Inverter can achieve one or two or even more, but need to follow some principles - Database & Sql Blog Articles

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Frequency converters can control one or more motors, but it's essential to follow certain guidelines. This article provides a brief analysis of key considerations when using frequency converters in multi-motor systems. First, equipment selection plays a critical role. When choosing an inverter, the operating conditions must be carefully considered. If multiple motors are running and need to be started or stopped at any time, the inverter’s capacity should be selected accordingly. If the motor does not require frequent starting or stopping during operation, the inverter’s rated power only needs to be greater than the total power of all connected motors. In such cases, it's important to ensure that the inverter is completely stopped before switching contactors or changing the operating state of the motor. During active operation, it's strictly prohibited to start or stop individual devices separately. However, if the motor requires frequent start-stop operations, special attention must be given to the inverter's capacity. The peak power required for starting the motor at any time should be calculated and multiplied by a factor of 5–7 (as starting current can be 5–7 times the rated current). This value should then be added to the total power of other motors that don’t require frequent start-stop. This total will determine the theoretical power needed for the inverter. If many devices need to be started and stopped frequently, this value can be used directly without further amplification, as it’s rare for all motors to start simultaneously. However, if only a few motors require frequent starts, the calculated power should be increased by one level to ensure safe operation. Next, the selection of AC contactors is crucial for motors that need to be started and stopped regularly. The general rule is to select a contactor with a rated current one level higher than the motor’s rated current. Additionally, thermal relays or motor protectors should be installed in the main circuit to prevent overloading and protect both the motor and the inverter. Thermal relays should be chosen based on the motor’s rated current, ensuring they fall within the relay’s operating range. Other important factors include cable length. When connecting multiple motors to a single inverter, long cables can cause issues like high-frequency currents, leakage, and inaccurate readings. To mitigate these problems, an output filter may be necessary. For example, Fuji inverters recommend that motor connections under 3.7 kW do not exceed 50 meters, while those above 3.7 kW should not go beyond 100 meters. When multiple motors are involved, the total wiring length must be calculated. In some cases, even with short wiring, thermal relays might not function properly, especially in 400V series systems. In such situations, using an output filter or reducing the inverter’s carrier frequency can help. When using output filters, the maximum allowed motor connection length is typically around 400 meters. In practical applications, frequency converters are commonly used in systems with many small motors, such as production lines or roller kilns. These setups offer cost savings, reduced failure rates, and easier maintenance. For instance, in the late 90s, a factory used a single 11 kW Fuji inverter to drive 15 0.55 kW cycloidal pin gear motors. These motors could be started or stopped at any time, and each had a local protection switch. The average distance between the inverter and the motors was about 30 meters. Despite the complexity, the system operated smoothly for many years without issues. Imagine how many inverters would be needed if each motor had its own inverter. That would increase costs, noise, temperature rise, and maintenance efforts. Using a single inverter for multiple motors is often a more efficient and practical solution. Finally, electrical diagrams are essential for proper installation. While the following is just an example, actual schematics should be designed based on specific control requirements.