Several important issues to be aware of during the installation process of the inverter
The following points should be determined when selecting the inverter:
1. The purpose of using frequency conversion; constant voltage control or constant current control.
2, the load type of the inverter; such as the vane pump or the volume pump, pay special attention to the performance curve of the load, the performance curve determines the way of application.
3. The matching problem between the inverter and the load;
1) Voltage matching; the rated voltage of the inverter matches the rated voltage of the load.
2) Current matching; common centrifugal pump, the rated current of the inverter matches the rated current of the motor. For special loads such as deep pumps, it is necessary to refer to the motor performance parameters to determine the inverter current and overload capability with *** current.
3) Torque matching; this may occur with constant torque loads or with a reduction gear.
4. When using a frequency converter to drive a high-speed motor, 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 for high-speed motors is slightly larger than that of ordinary motors.
5. If the inverter wants to run the long cable, it is necessary to take measures to restrain the influence of the long cable to the ground coupling capacitor and avoid the insufficient output of the inverter. Therefore, in this case, the inverter capacity should be amplified by one gear or in the inverter. An output reactor is installed at the output.
6. For some special applications, such as high temperature and high altitude, this will cause the inverter to derate, and the inverter capacity should be enlarged by one gear.
Inverter control principle:
1. First confirm the installation environment of the inverter
1) Working temperature. The inside of the inverter is a high-power electronic component, which is highly susceptible to the operating temperature. The product is generally required to be 0 to 55 ° C. However, in order to ensure safe and reliable operation, consideration should be given to leaving room for use. *** Control at 40 ° C the following. In the control box, the inverter should generally be installed in the upper part of the cabinet, and strictly follow the installation requirements in the product manual. It is absolutely not allowed to install the heating element or the heat-prone component close to the bottom of the inverter.
2) Corrosive gases. If the concentration of corrosive gas is large, it will not only corrode the leads of the components, printed circuit boards, etc., but also accelerate the aging of the plastic devices and reduce the insulation performance.
3) Ambient temperature. When the temperature is too high and the temperature changes greatly, the inside of the inverter is prone to condensation, and its insulation performance is greatly reduced, which may cause a short circuit accident. If necessary, desiccant and heater must be added to the tank. In the water treatment room, the water vapor is generally heavy. If the temperature changes greatly, this problem will be more prominent.
4) Electromagnetic interference. Due to the rectification and frequency conversion, the inverter generates a lot of interference electromagnetic waves around the inverter. These high-frequency electromagnetic waves have certain interference to nearby instruments and instruments. Therefore, the instrument and electronic system in the cabinet should use a metal casing to shield the inverter from interference with the instrument. All components should be grounded reliably. In addition, shielded control cables should be used for wiring between electrical components, instruments and meters, and the shielding layer should be grounded. If the electromagnetic interference is not handled well, the whole system will not work, resulting in failure or damage of the control unit.
5) Vibration and shock. When the control cabinet equipped with the inverter is subjected to mechanical vibration and shock, it may cause poor electrical contact. Huai'an Thermal Power has such problems. At this time, in addition to improving the mechanical strength of the control cabinet, away from the vibration source and the impact source, the anti-vibration rubber pad should also be used to fix the vibration-generating components such as the control cabinet and the internal electromagnetic switch. After the equipment has been in operation for a period of time, it should be inspected and maintained.
2. Distance between inverter and motor to determine cable and wiring method
1) The control cable is shielded cable, the power cable is shielded cable or the inverter is shielded from the inverter to the motor.
2) The distance between the inverter and the motor should be as short as possible. This reduces the capacitance of the cable to ground and reduces the source of interference.
3) The analog signal line related to the inverter *** select the shielded twisted pair cable, the power cable should be shielded three-core cable (the specification is larger than the cable of the ordinary motor) or follow the user manual of the inverter.
4) The motor cable should be *** other cable routing, the minimum distance is 500mm. At the same time, the motor cable should be avoided to run parallel with other cables in a long distance, so as to reduce the electromagnetic interference caused by the rapid change of the output voltage of the inverter. If the control cable and the power cable cross, they should be crossed as far as possible at a 90 degree angle. The analog signal lines associated with the drive are routed separately from the main return line, even in the control cabinet.
3, inverter control principle
1) Control circuit: manual switching with power frequency frequency conversion, in order to manually cut the power frequency when the frequency conversion fails, because the output terminal can not add voltage, the solid power frequency and frequency conversion must have interlock.
2) Main circuit: The function of the reactor is to prevent the higher harmonics generated by the inverter from returning to the grid through the input loop of the power supply and affecting other power receiving equipment. It is necessary to determine whether the reactor needs to be added 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 from the inverter to the motor is far away, the filter should be installed. Although the inverter itself has various protection functions, the phase loss protection is not ***. The circuit breaker is overloaded in the main circuit and lacks equal protection. When selecting the type, it can be selected according to the capacity of the inverter. The thermal relay can be replaced by the overload protection of the inverter itself.
4. Grounding of the inverter;
Proper grounding of the inverter is an important means to improve system stability and suppress noise. The grounding resistance of the grounding terminal of the inverter is as small as possible. The cross section of the grounding conductor 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 cannot be grounded. One end of the shield of the signal line is connected to the ground of the inverter, and the other end is floating. The inverter is electrically connected to the control cabinet.
