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dV/dt filters – FAQ

Jonathan Bullick | August 1st, 2017
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This post outlines some frequently asked questions regarding KEB’s dV/dt filters. When to use them, how they work, and approximate costs.


dvdt filters


Q. When do I require a dV/dt filter (choke)?

A. KEB strongly recommends the use of a dV/dt choke for all VFD installations where the motor is located 40 ft. or more away from the drive and electrical cabinet. Using a dV/dt choke in closer installations is recommended but optional.



Q. Can I use KEB dV/dt chokes with drives from other manufacturers?

A. Yes, in fact, this is a differentiating feature of KEB filters. Because the KEB dV/dt chokes have a low inductance they shouldn’t affect the drives ability to measure the motor parameters during an auto-tune or skew the internal motor model.



Q. Can I use a standard load reactor to mitigate high dV/dt on an installation with a long cable run?

A. It is not recommended. The high inductance and capacitive coupling found in these chokes will still result in high dV/dt while limiting the motor’s peak torque during acceleration.



Q. Can I use KEB dvdt filters for both AC servo and induction motors?

A. Yes. The KEB dVdt chokes effectively limit the voltage transients in both applications. Notably, they do not negatively affect the operation of either motor by adding significant inductance.



Q. Can I use the KEB dV/dt chokes for either 230V or 480V applications?

A. Yes. The chokes are designed to be used for voltages up to 550VAC. They are sized by the current requirements of the application.



Q. How much does a KEB dV/dt choke cost?

A. The dV/dt choke is typically a fraction of the cost of a motor. This represents a small investment up front to prevent a costly repair or replacement at a later date. Applications using specialty motors, motors from vendors overseas, and motors that are difficult to service and reach should take extra care to protect the motor investment.



Do you have a question we didn’t cover here? Drop us a line using the form below or contact a KEB engineer.


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