Abstract This paper introduces the frequency conversion retrofit scheme for condensate pumps and the commissioning process of high-voltage frequency converters at Luohe Power Plant. To improve equipment utilization, reduce power generation costs, and improve control accuracy, Luohe Power Plant adopted a high-voltage frequency converter to control the speed of the high-voltage motor of the condensate pump. The trial operation results show that the motor saves significant energy after the frequency conversion retrofit and can greatly improve the motor's operating conditions. The frequency conversion retrofit scheme for high-voltage motors is worth promoting. Keywords Condensate pump; High-voltage frequency converter; Energy saving 1 Introduction The total installed capacity of Luohe Power Plant in Huainan, Anhui Province, owned by China Datang Corporation, is 4×300 MW units. Each unit is equipped with two condensate pumps that serve as backups for each other. The flow regulation adopts the traditional valve regulation method. Therefore, the following drawbacks exist: large throttling losses and serious energy waste; the condensate pump operating efficiency is greatly reduced during peak shaving; frequent regulation easily leads to damage to valves and actuators, resulting in large equipment maintenance; the motor is often running at high speed, causing wear and heat generation of various components; the motor's power frequency start-up causes a large impact on the power grid and the motor; low degree of automation and poor control accuracy. To further improve equipment utilization, save energy, and reduce plant power consumption, after extensive research, Luohe Power Plant selected Yaskawa's highly reliable, ultra-energy-saving vector control high-voltage frequency converter, recommended by Shanghai Xinhua Control Technology (Group) Co., Ltd., to retrofit the condensate pumps of Units 3 and 4 with frequency converters. This eliminated power losses caused by valves and baffles, achieving energy savings and improving the economic efficiency of the power generation company. 2. Condensate Pump Frequency Conversion Retrofit The parameters of the condensate pumps of Units 3 and 4 at Luohe Power Plant are: rated voltage 6kV, rated power 1000kW, rated current 116.4A, and rated speed 1487 r/min. They are equipped with Yaskawa CIMR-MV1SDCl3C high-voltage frequency converters. The system interface and DCS logic configuration design changes were completed by Xinhua Group Co., Ltd. 2.1 Introduction to the Energy-Saving Principle of High-Voltage Frequency Converters For water pumps, fluid dynamics theory shows that flow rate is directly proportional to the first power of speed; torque is directly proportional to the square of speed; and pump power is directly proportional to the cube of speed. Let n and N represent speed and power respectively, and the subscript "0" represents the rated operating parameters. When the flow rate drops from the rated value Q[sub]0[/sub] to Q, compared with the rated power N0, the power consumption of the motor using speed regulation is: When the flow rate drops from 100% to 70%, the speed drops to 70% accordingly, and the power consumption of the motor drops to 34.3%, that is, saving 65.7% of electricity. After deducting the difference between the power consumption during valve regulation and the rated power consumption, and the decrease in motor efficiency caused by the speed drop, the energy-saving effect is also very significant. 2.2 Rerouting of the Main Electrical Circuit Given the redundant configuration of the condensate pump and the high reliability of the Yaskawa high-voltage frequency converter, the frequency conversion retrofit of the condensate pump did not consider the power frequency/frequency conversion switching circuit. The electrical main circuit design is shown in Figure 1. The power supply is sent from the plant's auxiliary power bus to the high-voltage frequency converter via the existing high-voltage circuit breaker QF. The frequency converter converts the electrical energy into frequency and directly drives the motor. This design only adds one frequency converter, has a simple structure, and lower investment and footprint. [align=center] Figure 1 Electrical Main Circuit Diagram[/align] 2.3 System Interface Design The frequency converter shares the following points: DI2 - frequency converter start/stop command; DO5 - frequency converter preparation end/operation/minor fault alarm/major fault alarm/self-protection trip high-voltage switch; A11 - DC4-20mA speed command; A12 - frequency output/current output. The interface diagram is shown in Figure 2: [align=center] Figure 2 Interface Diagram[/align] 2.4 Logic Configuration When the frequency converter is in normal use, the frequency converter and the mains frequency standby condensate pump are interlocked: when the frequency converter trips, the mains frequency standby condensate pump starts in an interlock; when the frequency converter is running and the condensate header pressure is low, the mains frequency standby condensate pump starts when the interlock signal is true. The original deaerator water level regulating valve control is retained as a backup means of regulation; when the frequency converter speed regulating pump trips, the standby constant speed pump starts; when the constant speed pump trips, the speed regulating pump is started in conjunction, and the maximum speed is set. 3 Debugging of the Frequency Converter System This frequency converter system modification was completed in just one day, and the frequency converter was tested under various working conditions and loads, and the operation was good. To ensure the safe operation of the equipment, before the main power supply was turned on, the frequency converter also underwent transformer insulation testing and control power supply confirmation tests. Frequency converter cabinet inspection and reinforcement. Inspect the cabinet and internal components to ensure there is no damage or loose screws; confirm that wiring positions and grounding are in good condition; the coupling