Stuart Foster, ABB's UK & IE Water Industry Sales Manager - Drives, writes: Let’s face it, as dinner party conversations go, telling people you’re responsible for keeping water pumps reliable is a bit of a non-starter. But tell them that last year you cut so many thousands of pounds of wasted energy, helping keep their water bills in check, and they start to take notice.
As a water industry professional, both aspects are important to you. With AMP6 focusing on a Totex approach to costs, keeping pumps reliable so they don’t need unplanned, i.e. expensive, maintenance and cutting the energy used to run them, is a priority.
But what happens if your pumps’ current demand exceeds your supply? That was the situation facing the Shire Group of drainage boards in its role to protect land around the River Trent from flooding. Its two submersible pumps at Susworth Pumping Station transfer water into the river, protecting land, people and agriculture. Yet the pumps’ combined demand of 202A exceeded the supply’s capacity of 100kVA.
This meant that only one pump could be run at a time, even when the area was under threat from inundation by prolonged rainfall.
ABB authorised value provider (AVP), Inverter Drive Systems, installed two 75 kW ABB general purpose drives as part of a four-week trial to determine the motors’ best speed for optimum pumping.
One drive runs pump one at 41 Hz, drawing 38 kW with pump two running at 37.5 Hz, drawing 28 kW. This means that both pumps run at 80 percent capacity, with 29 A in hand over the full load current for both pumps.
Running at this capacity means that the transformer is not overloaded, avoiding the need for an expensive upgrade, and together the two pumps achieve a higher pumping volume than a single pump working at full rate. The means the pumping system is now more reliable and can be operated fully unmanned.
With lower speeds and soft starts, the VSDs also place less stress on the motors, helping reduce wear.
It’s not just reliability that has been improved. Operating the pumps this way is expected to reduce their energy use by between 10 and 15 percent.
For the drainage board, the benefits are worth shouting about.
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