The variable frequency drive main circuit terminals shown as below Figure.
The power line’s input terminals connect to 3 phase AC power through line protection or leakage protection breaker, it does not need to consider the connection of phase sequence. What needs to pay attention is the three-phase AC power must NOT be connected to the VFD drive output terminals directly, otherwise it will lead to the ac drive’s internal components damaged.
The electric motor should be connected to the output terminals by correct phase sequence, if the motor is in the reverse direction, then change any two phase of (u/t1, v/t2, w/t3), it also can be achieved by setting the ac drive inverter parameters. It should be noted that the output terminal can not connect the phase capacitor and surge absorber.
DC reactor connection terminals connect to the DC reactor to improve power factor with a short-circuit conductor connected to the terminals, when using the DC reactor, remove the short-circuit conductor first.
Note: Do NOT need to remove the conductor if the DC reactor is not connected.
Generally small power variable frequency inverter (0.75 ~ 15kw) built-in braking resistor, while the 18.5kw and above need external braking resistor connection.
The DC input terminals of the external brake unit are the positive and negative terminals of the DC bus.
The inverter will generate leakage current, the higher the carrier frequency, the larger the leakage current. The leakage current of the whole variable frequency inverter is more than 3.5ma, the leakage current size is determined by the service conditions, in order to ensure safety, the variable frequency drive and electric motor must be grounded.
(1) The grounding resistance should be less than 10 ω. The grounding cable diameter should be determined by the variable speed drive power;
(2) Never share grounding wire with the welding machines and other power equipment;
(3) If the supply line is zero/earth wire shared, it is better to consider a separate laying for the earth wire;
(4) Multiple ac drives ground should be connected to the earth respectively, do not make the ground wire form a loop.
(1) As the low voltage frequency inverter over-current of the control circuit cables is generally small, so the size of the control cable can be standardized, in order to avoid the interference caused by malfunction, the control cables should be twisted shielded wires;
(2) The control line and the main circuit cable laying
The VFD drive control lines should be laid separate from the main circuit cable and other power cable, and as far away as possible from the main circuit like more than 100mm; And don’t parallel to the main circuit cable laying, do not cross the main circuit, if it must cross then it should be a vertical cross method.
The AC drive cable shielding can adopt grounded metal tube or shielded cable. One end of Shielded layer connects to the frequency inverter drive control circuit common (COM), but do not connect to the variable frequency drive ground end (e), the other end of the shield is vacant.
The variable speed drive switching control lines are allowed not to use the shielded wire, but two of the same signal lines must be twisted around each other, the twist pitch of the strands should be as small as possible, and the shielded layer connects to the ground terminal E of the AC drive, the signal cable maximum length should not exceed 50m.
– the weak voltage/current loop wire connect to earth, and the grounding wire should not be used as the transmitted signal circuit;
– the wire’s grounding should be in the inverter drive side, use a dedicated ground terminal and do not shared with other ground terminals.