Reminder from specialized frequency converter suppliers in the lifting industry: Crane frequency converters are power control devices that use frequency conversion technology and microelectronics technology to control AC motors by changing the frequency of the motor's working power supply. The frequency converter is mainly composed of rectification (AC to DC), filtering, inversion (DC to AC), braking unit, driving unit, detection unit, microprocessor unit, etc. The frequency converter we currently use mainly adopts the AC-DC-AC method, which first converts the power frequency AC power supply into a DC power supply through a rectifier, and then converts the DC power supply into an AC power supply with controllable frequency and voltage to supply power.
1、 When selecting a frequency converter, the following points should be determined:
1) The goal of adopting frequency conversion; Constant pressure control or constant current control, etc.
2) When using a frequency converter to drive a high-speed motor, the addition of high-order harmonics increases the output current value due to the small reactance of the high-speed motor. When selecting the frequency converter for high-speed motors, Wuxi Qide Electrical Machinery Co., Ltd. has a slightly larger capacity than the selection of conventional motors.
3) Matching problem between frequency converter and load;
I. Voltage matching; The additional voltage of the frequency converter matches the additional voltage of the load.
II. Current matching; A common centrifugal pump, the additional current of the frequency converter matches the additional current of the motor. For extraordinary loads such as deep water pumps, it is necessary to refer to the motor function parameters to determine the inverter current and overload based on the maximum current.
III. Torque matching; This situation can occur under constant torque load or with deceleration installation.
4) The load type of the frequency converter; For pumps such as vane pumps or volumetric pumps, special attention should be paid to the functional curve of the load, which determines the method of use.
5) Regarding some extraordinary usage scenarios, such as high temperatures and high altitudes, this can cause a reduction in the capacity of the frequency converter, and the capacity of the frequency converter needs to be expanded by one gear.
6) If the frequency converter needs to operate with a long cable, measures should be taken to suppress the impact of the long cable on the ground coupling capacitance and prevent a lack of output from the frequency converter. Therefore, in such a situation, the capacity of the frequency converter should be expanded by one level or an output reactor should be installed at the output end of the frequency converter.
2、 Precautions for frequency converters at high temperatures
The general environmental requirements for frequency converters are: minimum ambient temperature of -5 ℃, maximum ambient temperature of 40 ℃. There is research indicating that the failure rate of frequency converters increases exponentially with temperature, while the service life decreases exponentially with temperature. When the ambient temperature increases by 10 degrees, the service life of frequency converters will be halved. Summer is a season of frequent frequency converter problems. To ensure that the frequency converter can work stably and reliably for a long time, the key is to protect and maintain it regularly.
1. Carefully monitor and record all display parameters on the human-machine interface of the frequency converter, and promptly report any abnormalities.
2. When the temperature is high in summer, it is necessary to strengthen the ventilation and heat dissipation of the installation site of the frequency converter. Ensure that the surrounding air does not contain excessive dust, acids, salts, corrosive and explosive gases.
3. During normal operation of the frequency converter, a standard thickness A4 paper should be able to firmly adhere to the filter screen at the cabinet door inlet.
4. The ventilation and lighting in the frequency conversion room must be good, and the ventilation and heat dissipation equipment (air conditioning, ventilation fans, etc.) must be able to operate normally.
5. The filter screen on the door of the inverter cabinet should usually be cleaned once a week; If there is a lot of dust in the working environment, the cleaning interval should be shortened according to the actual situation.
6. Carefully monitor and record the ambient temperature of the frequency conversion room, which should be between -5 ℃ and 40 ℃. The temperature rise of the phase-shifting transformer cannot exceed 130 ℃.
7. The frequency conversion room must be kept clean and tidy, and should be cleaned at any time according to the actual situation on site.
8. Summer is a rainy season, so it is important to prevent rainwater from entering the interior of the inverter (such as entering through the tailwind outlet).
