First, the heat dissipation problem
The heating of the inverter is caused by internal losses. In the frequency converter, the main part of the loss is mainly the main circuit, accounting for about 98%, and the control circuit accounts for 2%. In order to ensure the normal operation of the inverter must be reliable, we usually adopt inverter heat dissipation cooling fan; inverter fan installed inside the box body can be internal heat converter away, if the fan is not working properly, should immediately stop running the inverter; inverter power also need to fan in the control cabinet, control cabinet design to air duct reasonable, all air inlet to set dustproof net, exhaust unobstructed, avoid the formation of vortex in the cabinet, the formation of dust accumulation in a fixed position; to select the matching according to the amount of ventilation fan inverter manual, fan installation should pay attention to the problem of earthquake.
Two, electromagnetic interference problems
1, inverter in the work of rectification and frequency as the electromagnetic interference generated around a lot, these high frequency electromagnetic waves in the vicinity of the instrument have certain interference, and will generate harmonics, the harmonics will enter the supply network through the power supply circuit, thus affecting other instruments. If the frequency converter power is large, accounting for more than 25% of the whole system, it is necessary to consider the anti-interference measures of control power supply.
2. When the system has high frequency impact load, such as welding machine, electroplating power supply, the frequency converter itself will be protected because of interference, then consider the power quality problem of the whole system.
Three, protection issues need to pay attention to the following points
1, waterproof and anti condensation: if the transducer placed in the scene, the need to pay attention to the converter cabinet above the pipe flange or other leak, splashes water flow in near field in converter, cabinet protection grade more than IP43. Micro signal technology training is worth your attention!
2, dust: all air inlet should be provided with dust-proof net, blocking floc entry, dust net should be designed as removable, so as to facilitate cleaning and maintenance. The mesh of the dustproof net is determined according to the specific conditions of the scene, and the combination of the dustproof net and the control cabinet is tightly handled.
3, corrosion resistance gas: in the chemical industry, this situation is more common, at this time you can frequency converter cabinet in the control room.
Four 、 frequency converter wiring specification
The signal line and the power line to separate the line: remote control frequency converter using analog signal, in order to reduce the interference from the inverter and other equipment analog signal line, please will control the inverter and the electrical circuit (the main circuit and the control circuit separately. Shun). The distance should be above 30cm. The same wiring specification shall be maintained even in the control cabinet. The control return path between this signal and the inverter shall not exceed 50m.
The signal line and the power line must be placed in different internal metal pipes or metal hose: signal line connecting PLC and inverter if not placed in the metal pipe, vulnerable to interference of frequency converter and an external device; at the same time because no built-in converter reactor, the inverter to the input and output stage power line on the outside have strong interference, metal tube or metal hose so placing a signal line has to be extended to the control terminal of the inverter, to ensure complete separation of signal and power lines.
1) analog control signal line should use double stranded wire shielding line, specifications for 0.75mm2. The wiring must note, cable stripping to be as short as possible (about 5-7mm), while the shielding layer after stripping with insulation tape wrapped shield to prevent line contact with other equipment into interference.
2) in order to improve the simplicity and reliability of the connection, it is recommended to use the line bar terminal in the signal line.
Five, the operation of the inverter and related parameters
The frequency converter has many set parameters, and each parameter has a certain range of selection. In use, it is often encountered that the frequency converter can not work properly because of the improper setting of individual parameters.
Control mode: speed control, distance control, PID control, or other means. After the control method is adopted, the static or dynamic identification is usually needed according to the control accuracy.
Minimum running frequency: that is, the minimum speed of motor running, when the motor runs at low speed, its heat dissipation is very poor, and the motor running for a long time at low speed will cause the motor to burn out. Moreover, in low speed, the current in the cable will also increase, also lead to cable heating.
The maximum operating frequency: the maximum frequency converter to the general 60Hz, some even to 400 Hz, the high frequency will make the motor running in high speed, the general motors, super rated speed operation of the bearing can not long time, whether the motor rotor can withstand the centrifugal force that.