ENERGY EFFICIENCY FEATURE Time for a practical approach
Murrelektronik offer some insight into how to improve energy efficiency within the industrial sector, at a time when it is becoming increasingly vital
Left: in every automation solution the power supply system is the core of the control cabinet. It consists of an electronic power supply and secondary protection. There are already switch mode power supplies available that are 95% energy efficient and that do not only feature low heat dissipation, but also a very compact design
E
nergy efficient machines and systems are a key challenge for industry today, and one that is something of a double- edged sword. On the one hand, to be energy efficient means more competitive advantages and process optimisation, while on the other hand it means time consuming analysis and implementation. Cutting ever increasing energy costs is surely the primary motivation of a manufacturing company for using energy efficient machines. However, when taking a closer look, there are even more positive effects for operators and machine builders. The power supply system in every automation solution is the core of the control cabinet. It consists of an electronic power supply and secondary protection. There are already switch mode power supplies available that are 95% energy efficient and that not only feature low heat dissipation, but also a very compact design. The Emparro from Murrelektronik is one of these new, efficient power supply units, available with output voltages of 12V / 24V / 48V and currents of 5-20A. Additionally, these units feature a power boost of 50% of the nominal voltage for four seconds to start-up units that need a lot of power when they are started.
A POSITIVE IMPACT Although this doesn’t solve all problems, components with these features also have a direct effect on the cabinet design - because less heat dissipation has a positive impact on the life of all cabinet components. The less space required in a cabinet, the smaller it can be. A smaller cabinet and a smaller air handling unit already have a positive effect on the total costs in the machine builder’s calculation and the end user will profit from lower maintenance costs and the need for a
less precious production area. Therefore, the saying ‘a penny saved is a penny earned’ gets more important for energy efficiency and most of all for the competitiveness of our industry. When reflecting upon energy in automation technology, often only the major key elements are taken into account such as power supply units, drive controls and peripheral devices, like motors. However, who so far, has thought about energy efficiency when it comes to the protection of 24V DC circuits?
APPLICATIONS A typical application consists of a power supply with 10A up to 20A output current and three up to six secondary fuses in the form of circuit breakers or electronic safety modules such as Murrelektronik’s MICO family. If circuit breakers are used as secondary protection, an unnecessary amount of energy is used and additional heat is lost. The reason is the high internal resistance of the circuit breakers. Compared to an electronic protection such as MICO, the internal resistance can be up to 40 times higher with circuit breakers, depending on the current range. To a technician who still uses circuit breakers, you could say, ‘you win some you lose some’. Our subject, however, is energy efficiency and therefore, we want to save energy in the power supply system and in the protection. Each machine builder and electrical
engineer who has already realised the problems caused when circuit breakers do not trigger and who uses electronic protection such as MICO, now has an additional benefit regarding energy efficiency of their system. Electronic power supplies have a defined short circuit and overload behaviour that
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protects the devices from short circuits. However, they also prevent there being enough high current available to trigger the circuit breaker in the event of a failure. Or more precisely, the loop resistance (current circuit from the power supply - protection - cable to the load - cable back to the current source) prevents that any amount of short circuit current flows. Therefore, circuit breakers can only offer very limited safety or no safety at all. For example, they do not work with cross sections below 0.75mm and currents below 10A. Therefore, those who haven’t yet had the opportunity to make their installation short circuit and overload protected, and energy efficient, should immediately switch over to electronic protection. This will increase availability and make the system more service friendly at the same time.
SPECIAL FEATURES As a special and energy efficient feature, MICO+ safety modules offer a standby function for current paths that are not used all the time. This is a very convenient feature, for example, to switch off peripheral devices that are currently not used in the production process. These paths can be conveniently deactivated via a 24V DC input and immediately switched on when required, while important components like the control are continuously supplied by the same module. Another challenge for the power supply is the often high inrush current, caused when several electronic components are switched on simultaneously. MICO solves this problem with energy management of the individual current paths. This does not only actively prevent overload in the power supply when the machine is started, but also a smaller power supply can be used. In the end, it’s worth it to pay attention
when selecting the components. Sometimes the most important ones are the ones you can’t see. One of the benefits of this power supply concept is that it is not only interesting for new systems, but it can be easily and quickly integrated into already existing systems. All of these options show there are
many ways to improve energy efficiency in machine tools and systems - not only for new systems but also for existing ones. It also clearly shows how easily they can be implemented.
Murrelektronik
www.murrelektronik.uk T: 0161 7283 133
Enter 215 ELECTRICAL ENGINEERING | NOVEMBER 2014 29
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