DRIVES & MOTORS FEATURE Developing an efficient drive train


One component that contributes significantly to the efficiency of the drive train is the variable speed drive. Paulo Krüger, european automation centre manager at WEG, explains


Typically, applications do not run at


full load 100% of the time, and this is especially true for variable torque applications like pumps and fans. Therefore, varying the speed of the drive by installing a VSD (variable speed drive) can help users save energy and money by controlling the speed of the process and adjusting it to the specific load at any time, compared with other techniques for flow control. Traditionally, physical barriers are


used to control the speed of flow, with one example being valves in pump applications and dampers in fan applications. However, on variable torque applications, such as a fan for airflow control, the motor normally operates at a fixed speed, meaning energy is being used. Two-thirds of the total electricity


Variable speed drives, like WEG’s CFW 501, can help towards energy efficiency


T


hree of the most important factors that designers need to consider when


setting up a drive chain are energy efficiency, reliability and total cost of ownership. However, motors today are responsible for generating over 40% of total global energy consumption. So, careful consideration of the choice of motor – taking into account new energy standards IE2 and IE3, and motors designed with efficiency as a priority – will help towards these goals by enabling considerable energy savings to be made. One example here is WEG’s W22 Super Premium, which exceeds the yet to be implemented IE4 regulations. There are, however, other steps that


The Super Premium range exceeds the yet to be implemented IE4 regulations


need to be taken. The most significant of these, especially in a fan or pump application, is the control of the motors. Optimising the motor using a variable speed drive or inverter enables energy savings of between typically 40% and 60% to be realised.


consumption in industry is used for driving electric motors. Of this, an estimated 20% is wasted in throttling mechanisms that are used to regulate the flow of air and liquids. Therefore, if the system requires varied airflow, then installing a variable-speed drive can save a lot of energy. Typically, the power requirement varies


as the cube of the speed. So if airflow requirements are only half the air volume, then the VSD can operate at half the output frequency – resulting in motor speed at a low 900 rpm. The resultant power requirement is only 1/8th of that required to operate at full speed.


CONSIDERATIONS To determine which VSD and drive solution will offer the most energy savings, a number of points will need to be considered. These include: when and how long the motor will be running for; the application; and the cost of energy. However, there is no ‘one-size fits all solution’, and this is where experts can


Applications do not typically run at full load all the time. By installing an inverter such as WEG’s new CFW500 drive, it is possible to save money by controlling the speed of a process and adjusting it to the specific load at any time. The CFW500 range, which is said to give exceptional performance for three-phase induction motor control, features state-of-the-art technology to deliver a high level of control, but at an affordable price. Robust, flexible and smart, this is available in power ratings from 0.18kW up to 22kW and is suitable for industrial automation applications including centrifugal and process pumps, fans, compressors and conveyors. Based on a modular plug and play design, these include a built-in micro-PLC which can be programmed according to standard protocol IEC 61131-3. The drives also come with pre-programmed macros for a range of applications, and users can simply program them using the LCD HMI display, or via a computer through a variety of interfaces. WEG’s WLP software for programming and monitoring is available free of charge.


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help by monitoring the application before and after a VSD has been fitted and reviewing the difference to calculate potential savings. In one example, the main extract fan


on an asphalt plant used a 110kW fan motor. After installing a VSD to slow the motor and control demand via an incorporated PLC, the power used per motor reduced from 104kW to 64kW and the electrical consumption halved. The overall return on investment of installing the VSD was less than 12 months. Another example was fans at a


university. A detailed site survey suggested it should be possible to slow the fans down by 20% without any impact on air quality or cooling capacity. The first phase comprised the fitting of 7.5kW inverters to six fan motors on HVAC systems. The variable speed drives chosen were specifically designed for integration into systems requiring variable speed control on pump and fan applications including HVAC. They have an integrated kWh measurement capability for energy consumption monitoring. In addition, they provide comprehensive protection for both the motors and inverters themselves against under/over-voltage, over temperature, earth faults, short circuits, motor thermal protection and stall prevention. Having achieved a reduction in running


speed of 20%, the energy consumption of the motors was reduced by 50%, resulting in an energy saving of some 30,500 kWh per motor per year, or £3,050. The total energy saving for the first phase of the project is an estimated £18,300 – giving a projected payback period of approximately six months.


ENERGY EFFICIENCY While each component in the energy chain on its own can contribute to increasing energy efficiency, reviewing the system as a whole will make the most significant impact. By understanding the motors, drives


and gearboxes, WEG can tailor the most suitable drive system to customer demands in order to provide the most energy efficient solution.


WEG www.weg.net/uk Enter 206


DESIGN SOLUTIONS | APRIL 2014 13


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