How can an ABB 4kW ACS355 inverter drive can do all this?

By installing an ACS355 inverter drive to a 4kW sewage aerator improved reliability, reduced energy consumption, cut ammonia levels and reduced maintenance.

The aerator was on an unmanned site, operated by Anglian Water, where the vertical rotor of the aerator was set on a duty cycle of 20 minutes off, 20 minutes on. Controlled by a 4kW DOL motor, the frequent sudden stops and starts caused shock loads on the motor and gearbox, leading to electrical and mechanical failure of the aerator, causing interruptions to sewage treatment and a possible subsequent failure to consent.

Reduced blockages

The middle of the aerator has a tube to pull effluent from the bottom of the tank to the top of the tank, similar to an aquarium air lift, which ensures all the content is treated. The old 20-minute duty cycle allowed detritus to settle at the bottom of the tank during the off phase, causing the tube to block over time. We needed a solution that would solve these problems and hopefully also produce energy savings by matching sewage treatment more closely to demand.

Following a site survey, a 4 kW ABB ACS355 machinery drive was recommended. The drive’s internal timer outputs a signal to switch the motor on and off and to alter the frequency to achieve different speeds at different times.

Improved control

Site staff experimented with the timings and speeds to find the minimum that would still draw the effluent and aerate the sewage, and finally settled on four different time periods, during which the motor would be constantly on but working at different speeds to match the demand at those times. The improved control meant the aerator motor achieved a minimum of 10 percent reduction in speed even at peak times, while the ramping and soft start capability removed shocks to the motor and gearbox.

Improved reliability and reduced energy consumption
The original energy cost of the application was £762 per annum, but this fell to only £374 following the introduction of the ABB drive, a energy reduction of nearly 50 percent. Since installing the drive, the application has become very reliable, and with no maintenance issues within the aerator stem

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