Danfoss VLT® Sine-Wave Filters
Sine-wave Filters reduce motor insulation stress and eliminate switching acoustic noise from the motor. Bearing currents are also reduced, especially in larger motors above 50 kW. Sine-wave filters prevent disturbing pulses from being transmitted to the motor. Capacitance’s in screened motor supply cables can otherwise cause high oscillating circuit currents through motor bearings, vaporising lubricant and causing damage to the bearings.
The eddy current losses in the motor can also be minimised in this manner, resulting in a cooler motor and thus extended motor life-time. In addition to protecting the motor, the sine-wave filter also provides protection for the inverter, because the lower pulse load is reflected in lower semiconductor losses. It should however be noted that this filter does not operate in common mode and the leakage currents are not reduced, therefore it does not enable the use of unlimited motor cables lengths.
Danfoss VLT® dU/dt Filters
dU/dt filters reduce the dU/dt values on the motor terminal phase-to-phase voltage – an issue that is important for short motor cables. dU/dt filters are differential-mode filters which reduce motor terminal phase-to phase peak voltage spikes and reduce the rise time to a level that lowers the stress on the insulation of motor winding’s.
Compared to sine-wave filters, the dU/dt filters have a cut-off frequency above the switching frequency. The voltage at the motor terminals is still PWM pulse shaped, but the rise time and Upeak are reduced. They are smaller, weigh less and have a lower price compared to sine-wave filters. Furthermore, because of the smaller inductance and capacitance, the dU/dt filters introduce a negligible reactance between inverter and motor and are therefore suitable for high dynamic applications.
Danfoss VLT® Common Mode Filters
VLT® Common Mode Filters MCC 105 core kit reduce electromagnetic interference and eliminate bearing damage by electrical discharge. VLT® Common Mode Filters MCC 105 (HF-CM) cores are special nanocrystalline magnetic cores which have superior filtering performance compared to regular fer-rite cores. They act like a common-mode inductor (between phases and ground).
Installed around the three motor phases (U, V, W), they reduce high-frequency common-mode currents. As a result, high-frequency electromagnetic interference from the motor cable is reduced. However, the core kit should not be used as the sole mitigation measure, and even when the cores are used, the EMC installation rules shall be followed.
Common Mode Filters
- High-performance nanocrystalline magnetic material
- Oval shape
- Scalable solution: longer cables handled by stacking more cores
- Only 5 core sizes cover the entire VLT® power range
- Easy logistics, fast delivery and comprehensible product program
- Low investment
- Reduces voltage peaks in motor
- Diminishes over voltages and voltage spikes caused by cable reflections
- Reduces du/dt stresses
- Lowers the magnetic interference propagation on surrounding cables and equipment
- Eliminates acoustic noise in motor
- Reduces high frequent losses in motor
- Reduces dU/dt stresses
- Lowers the magnetic interference propagation on surrounding cables and equipment)
- Low voltage drop makes dU/dt filters the ideal solution for highly dynamic applications with flux vector regulation