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Energy saving opportunities with motors and drives
Industry could save significant amounts of energy by installing drives and switching to higher efficiency electric motors. In Europe, encouraging the use of higher efficiency motors has already brought certain savings but more could be done, and even bigger savings could be achieved with drives. Reduced energy consumption translates directly into lower CO2 emissions.
The energy saving potential in motor drive systems has been the subject of several studies during the past few years, in response to the threat of global warming and the Kyoto agreement, which was ratified by EU members. It has been estimated that in 2015 the total electrical energy used in Europe will be about 1320 TWh a year, and electric motor systems will account for about 707 TWh of this by far the largest single user group.
The energy saving potential in Europe has been identified at about 90 TWh a year in 2015. This corresponds to a reduction of about 36 million tonnes of CO2 emissions. The figure is based on the use of two technologies. Using high efficiency motors instead of standard ones would save about 35 TWh, and using drives about 56 TWh.
High efficiency motors - Voluntary agreement boosts sales
During the past few years, the EU and the European Committee of Manufacturers of Electrical Machines and Power Electronics (CEMEP) have operated a voluntary agreement that aims to reduce sales of lowest efficiency EFF3 motors and promote sales of higher efficiency EFF2 and EFF1 motors. This raised the proportion of EFF2 motors of the total number of motors sold per year from 29% to 86% between 1998 and 2004, while the share of EFF3 motors declined from 68% to 9% over this period. This has already saved about 7 TWh of energy per year.
Even greater savings with drives
The energy saving potential from using drives is significantly higher than what can be achieved by using high efficiency motors. This is basically because when a drive is used, only the energy that the process needs is taken from the mains, no extra energy input is needed to drive the process against some sort of control mechanism. The greatest savings are seen in pump and fan applications, where the flow is proportional to the speed of the pump or fan but the power required to drive it is proportional to the third power of the speed. This means that even a small drop in speed leads to huge energy savings.
Systems are designed to handle a defined maximum load. In the case of a pump system, for example, a certain pressure must be maintained even when all the consumers are using liquid at the same time. In fact this maximum load situation occurs rarely, and the system is throttled down to actual needs. Using a drive to control the process significantly reduces the energy required at part loads. If the process needs are at 90% of maximum, which is a relatively small drop, the energy required will fall to 73%, a significant reduction.
Similar but smaller savings are possible with other types of loads. In a compressor, for example, the power requirement drops linearly with the speed, so a 90% load means a 90% power requirement. Optimizing a process also offers considerable potential for savings for example cooling needs can be reduced by controlling the flow of material though the process.
In smaller, stand alone systems, such as ships and oil rigs, the use of AC drives saves a substantial amount of primary energy, for example diesel fuel. Since AC drives use only active power, the generators do not need to produce reactive power, which means a smaller load on them. Replacing hydraulic control systems with AC drives can reduce fuel consumption by tens of percentage points.
Lower energy consumption, lower CO2 emissions
The energy saved is multiplied through the entire distribution chain lower energy usage means lower losses in transmission and distribution of electricity, which in its turn means that the power plants are not as heavily loaded. These savings translate directly into less CO2 emissions - in Europe about 400 g of CO2 per kWh of electricity generated, in the US - due to a higher proportion of coal fired power plants about 700 g/kWh. To put things into perspective cars emit about 100 250 g of CO2 per kilometre driven.
Industry and the civil engineering sector have genuine savings potential. Seeing that so much of the electricity generated is used by motors in various applications, it pays to optimize the efficiency of the electric motor systems in use by installing drives with high efficiency motors.
Published in Vacon "Driven" Customer Magazine 2/2007
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