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EMI in HVAC

2021/05/31 > Back


A heating, ventilation and air conditioning (HVAC) system is an integral part of almost every building or facility regardless of its function. HVAC systems can be trivial, but they can also be highly sophisticated with numerous additional functions besides air supply and exhaust. The more sophisticated the building systems are, the more electrical and electronic components they have, and, therefore, the more attention should be paid to the aspects of electromagnetic compatibility (EMC). Since variable frequency drives (VFD) are potential sources of electromagnetic interference, especially high frequency emission, it is natural that they are part of the EMC compliance.

The two aspects affecting VFD's EMC performance most are the design of the VFD and the installation practices. Poorly designed or installed VFDs can produce significant high frequency disturbances which are able to affect operation of other electronic equipment. High frequency disturbances are quite harmful within an electrical system and can cause serious problems for both end users and building owners.

Equipment grounding is an important aspect when considering system EMC performance. Grounding of a VFD as a potential source of EMI requires attention in particular. Motor and power supply cables should be grounded 360 degrees. EMC cable glands are the optimal solution, but metal cable clamps with full cable shield contact are also sufficient. The motor cable shield should be grounded at the motor end as well. Furthermore, it is important to remember that EMC performance of a certain drive depends on the length and type of motor cable. Thus, a drive fitted with an internal or external filter that complies with EMC requirements at a certain cable length, may not comply with requirements at longer lengths.

Grounding systems help to achieve EMC compliance by maintaining the same ground potential throughout the building. If a grounding system is not equipotential, high frequency stray currents start flowing between different parts of the building electrical system throughout the ground. This may disturb sensitive equipment connected to the system. In such cases it is very difficult to determine the root cause of electromagnetic disturbances since the source may be in an entirely different part of the building. If the entire grounding system of a building is equipotential, the difference in potential between devices is low and a large number of EMC issues disappears.


Data source: ABB

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