Motors and Drives
effective, like using a microphone or accelerometer to indirectly sense the condition of equipment as James explains: “Accelerometers and microphones are almost interchangeable - where a microphone picks up acoustic signals, an accelerometer picks up physical vibrations and the two are so tightly coupled you can use one or the other depending on the nature of the application. “You can listen to an electric motor’s acoustic signature,
and you can hear when it is starting to whine or when the load is off-balance. This function can be performed by someone with a trained ear, but alternately machine algorithms can be used to ascertain whether the acoustic signature is right or wrong. “There is also a lot of information you get from transients
and short duration pulses, and in a motor, a transient can be indicative of something instantly failing. Frequency analysis is useful for long-term trend analysis whereas transient analysis can alert a more catastrophic event, like the fact that a rotor shaft has snapped for example.
Two dollar DSP
“Developing an algorithm that extracts all the data and converts it to real information is the key. It is very easy to prove that an algorithm works on a desktop PC, but the challenge is implement this algorithm on a digital signal processor (DSP) costing a couple of dollars.” Ackworth School in Pontefract, West Yorkshire, has
reduced its swimming pool energy bills by also taking a holistic approach, using VSDs, remote device monitoring equipment and voltage optimisation/stabilisation. Peter Cheseldine, clerk of works at Ackworth School, recommended to the governors that VSDs be installed to reduce energy costs.
IWEMS is Powermaster’s VRS voltage optimiser/stabiliser, which reduces electricity consumption by automatically reducing site voltage to a constant, stable 380V. “VRS controls the voltage on site to stable levels and
gets rid of harmonics, and we are looking to further reduced energy costs in the region of 7-10 per cent,” Cheseldine adds. “Return on investment has been quick on this equipment, especially with speed control on the swimming pool pumps, where we are saving anything up to 30 per cent now. Total payback was only about three years, so we have now had five years of pure saving.” Three years payback appears to be typical for VSDs
generally, as the case of Associated British Ports (ABP) also shows. Together with its sister port of Grimsby, ABP Immingham is the UK’s largest port by tonnage. In order for shipping to operate continuously, the water levels in the port need to remain at a consistently high level, so water must be pumped into the port. The equipment used was first installed in 1973 and was no longer efficient. It controlled the flow of water into the port through the use of three pumps. The motors could only be operated in on/off mode, with
no control of how quickly or slowly the water was pumped in. Furthermore, the equipment was subject to frequent repairs and spare parts were difficult to come by and costly. Siemens calculated the energy savings that ABP could expect by installing a new VSD and motors to allow the speed of water flow into the port to be reduced.
Longer running for better efficiency
Under the old system, running the equipment for seven hours per day, 365 days per year, cost ABP £92,893 per annum, based on a cost of £.0.66 per kWh. By installing the new variable speed equipment and reducing the speed at which it is run down to 70 per cent, but increasing the length of time that it is in operation to ten hours per day, it was predicted that ABP would make a saving of £47,376 per annum. This meant a predicted saving of more than 50 per cent
annually, and a payback time of approximately three years. Taking into account energy cost rises since then, payback time could be even less. Then one day, a motor breakdown on one pump meant that a solution had to be found immediately to minimise the cost of down-time, as the cost of repair would come to a six figures sum. Since the Siemens equipment was installed an average
Fig. 2. Ackworth School has reduced its swimming pool energy bills by using VSDs, remote device monitoring and voltage optimisation/stabilisation.
“Getting the financing for VSDs approved by my superiors was an uphill struggle initially,” Cheseldine recalls. “However, as energy prices went up, they realised that they should be doing something. Last year, we also went on to install Powermaster’s Integrated Water & Energy Management System (IWEMS), which automatically tests swimming pool water quality and dosing.” IWEMS constantly monitors the chemical demands of
each individual pool, and recognises when bathing loads have changed. The system signals the VSDs to reduce motor speed when bathing loads are low and chemical demand has fallen, and vice versa when chemical demand rises. Complementing
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of 16 maintenance hours per month have been saved. Mark Hennessy, Control Systems Engineer at ABP says: “The system installed by Siemens and Southern and Redfern has made our site more energy efficient, improved operational efficiency and reduced the man hours spent on maintenance.” One of the leading gluttons of energy is of course
wherever there are HVAC installations, whether they are in buildings and data centres or in trains, boats and planes. A control system for a hydrofoil in Italy posed a particular challenge for Esposito Orfino, managing director of Syel, an Italian Rockwell Automation partner. He was asked by the manufacturer to optimise electricity consumption and to use only one generator, instead of the two that were usually required to start the electric motor driving the compressor. This could often cause serious voltage drops during the motor starting phase.
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