Welcome to our website.
You can choose another country to view available products or go to our Global website for company information.
In industrial environments, connecting motors to variable speed drives (VSDs) via cables delivers flexible control, energy efficiency, and low-cost maintenance. But precautions are necessary to prevent overvoltage, which can compromise motor lifetime or cause a shutdown.
How cable length can create issues
For motors connected to VSDs, a combination of fast-switching transistors and long motor cables can cause a temporary overvoltage at the motor terminal connection. In extreme cases, high peak voltage can prematurely age the motor winding insulation, causing overall motor failure.
Consequences of overvoltage and overcurrent conditions
Effect on VSD: The main risk of overcurrent in a VSD is a short circuit fault.Capacitive peak current can also cause power transistor temperature to rise, and this above-normal temperature can reduce VSD lifetime.
Effect on the electric cabinet: Disturbances that result from long cable and motor interactions create high frequency circulation current into the ground that can disturb appliances connected on the same network. High frequency currents also generate radiated emission, which can disturb electronic devices around the motor cable.
Effect on motor: Overvoltage at the motor terminal can occur between two motor windings. Depending on the class of winding insulation, partial discharge and insulation ageing can occur, leading to motor failure.
Side effects of a long motor cable: In standard applications, overvoltage occurs whenthe motor cable exceeds 32 feet (10 meters) in length. The longer the motor cable, the higher the overvoltage, an effect that amplifies with a shielded cable. Calculating the cable length correctly helps protect the VSD from any unexpected tripping.
Another side effect is motor bearing degradation, caused by common-mode voltage that the VSD inverter generates, which throws high frequency current into the motor bearings.
Four preventive measures
Often overlooked in design planning, these measures can help avoid overvoltage and related effects.
Best practices for safeguarding VSDs and motors include:
By following these steps, a cable that is 984 feet (300 meters) or shorter will work without any additional options. For applications that involve longer cables, unknown motor insulation levels, or nonstandard motors, a dV/dt output filter or sinus filter is the best preventive measure.
Motor cable length
|Motor NOT conforming
|1 m (66 ft) < Lm < 50 m (164 ft)||Filter not required||dVdt filter|
|50 m (66 ft) < Lm < 100 m (328 ft)||Filter not required||Sinus filter|
|100 m (328 ft) < Lm < 300 m (984 ft)||Filter not required||Sinus filter|
|300 m (328 ft) < Lm < 500 m (984 ft)||dVdt filter||Sinus filter|
|500 m (328 ft) < Lm < 1000 m (984 ft)||Sinus filter||Sinus filter|
Selecting the right preventive measures depends on motor characteristics and cable length