The inverter should be installed inside the control cabinet. The control cabinet should pay attention to the following problems when designing.
1. Heat dissipation problem: The heat generated by the inverter is generated by internal losses. The main circuit is mainly used in the loss of each part of the inverter, accounting for 98%, and the control circuit accounts for 2%. In order to ensure the normal and reliable operation of the inverter, we must heat the inverter. We usually use the fan to dissipate heat. The built-in fan of the inverter can remove the internal heat dissipation of the inverter. If the fan does not work properly, stop the inverter immediately. The high-power inverter needs to add a fan to the control cabinet. The air duct of the control cabinet should be designed reasonably. All the air inlets should be equipped with a dust-proof net, and the air is ventilated smoothly, avoiding the formation of eddy currents in the cabinet and forming dust accumulation at a fixed position; Select the matching fan according to the ventilation of the inverter manual. Pay attention to the anti-vibration problem when installing the fan.
2. Electromagnetic interference problem:
1) When there are high-frequency impact loads in the system such as electric welder and electroplating power supply, the inverter itself will be protected due to interference, then consider the power quality problem of the whole system.
2) In the working frequency, the inverter generates a lot of interference electromagnetic waves due to rectification and frequency conversion. These high-frequency electromagnetic waves have certain interference to nearby instruments and instruments, and will generate high-order harmonics. The power supply circuit enters the entire power supply network, thereby affecting other instruments. If the power of the inverter accounts for more than 25% of the entire system, it is necessary to consider the anti-interference measures of the control power supply.
3, protection issues need to pay attention to the following points:
1) Dust-proof: All air inlets should be equipped with a dust-proof net to block the entry of floc-like debris. The dust-proof net should be designed to be detachable for easy cleaning and maintenance. The grid of the air filter is determined according to the specific conditions of the site, and the joint between the air filter and the control cabinet should be handled strictly.
2) Corrosion-resistant gas: This situation is more common in the chemical industry. In this case, the inverter cabinet can be placed in the control room.
3) Waterproof and anti-condensation: If the inverter is placed on the site, you need to pay attention to the pipe flange or other leaking points above the inverter cabinet. There should be no splashing water flow near the inverter. In general, the protection level of the on-site cabinet should be IP43. the above.
Inverter wiring specification:
The signal line and the power line must be separated. When using the analog signal for remote control of the inverter, in order to reduce the interference of the analog quantity from the inverter and other equipment, please control the signal line and the strong circuit of the inverter (main circuit). And the sequence loop) separate the lines. The distance should be more than 30cm. Even in the control cabinet, it is necessary to maintain such wiring specifications. The control circuit between the signal and the inverter must not exceed 50m.
The signal line and the power line must be placed inside 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 is highly susceptible to interference from the inverter and external equipment; There is no built-in reactor, so the input and output stage power lines of the inverter will have strong interference to the outside. Therefore, the metal tube or metal hose for placing the signal line should be extended to the control terminal of the inverter to ensure the signal line. Completely separated from the power line.
1. The analog control signal line should use double stranded shielded wire with a wire size of 0.75mm2. When wiring, be sure to note that the cable stripping should be as short as possible (5-7mm), and the shield after stripping should be wrapped with insulating tape to prevent the shield from coming into contact with other equipment to introduce interference.
2. In order to improve the simplicity and reliability of the wiring, it is recommended to use the crimping bar terminal on the signal line.
The operation of the inverter and the setting of related parameters:
There are many setting parameters of the inverter, and each parameter has a certain range of selection. In use, it is often encountered that the inverter cannot work normally due to improper setting of individual parameters.
***Operating frequency: that is, the minimum running speed of the motor. When the motor runs at low speed, its heat dissipation performance is very poor. When the motor runs at low speed for a long time, the motor will burn out. At low speeds, the current in the cable also increases, which can also cause the cable to heat up.
Control mode: speed control, torque control, PID control or other means. After the control method is adopted, it is generally required to perform static or dynamic identification according to the control precision.
Carrier frequency: The higher the carrier frequency setting, the higher the higher harmonic component, which is closely related to the length of the cable, the heating of the motor, and the heating of the cable heating inverter.
***Operating frequency: The general frequency converter *** frequency to 60Hz, some even *** to 400Hz, high frequency will make the motor run at high speed, which for ordinary motor, its bearing can not exceed the rated speed for a long time Running, the rotor of the motor can withstand such centrifugal force.
Frequency hopping: At a certain frequency point, resonance may occur, especially when the whole device is relatively high; when controlling the compressor, avoid the surge point of the compressor.
Motor parameters: The inverter sets the power, current, voltage, speed and *** frequency of the motor in the parameters. These parameters can be directly obtained from the motor nameplate.
Common fault analysis:
Overcurrent fault: Overcurrent fault can be divided into acceleration, deceleration, and constant speed overcurrent. It may be caused by the acceleration/deceleration time of the inverter being too short, the load is abrupt, the load is not evenly distributed, and the output is short-circuited. At this time, it is generally possible to increase the acceleration/deceleration time and reduce the sudden change of the load.
(1) Adjust the V/F curve;
(2) extend the acceleration time;
(3) Re-enter the motor parameters and perform self-measurement of the parameters;
(4) Set the speed detection and restart function;
(5) reduce the torque boost current;
(6) Check the grid voltage and reduce power usage;