If you want to know how to connect the inverter, you need to know what the inverter is. The inverter is a motor speed regulating device, which outputs different voltages and frequencies to change the speed of the motor. From this point of view, it is a variable AC power supply, which can receive command control of high-power power power supply. The essence of high-power power supply is a kind of power transformation technology, They need to supply high-power input power, so they need the so-called main circuit; The output voltage and frequency of this power supply are controlled by people or other equipment directed by people, which requires control circuit.
The structure of the frequency converter is that the power frequency power supply is first rectified into DC, and then inversely transformed into a variable voltage and frequency power supply to drive the motor. Any frequency converter is the same, as long as it is connected to the main circuit and control circuit.
Connection method of frequency converter
1、 Connection of main circuit
1. The power supply should be connected to the input terminals R, s and t of the frequency converter, and must not be connected to the output terminals (U, V and W) of the frequency converter, otherwise the frequency converter will be damaged. After wiring, the broken wire ends must be cleaned. The broken wire ends may cause abnormality, failure and fault. The inverter must be kept clean all the time. When drilling holes on the console, pay attention not to let fragments and powder into the inverter.
2. Do not connect anything other than the recommended brake resistor option between terminals + and PR, or do not short circuit at all.
3. Electromagnetic wave interference, the input / output (main circuit) of frequency converter contains harmonic components, which may interfere with the communication equipment near the frequency converter. Therefore, install the optional radio noise filter fr-bif or frbsf01 or fr-blf line noise filter to minimize the interference.
4. In long distance wiring, due to the influence of parasitic capacitor charging current, the fast response current limiting function will be reduced, and the instrument connected to the secondary side will malfunction. Therefore, the maximum wiring length should be less than the specified value. Pr.156 should be set to 1 when the length of the necessary wiring exceeds.
5. Do not install power capacitors, surge suppressors and radio noise filters on the output side of the inverter. Otherwise, it will lead to inverter failure or capacitor and surge suppressor damage.
6. In order to keep the voltage drop within 2%, the appropriate type of wire should be used for wiring. When the connection distance between the inverter and the motor is long, especially in the case of low frequency output, the torque of the motor will decrease due to the voltage drop of the main circuit cable.
7. After operation, the operation of changing the wiring must be carried out after the power supply is cut off for more than 10 minutes and the voltage is checked with a multimeter. After a period of power failure, there is still dangerous high voltage on the capacitor.
2、 Wiring of control circuit
The control circuit of frequency converter can be divided into analog and digital.
1. Shielded wire or twisted pair wire shall be used for terminal connection of control circuit, and the wiring must be separated from main circuit and strong current circuit (including 200V relay program circuit).
2. Because the frequency input signal of the control circuit is a small current, in order to prevent poor contact, the small signal contact should use two parallel nodes or twin contacts.
3. 0.3-0.75 square meter cable is generally used for control circuit wiring.
3、 Connection of ground wire
1. Due to the leakage current in the inverter, in order to prevent electric shock, the inverter and motor must be grounded.
2. Special grounding terminal is used for inverter grounding. Tinned crimping terminals shall be used for the connection of grounding wires. When tightening the screw, be careful not to damage the screw buckle.
3. There is no lead in tin plating.
4. The diameter of grounding cable should be as thick as possible, which must be equal to or greater than the specified standard. The grounding point should be close to the frequency converter as far as possible, and the shorter the grounding wire is, the better.
4、 Precautions for inverter wiring.
1. The connection principle of different brands and models of frequency converter is similar, so it is necessary to connect in strict accordance with the wiring drawings or instructions of frequency converter.
2. High frequency switch status will appear in the operation of frequency converter, and its leakage inductance may induce dangerous voltage on the heat sink or shell. In order to prevent electric shock, terminal e of frequency converter box needs to be grounded!
3. It is better to connect an air switch at the input end of the frequency converter, and the protection current value should not be too large for short-circuit protection.
4. The control circuit should be as short as possible. If the control circuit is too long, it is easy to make the control board misoperate due to electromagnetic interference, which will affect the normal operation of the inverter to a certain extent.
5. In order to prevent electromagnetic interference, the input line, output line and control line of frequency converter should preferably use shielded cable, and the shielding layer should be grounded. If necessary, the filter can be added.
6. The most important: must not let zero line n ground!! Because when the inverter drives the motor in the braking state, the motor is similar to the generator at the moment, and the electric energy will be “blocked” to the main circuit board by the internal rectifier module of the inverter. Under normal wiring conditions, the inverter will carry out protection and step-down, but if the zero line n is directly grounded, it will form a loop, generate large current, and exceed the withstand voltage of the circuit board, the module will burst!