Variable Frequency Drive


In the industry, many devices work with variable speed drives. The drivetrain of these devices typically consists of a 2-Level voltage source inverter with a DC link, a motor cable, the electrical motor itself, and attached devices such as gearboxes, rotor resolver, or driving pulleys. In big factory buildings, such as those with spinning machines for cotton or synthetic fibres or bottling facilities, several drivetrains are nearby each other and all are connected to the same factory grid, which can cause unwanted problems.

Working principle

Each voltage source inverter has feedback on the factory grid with leakage currents, which causes local harmonic distortion on the grid. These parasitic currents are mainly in a loop beginning and ending in the frequency inverter via the motor cable, drive, potential earth wires, etc. If current flows via potential earth wires, it could affect other devices by changing the grounding potential.

Damaging effects

Parasitic currents can lead to unexpected triggering of security components, such as residual-current-operated protective devices (RCDs), or these currents can damage grounded metallic parts via electrical corrosion. In addition, if a sufficient part of these currents flows via the motor bearing, it can also damage them within a year by changing the smooth bearing surface into fluting.

The Solution

If all drivetrains with variable frequency drives are equipped with Blueferrite-Nanocrystalline cores, the leakage currents at the factory grid can be reduced to a harmless level. This will solve unexpected triggering of security devices and motor bearing damage caused by circulating or rotor-to-ground bearing currents. Our cores are specially designed for electrical drives to withstand high load currents without going into saturation.

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