Should motors with a power rating of over 10,000 KW be controlled using soft starters or frequency converters?

Regarding the starting of high-power motors exceeding 10,000 kW (10 MW), both soft starters and frequency converters (variable-frequency starting) have their respective advantages and disadvantages. The specific choice of startup method depends on various factors, including cost, system requirements, operational efficiency, and control complexity. A soft starter is primarily used to reduce the current surge during startup; it enables the motor to start smoothly by gradually increasing the voltage, thereby minimizing the peak values of current and torque at the time of startup. The advantages of soft starters are their relatively low cost and relatively simple installation and maintenance. However, soft starting does not provide speed control; it merely simplifies the startup process. It has no speed regulation capability for motors that have already been started. On the other hand, frequency converters (also known as Variable Frequency Drives or VFDs) can provide complete speed control and energy savings. An inverter controls the speed of a motor by changing the frequency of its power supply; it can be used as a starting device as well as to adjust the speed of a motor that is already running, thereby meeting various load requirements. The advantage of inverters is that they enable higher efficiency and energy savings, as well as improved control performance and flexibility of the system. However, the cost of variable frequency drives is usually higher than that of soft starters; the system is also more complex, and maintenance costs may be higher as well. For your company’s case, if units such as syngas compressors need to have their load adjusted frequently, or if energy-saving requirements exist, using frequency converters might be a better option. Variable frequency drives can provide better process control, meeting the requirements of the process flow. If the motor only needs to be started occasionally and there is no need for continuous speed adjustment, then a soft starter may be sufficient. When choosing a brand and specific equipment, one can consider some internationally renowned brands such as ABB, Siemens, Schneider Electric, Rockwell Automation, Danfoss, etc. These companies all have experience and proven track records in manufacturing high-power frequency converters and soft starters. When making a decision, it is recommended that you consult a professional electrical engineer and discuss your specific requirements with the manufacturer, so that they can provide solutions and case studies suitable for your needs. Before making a decision, you may need to consider the following aspects comprehensively: – Startup frequency: If startups are frequent, an inverter might be a better choice. - Energy efficiency: Inverters can improve energy efficiency and reduce energy consumption. - Control requirements: If precise control over speed and torque is needed, a variable frequency drive is the better choice. - Cost budgeting: Consider the long-term costs of equipment and maintenance. - Reliability and maintenance: Consider the reliability of the equipment and your ability to maintain it. The final decision should take into account various factors such as long-term operating costs, system reliability, and process requirements. Before implementation, it is essential to conduct a thorough techno-economic analysis and risk assessment. .

This definitely has to be done in accordance with the process requirements; if variable frequency speed control is required, then an inverter has to be used. If there is no requirement for speed control, then soft starting should be the preferred option, as the investment cost is much lower.

If you have a factory with an 110kV substation, then high-power soft starters can be used; otherwise, if a 10kV supply is used with a soft starter, the set values are not sufficient, and it may cause problems if the system trips at the higher voltage level.