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Several important issues to pay attention to during the installation of the inverter
| 作者: lytrannet | 发布时间: 2019-06-02 | 435 次浏览 Source: | Author: lytrannet | Published: 2019-06-02 | 435 views 分享到: | Share to:
Operating temperature. Inside the inverter are high-power electronic components, which are easily affected by the operating temperature. The product is generally required to be 0 ~ 55 ℃, but in order to ensure safe and reliable work, you should consider leaving room when using, it is best to control below 40 ℃ . In the control box, the inverter should generally be installed on the upper part of the box, and strictly follow the installation requirements in the product manual. It is absolutely not allowed to install heating elements or components that are easy to generate heat close to the bottom of the inverter.

The following points should be determined when selecting the inverter:

1. The purpose of frequency conversion; constant voltage control or constant current control.

2. The load type of the inverter; such as a vane pump or a positive displacement pump. Pay special attention to the performance curve of the load. The performance curve determines the method and method of application.

3. The matching problem between inverter and load;

1) Voltage matching; the rated voltage of the inverter matches the rated voltage of the load.

2) Current matching; for ordinary centrifugal pumps, the rated current of the inverter matches the rated current of the motor. For special loads, such as deep-water pumps, you need to refer to the motor performance parameters to determine the inverter current and overload capacity with the maximum current.

3) Torque matching; this situation may occur under constant torque load or with a reduction gear.

4. When a high-speed motor is driven by an inverter, the output current value increases due to the small reactance of the high-speed motor and the increase of higher harmonics. Therefore, the selection of the inverter used for high-speed motors has a slightly larger capacity than the selection of ordinary motors.

5. If the inverter needs to run with a long cable, measures must be taken to suppress the influence of the long cable to the ground coupling capacitor at this time to avoid insufficient output of the inverter, so in this case, the capacity of the inverter should be enlarged by one gear or An output reactor is installed at the output end.

6. For some special application occasions, such as high temperature and high altitude, the inverter will be derated at this time, and the inverter capacity must be enlarged by one block.

Inverter control principle:

1.First confirm the installation environment of the inverter

1) Working temperature. Inside the inverter are high-power electronic components, which are easily affected by the operating temperature. The product is generally required to be 0 ~ 55 ℃, but in order to ensure safe and reliable work, you should consider leaving room when using, it is best to control below 40 ℃ . In the control box, the inverter should generally be installed on the upper part of the box, and strictly follow the installation requirements in the product manual. It is absolutely not allowed to install heating elements or components that are easy to generate heat close to the bottom of the inverter.

2) Corrosive gas. If the use environment has a high concentration of corrosive gas, it will not only corrode the leads of components, printed circuit boards, etc., but also accelerate the aging of plastic devices and reduce the insulation performance.

3) Ambient temperature. When the temperature is too high and the temperature changes are large, the inverter is prone to dew condensation, its insulation performance will be greatly reduced, and even short circuit accidents may be caused. If necessary, a desiccant and heater must be added to the box. In the water treatment room, the water vapor is generally heavy. If the temperature changes greatly, this problem will be more prominent.

4) Electromagnetic wave interference. Due to the rectification and frequency conversion of the inverter, a lot of interference electromagnetic waves are generated around the inverter. These high-frequency electromagnetic waves have some interference with nearby instruments and instruments. Therefore, the instrument and electronic system in the cabinet should use metal shells to shield the inverter from interference with the instrument. All components should be reliably grounded. In addition, the connection between electrical components, instruments and meters should be shielded control cables, and the shielding layer should be grounded. If the electromagnetic interference is not handled properly, the entire system will often be inoperable and the control unit will malfunction or be damaged.

5) Vibration and shock. When the control cabinet with the inverter is subjected to mechanical vibration and shock, it will cause poor electrical contact. Huaian Thermal Power has such a problem. At this time, in addition to improving the mechanical strength of the control cabinet and keeping it away from vibration and shock sources, vibration-proof rubber pads should also be used to fix components that generate vibration outside the control cabinet and internal electromagnetic switches. After the equipment has been running for a while, it should be inspected and maintained.

2. The distance between the inverter and the motor to determine the cable and wiring method

1) Use shielded cables for the control cables and shielded cables for the power cables or use conduits for shielding from the inverter to the motor.

