Knowledge

What are the requirements for inverter installation and wiring?

Regarding the knowledge about frequency converters, before installing the frequency converter, you must determine the installation environment, and then use the appropriate installation method.

When wiring the VFD, you must make the correct wiring of the main circuit and control circuit. 

Let’s look at it in details as below.

Ⅰ. Installation requirements of frequency converter

1. Installation environment of the inverter 

(1) Ambient temperature -10℃~40℃;

(2) Ambient relative humidity not exceeding 90% (no condensation);

(3) Other conditions: no direct sunlight, no corrosive gases and Flammable gas, less dust, altitude below 1000m.

2. How to install the inverter 

(1) Wall-mounted installation: The distance between the inverter and surrounding objects should meet the conditions: ≥100mm on both sides and ≥150mm on the top and bottom;

(2) Cabinet installation: The installation of a single inverter should be as far as possible Use the cooling method outside the cabinet (when the environment is relatively clean and there is little dust); when a single inverter adopts the cooling method inside the cabinet, an exhaust cooling fan should be installed on the top of the cabinet, and try to install it directly above the inverter; when installing multiple inverters They should be installed side by side as much as possible. If vertical installation is necessary, a partition should be installed between the two inverters. Either way, the frequency converter should be installed vertically.

Ⅱ. Wiring of frequency converter

1. Main circuit wiring

(1) The inverter input (R, S, T) and output (U, V, W) must not be connected incorrectly;

(2) Main circuit path selection ① Power supply and inverter wiring are the same as the wire diameter selection method for motors with the same capacity;② The line voltage drop △U must be considered for the wiring between the inverter and the motor. The general requirement is: △U≤(2～3)%Un. The calculation formula of △U is: (not copied) where: Imn - rated current of the motor ( A) R0 - Resistance (mΩ/m) of wire per unit length (per meter), please check the following table:

L - length of wire (m) 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: Resistance value per unit length of the motor lead wire

2. Control circuit wiring 

(1) The analog control line should use a shielded wire. The shielded end is connected to the common terminal (COM) of the inverter control circuit and not to the ground terminal (E) of the inverter or the earth, with the other end suspended in the air. 

(2) Switching control lines are not allowed to use shielded wires, but two wires of the same signal must be twisted together.

3.Grounding of frequency converters If multiple frequency converters are grounded, each frequency converter should be connected to the earth respectively.

It is not allowed to connect the grounding of one frequency converter to the ground terminal of another frequency converter and then ground it. Improve the power factor of the frequency converter and add DC reactor and AC reactor. In addition to improving the power factor, it can also play the following roles: 

(1) Suppress the surge current in the input; 

(2) Weaken the impact of power supply voltage imbalance. Reactor selection: 

1) The voltage drop of the reactor should not be greater than 3% of the rated voltage; 

2) When the transformer capacity is greater than 500KVA or the transformer capacity exceeds the frequency converter capacity by more than 10 times, a reactor should be equipped.