High-voltage frequency converters have a speed regulation range of 0-100%. If the mechanical strength of the motor and load allows, and the motor is not overloaded, the frequency converter can even allow the machinery to run at overspeed. Hydraulic couplings typically have a speed regulation range of 40-95%, meaning that the high-speed range causes approximately 5% speed loss, affecting the unit's output. Hydraulic couplings can generally only operate at 40% of their rated speed, which in some cases cannot meet speed regulation needs and sometimes hinders further energy-saving benefits (for example, in smelting furnace dust removal, the fan can often run at very low speed or even not at all, but the hydraulic coupling has to continue operating at 40% speed, wasting energy). High-voltage frequency converters have high efficiency (greater than 96%) throughout the entire speed regulation range, while the efficiency of hydraulic couplings decreases at lower speeds, resulting in significant losses and greatly reducing the energy-saving effect of speed regulation. High-voltage frequency converters achieve true soft starting for motors and load machinery, completely solving the starting shock problem. If the process requires, the motor can be repeatedly started multiple times in a short period. Hydraulic couplings cannot solve the motor starting problem; the motor still requires direct starting, necessitating a starting device, resulting in significant starting shock and limiting frequent starting. When modifying a motor's speed using a high-voltage frequency converter, simply disconnect the original switch and motor connection cable, add the frequency converter, and leave the motor and machinery connection unchanged. No foundation modifications are needed, and there are no site limitations. However, speed modification with a hydraulic coupling requires inserting the coupling into the motor-machine connection shaft, necessitating relocation and recasting of the equipment foundation, which may not be feasible in some locations. With high-voltage frequency converters, if the frequency converter fails, the motor can still operate directly on the mains power grid without production loss. In contrast, the hydraulic coupling, being the connecting link between the motor and machinery, will render the machinery inoperable if it fails, requiring shutdown for coupling repair and resulting in production losses. High-voltage frequency converters are high-tech equipment with high reliability and are essentially maintenance-free. Hydraulic couplings are mechanical devices containing multiple systems, including oil and water circuits. They have a high failure rate and require significant maintenance, resulting in reduced effective production time. High-voltage frequency converters do not increase costs based on motor speed, but using hydraulic couplings for speed regulation of low-speed, high-capacity motors significantly increases the cost of the hydraulic coupling, sometimes making it impossible. Comparatively, for general motor speed regulation, the initial investment for high-voltage frequency converters is higher than that for hydraulic couplings, but frequency converters have almost no operating costs afterward. Hydraulic couplings, on the other hand, require frequent maintenance, including maintaining a dedicated maintenance team and regularly changing water and oil, resulting in higher operating costs. High-voltage frequency converters offer a high level of intelligence, high speed regulation accuracy, and can operate in a closed-loop manner, improving factory automation, reducing manpower, improving the working environment, and reducing workload. Hydraulic couplings have poor speed regulation accuracy, lack automatic control, cannot interface with computers, and are prone to water and oil leaks, often resulting in a dirty and unpleasant working environment. In summary, if users have equipment that requires speed adjustment, from our perspective, unless funds are particularly tight, we recommend against using hydraulic couplings.