How to extend the life of the inverter

- Jul 25, 2019-

In addition to maintenance, the extension of the service life of the inverter is also important, mainly in the following four aspects.

1. The effect of electromagnetic interference

on the inverter In the modern industrial control system, the use of microcomputer or plc control technology, in the process of system design or transformation, we must pay attention to the inverter to the computer control panel interference problem. Due to the user's own design of the microcomputer control board generally poor process level, does not meet EMC international standards, after the use of inverters, the conduction and radiation interference, often lead to abnormal control system operation, so the following necessary measures need to be taken.

(1) Good grounding. The ground wire of a strong electrical control system such as a motor must be reliably grounded by ground convection row, and the shielded ground of the microcomputer control board should be grounded separately. For some cases where interference is severe, it is recommended that the sensor, i/0 interface shield and the control area of the control panel be connected.

(2) The computer control board input power supply equipped with EMI filter, common mode inductor, high frequency magnetic ring, etc., can effectively suppress conduction interference. In addition, in the case of serious radiation interference, such as the presence of GSM, or small Lingtong base station, the microcomputer control panel can be added to the metal mesh shield for shielding treatment.

(3) Adding an EMI filter to the input of the inverter can effectively suppress the transmission interference of the inverter to the power grid, and the input AC and DC reactor can be added to improve the power factor, reduce harmonic pollution, and the comprehensive effect is good. In some cases where the distance between the motor and the drive exceeds 100m, an AC output reactor needs to be added to the inverter side to address leakage current protection and reduced external radiation interference due to the output wire-to-ground distribution parameters. An effective method is to use the steel pipe threading or shielding cable method, and the steel pipe shell or cable shield layer to the earth reliable connection. It is worth noting that when not adding ANIS or IRESISTors, if the method of steel pipe threading or shielding cableises is used to increase the distribution capacitance of the output to the ground, it is easy to have a stream. Of course, in practice, one or more of these methods are generally taken.

(4) Electrical shielding and isolation of analog sensor detection inputs and analog control signals. In the design process of the control system composed of inverters, it is recommended not to use analog control as far as possible, especially if the control distance is greater than 1m and the cross-control cabinet is installed. Because the inverter generally has a number of speed setting, switching frequency input and output, can meet the requirements. If you have to use analog quantity control, it is recommended to use a shielded cable and achieve a point of remote ground on the sensor side or on the drive side. If the interference is still severe, DC/DC isolation is required. Standard DC/DC modules can be used, or the v/f conversion light isolation, and then the frequency setting input method.

2. The impact of the working environment of the inverter

In the practical application of inverter, because the domestic customers in addition to a few have a dedicated room, mostly in order to reduce costs, the inverter will be installed directly in the industrial site. Work site generally has large dust, high temperature, high humidity problems, as well as the aluminum industry has metal dust, corrosive gases and so on. Therefore, according to the situation on the ground to make the corresponding countermeasures.

(1) The drive should be installed inside the control cabinet.

(2) The inverter is best installed in the middle of the control cabinet, the drive should be installed vertically, directly above and directly below to avoid the installation of large components that may block the exhaust, wind intake.

(3) The minimum spacing on the drive and the lower edge from the top, bottom, or partition, or large components that must be installed, etc., shall be greater than 300mm.

(4) If special users need to remove the keyboard in use, then the keyboard holes of the drive panel, must be strictly sealed with tape or replaced with false panels, to prevent a large amount of dust into the drive interior.

(5) In multi-dust places, especially in the multi-metal dust, flocs of the site when using inverters, the overall requirements of the control cabinet overall seal, specially designed air inlet, air outlet ventilation;

(6) Most inverter manufacturers inside the printing plate, metal structure parts are not carried out to prevent moisture mold special treatment, if the inverter long-term in a harsh working environment, metal structure stoicism is easy to produce corrosion. Conductive copper in the high temperature operation, will be more dramatic rusting process, for the microcomputer control board and drive power supply board of the small copper wire, rust will cause damage. Therefore, for wet and corrosive gases, the internal design of the drive used must be based on basic requirements, such as the printed circuit board must be coated with three anti-paint, for structural parts must be nickel-plated chromium and other treatment process. In addition, other positive, effective and reasonable anti-moisture, anti-corrosion gas measures need to be taken.