2) The distance between the inverter and the motor should be as short as possible. This reduces the cable's capacitance to ground and reduces the sources of interference.

3) It is best to use shielded twisted-pair wires for the analog signal lines related to the inverter. Use shielded three-core cables for power cables (the specifications are larger than those of ordinary motor cables) or follow the user manual of the inverter.

4) The motor cable should be independent of other cable routing, and its minimum distance is 500mm. At the same time, avoid long-distance parallel running of the motor cable and other cables, so as to reduce the electromagnetic interference caused by the rapid change of the inverter output voltage. If control and power cables cross, they should cross as much as possible at a 90-degree angle. The analog signal wires related to the inverter are routed separately from the main circuit wires, even in a control cabinet.

3.Inverter control principle

1) Control loop: manual switching with power frequency conversion, so that when the frequency converter fails, the power frequency can be manually switched to run. Because the output can not be applied with voltage, the solid power frequency and frequency conversion must be interlocked.

2) Main circuit: The role of the reactor is to prevent the higher harmonics generated by the inverter from returning to the power grid through the input circuit of the power supply, which affects other power-receiving equipment. It is necessary to determine whether a reactor is required according to the capacity of the inverter; The filter is installed at the output of the inverter to reduce the higher harmonics of the inverter output. When the distance between the inverter and the motor is far, a filter should be installed. Although the inverter has various protection functions, the lack of phase protection is not perfect. The circuit breaker is overloaded in the main circuit and lacks equal protection. When selecting, you can choose according to the capacity of the inverter. The thermal relay can be replaced by the inverter's own overload protection.

4. Grounding of the inverter;

Correct grounding of the inverter is an important means to improve the stability of the system and the ability to suppress noise. The smaller the grounding resistance of the ground terminal of the inverter, the better. The cross section of the grounding wire is not less than 4mm, and the length is not more than 5m. The grounding of the inverter should be separated from the grounding point of the power equipment and should not be shared. One end of the shielding layer of the signal line is connected to the ground terminal of the inverter, and the other end is floating. The inverter is in electrical communication with the control cabinet.

The inverter should be installed inside the control cabinet. When designing the control cabinet, pay attention to the following issues:

1. Heat dissipation problem: The heat generated by the inverter is caused by internal losses. The main circuit is the main part of the loss in the inverter, accounting for 98%, and the control circuit accounts for 2%. In order to ensure the normal and reliable operation of the inverter, the inverter must be dissipated. We usually use a fan to dissipate the heat. The built-in fan of the inverter can take away the internal heat dissipation of the inverter's cabinet. If the fan cannot work normally, stop the inverter immediately; High-power inverters also need to add fans to the control cabinet. The control cabinet's air duct must be reasonably designed. All air inlets must be equipped with dust screens to allow the exhaust air to be unobstructed to avoid eddy currents in the cabinet and dust accumulation in fixed locations. Select the matching fan according to the ventilation volume of the inverter's instruction manual. Pay attention to the problem of anti-vibration when installing the fan.

2. Electromagnetic interference issues:

1) When there are high-frequency impact loads in the system, such as electric welding machines and electroplating power supplies, the inverter itself will be protected due to interference. Consider the power quality of the entire system.

2) Due to rectification and frequency conversion, a lot of interference electromagnetic waves are generated around the inverter. These high-frequency electromagnetic waves will interfere with nearby instruments and instruments, and will generate high harmonics. Such high harmonics will Enter the entire power supply network through the power supply loop, thereby affecting other instruments. If the power of the inverter accounts for more than 25% of the entire system, anti-interference measures of the control power supply need to be considered.

3. Protection issues need to pay attention to the following points:

1) Dust-proof: All air inlets should be equipped with dust-proof nets to prevent floc debris from entering. The dust-proof nets should be designed to be removable for easy cleaning and maintenance. The grid of the air filter is determined according to the specific conditions of the site, and the joints around the air filter and the control cabinet must be handled tightly.

2) Anti-corrosive gas: This situation is more common in the chemical industry. At this time, the inverter cabinet can be placed in the control room.

3) Waterproof and dew condensation: If the inverter is placed on the site, please note that there are no pipeline flanges or other leaks above the inverter cabinet. There should be no splashing water near the inverter. In short, the site cabinet protection level should be IP43. the above.

