Articles & Case Studies

New medium voltage drives improve life cycle costs at Pumping Station

Posted: Monday 25th November 2013

The first UK installation of a new type of medium voltage AC drive has been commissioned at Yorkshire Water’s Blackburn Meadows Wastewater Treatment Works in Sheffield.

Six ACS 2000 drives from ABB have replaced a DC drive system used to control a set of pumps, with motors rated at 2 x 645 kW, 2 x 505 kW and 2 x 300 kW. The multi-pump arrangement is used to transfer wastewater 25 metres below ground to the head of the treatment works. Medium voltage drives were selected instead of low voltage drives due to the long cable lengths and overall project costs including the electrical distribution system, variable-speed drives and motors.

The existing DC drive system used dry-type cast-resin indoor transformers feeding DC drives controlling the DC motors. While Yorkshire Water Services’ specification for the new system would permit indoor transformers, they would need to be integrated into the new variable-speed drives and would, therefore, not be free-standing.

The ACS 2000 was selected as it can be used without an input isolation transformer, thereby allowing a direct connection to the 6.6 kV line supply (direct-to-line). The active front end (AFE) enables the transformerless operation with reduced harmonic loadings.

“The ACS 2000 has a lot of benefits over drives from other companies in that it is very interactive and highly modular,” says David Batty of ETM, Aecom Design Build. “To change a component is very straight forward: you just pull out a drawer and put in a new drawer. Each of the drawer modules takes only about five minutes to change.

“As the drive has no transformer, the heat output is significantly reduced. A drive with a transformer would weigh twice as much and because our installation is on a raised floor, we don’t have as many concerns over the integrity of the floor.”

Direct-to-line combines the cost savings of a transformerless variable-speed drive system with the benefits of voltage source inverters (VSIs), including excellent availability and reliability, high and constant power factor and superior dynamic control performance.

Yorkshire Water is benefiting from lower energy consumption and reduced maintenance costs.

“The existing system was rated at 1750 kilowatt (kW), whereas the new system is reduced to 1450 kW so the overall operating capacity is lower but the flow characteristics and performance are a lot greater,” explains Batty.

The overall system, including drive, motor and pump, is more efficient partly through lower heat losses and the use of AC motors, therefore providing the best life cycle cost of any solution.

“With the old system we would have had one of our engineers checking the condition of the brushes on the DC motors at least monthly,” explains Richard Adamson, Project Engineer, Yorkshire Water “This has now been taken away completely resulting in just an annual visit to each drive.”

The ACS 2000 drive control platform uses ABB’s award-winning direct torque control (DTC), resulting in the highest torque and speed performance as well as the lowest losses ever achieved in medium voltage AC drives. Control of the drive is immediate and smooth under all conditions.

The drive provides near sinusoidal current and voltage waveforms making it compatible for use with standard motors and cable insulation. This is achieved with ABB’s patented multilevel topology which utilises one DC link enabling a multi-level output waveform with a minimum number of power components.

It’s typical for ABB on medium voltage projects of this nature to provide full engineering resource. So at the start of the project ABB designs the interface and works with the customer and the end-user to provide the interface to the product, exactly as they need.

“One of the things we were impressed with is that ABB is able to adapt the product to suit our ways of working and safe system of work. We required an additional earth switch and some Castell interlocks fitted; ABB were able to do this for us,” adds Adamson.

“That’s not the end of ABB’s interaction on site,” says Mark Land, MV Drives Engineer from ABB. “As we’ve completed project execution and the drive has been commissioned, we then go on to provide after care. It’s very normal with medium voltage drive installations that ABB provides a service contract and with that service contract and extended warranties on the product we provide a fast turnaround for visits to site to do any diagnostic or any repair work on the product itself.”

“We’ve also had very quick turn-around on problems and we’ve also had a day’s training for each of our current staff. It was well received by them and now gives us the ability to fault-find on our own,” concludes Adamson.

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