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Connecting variable frequency drive to motor

Gozuk VFD specialists recommend connecting the motor to the variable frequency drive using shielded cables.
  • Connect the cable shield to PE potential properly, i.e. with good conductivity, on both sides.
  • The motor cables must be kept physically separate from the control and network cables.
The variable frequency drive users must comply with the applicable limits stipulated in the relevant national and international directives as regards the application, the length of the motor cable and the switching frequency.

Connect in delta connection or star connection according to the motor data.
Motor delta connection and star connection
Maximum tightening torque: 0.5 Nm

Length of VFD cables, without filter
Permissible length of VFD cable without output filter
Variable frequency drive
unshielded cable
shielded cable
0.37 kW … 2.2 kW
50 m
25 m
4.0 kW
100 m
50 m
5.5 kW… 11.0 kW
100 m
50 m
The specified lengths of the variable frequency drive cables must not be exceeded if no output filter is installed.

VFD cable length, with output filter dU/dt
Longer variable frequency drive cables can be used after taking appropriate measures, e.g. use of low-capacitance cables and output filters. The following table contains recommended values for the use of output filters.
VFD cable length with output filter
Variable frequency drive
unshielded cable
shielded cable
0.37 kW … 2.2 kW
150 m
100 m
4.0 kW
300 m
200 m
5.5 kW… 11.0 kW
300 m
200 m

VFD cable length, with sinus filter
Variable frequency drive cables can be longer if sinus filters are used. By conversion in sinus-shaped currents, high frequency portions which might limit the VFD cable length are filtered out. Consider the voltage drop across the cable length and the resulting voltage drop at the sinus filter. The voltage drop results in an increase of the output current. The variable frequency drive must be suitable for the higher output current. This must be considered in the projecting phase.
In the case of variable frequency drive cable lengths exceeding 300 m, contact the VFD manufacturers service.

Group VFD
In the case of a group VFD (several motors at one variable frequency drive), the total length must be divided across the individual motors according to the value given in the table.
Use a thermal monitoring element on each motor (e.g. PTC resistor) in order to avoid damage. A group VFD with synchronous server motors is not possible.

Brake resistor
Gozuk recommends installing a brake resistor to the variable frequency drive if feedback of generator energy is expected. Overvoltage shutdowns can be avoided by this.

Warning!
warningDuring operation, the surface of the brake resistor can reach high temperatures. The surface can keep high temperatures after operation for a certain time. Do not touch the brake resistor during operation or operational readiness of the variable frequency drive. Noncompliance may result in skin burn.
Install a safeguard for protection against contact or fix warning labels. Do not install the brake resistor in the proximity to flammable or heat-sensitive materials. Do not cover the brake resistor.

Caution!
Gozuk recommends using a temperature switch. The brake resistors available from Gozuk in resistor size 4 (92 Ohm, 696 W continuous power) and above are equipped with a temperature switch by standard. In resistor sizes 2 and 3 (300 Ohm, 213 W and 136 Ohm, 471 W) the temperature switch is available optional. The temperature switch disconnects the variable frequency drive from mains supply if the brake resistor is overloaded.
Using Brake resistors without temperature switches can result in critical states.

Minimize cable lengths
Minimize VFD cable lengths
DC-connection requires a power estimation of the complete system. The brake resistor is operational dependent on the enable of the variable frequency drive. The contactor K1 must disconnect all plant components from the mains.

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