Exploring the Voltage Doubling Effect at Motor Terminals: Causes and Prevention

 Voltage doubling due to capacitance at a motor terminal can occur when there is a significant amount of capacitance present in the circuit, such as when the motor cable is longer than a few meters, or when the motor is located far away from the power source.

Capacitance occurs whenever two conductive surfaces are separated by a dielectric material, such as insulation or air. In an AC circuit, capacitance causes a current to flow between the conductive surfaces, which can lead to a voltage drop across the capacitance. In the case of a motor cable, the capacitance between the conductors can cause a voltage drop that can be significant when the cable is long.

When a motor is connected to a power source with a long cable, the capacitance between the conductors can cause a voltage drop that is proportional to the cable length and the frequency of the AC signal. This can lead to a reduction in the voltage available at the motor terminal, which can cause the motor to operate at a lower speed than expected or even stall.

In some cases, the capacitance between the conductors can also cause a voltage doubling effect, which can lead to overvoltage at the motor terminal. This can cause the motor to draw excessive current and overheat, which can lead to damage or failure.

To prevent voltage doubling due to capacitance at a motor terminal, it is important to ensure that the motor cable is not excessively long and is properly sized for the application. If the motor cable is long, it may be necessary to use a cable with a larger cross-sectional area or to install a voltage stabilizing device such as a line reactor or a drive with a DC link choke. These devices can help to reduce the voltage drop across the capacitance and prevent voltage doubling at the motor terminal