Why we must keep shorter distance between the Motor and VFD?

Posted on 10th Dec 2022

The VFD also known as Variable Frequency Drive is a crucial element to control motor speed. By using Darwin Motion – VFD you can get any specified speed.

But, it’s important to know the appropriate distance between a motor and a VFD (Variable Frequency Drive). It is the most crucial factor to run a motor efficiently and for longer life.

Here you will know the effect of long distance between motor and VFD, and why you have to avoid it.

Remember that the usual distance between Variable Frequency Drive and the motor must not exceed 30 meters. We will explain you why? The VFD output is a sine wave. For a adjustable sine wave to correctly control the motor’s speed, the cables, Variable Frequency Drive, and motor all have to be correctly grounded.

Now, when it comes to the cable length, it must be appropriately shielded in its very initial place. If the cable is correctly armored and grounded, then the generation of noise within the cable is narrowed to itself only.

Or else, the noise will be expended outside the cable as well. And the higher noise can become the cause of current leakage. And in case the distance is long, then the spread of noise will cover more area, and it rises the possibility of motor damage too. Therefore, this is the initial step in distance point – the cables have to be correctly grounded, whether they are shorter or longer distances.

Now, we will examine the next point. Remember a capacitance continuously exists in the sine wave current (PWM signal) which flows in Variable Frequency Drive cables to the motor. The main reason behind this is voltage reflection. In case of long distance, the power cables and the motor impedance is not consistent. It is typically steady in shorter distances.

Now, if this impedance strike with a normal PWM flowing signal then there will be maximum voltage reflection chances. Impedance plays highly crucial part in PWM signals. The drive continuously transmits output sine waves down the wire to the motor, but as soon as they arrive at the motor they are reflected back to the drive by the impedance of the motor.

You may be aware that the capacitance from the cables can also create sufficient current to ground where there can be irritant ground fault trips.

Because of improper impedance, capacitance and voltage reflections causes the reflected wave could be added to the essential waveform arriving from the drive causing considerably higher voltage at the terminals of motor.

So, in case of longer distance there will be higher chances of unbalanced voltage peaks in between. This will even enhance rise steepness (dv/dt) to a higher extent. If the peak is more and unstable, then the voltage rise will take place regularly.

The rise steepness (dv/dt) and the maximum value of the voltage causes danger for the motor insulation. Because of this the motor will not work accurately and even after specific time frame, the motor insulation and bearings will get damage too.

The surge voltage can occur at both ends of the motor winding in case there is a long-distance between connection, the overlaid surge voltage will raise the motor winding current and the motor temperature, thus harming the winding insulation.

This clearly highlight that the distance between the motor and VFD must be shorter. If you like our article, then please check out Darwin Motion stock of AC Drive, Solar Drive - MATRIX 180, VFD/SVC/Drive - MATRIX 190, Torque Mode Drive - MATRIX 500, High Performance Drive - MATRIX 680, Regenerative Drive -MATRIX 880, High Frequency Drive HF - MATRIX 500-HF for Engine & Motor Testing Dynamometer, Textile Machine, Winding Industry, Tower Crane, Extruders, Cross Cutter Metal Cutting, Flying Shear, High Speed CNC Spindal Drive applications.