Reaching For Higher Energy Efficiency

 

 

 

The need to reduce energy consumption overall and deliver greater energy efficiency in design, manufacturing, assembly and distribution is greater than ever. The world’s resources are becoming ever more depleted, energy costs are rising fast, and clearly there are serious and well-known concerns over the future global environment. The European Union for example is aiming for a 20 percent cut in Europe’s annual primary energy consumption by 2020. The European Commission has proposed several measures to increase efficiency at all stages of the energy chain including generation, transformation, distribution and final consumption, including the introduction of smart meters to encourage consumers to manage energy use better.

Increasing industrialisation worldwide means the expansion of automation, and in particular the increased usage of electric motors. In fact, according to a 2011 report from the IEA (International Energy Authority), electric motors and the systems they drive were the single largest electrical end use, accounting for approximately 45% percent of all electricity consumption globally. And of course it is in industry that electric motors dominate and account for the largest amount – approximately two thirds – of total electricity consumption with use for pumping, fans, air and liquid compression, conveyance and many other forms of mechanical handling and processing. So, the failure to invest in more efficient motors, products and machinery to gain short- term cost savings could be a false economy.

 

 

Motor Efficiency

The largest proportion of motor electricity consumption is due to mid- size low-voltage AC motors that deliver an output power over the 0.75 to 375kW range. The IEC 60034-30:2009 standard defines efficiency classes for low-voltage three-phase asynchronous motors over this power range: IE1 is standard; IE2 is high; and IE3 is premium. In 2010, the IE4 classification was also added to the standard and manufacturers are already starting to launch motors that meet this enhanced performance level.

Since 2011, only motors with a minimum performance of IE2 have been able to be sold in the European Economic Area, and only a minimum of IE3 or equivalent will be permitted by 2017. More specifically: from 2015, IE3 will be the legally specified minimum efficiency required for power ratings from 7.5kW up to 375kW, or an IE2 motor plus Variable Speed Drive (VSD); and from 2017, the IE3 will be the minimum efficiency mandatory for ratings from 0.75kW up to 375kW, or an IE2 motor plus VSD. Therefore it makes sense in the medium and long term to ensure all new or replacement motors are either IE2 or IE3 performance, and choosing to fit these new motors instead of having old motors re-wound can offer real savings.

A key factor in the drive to reduce energy costs and improve operational efficiency is better motor control. While there are several options for motor starting, part of the solution increasingly includes the use of ‘soft starters’ and Variable Speed Drives (VSDs), which can dramatically reduce costs. There are estimates that approximately 90 percent of motors used in industrial applications have no form of control other than simple electromechanical switching, which can result in large costs in terms of maintenance and mechanical wear on equipment.

 

Starting

Looking at the more traditional three- phase motor starting methods, Direct- on-line (D.O.L) is a very simple and common way of starting three-phase motors that uses only a main contactor and thermal overload to directly connect the supply to the motor. It is of course very cost effective, but disadvantages include a very high starting current and starting torque, which causes stress to the motor and drive train. Also it does not lend itself to remote control, as the high in-rush current of large contactors is unsuitable for direct control from PLC (Programmable Logic Controller) transistor outputs.

A second method, Star-Delta (SD), changes the wiring of the three motor windings from delta (230V across each winding) to star (400V across each winding) reducing the starting current by 60% compared to a D.O.L starter. Star-Delta starters comprise three contactors, thermal overload and a timer. The advantage is a reduced starting current and torque lowering mechanical stresses. The disadvantage is that it is more expensive than a D.O.Lstarter, it has multiple points of potential failure, and also will prevent the starting of motor loads that require more than 50% of the full motor rated torque. Both these control methods have disadvantages and while Star-Delta starting does reduce in-rush starting current and limits the torque, it cannot be ‘fine-tuned’ for the application and does not lend itself to continuous start/ stop operation. However, savings can be achieved by using a soft-starter in a number of ways. For example, by matching the start-up torque and duration to the load, wear and tear is reduced along with transmission and drive train stresses, which in turn also reduces maintenance and downtime.

Energy saving can be achieved as integrating the soft-starter into the machine’s automation and removing elements of manual control, which mean the motor can be left running when not in use. A common application is stopping out-feed conveyors when there is no product. By using a simple photoelectric sensor to detect product, the conveyor can be quickly brought up to speed when product arrives and halted when no product is available.

Because soft-starters do not use mechanical contactors with moving parts, their operation life is considerably longer and they combine all the components found in a traditional starting solution in a single compact unit.

 

Variable Speed Drives

Many applications will have variable loads and many industrial processes, such as assembly lines, have the requirement to adjust the motor speed. By adapting motor speed and torque to the required load, it is possible to make large gains in efficiency via the use of a Variable Speed Drive (VSD).

By matching the speed and torque to the current load, savings can be made in many applications such as small size cranes, car washes, conveyor, elevators, drilling or woodworking machinery. However, if the VSD is used in a pump or fan-control application, savings of up to 50% are possible. For example, a fan running at 80% speed only uses 50% of the energy, compared to one running at full speed. Yet far too many pumps and fans run continuously at full speed with the output regulated by inefficient throttling devices such as dampers or valves.

Combined with these energy saving opportunities Variable Speed Drives also allow machines to run more efficiently, and in some cases faster, as the speed can be smoothly altered by the PLC or logic controller to suit the process requirements – avoiding time consuming, and mechanically stressful stops and starts.

 

An Extensive Energy-Efficient Range

A vast range of AC motors, DOL, Star-Delta and Soft Start-up starter

devices and VSDs are available from RS Components, representing many leading brands including ABB, Eaton, Mitsubishi, Omron, Schneider Electric and Siemens among many others.

The increased need for energy efficiency is also leading to the better performance metrics in a range of products and technologies aimed at automation markets, including DIN rail and panel-mount power supplies with devices from Omron, Phoenix Contact and PULS leading the way with ever- higher efficiency ratings. In addition, SMC continues to deliver high efficiency products within pneumatics such as KQ2 fittings and the AC range of FRL (Filter-Regulator-Lubricator) units, which also deliver improved installation efficiency. And with the move to LEDs, beacons and industrial pushbuttons are now more efficient than ever before, while electric linear actuators can reduce running costs within pneumatic installations.

 

For more information visit: www.rs-components.com/ energy-efficiency

 

Related products

Eaton DS7 Soft Starter

 

 

 

 

 

 

Schneider TeSys Range DOL Starters

 

 

 

 

 

Mitsubishi D720-SC Single Phase Drives

 

 

 

 

 

Siemens AC Motor