Instructions for use of frequency converters
1. The frequency converter must be selected correctly.
2. Read the product instruction manual carefully, and follow the instructions for wiring, installation and use.
3. The inverter device should be reliably grounded to suppress radio frequency interference and prevent electric shock caused by leakage in the inverter.
4. When using a frequency converter to control the motor speed, the temperature rise and noise of the motor will be higher than when using grid power (power frequency); when running at low speed, due to the low speed of the motor fan blades, attention should be paid to ventilation. Cool down or reduce the load appropriately to prevent the motor temperature from exceeding the allowable value.
5. The impedance of the power supply line cannot be too small. When the frequency converter is connected to the low-voltage power grid, when the capacity of the distribution transformer exceeds 500KVA, or when the capacity of the distribution transformer is 10 times greater than the capacity of the frequency converter, or when the frequency converter is connected very close to the distribution transformer, due to the small loop impedance, the instantaneous operation Producing a large inrush current to the frequency converter will damage the rectifier components of the frequency converter. When the line impedance is relatively small, an AC reactor should be installed between the transformer and the frequency converter.
6. When the three-phase voltage imbalance of the power grid is greater than 3%, the peak value of the inverter input current will be very large, which will cause the inverter and connecting wires to overheat or damage electronic components. This will It is also necessary to install an AC reactor. This is especially true when the transformer is connected in a V-shape. In addition to installing a reactor on the AC side, a DC reactor needs to be installed on the DC side.
7. Do not install too large capacitors on the incoming line side to increase the power factor, nor install capacitors between the motor and the inverter. Otherwise, the line impedance will decrease, causing overcurrent and damage. Frequency converter.
8. Compensation capacitors cannot be connected in parallel on the outlet side of the inverter, nor can capacitors be connected in parallel to reduce high-order harmonics of the inverter’s output voltage, otherwise the inverter may be damaged. To reduce harmonics, a reactor can be connected in series.
9. Starting and stopping with frequency converter speed regulation cannot be directly operated by circuit breakers and contactors, but should be controlled by the control terminals of the frequency converter. operation, otherwise it will cause the inverter to lose control and may result in severe penalties.
10. It is generally not advisable to install an AC contactor between the inverter and the motor to avoid overvoltage at the moment of current interruption and damage to the inverter. If additional installation is required, the output contactor should be closed before the inverter is running; and before being disconnected, the inverter should stop output.
11. For situations where the inverter drives ordinary motors to operate at constant torque, long-term low-speed operation should be avoided as much as possible, otherwiseThe heat dissipation effect of the motor becomes poor and the heat is serious. If long-term operation at low speed and constant torque is required, a variable frequency motor must be selected.
12. For situations where the load is increased and frequent starts and stops occur, negative torque will be generated, and a braking resistor with appropriate parameters is required, otherwise the inverter will trip due to overcurrent or overvoltage faults.
13. When the motor has a brake, the inverter should work in free stop mode, and the braking action signal should be sent after the inverter issues a stop command.
14. The resistance value of the external braking resistor of the frequency converter cannot be less than the allowed braking resistor requirement of the frequency converter. On the premise of meeting the braking requirements, the braking resistor should be larger. Do not short-circuit the terminals that should be connected to the braking resistor. Otherwise, a short-circuit accident will occur through the switch tube during braking.
15. When the inverter is connected to the motor, it is not allowed to use a megohmmeter to measure the insulation resistance of the motor. Otherwise, the high voltage output by the megohmmeter will damage the inverter.
16. Correctly handle the issues of speed up and deceleration. If the acceleration and deceleration time set by the frequency converter is too short, the frequency converter may be easily damaged by “electric shock”. Therefore, when using a frequency converter, the acceleration and deceleration time should be extended as much as possible, subject to the permission of the load equipment.
(1) If the load is heavy, the acceleration and deceleration time should be increased; otherwise, the acceleration and deceleration time can be appropriately reduced;
(2) If the load equipment needs to accelerate in a short time , decelerate, you must consider increasing the capacity of the frequency converter to avoid too large a current, exceeding the rated current of the frequency converter;
(3) If the load equipment requires a short acceleration and deceleration time (such as within 1s), you should consider using a braking system on the inverter. Generally, larger-capacity inverters are equipped with braking systems.
17. Avoid the mechanical resonance point of the load equipment. Because the motor may encounter the mechanical resonance point of the load device within a certain frequency range, causing mechanical resonance and affecting the operation of the system. To this end, it is necessary to set a jump frequency (or avoidance frequency) for the frequency converter, and jump over (avoid) this frequency to avoid the resonance point.
