From the updated CEMEP paper Energy Efficiency with Electric Drive Systems, come examples of best practice for applications with potential energy savings.  In the context of automation technology, the use of energy-efficient motors, of variable speed drives and of a cost-efficient motor/gear-unit combination plays an important role in saving energy. Various typical applications show how with an optimised drive solution the consumption, and thus the energy costs as well, can be dramatically reduced to meet a 24 month or less payback time.

Pump drive: speed control instead of mechanical throttling

Pump systems offer significant potential savings, not least because they are mostly operated in the partial load range. The delivery volume actually needed usually lies below the rated operating point, due to over dimensioning of the system, and in many cases is regulated by mechanical control devices, such as valves or throttles. To give an example: at a coolant pumping station featuring five centrifugal pumps and five motors each rated at 55 kW in a production facility of the automotive industry, all pipe restrictors were removed and the throttle valves opened. To regulate the delivery volume, speed control with variable speed drives was used instead. This resulted in impressive energy savings of 60 per cent; the energy costs were reduced by 96,000 Euros a year.

Fan drive: speed control instead of mechanical throttling

Fans have a wide range of applications. They range from small models for room ventilation via air-conditioning systems in buildings all the way to fresh-air and exhaust-gas blowers in cement plants. In the application described here, a fan with a power rating of 7.5 kW is used in the extraction system of a woodworking company. The flow rate is matched to the quantity actually needed using a variable-speed three-phase motor instead of being mechanically throttled. Given 4,000 operating hours, this saves 756 Euros a year in electricity costs. The capital investment costs for the variable speed drive and control cabinet thus pay for themselves in around 25 months.

Variable speed drives: intelligent functions help to save energy

Since modern AC variable speed drives were introduced over thirty years ago, the manufacturers have significantly improved their energy saving functions. Users can fine-tune the process concerned in order to make optimum use of the energy available,  and many offering offer self-tuning. One example is the energy-optimising mode, which increases the efficiency of the system comprising variable speed drive and motor, particularly in the partial-load range, by up to 20 per cent. Integrated energy-efficiency computers support the users in analysing and optimising their processes.

Special variable speed drives for water and wastewater applications, moreover, offer intelligent pump control functions for individual pumps and multi-pump systems, designed to upgrade their energy efficiency. At a pressure-boosting station with two 75-kW pumps and one 37-kW pump, a multi-pump control system, a pump priority changeover feature and a flow rate computation capability were used. When water consumption is low from the mains during the night, the small pump is activated, while during the daytime the two large pumps take over. This means the pumps can be run closer to their optimum operating point. By using variable speed drives with intelligent pump functions, the energy consumption was reduced by 30 per cent.

Multi-drive concept: saving electricity by energy equalisation

In many applications, some of a system’s drives are operated in motor mode, while at the same time others are operated in regenerative mode. Here, a multi-drive system with a DC bus is the preferable option instead of several separate drives. In contrast to a stand-alone drive, in the multi-drive concept several inverters of different ratings are supplied from a shared feed-in unit via a DC bus. Via this DC bus, efficient, direct energy equalisation can be provided by all inverters, without energy having to be converted into heat in a braking resistor or without any necessity for a regenerating unit. Examples here include conveyor systems or paper machines, in which the unwinder is run continuously in regenerative mode and the winder in motor mode. In the case of machines that are cyclically decelerated, as is the case, for example, with centrifuges and cranes, a feed-in/feedback unit is an obvious option. It feeds the braking energy back into the supply grid, and thus increases the machine’s efficiency.

Summary

With drive systems, there are many options for saving substantial amounts of energy with the right solution for the particular application involved, thus also reducing the operating costs and contributing towards the energy turnaround. The payback period is often less than two years.

About CEMEP

CEMEP is the European Committee of Manufacturers of Electrical Machines and Power Electronics, representing an industry with a market value of €6.3 billion and 130,000 employees. The members of CEMEP are the National Associations in Europe, representing manufacturers of electric motors, variable speed drives and uninterruptible power supplies. In the UK they are represented by the GAMBICA organisation

Go here for the full CEMEP White Paper “Energy Efficiency with Electric Drive Systems” from GAMBICA

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