacitive reactive power required for load compensation (Kvar) P——Average active load power on the bus φ1——Power factor angle before compensation φ2——Power factor angle after compensation Source: http://tede.cn 2) The required capacity of the transformer compensation device Kvar (kilovar) is considered by the following formula: QC2= (UK%/100+IO%/100) Se Qc2——Capacitive reactive power required for transformer compensation (Kvar) Uk%——Percentage of transformer impedance voltage I0%——Percentage of transformer no-load current Se——Rated capacity of transformer (KVA) (III) Selection of low-voltage group compensation equipment: When selecting compensation equipment, safety should be fully considered, and practicality and reliability should be taken into account according to the actual situation of each plant to maximize the cost-effectiveness ratio. 1. Selection of switching method: There are two ways to switch capacitors: manual switching and automatic switching. Manual switching is a heavy workload for operators and is difficult to perform in a timely and accurate manner, affecting the quality of power supply voltage. We adopt an automatic switching method. This allows for automatic switching of capacitors. We use the JKG series automatic reactive power compensation controller. This controller can arbitrarily set parameters such as switching threshold, switching delay, switching delay, overvoltage threshold, overvoltage delay, and undercurrent switching. It can automatically track power factor changes to rationally select the number of capacitor banks and quickly disconnect switched capacitors when the power factor is leading. In our factory's application, this control method meets our actual requirements. 2. Selection of Phase-Shifting Capacitors The selected capacitors are BSMJ0.415-18-3 type self-healing phase-shifting capacitors. These capacitors have a rated operating voltage of 415V, a capacity of 18Kvar, a three-phase delta connection, self-discharge function, a maximum overvoltage of 110% of the rated voltage, and a maximum overcurrent of 130% of the rated current. The determination of the capacitor capacity must consider the capacity of the switches and contactors, the impact of the compensation gradient on electrical equipment and maintenance costs, as well as the actual usage habits of each factory. 18 kvar three-phase phase-shifting capacitors are widely used because their compensation gradient is considered reasonable and their cost-effectiveness is high. The determination of the rated voltage must consider the fluctuation of the transformer's low-voltage bus voltage and the increase in bus voltage after compensation. The rated voltage of the parallel-connected phase-shifting capacitors should be greater than their actual operating voltage. 3. Circuit breaker selection: QF1-QFn provide main protection for individual capacitors, and a Schneider GV3-M40 air circuit breaker is selected. This circuit breaker has overcurrent and instantaneous trip protection functions. The overcurrent setting is generally set at around 30A, which effectively protects the capacitor from overcurrent. This circuit breaker has a strong breaking capacity, with a breaking current of up to 35kA, and relatively high reliability. It can reliably disconnect the circuit when a single capacitor fails, without affecting the operation of other capacitors. For QF, we select a Schneider NS type molded case circuit breaker. This circuit breaker has electronic overcurrent and instantaneous trip protection functions, accurate and reliable operation, extremely strong breaking capacity, and stable and reliable current limiting capability, and can be used as backup protection for the entire capacitor bank. Using the two types of switches mentioned above, capacitor faults can be completely confined to the capacitor bank without affecting the power distribution system. Compensation Effect: By installing parallel phase-shifting capacitor banks in the entire plant's power supply and distribution system, capacitive reactive power that can be adjusted in stages is provided to the grid to compensate for excess inductive reactive power, increasing the actual power factor to over 0.95, demonstrating a significant compensation effect. Reduced Power Loss and Cost Savings: Taking line loss as an example, the plant's annual electricity consumption is approximately 200 million kWh. Before compensation, the line loss rate was approximately 5%. After compensation, the power factor increased from 0.87 to 0.95, resulting in a reduction of approximately 2 million kWh of line loss annually. At 0.4 yuan per kWh, this translates to savings of 800,000 yuan in electricity costs. Adding the 600,000 yuan power system power factor bonus, the total annual savings in electricity costs is 1.4 million yuan. Improved Equipment Utilization: With the power factor increasing from 0.85 to 0.95, equipment utilization increases by 11.8%. Reduced Equipment Investment and Fully Utilization of Equipment Potential: Improved Power Supply Quality: Reduced voltage loss and voltage fluctuations effectively improve power supply quality. Conclusion Based on the characteristics of the enterprise and the actual application in the factory, this article introduces the main factors affecting the power factor and proposes corresponding solutions. It focuses on the experience of using parallel phase-shifting capacitors to improve the power factor.