Case study: variable-speed drives score a pumping station victory
25 Oct 2016
Surface water pumping station doubles its pump potential with variable-speed drives installation.
Susworth Pumping Station in Lincolnshire utilises two submersible pumps that transfer surface water runoff from the low lying catchment into the River Trent.
The pumps are rated at 65 kW and 75 kW respectively, and boast a combined full load current of 202 amps. Both pumps also have the capacity to run at 950 rpm.
The pumping station’s electrical supply comes via a remote pole transformer rated at 100 kVA, but due to the transformer’s rating, only one pump could be run at a time, even during periods of prolonged rainfall.
To overcome this issue, the station installed two ABB 75 kW general purpose variable speed drives (VSDs) to run the pumps simultaneously.
As part of a four-week trial, Inverter Drive Systems installed the VSDs to determine the motor’s best speed for optimum pumping
The Shire Group, which manages Susworth Pumping Station, called on Lincoln Electrical Services and Inverter Drive Systems to help come up with the solution.
As part of a four-week trial, Inverter Drive Systems installed the VSDs to determine the motor’s best speed for optimum pumping.
“We were asked to obtain several quotes for the work of improving the pumping system, and the proposal offered by Inverter Drive Systems was the best,” says Peter Mayo, managing director at Lincoln Electrical Services.
“[Inverter Drive Systems] was keen to conduct a trial to prove the benefits of their solutions to us,” Mayo adds. During the trial, the normal pumping rate within ‘non-storm’ conditions was optimised to achieve the lowest energy use for each cubic meter of water pumped.
Go with the flow
This was set to match natural flow in the nearby dyke, avoiding surges and unnecessary starts.
Throughout the trial, pump one was operated at 41 Hz, drawing 38 kW, while pump two was operated at 37.5 Hz, drawing 28 kW. Adding VSDs to the pumping station meant both pumps could run at 80% capacity, with 29 amps spare, over the full load current for both pumps.
Following the trial, the two VSDs were fitted in a permanent installation, which is expected to see the energy use of the two submersible pumps cut by between 10% and 15%
Running at this capacity meant that the site’s transformer was not overloaded and together the two pumps could achieve a higher pumping volume than a single pump working at full rate.
Following the trial, the two VSDs were fitted in a permanent installation, which is expected to see the energy use of the two submersible pumps cut by between 10% and 15%.
According to ABB, with lower speeds and soft starts, the VSDs place less stress on the system’s motors, helping reduce wear.
What’s more, ABB says that better control of the outflow also alleviates ditch erosion by avoiding water pressures that would damage the bank of the river.
