Abstract: This paper introduces the application of domestically produced medium-voltage frequency converters in submersible electric pump wells. Keywords: submersible electric pump, frequency conversion speed regulation, three-level submersible electric pump. Due to the large starting load of power frequency, the motor power is relatively large, and the phenomenon of "overpowered motor for small load" is common, resulting in a lot of reactive power loss and high power consumption. In addition, the submersible electric pump cannot achieve soft start and stop on its own, which reduces the insulation performance of the motor and cable, affecting the service life of the submersible electric pump to varying degrees. In order to achieve energy saving and efficiency improvement in electric pump wells, after careful research, we introduced submersible electric pump frequency conversion technology and installed and tested a set of JD-BP series 1140V submersible electric pump dedicated frequency converters produced by Shandong Fengguang Electronics Co., Ltd. in Liang 23-Ping 1 well. After on-site testing, significant effects were observed. I. Working principle of submersible electric pump dedicated frequency converter. 1. Frequency conversion speed regulation principle The frequency converter can change the motor speed by changing the stator power supply frequency of the submersible motor, so as to realize the speed regulation of the submersible motor. The formula for the rotational speed of an AC asynchronous motor is: n = 60F1(1-S)/P, where n is the motor speed, F1 is the stator power supply frequency, P is the number of pole pairs, and S is the slip. 2. Inverter Working Principle: This device is an AC-DC-AC voltage source type variable frequency speed control system. It first rectifies the AC input to DC, then inverts the DC to AC at the desired frequency. The output frequency can be freely changed through the control program, allowing for smooth soft-start and soft-stop of the motor. Furthermore, the inverter has an output filter, providing better output waveform compensation, thus reducing transmission losses caused by long output lines. The inverter section adopts a three-level scheme. Compared to the two-level scheme, it has a higher inverter voltage, achieving over 1000 volts using conventional voltage IGBT devices, and the waveform is better than the two-level scheme. The schematic diagram is as follows: [align=center] Figure 1. Schematic diagram of a three-level inverter[/align] II. Field Application On September 10, 2001, we installed and tested a 1140V submersible pump dedicated frequency converter in Liang 23-Ping 1 well. Its main technical specifications are as follows: Input: Three-phase, 50Hz, line voltage 1140V +15%～20% Capacity: 75KW Output: Frequency 2～50 Hz continuously adjustable, rated voltage 1140V Overload capacity: 150%, 1-minute protection function: overvoltage, undervoltage, overcurrent, short circuit, phase loss, excessive temperature rise, stall, etc. Installation method: Connected in series with the control panel, that is, the output of the control panel is connected to the input of the frequency converter, and the output of the frequency converter is connected to the downhole unit (see Figure 2). [align=center]Figure 2. Wiring Diagram[/align] After installation, the frequency was adjusted to 40 Hz and tested for one day. The daily liquid production decreased by 10 m³. On September 11, the frequency was adjusted to 47 Hz, and the production returned to its original state. Currently, the frequency converter is operating normally. The operating data is shown in Table 1. III. Effect Evaluation and Economic Benefits 1. Effect Evaluation On September 28, 2001, the Energy Monitoring Station of Chunliang Oilfield used a DJYC-95 type motor economic operation tester (current and voltage level 0.5, power level 1.0) to conduct on-site testing on the energy-saving effect of the 1140V submersible electric pump dedicated frequency converter of Liang 23-Ping 1 well. The conclusions are as follows: A. The power factor was improved from 0.671 to 0.759. B. The active power was reduced significantly, with an active power saving rate of 22.49%, a reactive power saving rate of 39.85%, and a comprehensive power saving rate of 23.04%, indicating a good energy-saving effect. (See Table 2) 2. Economic Benefits: After installing the frequency converter, the overall power saving rate is 23.04%, saving 152,200 kWh annually. Based on a basic electricity cost of 0.435 yuan/kWh, the annual electricity cost savings are 66,200 yuan, allowing the investment to be recovered in less than two years (the frequency converter costs 125,000 yuan). Furthermore, because the frequency converter enables soft start/stop of the electric pump, it greatly benefits the extension of the pump's lifespan, saving maintenance costs and improving economic efficiency. IV. Application Prospects: The dedicated frequency converter for submersible electric pumps effectively solves the technical problem of the inability to freely adjust the output of submersible electric pumps, ensuring safe and reliable operation and achieving energy saving and efficiency improvement. However, the application of frequency conversion speed control technology in submersible electric pump wells is still in its initial stage. Our plant has a total of 16 electric pump wells. Currently, this technology is only applied in the Liang 23-Ping 1 well. If it can be applied to all electric pump wells, it will greatly improve the economic benefits of our plant's electric pump wells; therefore, its application prospects are very broad. V. Several Understandings on the Application of Variable Frequency Technology in Submersible Electric Pump Wells 1. The application of variable frequency technology in submersible electric pump wells can ensure that the pump unit operates under optimal conditions, extend the service life of the submersible electric pump, and achieve significant energy savings. 2. The dedicated variable frequency drive for submersible electric pumps has the problem of a large initial investment, requiring further cost reduction to facilitate large-scale application. 3. Further improvements are needed in the hardware design, software development level, and quality of related components of the variable frequency drive to ensure its stability and reliability during use. References: Han Wenzhao, Li Ruilai, Cheng Xudong, "1140V Dedicated Variable Frequency Drive for Submersible Electric Pumps," *Electrical Transmission*, 2002, Issue 3; Li Ruilai, He Hongchen, Han Wenzhao, "2300V Dedicated Variable Frequency Drive for Submersible Electric Pumps," *China International Power Supply Technology Papers*, May 2002. Author Biography: Guan Zhenhua, male engineer, currently engaged in the technical management of electric submersible pump oil production at the Process Institute of Chunliang Oil Production Plant, Shengli Oilfield.