Whether the frequency converter wiring is accurate or not is directly related to whether the frequency converter can start normally, whether it can input and output normally, and plays a leading role in the accuracy of the results. Then we will come to understand the attention of the frequency converter wiring.
1. The main circuit wiring:
1, the input (R, S, T) output (U, V, W) can absolutely not be mistakable
2, the main circuit and inverter power supply: Path Selection and connection with the capacity of motor line path selection method is the same as the wiring between the inverter and the motor; to drop U, considering line voltage is usually required: Delta U is less than or equal to (2~3) Un type: Imn- motor rated current (A), R0- (per unit length meter the resistance of a wire) (m /m).
Two. The wiring of the control circuit:
1, the analog control line should use shielded line to shield one end to the common end (COM) of the frequency converter control circuit, and do not connect the inverter terminal (E) or the earth, and the other end will be suspended.
2, the switch control line allows no shield line to be used, but the two lines of the same signal must be twisted together.
Three, the inverter's grounding: multiple inverters are grounded, and the frequency converters should be connected to the earth respectively. It is not allowed to connect the ground of one frequency converter to the grounding terminal of the other inverter and then connect to the ground.
(1) in the input side of the power supply and frequency converter, a circuit breaker with earth leakage protection should be installed on the input side of the power supply and frequency converter. It will compare the frequency conversion current with the rest, and add another air switch and AC electromagnetic contactor. The air switch itself has the function of overcurrent protection, and it can be reset actively. Under the disadvantage conditions, the air switch can be operated manually. AC electromagnetic contactor is controlled by contact input. It can connect the output of the inverter and output of the motor overheating protection relay, so as to block the power supply from the input side and achieve timely protection when the disadvantage is. If the AC contactor and the leakage protection switch are presented together with the disadvantages, the air switch can also provide reliable protection.
(2) the heat relay should be installed between the inverter and the motor, and it is especially necessary to drag the high-power motor with the frequency converter. Although the converter has a thermal protection function, it may not be possible to protect the external motor. The rated capacity of users to choose the capacity of the inverter is often greater than the value of the motor, when the protection value set by the user is poor, the inverter in the motor burned once perhaps before action; perhaps, inverter failure protection, motor protection relay requires external heat supply. In particular, when driving some old motors, it is necessary to take into account the load of rust and aging. To sum up these elements, the external thermal relay can set the protection value very intuitively and quickly. The protection of thermal relay is more and more necessary in a system with multiple motor work or power frequency / frequency conversion.
When the connection line between the frequency converter and the motor is too long, the thermal relay will be misoperated because of the effect of high order harmonics. Therefore, it is necessary to exchange the reactor between the frequency converter and the motor, or to replace the thermal relay with the current sensor cooperative relay for thermal protection.
The primary purpose of the grounding of the frequency converter system is to prevent the leakage and disturbing intrusion or external radiation. The circuit is necessary to be grounded according to the technical standards and rules of the electrical equipment, and a useful and robust grounding pile is selected.
For unit type inverters, the earthing wires can be directly connected to the grounding terminals of the inverters. When the inverter devices are in the distribution cabinet, they are connected to the grounding terminals or the grounding busbars of the distribution cabinet. In any case, it is not possible to pass the ground terminal or grounding bus of other equipment, but it is necessary to connect directly with the grounding electrode or the grounding bus. According to the technical standard of electrical equipment, the grounding wire is necessary to use the soft copper wire of more than 1.6mm in diameter.
In order to enhance the reliability of transmission system, the principle of protection is usually multiple redundancy. Although a single protection plan can save money, it will reduce the overall safety factor of the system.