An inferior power grid quality along with the growing use of sensitive electronics has led to increased downtimes. There is a competitive advantage to be had where the production process runs smoothly even when the grid quality is deficient. Special attention should therefore be paid to the power supply, which is the core of any installation. In this way, unexpected costs due to voltage drops can be avoided in advance.
Voltage interruptions affect the production process: they lead to loss of data as well as a breakdown of the control system, resulting in expensive damage to equipment and the product when a machine restarts automatically. The effects of the damage caused by poor grid qualities depends on how sensitive the equipment is. Even short downtimes can lead to high costs. The VW factory in Wolfsburg can manufacture 2200 Golf A5 cars a day. If the system breaks down for even half an hour, the daily production is affected to such an extent that it is not possible to make up for the loss even at full production capacity. In such cases, investment in uninterruptible power supplies (UPS) pays off in a very short time.
According to the study 'Distributed and Cogeneration', conducted by the American market research firm Darnell, it is estimated that power failures and fluctuations in the US result in losses of 12 to 26 bn US dollars each year.
Reliability of power supply
Plant operators all over the world are faced with unstable grids that necessitate the use of power supplies with a high failure bridging time, buffer modules or uninterruptible power supplies. Even with a high supply security, the quality of power supply is gaining increasing importance, even in Germany, which has a quoted availability of 99,99% for high and medium voltage grids. This is very good compared with international standards, however, power failures cannot be ruled out. According to breakdown statistics compiled by VDN, there were over 12 000 breakdowns in the medium voltage grids in 2001 due to weather conditions, short circuits, line interruptions or technical failures. Almost half of these breakdowns led to interruptions in power supply. From 1997 to 2001, 3167 failures were recorded in the 110 kV grid, of which 982 led to power breakdowns with an average duration of half an hour.
The liberalisation of the electricity markets has increased the cost pressure on network operators. Longer maintenance intervals are a direct outcome of this cost pressure. This in turn will lead to deterioration in grid quality in the near future. At the same time, with the growing use of sensitive electronics, the industry buyer of electricity is becoming increasingly quality conscious.
According to the 'Study of reliable operation of 110 kV and 20 kV grids in North West Lower Saxony' by the University of Applied Sciences in Wilhelmshaven, the liberalisation of the electricity markets is expected to lead to a decline in the reliability of supply: 'Causes include the higher level of supply reliability as compared to international standards and declining willingness to invest because of price competition in the electricity market'. Darnell consequently predicts significant growth in uninterruptible power supplies because 'big companies are beginning to notice the costs incurred due to downtimes.'
DC-UPS versus AC-UPS
If high security requirements decide in favour of an uninterruptible power supply, both DC and AC devices are available. An AC-UPS is recommended if the connected device requires an alternating current, for example in IT systems. DC-UPS systems are suitable in industrial applications requiring the usual direct voltage of 24 V. They are comparatively economical as well as more compact and ensure a higher degree of efficiency. The DC-UPS also enables an easy connection between the battery and the device.
Comprehensive range increases system availability
Phoenix Contact offers a complete product concept for a more reliable power supply: all power supplies of its Step, Mini and Quint models offer a power failure bridging time of more than 20 ms under full load.
The Quint Buffer modules store the power required in maintenance-free capacitors. These require a power failure bridging time of 200 ms at a power supply of 20 A. If the power requirement is less, the time increases proportionately. According to statistics, this economical solution already captures 80% of all errors in the supply voltage, is compact and can be connected easily.
In case of high currents, the Quint DC-UPS provides long buffer times with long-life lead-acid storage batteries. Various solutions are available depending on the requirements. The model with a 10 A output current for 1,5 min includes a 1,3 A.h battery. The 20 A and 40 A devices can be combined with 3,4 A.h, 7,2 A.h and 12 A.h battery modules as desired. When the current requirement is low, the buffer time is up to 3 h. They are especially suitable for an uninterrupted supply to control units, machines and systems with high downtime costs or those where the downtime could damage expensive products and equipment.
The currently available solutions are generally too big for the DIN rails and difficult to wire. Phoenix Contact thus developed UPS modules whose uniform and small design minimises the space required for the mounting rails and ensures neatness with short wiring routes.
The current limiting signal output is so far a unique feature, which does not lead to high currents in the case of a faulty connection and so prevents the welding of relay contacts. In this way, an appropriate signal is always displayed.
Owing to the decoupled input, the devices connected to the buffer module or to the UPS can be divided into buffered and unbuffered loads. As a result, the buffer time, which depends on the output current, increases.
Conclusion
Minimum downtimes offer a definite competitive advantage. Phoenix Contact offers a comprehensive product range for a reliable power supply that enables individual solutions for a smooth production process.
For more information contact Duncan Venter, Phoenix Contact, +27 (0)11 793 7121, duncanv@phoenixcontact.co.za
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