Heat, Ventilation, and Air Conditioning (HVAC) is a collective term for the generation of pleasant indoor air quality. These systems control the temperature and humidity. The power range of these systems starts from small sizes for private households and goes up to large systems for warehouses, data centres, and hospitals. Especially with larger devices, reliability is of great importance to avoid consequential damage in case of failure.

Working principle

A cooling medium extracts heat from the air or directly cooled elements. The heat is released into the ambient air via an outdoor unit. The physical basis is a counter clockwise thermodynamic cycle. Common to these systems are the compressor and fan drives. To increase the overall energy efficiency, the drives are controlled via a variable frequency inverter to adjust the rotor speed depending on the actual load.

Damaging effects

The variable frequency drives in HVAC systems can suffer from bearing currents due to the voltage switching events of the inverter. In inverter-fed drives with frame sizes above 280 mm, a bearing current type called circulating bearing current can easily damage the bearings during long, low-speed operation. The cause of this bearing current is the high-frequency common-mode current, which generates a high-frequency (HF) circulating flux in the electrical machine. This HF circulating ring flux induces a shaft voltage between the drive end and non-drive end side of the machine. At low rotor speed, the film thickness of the lubrication in the bearing between rolling elements and raceway is very thin, so the shaft voltage can drive a circulating bearing current in the loop “rotor shaft – bearing drive end – stator frame – bearing non-drive end.”

The Solution

Our Blueferrite nanocrystalline cores are highly resistant to common-mode currents. By reducing the common-mode currents, we can also reduce the high-frequency circulating bearing currents and protect the motor bearings. The cores can be mounted at the inverter output over the three motor phases U, V, W. The core sizes, quantity of cores, and the magnetic properties must be adapted to the respective application, mostly depending on the rated power and motor cable length. Our selection guide and engineering team will help you find the right cores for your application.

Copyright © 2023 Blueferrite.com. All rights reserved.