3. The impact of power grid quality on inverters

In the impact load such as welding machine, arc furnace, rolling mill and other occasions, the voltage often appears flash, in a workshop, there are multiple inverters and other capacitive rectifier load in the work, the resulting harmonics for the quality of the grid has a serious pollution, the equipment itself has a considerable destructive effect, light is not able to continuously run, Heavy damage to the device input circuit. The following measures could be taken.

(1) In the impact load such as welding machine, arc furnace, rolling mill and other occasions to recommend the user to increase the reactive static repair device, improve the power factor and quality of the power grid.

(2) In the workshop where the inverter is concentrated, it is recommended to use centralized rectification and DC co-bus power supply. It is recommended that the user adopt the 12 pulse rectifier mode. The advantage smaller harmonic, energy-saving, especially suitable for frequent starting, braking, electric motor in both electric operation and power generation operation.

(3) The passive LC filter is installed on the input side of the drive, which reduces the input harmonics, improves the power factor, high reliability and has good effect.

(4) The input side of the drive is equipped with the source PFC device, which works best, but the cost is high.

4. Other

1) The use of the drive environment

 a, operating temperature. The inside of the inverter is a high-power electronic component, very vulnerable to the impact of operating temperature, the general requirements of the product is 0 to 55 degrees C, but in order to ensure safe and reliable work, the use should be considered to leave room, the best control below 40 degrees C. In the control box, the inverter should generally be installed in the upper part of the box, and strictly abide by the installation requirements in the product specification, absolutely do not allow the heating element or heat-prone components close to the bottom of the drive installation.

 b, environmental humidity. When the humidity is too high and the temperature changes greatly, the inverter is prone to dew phenomenon, its insulation performance will be greatly reduced, and may even cause short-circuit accidents. If necessary, the desiccant and heater must be added to the box.

 c, corrosive gas. If the use of the environment if the concentration of corrosive gases, not only will corrode the component's leads, printed circuit boards, etc., but also will accelerate the aging of plastic devices, reduce insulation performance, in this case, the control box should be made into a closed structure, and ventilation.

 d, vibration and shock. When the control cabinet with the inverter is subjected to mechanical vibration and shock, it can cause poor electrical contact.

At this time, in addition to improving the mechanical strength of the control cabinet, away from the vibration source and impact source, should also use anti-seismic rubber pad fixed control cabinet outside and internal electromagnetic switches and other components to produce vibration. After the device has been in operation for a period of time, it should be inspected and maintained.

e. Prevent electromagnetic interference. Welding machines, power machinery, away from radioactive substances and combustibles, avoiddirect sunlight: away from corrosive liquids, gas

f, prevent the input from overvoltage. The drive power input often has voltage protection, but if the input high voltage effect is long, it can damage the drive input. Therefore, in practice, to verify the input voltage of the drive, single-phase or three-phase and the drive using the rated voltage. In particular, the power supply voltage is extremely unstable when there must be a regulatory device, otherwise it will have serious consequences.

2) The design of the variable frequency control cabinet

The electrical schematic design of the variable frequency control cabinet is reasonable: no leakage protector on the upper port of the inverter, no contactor on the lower port (no variable frequency conversion), capacitance, inverter cabinet has a cooling fan, the inverter does not use the upper mouth contactor control start and stop

3) The layout of components in the inverter cabinet.

The reasonable layout and effective distance of the device in the variable frequency cabinet should have enough cooling space and reasonable line

4) Reasonable setting of inverter parameters

The start-up stop of the drive should reasonably not use the upper mouth contactor to control the start-stop, set up free parking or slow-down stop as needed. Acceleration deceleration time of the drive, motor parameters in the drive

5) Maintenance of the drive

The inverter should be cleaned in time. Maintenance to remove the inverter inside and inside the wind road ash, dirt, at the same time to carefully check the inverter, to see if there is a heat color change inside the inverter, cement resistance whether there is cracking phenomenon, electrolytic capacitor whether there is expansion leakage explosion-proof hole prominent and other phenomena, PCB board whether there is an anomaly, there is no heat burning yellow ingenuity. After maintenance, restore the parameters and wiring of the drive, send power, with the motor operating at 3Hz low frequency operation, to ensure that the drive is working properly.

6) The reasonable use of the inverter

The inverter should not start and stop frequently, the inverter is electronic products such as long-term placement before the use of proper charging;