VFD-Driven Motor Applications

The Multilin 869 provides protection for motors fed through VFDs (Variable

Frequency Drives). A wide range of the frequency tracking (3-72Hz) allows

the 869 to track the motor frequency and adjust its sampling rate to

accurately measure phasors. An advanced algorithm allows switchable

current and voltage tracking in case VFD is bypassed.

Thermal protection also considers the extra heating generated by the

higher harmonics due to VFD to achieve the accurate response to the

actual motor heating. RMS currents fed to the various motor protection

elements are further processed through the averaging filter to eliminate

oscillations in current signals to ensure the security.

Additionally, users may indicate a  starting  VFD  frequency  that  helps

the device to track the motor frequency faster and therefore accurately

measures the phasor quantities, which, otherwise, could cause delayed or

false protection operation of the protection.