What makes a water VSD the right choice?
Pumping applications in the water industry present some unique challenges. Clayton Mead, UK Water Industry Manager for ABB, explains how the latest generation of ABB variable speed drives contain an array of features designed specifically for use in the water industry, helping to achieve resilience and reliability while also improving the sustainability of operations.
When discussing the benefits of using variable speed drives (VSDs), the focus is often on energy saving. Indeed, in variable torque applications such as pumps, they can reduce energy costs by up to 60% by varying a motor’s speed in accordance with actual demand. This can help to significantly cut costs and reduce carbon footprint – particularly important against the backdrop of the ongoing push towards net-zero.
However, a VSD, and more specifically a VSD designed specifically for the water industry, has much more to offer beyond energy efficiency. ABB’s ACQ range of VSDs, also known as water drives, has been engineered with additional features and functions on top of those typically found in general-purpose or industrial VSDs. These are designed to help tackle some of the many challenges encountered in the operation and maintenance of water industry pumping applications.
Cavitation
Cavitation is generally bad news for any pumping system, and its effects can have a severe impact on the performance and lifetime of pumps and pump components. It is caused by pump impeller blades creating a vacuum on the suction side/inlet of a pump – the vacuum results in tiny steam bubbles, which collapse to produce a shockwave. Over time, enough of these shockwaves will gradually erode the impellers and, if left unchecked, can cause the pump to catastrophically fail.
ACQ VSDs can detect and prevent cavitation in real-time. The VSD monitors a pump’s speed and torque directly from the motor shaft, allowing any potential flow issues to be picked up immediately with zero latency and no need for additional sensors or other equipment. The VSD contains integrated anti-cavitation software, which uses patented algorithms to look for specific patterns in the motor and VSD operating data. It can then pre-emptively and automatically reduce pump speed to prevent cavitation before it occurs, helping to increase the pump’s lifetime significantly.
Pump cleaning
Obstructions to the impeller are a major cause of pump system downtime and are a common occurrence in wastewater treatment. A VSD’s pump cleaning (also known as anti-jam or anti-ragging) function uses a programmable sequence of forward and reverse rotations of the pump to shake off any build-up on the impeller. This reduces the need for manual cleaning. The VSD can automatically trigger a cleaning cycle by monitoring the pump load for an under-load or over-load curve, or cycles can be scheduled for set intervals, on-demand, or through a Fieldbus command. If the drive is cleaning more frequently than usual, this can suggest that it will take more than cleaning cycles to clear the obstruction. In this case, the VSD can trigger a warning to indicate that the pump may require additional attention, or even manual intervention, to prevent the situation from worsening.
Harmonic mitigation
Harmonics can affect system efficiency and cause electrical equipment to run erratically. They can affect power quality, and in some cases lead to unreliable operation and trips on critical equipment such as generators, which are vital in the water industry. Traditionally harmonics are mitigated by adding additional equipment such as filters, multi-pulse transformers, or by over-sizing equipment. ABB’s Ultra-Low Harmonic (ULH) drives have harmonic mitigation built-in, including an active supply unit and integrated low harmonic line filter. In practice, this can reduce harmonic content by up to around 90% compared to a conventional VSD. This is particularly useful when installing VSDs with generators, in hydro installations, or at facilities in remote areas where power quality is an issue.
Multi-pump control
Many water treatment facilities use multi-pump configurations. With each pump requiring its own drive, a multi-pump configuration allows for the daisy-chaining of up to eight ACQ580 drives, thus creating an intelligent multi-pump control system that makes it easier to maintain a stable water flow whilst accounting for varying water pressures and variances in pump speeds. Most importantly, this is achieved without the need for an external logic controller.
The built-in multi-pump functions also provide backup redundancy to provide stability and ensure continuous operations – balancing the load across all pumps for greater efficiency should one of the pumps fail and the multi-pump configuration break down or require maintenance.
Multi-pump control can also work well in combination with another feature known as pump auto change, which balances the operating time of pumps in a parallel pump system, helping to reduce strain on pumps both individually and collectively.
More complex operations can also be programmed, for instance to favour the most efficient pump in a series. A sleep/boost feature reduces equipment wear in such a configuration even further by increasing pressure just before shutting a pump down to allow for extended sleep periods.
Soft pipe filling
Water VSDs also incorporate features for very specific pumping applications and scenarios. Soft pipe filling provides a pump with soft-start, enabling a smooth build-up of pressure in empty pipes. This avoids pressure peaks in, for example, irrigation systems, where pipes are momentarily empty and controlled pipe filling is required, reducing overpressure and water hammer. As a result, this helps to avoid excess stress to sprinkler heads and pipe joints as the pipe is filled.
In summary
VSDs are widely known for their energy-saving capabilities, but they also have a lot more to offer. ABB’s ACQ series provides a wide range of features tailored specifically to meet the challenges that pumping applications can present. In addition to the features outlined above, ABB VSDs also incorporate coated boards, and an enclosure class up to IP55 to protect against the harsh conditions commonly found in the water industry.
