I. Overview The heat dissipation and operating environment of equipment in high-voltage inverter applications directly affect the safety of the equipment itself. With the continuous increase in inverter power, the investment and operating costs of auxiliary cooling have gradually attracted the attention of the industry and customers. Adopting a professional high-voltage inverter-specific cooling system to improve equipment safety and stability, and reduce the operating costs of the auxiliary cooling system, has become one of the important issues to consider in high-voltage inverter applications. The following section takes the cooling solution for a 2240kW condensate pump high-voltage inverter as an example to conduct a feasibility analysis and demonstration of several cooling methods. II. System Analysis 1. Air Conditioning-Sealed Cooling Method 1.1 System Introduction To improve the application stability of high-voltage, high-power inverters and solve the problem of heat dissipation in the high-voltage inverter environment, the commonly used method is to adopt a sealed air conditioning cooling method. This method mainly provides a fixed room with heat insulation for the high-voltage inverter. The cooling capacity of the air conditioner is calculated based on the heat generation of the high-voltage inverter and the size of the room, thus equipping a certain number of air conditioners. 1.4 Air Conditioning Selection Principles The condensate pump high-voltage inverter is installed in a separate room on the turbine side. Based on the rated power of the high-voltage frequency converter of 2240kW and an operating efficiency of 96%, the following calculations are made: Rated heat output of the condensate pump high-voltage frequency converter: Since not all the hot air discharged from the high-voltage frequency converter is used for heat exchange by the air conditioner, and not all the cold air discharged from the air conditioner can directly enter the equipment for cooling control, the heat exchange environment temperature control system of the high-voltage frequency converter room typically has an exchange efficiency of only 67% to 70%. That is, when considering the heat exchange power of the cooling equipment, combined with the heat output under extreme operating conditions and the system exchange efficiency, the capacity design calculation margin of the air conditioner should be 1.2 to 1.3 times to meet the requirements of safe system operation. Therefore, four 12P air conditioners need to be installed in the condensate pump high-voltage frequency converter room. 1.5 System Installation The dimensions of the condensate pump high-voltage frequency converter room are: length 11700mm, width 4000mm, height 3500mm. The dimensional layout is shown in Figure 1. [align=center] Figure 1: Simplified Dimensional Layout of the Condensate Pump High-Voltage Frequency Converter Room[/align] 2. 2.1 System Introduction of Air-Water Cooling Method The hot air from the high-voltage frequency converter directly enters the air-cooling unit through the air duct for heat exchange. The cooling water directly carries away the heat lost by the high-voltage frequency converter; the cooled air is then discharged back into the room. The temperature of the cooling water in the air-cooling unit is below 33℃, ensuring that the ambient temperature inside the high-voltage frequency converter room is controlled below 40℃ after the hot air passes through the heat sink, meeting the environmental requirements for high-voltage frequency converter operation. This ensures a good operating environment inside the high-voltage frequency converter room. The cooling water and circulating air are completely separated, and the water pipeline is clearly separated from the high-voltage equipment outside the high-voltage frequency converter room, ensuring that the high-voltage equipment room is not subject to safety threats or accidents such as waterproofing or insulation damage. 2.4 Selection Principles of Air-Water Cooling System Based on the rated power of the high-voltage frequency converter of 2240kW and the operating efficiency of 96%, the maximum heat dissipation power of the 2240kW high-voltage frequency converter is 2240 × 4% = 89.6kW. Because this system achieves heat exchange of all the hot air discharged from the high-voltage frequency converter through an air-water cooling device, and then exhausts the cold air back into the room, its air circulation efficiency is greatly improved. The air circulation efficiency is close to 99%. Considering the heat generation under extreme operating conditions, as well as factors such as high water temperature and system exchange efficiency, the design margin of the air cooler is usually selected as 1.15 to 1.2 times. Calculated with a design margin of 1.15, the heat exchange power of the air cooler is not less than 103.04kW/unit, and the actual selected air cooler power is 105kW. 2.5 The indoor dimensions of the high-voltage frequency converter room at the system installation site are required to be: length 10700mm, width 3600mm, and height 3500mm. The specific dimensions and structural layout are shown in Figure 2. [align=center] Figure 2: Specific dimensions and structural layout of the high-voltage frequency converter room at the site[/align] 3. 3.1 System Introduction Forced Closed Cooling System As an auxiliary device outside the power cabinet of high-voltage frequency converter, the forced closed cooling system can ensure that the power cabinet of high-voltage frequency converter is always in an operating environment of 25-35℃, greatly extending the filter replacement cycle and reducing on-site maintenance. No separate building is needed for the high-voltage frequency converter; the transformer cabinet adopts open cooling. The forced cooling device is integrated with the power cabinet of the high-voltage frequency converter and attached to the top of the power cabinet. The refrigeration compressor unit is installed near the high-voltage frequency converter. 3.4 Applicable Occasions and Principles (1) Applicable to the self-cooling of high-voltage frequency converter equipment with a rated power of 1000 kW and above. (2) On-site installation location is limited; the high-voltage frequency converter needs to be laid out in an open space in the factory. Operating occasions with high ambient temperature, dust, and no obvious water leakage or rain characteristics. (3) Indoor environments where the installation space is small and a building cannot be constructed. (4) Two 380VAC/3PH power supplies can be provided on-site. (5) Space height is greater than 3.5 meters. There should be a space greater than 695mm in front of the high-voltage frequency converter power cabinet to facilitate cabinet door opening. 3.5 Selection Principles of Forced Closed-Loop Cooling Devices Forced closed-loop cooling devices are configured on an equal footing based on the power cabinet of a single high-voltage frequency converter. The power value of the closed-loop cooling device configured for a 2240kW frequency converter = 2240 × 2% × 1.25 (design margin) = 56kW. A 56kW closed-loop cooling device is actually selected. According to the design principles of closed-loop cooling devices, this cooling system is limited to power cabinets with high temperature requirements. The transformer cabinet adopts open cooling, allowing temperature dissipation into the environment; the allowable temperature rise of 80K and the high-temperature alarm value of 120℃ fully meet the requirements for operational safety. 3.6 System installation does not require a separate room; the installation location of the high-voltage frequency converter is sufficient. 4. Comparison of Cooling Methods III. Conclusion The above comprehensive analysis of the technical feasibility, safety, reliability, and economy of the cooling problem for the 2240kW condensate pump high-voltage frequency converter shows that the new cooling system (air-water cooling, forced closed-loop cooling) fully considers safety protection measures such as equipment failure, heat exchange medium leakage, emergency bypass of the air duct, ease of operation, and maintainability. Although the initial investment in the new cooling system is slightly higher than that of air conditioning equipment, the investment can usually be recovered in 2-3 years through electricity savings compared to air conditioning cooling. Furthermore, the forced closed-loop cooling scheme can save nearly 100,000 yuan in building construction costs. In conclusion, in the 2240kW condensate pump frequency converter retrofit project, the forced closed-loop cooling scheme has the advantages of saving space and high cost-effectiveness. Therefore, this scheme is recommended for cooling the high-voltage frequency converter.