I. Energy-saving principle of frequency converters
1. Variable frequency energy saving
The energy-saving benefits of frequency converters are mainly seen in the application of fans and pumps. To ensure production reliability, various production machines are designed with a certain margin of safety in their power drives. When a motor cannot operate at full load, the excess torque beyond meeting the power drive requirements increases active power consumption, resulting in wasted energy. Traditional speed control methods for equipment such as fans and pumps involve adjusting the opening of inlet or outlet baffles and valves to regulate air and water flow. This method has high input power and consumes a significant amount of energy during the flow throttling process of baffles and valves. When using frequency converter speed control, if the flow requirement decreases, the requirement can be met by reducing the pump or fan speed.
According to fluid mechanics, P (power) = Q (flow rate) × H (pressure). Flow rate Q is proportional to the first power of rotational speed N, pressure H is proportional to the square of rotational speed N, and power P is proportional to the cube of rotational speed N. If the pump efficiency is constant, when the required flow rate is reduced, the rotational speed N can be reduced proportionally, and the shaft output power P decreases cubically. That is, the power consumption of the pump motor is approximately cubically proportional to the rotational speed. Therefore, when the required flow rate Q decreases, the output frequency of the frequency converter can be adjusted to reduce the motor speed n proportionally. At this time, the motor power P will decrease significantly according to a cubic relationship, saving 40%-50% more energy than adjusting baffles and valves, thus achieving the purpose of energy saving.
2. Power factor compensation energy saving
Increased reactive power leads to increased line losses and equipment heating. More importantly, the decrease in power factor results in a decrease in the active power of the power grid. A large amount of reactive power is consumed in the lines, leading to low equipment efficiency and serious waste. After using a variable frequency drive (VFD), the internal filter capacitor of the VFD reduces reactive power loss and increases the active power of the power grid.
3. Soft start energy saving
Hard starting of motors causes severe impacts on the power grid and places excessive demands on grid capacity. The large current and vibrations generated during startup cause significant damage to baffles and valves, severely shortening the lifespan of equipment and pipelines. However, using a variable frequency drive (VFD) energy-saving device utilizes the VFD's soft-start function, allowing the starting current to begin from zero and exceed the rated current at its maximum value. This reduces the impact on the power grid and the demands on power supply capacity, extending the lifespan of equipment and valves and saving on equipment maintenance costs.
II. How to extend the service life of frequency converters
Everyone knows that for every 10°C increase in ambient temperature, the lifespan of a frequency inverter is halved. Therefore, in daily use, a reasonable inspection cycle and system should be established based on the actual operating environment and load characteristics of the inverter. After each operating cycle, a comprehensive maintenance of the inverter should include disassembly, inspection, and measurement. Today, we'll share eight maintenance tips to effectively extend the lifespan of your frequency inverter.
1. Determine the cycle interval length based on the actual environment and conduct a comprehensive inspection and maintenance of the frequency converter. If necessary, disassemble, inspect, measure, clean dust, and tighten the circuit boards in the rectifier module, inverter module, and control cabinet. The lower air inlet and upper air outlet of the frequency converter are frequently blocked due to dust accumulation. Given its high heat dissipation and requirement for large ventilation volumes, dust accumulates on its base plate (due to electrostatic discharge) after a certain period of operation, necessitating cleaning and inspection.
2. After installing the inverter's circuit boards and busbars, perform necessary anti-corrosion treatment, apply insulating coating, and remove burrs and insulate busbars showing partial discharge or arcing. Damaged insulating posts must be removed, carbonized, or replaced.
3. Tighten all terminals to prevent serious damage caused by loosening, and conduct a comprehensive inspection and measurement. Replace any terminals (including output terminals), rectifier modules, inverter modules, DC capacitors, and fast-melting equipment that are found to be burnt out or have significantly fluctuating parameters.
4. The rotation status of the fan in the frequency converter should be carefully checked. After power is off, rotate the fan blades by hand to observe whether the bearings are stuck or do not rotate freely, and replace them if necessary.
5. Carefully inspect the electronic components on the inverter control circuit board, check and handle abnormalities such as solder detachment, discoloration, expansion, cracks, and broken lines (printed circuit board lines). If necessary, for components with abnormal appearance, you can measure and check the solder detachment from the circuit board or replace them.
6. Use multimeters, bridges, and other instruments and tools to test and withstand voltage of high current-carrying devices such as rectifier blocks and inverter GTRs (or IGBTs), measure their forward and reverse resistance values, record the results in a table, and replace modules with significantly different parameters.
7. Inspect the main contactor and other auxiliary relays. Carefully observe whether there are arcs, burrs, surface oxidation, or bumps on the moving and stationary contactors of each contactor. If these problems are found, replace the corresponding moving and stationary contactors to ensure contact safety.
8. Regularly check the fluctuations in the inverter's power supply voltage to mitigate the impact of high current surges on the inverter's operation, which can affect its normal operation, especially given the special operating environment and large load fluctuations.