on the motor side is disconnected. Transformer insulation test. Test the transformer's insulation performance to ground; the measured value is 2000 MQ, exceeding the standard of 30 MQ, and the test is qualified. Control power supply confirmation. The control power supply provides power to the cooling fan and frequency converter. The test starts from the main control power supply circuit and sequentially tests each power module on the control board to ensure the normal operation of each control power supply before the main power supply of the frequency converter is powered on. The test results show that each control power supply is in good condition. Self-learning mode. This mode is unique to Yaskawa high-voltage frequency converters. Through this mode, the frequency converter can automatically read motor parameters and complete the optimal operation and vector control environment settings of the frequency converter based on these parameters. Before executing the self-learning mode, the motor rotation direction must be determined using the frequency converter's built-in jog function. Motor operation test (no load). Before the motor is loaded, to ensure the reliable operation of the frequency converter, a no-load test of the frequency converter driving the motor is first performed. The test data is shown in Table 1, and the results show that the inverter is operating normally. [align=center]Table 1 Motor No-Load Operation Test Data[/align] Motor Operation Test (Load). This test measures the inverter's load operation. The test process is divided into several stages according to different frequency ranges. After the inverter's parameters stabilize at each frequency stage, it gradually moves to higher frequency stages. The test data is shown in Table 2, and the results show that after the motor operates at the variable frequency, the input current and input voltage of the motor significantly decrease under different loads. [align=center]Table 2 Motor No-Load Operation Test Data[/align] Motor Operation Test (Load Speed ​​0-100% 60 s). This test measures the inverter's load acceleration capability, with an acceleration time set to 60 s. The waveform shows that the inverter's acceleration process is smooth and in good condition. Motor Operation Test (Load Speed ​​0-100% 30 s). This test measures the inverter's load acceleration capability, with an acceleration time set to 30 s. The waveform shows that the inverter's acceleration process is smooth and in good condition. Actual operating data of the unit (the valve opening is set to 100% under frequency conversion). [align=center] Figure 3 60 s acceleration waveform of the motor Figure 4 30 s acceleration waveform of the motor[/align] As can be seen from the data analysis in Table 3, the energy saving effect after frequency conversion is significant. According to a rough estimate, under the same operating conditions when the original power frequency is running, the condensate pump of Unit 4 consumes about 20,000 kW·h per day. After the frequency conversion, the power consumption of the condensate pump of Unit 4 is reduced to 10,000 kW·h. [align=center] Table 3 Performance comparison of actual operating conditions[/align] 4 Other benefits brought about by frequency conversion 4.1 Reduction of motor starting current The maximum starting current of the motor when directly starting at power frequency is 7-8 times the rated current, and the motor soft starter also needs to reach 2.5 times. However, the load curve of starting by frequency converter shows that there is basically no impact when it starts, and the maximum starting current is only slightly higher than the rated current of the motor. Therefore, variable frequency speed control solves the problem of high current surge during motor startup, eliminating the impact of high starting current on the motor, transmission equipment, and main unit, and reducing daily maintenance costs. 4.2 Extending Equipment Lifespan Variable frequency speed control changes the acceleration and deceleration characteristic curve of motor speed changes, eliminating stress loads on the bearings and extending the lifespan of the bearings and motor. Furthermore, relevant data shows that mechanical lifespan is directly proportional to the reciprocal of speed; reducing the condensate pump speed can significantly increase the condensate pump's lifespan, naturally reducing operating costs. 4.3 Reducing Noise After our plant's condensate pumps were converted to variable frequency drives, noise levels were significantly reduced while operating at lower speeds. When the speed was reduced by 50%, noise levels decreased by several decibels. It also eliminated slippage and whistling noises during stopping and starting, overcoming the defects caused by poor valve linearity and adjustment quality, which led to pipe hammering and resonance, resulting in strong vibrations in the water supply system. After the condensate pumps were operated with variable frequency, noise and vibration were greatly reduced, with considerable improvements. 5 Conclusion From the results of the trial run: the frequency converter operates stably and all performance indicators are excellent; the modified control system has clear and logical logic, simple operation process, and overall performance meets the expected goals. In conclusion, the promotion and use of frequency converters in the condensing pumps of large steam turbine generator sets can significantly reduce the plant power consumption rate, reduce power generation costs, and improve the competitiveness of grid connection. References : [1] Li Zunji. Principles and Applications of Frequency Conversion Control [M]. Beijing: North China Electric Power University Press, 2001. [2] Leng Zengxiang. Overview of Medium and High Voltage Frequency Converters [J]. Jiangsu Electrical Engineering, 2002, (4): 32. [3] Zhang Yanbin. SPWM Frequency Conversion Speed ​​Regulation Application Technology [M]. Beijing: Machinery Industry Press, 2001. [4] Han Anrong. General Frequency Converters and Their Applications [M]. Beijing: Machinery Industry Press, 2000.