What are the requirements for the installation and wiring of a frequency converter?
Knowledge about frequency converters: Before installing a frequency converter, it is necessary to determine the installation environment and then use the appropriate installation method. When wiring the frequency converter, it is essential to ensure the correct wiring of the main circuit and the control circuit. Let's take a closer look at this below.
1. Installation Requirements for Frequency Converters
Installation environment of the frequency converter
(1) Ambient temperature: -10℃ to 40℃;
(2) Relative humidity: No more than 90% (no condensation);
(3) Other conditions: No direct sunlight, no corrosive gases or flammable gases, less dust, and an altitude of less than 1000m.
Installation method of the frequency converter
(1) Wall-mounted installation: The distance between the frequency converter and surrounding objects should meet the following conditions: both sides ≥ 100mm, top and bottom ≥ 150mm;
(2) Cabinet installation: For a single frequency converter, the cooling method outside the cabinet should be adopted as much as possible (when the environment is relatively clean and there is less dust); when a single frequency converter uses the cooling method inside the cabinet, a fan for forced air cooling should be installed on the top of the cabinet, and it should be placed as close as possible to the top of the frequency converter; for the installation of multiple frequency converters, they should be installed side by side as much as possible. If the longitudinal installation is necessary, a partition should be added between the two frequency converters. Regardless of the method, the frequency converter should be installed vertically.
2. Wiring of the Frequency Converter
Main Circuit Wiring
(1) The input (R, S, T) and output (U, V, W) of the frequency converter must not be connected incorrectly.
(2) Selection of main circuit wire diameter: ① The wiring method between the power supply and the frequency converter is the same as that for a motor of the same capacity.
② The wiring between the frequency converter and the motor should take into account the line voltage drop △U. Generally, it is required that: △U ≤ (2~3)%Un. The calculation formula for △U is: (copied from the original text) Where: Imn - rated current of the motor (A) R0 - resistance of the wire per unit length (per meter) (mΩ/m), which can be found in the following table:
The length of the L-wire (in meters) and the nominal cross-sectional area / 1.0 1.5 2.5 4.0 6.0 10.0 16.0 25.0 35.0 / (mΩ/m) 17.8 11.9 6.92 4.40 2.92 1.73 1.10 0.69 0.49
Table: Unit Length Resistance Values of Motor Leads
Wiring of Control Circuit
(1) Analog control lines should use shielded cables. One end of the shield should be connected to the common terminal (COM) of the frequency converter control circuit, and not to the ground terminal (E) or the earth. The other end should be left open.
(2) Switching control lines do not need to use shielded cables, but the two wires of the same signal must be twisted together.
Grounding of Frequency Converter
When multiple frequency converters are grounded, each frequency converter should be connected to the earth separately. It is not allowed to connect the grounding terminals of one frequency converter to the grounding terminal of another frequency converter and then ground again.
To improve the power factor of the frequency converter, add a DC reactor and an AC reactor. In addition to improving the power factor, they can also have the following effects:
(1) Suppress the surge current in the input;
(2) Weaken the influence caused by the imbalance of the power supply voltage.
Selection of Reactance:
1) The voltage drop of the reactor should not exceed 3% of the rated voltage;
2) When the transformer capacity is greater than 500 KVA or the transformer capacity is more than 10 times the capacity of the frequency converter, a reactor should be used.