3、 Inverter shutdown protection
1. Carefully monitor and record the various display parameters on the touch screen of the frequency converter, and promptly report any abnormalities.
2. The temperature of the air outlet of the inverter power unit cabinet cannot exceed 55 ℃.
3. The filter screen on the door of the inverter cabinet should generally be cleaned once a week; If there is a lot of dust in the work environment, the cleaning distance should be shortened according to the actual situation.
4. The ventilation and lighting of the frequency conversion room need to be outstanding, and the ventilation equipment can work normally.
5. It is necessary to keep the frequency conversion room clean and clean it at any time according to the actual situation on site.
6. Carefully monitor and record the ambient temperature of the frequency conversion room, which should be between -5 ℃ and 40 ℃.
7. During normal operation of the frequency converter, a standard thickness A4 paper should be able to adhere to the filter screen at the cabinet door inlet.
4、 Precautions for the use of frequency converter shutdown
1. Tighten the connecting nuts of the internal cables of the frequency converter every six months after six months.
2. After the trial work of the frequency converter is completed, the connection nuts of the internal cables of the frequency converter should be rechecked and tightened.
3. Check that all grounding inside the frequency converter cabinet is secure and the grounding point is free of rust.
4. Use a vacuum cleaner with a plastic nozzle to thoroughly clean the inside and outside of the inverter cabinet, ensuring that there is no excessive dust around the equipment.
5. The operation of the high-voltage switch in the inverter bypass cabinet should be normal, and it should be able to accurately close and disconnect.
6. The connection between the cables inside the frequency converter should be accurate and secure.
7. After long-term shutdown of the frequency converter, the insulation of the frequency converter (including phase-shifting transformer and bypass cabinet main circuit) should be measured, and a 1500V megohmmeter should be used for rehabilitation work. Only after passing the insulation test can the frequency converter be started.
8. Check the ventilation and lighting of the frequency conversion room, and ensure that the ventilation equipment is working properly.
9. Within six months, tighten the connecting nuts of the internal cables of the frequency converter again.
5、 Daily maintenance of frequency converter
1. Strengthen inspections and organize dedicated personnel to be responsible for the regular protection of frequency converters;
2. Record of work data. Record and monitor the operating frequency, current, and temperature of the phase-shifting transformer of the frequency converter at any time. The temperature rise of the phase-shifting transformer cannot exceed 130 ℃.
Write a frequency converter work record table to timely record the working data of the frequency converter and motor, including the output frequency, output current, output voltage, internal DC voltage of the frequency converter, radiator temperature and other parameters, and compare them with reasonable data to facilitate the early detection of faults and dangers
3. Ensure that the ambient temperature in the frequency converter room is between -5 and 40 ℃. Assign a dedicated person to check if the cooling fan on the top of the inverter cabinet is functioning properly and if the filter screen on the cabinet door is clogged. Ensure the smoothness of the cooling air duct. The specific method is to place a standard thickness A4 printing paper on the filter screen of the cabinet door, and the paper should be attached to the air intake window.
In order to ensure the smoothness of the cooling air duct, the filter should be cleaned once a week. If there is a lot of dust on site, the cleaning distance should be shortened.
4. Environmental monitoring
(1) When the temperature is high in summer, the ventilation of the variable frequency device site should be strengthened. Ensure that there is no excessive dust, acid, salt, corrosive, or explosive gas in the surrounding air;
(2) Summer is a rainy season, so avoid the environment of the inverter device and prevent raindrops from entering the interior of the inverter. 6. Check the tightness of all electrical connections, and ensure that there are no abnormal discharge traces, strange odors, discoloration, cracks, damage, or other phenomena in each circuit.
5. After each protection of the frequency converter, carefully check for any missing screws, wires, etc. to avoid small metal objects causing short circuits in the frequency converter. Especially after making significant changes to the electrical circuit, ensure accurate and reliable connection of the electrical wiring to avoid the occurrence of "backflow" incidents.