18. Before the motor is used for the first time or is connected to the inverter after being left for a long time, the insulation resistance of the motor must be measured (using a 500V or 1000V megohmmeter, the measured value should not be less than 5MΩ. If the insulation If the resistance is too low, the inverter will be damaged.
19. The inverter should be installed vertically, leaving space for ventilation, and the ambient temperature should be controlled not to exceed 40°C.
20. Resistors must be used Interference measures should be taken to prevent the frequency converter from being interfered with and affecting its normal operation, or the high-order harmonics generated by the frequency converter interfering with the normal operation of other electronic equipment.
21. Pay attention to the thermal protection of the motor. If the motor is connected to the frequency converter If the capacity of the inverter matches, the thermal protection inside the inverter can effectively protect the motor. If the capacities of the two do not match, the protection value must be adjusted or other protection measures must be taken to ensure the safe operation of the motor. Electronic thermal protection value of the inverter ( Motor overload detection), can be detected at 25% of the rated current of the inverterSet within the range of %~105%.
Precautions for using the inverter
1. Physical environment
1) Operating temperature. There are high-power electronic components inside the inverter, which are easily affected by the operating temperature. The product generally requires a temperature range of 0 to 55°C. However, in order to ensure safe and reliable work, allowance should be made when using it. It is best to control it below 40°C. . In the control box, the frequency converter should generally be installed on the upper part of the box, and the installation requirements in the product manual should be strictly followed. It is absolutely not allowed to install heating elements or components that are prone to heat close to the bottom of the frequency converter.
2) Ambient temperature. When the temperature is too high and the temperature changes greatly, condensation is likely to occur inside the inverter, and its insulation performance will be greatly reduced, and it may even cause a short circuit accident. If necessary, desiccant and heater must be added to the box.
3) Corrosive gas. If the concentration of corrosive gas is high in the use environment, it will not only corrode the leads of components, printed circuit boards, etc., but also accelerate the aging of plastic components and reduce the insulation performance. In this case, the control box should be made into a closed structure. , and perform ventilation.
4) Vibration and shock. When the control cabinet equipped with a frequency converter is subjected to mechanical vibration and impact, poor electrical contact may occur. At this time, in addition to improving the mechanical strength of the control cabinet and keeping it away from vibration and impact sources, anti-seismic rubber pads should also be used to fix vibration-generating components such as electromagnetic switches outside and inside the control cabinet. After the equipment has been running for a period of time, it should be inspected and maintained.
2. Electrical environment
1) Prevent electromagnetic wave interference. Due to the rectification and frequency conversion of the frequency converter during operation, a lot of interfering electromagnetic waves are generated around it. These high-frequency electromagnetic waves have certain interference on nearby instruments and instruments. Therefore, the instruments and electronic systems in the cabinet should use metal casings to shield the interference from the frequency converter on the instruments. All components should be reliably grounded. In addition, shielded control cables should be used for connections between electrical components, instruments and meters, and the shielding layer should be grounded. If electromagnetic interference is not handled well, the entire system will often fail to work, causing the control unit to malfunction or be damaged.
2) Prevent input overvoltage. The power input end of the inverter often has over-voltage protection. However, if the high voltage at the input end acts for a long time, the input end of the inverter will be damaged. Therefore, in actual application, it is necessary to verify the input voltage of the frequency converter, single-phase or three-phase and the rated voltage used by the frequency converter. Especially when the power supply voltage is extremely unstable, voltage stabilizing equipment is required, otherwise serious consequences will occur.
3. Grounding
Correct grounding of the inverter is an important means to improve the sensitivity of the control system and suppress noise. The grounding terminal E (G) of the inverter is grounded The smaller the resistance, the better. The cross-sectional area of the grounding wire should be no less than 2mm2 and the length should be controlled at 20m.Within. The grounding point of the frequency converter must be separated from the grounding point of the power equipment and cannot be grounded together. The shielding layer of the signal input line should be connected to E (G), and the other end must not be connected to the ground, otherwise it will cause signal changes and fluctuations, causing the system to oscillate. The frequency converter and the control cabinet should be electrically connected. If there are difficulties in actual installation, copper core wires can be used for jumper connection.
4. Lightning protection
In the inverter, there is generally a lightning absorption network, which mainly prevents instantaneous lightning intrusion and damage to the inverter. However, in actual work, especially when the power line is introduced overhead, the absorption network of the frequency converter alone cannot meet the requirements. This issue is particularly important in areas with active lightning. If the power supply is an overhead incoming line, install a special lightning arrester (optional) for frequency conversion at the incoming line, or embed a special steel pipe 20m away from the inverter as required by the specification. Ground protection. If the power supply is introduced by cable, a lightning protection system in the control room should be installed to prevent lightning from entering and damaging the equipment.
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