Inverter wiring specifications:

The signal line and the power line must be routed separately: When using an analog signal to remotely control the inverter, in order to reduce the interference of the analog quantity from the inverter and other equipment, please control the signal line of the inverter and the strong current circuit (main circuit). And sequence loop). The distance should be above 30cm. The same wiring specifications must be maintained even in the control cabinet. The control circuit line between this signal and the inverter must not exceed 50m.

The signal line and power line must be placed in different metal pipes or metal hoses separately: If the signal line connecting the PLC and the inverter is not placed in the metal pipe, it will be easily interfered by the inverter and external equipment; There is no built-in reactor, so the input and output stage power lines of the inverter will cause strong interference to the outside. Therefore, the metal pipe or metal hose where the signal line is placed must be extended to the control terminals of the inverter to ensure the signal line. Completely separated from the power line.

1. Double-stranded shielded wires should be used for analog control signal wires, and the wire size is 0.75mm2. When wiring, be sure to pay attention that the cable stripping should be as short as possible (about 5-7mm). At the same time, the shielding layer after the stripping should be wrapped with insulating tape to prevent the shielded cable from introducing interference with other equipment.

2. In order to improve the simplicity and reliability of the wiring, it is recommended to use crimping rod terminals on the signal line.

Operation of the inverter and setting of related parameters:

There are many setting parameters of the inverter, and each parameter has a certain selection range. In use, the phenomenon that the inverter cannot work normally due to improper setting of individual parameters is often encountered.

即电机运行的最小转速,电机在低转速下运行时,其散热性能很差,电机长时间运行在低转速下,会导致电机烧毁。 Minimum operating frequency: the minimum speed at which the motor runs. When the motor runs at low speed, its heat dissipation performance is poor. If the motor runs at low speed for a long time, it will cause the motor to burn out. And at low speed, the current in the cable will increase, which will also cause the cable to heat up.

即速度控制、转距控制、PID控制或其他方式。 Control mode: speed control, torque control, PID control or other methods. After the control method is adopted, static or dynamic identification is generally required according to the control accuracy.

载波频率设置的越高其高次谐波分量越大,这和电缆的长度,电机发热,电缆发热变频器发热等因素是密切相关的。 Carrier frequency: The higher the carrier frequency is set, the higher the higher harmonic components are. This is closely related to the cable length, motor heating, cable heating, and inverter heating.

一般的变频器最大频率到60Hz,有的甚至到400Hz,高频率将使电机高速运转,这对普通电机来说,其轴承不能长时间的超额定转速运行,电机的转子是否能承受这样的离心力。 Maximum operating frequency: The maximum frequency of general inverters is 60Hz, some even 400Hz. High frequencies will make the motor run at high speed. For ordinary motors, the bearings cannot run for a long time beyond the rated speed. Is the rotor of the motor able? Withstand such centrifugal forces.

在某个频率点上,有可能会发生共振现象,特别在整个装置比较高时;在控制压缩机时,要避免压缩机的喘振点。 Frequency hopping: At a certain frequency point, resonance phenomenon may occur, especially when the entire device is relatively high; when controlling the compressor, avoid the surge point of the compressor.

变频器在参数中设定电机的功率、电流、电压、转速、最大频率,这些参数可以从电机铭牌中直接得到。 Motor parameters: The inverter sets the power, current, voltage, speed, and maximum frequency of the motor in the parameters. These parameters can be obtained directly from the motor nameplate.

Common fault analysis:

过流故障可分为加速、减速、恒速过电流。 Overcurrent fault: Overcurrent fault can be divided into acceleration, deceleration, and constant speed overcurrent. It may be caused by the inverter's acceleration / deceleration time being too short, sudden changes in load, uneven load distribution, and output short circuit. In this case, you can generally increase the acceleration and deceleration time and reduce the sudden change of load.

Solution:

1 )调整 V/F 曲线; ( 1 ) Adjust the V / F curve;

(2) Extend the acceleration time;

3 )重新输入电机参数并进行参数自测定; ( 3 ) Re-enter motor parameters and perform parameter self-determination;

4 )设定检速再起动功能; ( 4 ) Set the speed detection restart function;

5 )降低转矩提升电流; ( 5 ) Reduce the torque boost current;

6 )检查电网电压,降低功率使用; ( 6 ) Check grid voltage and reduce power usage;

如何为电机选择合适的变频器 Next: How to choose the right inverter for your motor
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