© ebm-papst

Auto­matic reso­nance detec­tion for more oper­a­tional reli­a­bility

Today, centrifugal fans are used in a wide range of appli­ca­tions. Depending on where they are installed, reso­nances with increased vibra­tion veloc­i­ties may occur in unfore­seen speed ranges. If the fan is often oper­ated in such crit­ical ranges, the drive motors’ bearing system may be damaged, leading to prema­ture fan failure. Although these vibra­tions are measur­able for the system oper­ator, it is not easy to stop them. Auto­matic reso­nance detec­tion provides a remedy. It avoids oper­a­tion at crit­ical speeds, which increases the service life and oper­a­tional reli­a­bility of the fans

Fans for use in venti­la­tion, refrig­er­a­tion and air condi­tioning tech­nology and other indus­trial appli­ca­tions are usually subjected to rigorous testing. They have to prove them­selves with the manu­fac­turer in long endurance tests under harsh condi­tions and are balanced to the latest state of the art. But in prac­tice, fail­ures still occur in some appli­ca­tions after far fewer hours of oper­a­tion than spec­i­fied in the cata­logs.

A typical example is a damaged bearing system, usually caused by vibra­tions resulting from the way the fans are installed. If several fans are used in parallel, e.g. in a FanGrid (fan wall), this problem can be exac­er­bated by inter­ac­tions between the fan and the design prop­er­ties of the system. In addi­tion, fan vibra­tion char­ac­ter­is­tics usually change when the fans are installed in the customer’s device. An addi­tional imbal­ance caused, for example, by damage during trans­port or handling can also have a nega­tive impact on the service life and lead to the fan falling short of its usual 40,000 oper­ating hours.

Crit­ical speed ranges “overrun”

If a fan is oper­ated frequently at exces­sive vibra­tion levels, the bearing system may be damaged and prema­ture fail­ures may occur. Although vibra­tions can be measured, it is not easy to stop them. Motor and fan specialist ebm-papst now solves this problem with its RadiPac centrifugal fans with auto­matic reso­nance detec­tion: in as-deliv­ered condi­tion, each RadiPac centrifugal fan has its own reso­nance char­ac­ter­is­tics, induced, for example, by an unavoid­able residual imbal­ance.

Vibra­tion char­ac­ter­is­tics of the fan. (Graphic | ebm-papst)

If the fan is now installed in a venti­la­tion unit, the reso­nant frequency range may shift and/or the vibra­tion velocity increases to imper­mis­sible values. Inte­grated vibra­tion sensors detect reso­nances and the soft­ware prevents oper­a­tion in the detected crit­ical ranges. In addi­tion, a test start-up can be performed during commis­sioning in which the vibra­tion velocity is analyzed over the entire speed progres­sion from stand­still to nominal speed.

Vibra­tion behavior built into an AHU. (Graphic | ebm-papst)

If exces­sive vibra­tion velocity are detected in certain areas, the control soft­ware adjusts itself after acti­va­tion by the customer so that these speed ranges are “passed over” in the future. This means that the ranges are passed through, but contin­uous oper­a­tion in them is avoided. Oper­a­tors can manu­ally edit the soft­ware settings at any time, meaning that they always have full control.

Vibra­tion behavior with omitted speed range. (Graphic | ebm-papst)

Protec­tion during oper­a­tion

However, the vibra­tion velocity may also increase during oper­a­tion, for example due to dirt deposits on the impeller, which results in addi­tional imbal­ance. In this case, the soft­ware emits an auto­matic warning. The oper­ator can now check the system for addi­tional imbal­ances and can perform trou­bleshooting measures (e.g. cleaning and/or new start-up). Vibra­tions that are injected by devices that are installed nearby, e.g. from defec­tive compres­sors, can be detected but not avoided. In this case, the oper­ator can initiate suit­able measures.

Vibra­tion char­ac­ter­is­tics in the AHU with addi­tional external vibra­tion source, e.g. a compressor. (Graphic | ebm-papst)

This makes auto­matic reso­nance detec­tion a useful option for increasing the oper­a­tional reli­a­bility of the centrifugal fans in crit­ical appli­ca­tions. The RadiPac product range also has a lot to offer. Thanks to aero­dy­namic opti­miza­tions, inno­v­a­tive mate­rials, sophis­ti­cated design details, and highly effi­cient EC motors with intel­li­gent control elec­tronics, they not only deliver a lot of air perfor­mance, but they are also partic­u­larly quiet and effi­cient. High speeds ensure high air flow and high pres­sures, meaning that even high-pres­sure appli­ca­tions can be covered. A static pres­sure increase of well over 2,000 Pa can be achieved.

Energy-effi­cient, quiet and adapt­able

The driving force behind RadiPac centrifugal fans are high-effi­ciency Green­Tech EC motors in the power range from 500 W to 8 kW with config­urable control inter­face for analog and digital signals, which can be indi­vid­u­ally adapted, as well as a serial MODBUS RTU inter­face. This enables oper­ating data such as speed, power consump­tion or oper­ating time to be read out and processed digi­tally, for example. The external rotor motors also achieve high effi­ciency levels in accor­dance with the require­ments for effi­ciency class IE5 set out in IEC/TS 60034-30-2. They do not require any rare earths and are also very compact thanks to the typical ebm-papst external rotor design.

The impeller plays a signif­i­cant role in creating high effi­ciency levels. A glass-fiber rein­forced composite mate­rial was used, enabling the complex shape of the five spatially twisted and strength-opti­mized 3D blades. The opti­mized blade chan­nels achieve high effi­ciency levels and the fans operate extremely quietly.

Flex­ible instal­la­tion options

To meet the require­ments of different instal­la­tion situ­a­tions, the new centrifugal fans are avail­able in a stan­dard and short version. For the most powerful stan­dard types, the impeller is attached to the motor in such a way that it has no nega­tive influ­ence on aero­dy­namic effi­ciency. In the short version, the motor is immersed in the impeller. These fans are more compact and are much more effi­cient than compa­rable prede­cessor models in spite of the slightly shorter axial instal­la­tion dimen­sions in compar­ison to the stan­dard version.

Both RadiPac versions are avail­able as a motor-impeller combi­na­tion or as a ready-to-install plug & play solu­tion in a compact support bracket for easy wall mounting. The support plates have been dimen­sioned to make the best possible use of space on a Euro pallet, thereby saving trans­port costs and improving the CO2 foot­print.

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