Feature Drives & motors
Vic Harris of ERIKS considers how the costly and damaging effects of poorly scheduled maintenance programmes on modern DC, AC and servo drives can be avoided with minimum downtime
Extending life expectancy W
hen maintained effectively and correctly, most modern DC, AC and servo drives used in industrial applica- tions can have a life expectancy of around 40,000 hours, or five years of continuous operation. However, these figures may drop by as much as half where environmental factors such as excess heat due to poor ventilation occur.
When drive failures occur replace- ment can be costly in both time and money, especially where new technology has to be integrated into an older production system.
A cost-effective alternative to replacement is to upgrade or retrofit existing units with effective repair and maintenance that will extend the life and efficiency of the drives.
Causes of premature failure Moisture, heat, dust and other air- borne pollutants present in many operating environments can all make a huge difference to the life expectancy of servo drive components such as fans and circuit boards. For example, high levels of localised dust and other airborne pollutants drawn through the cooling vents of the drive casing can cause dirt to build-up around the fan unit and fan motor shaft, leading to premature malfunction or failure. If the fan stops, other drive compo- nents such as electrolytic capacitors
Heat caused by lack of airflow within poorly
ventilated cabinets or through accumulation of dust can
drastically reduce drive life
will overheat and eventually fail. Excess dust in the atmosphere is also a serious safety issue and in certain situations can create a flammable environment. Conversely, dust attracts moisture which can contribute to the failure of electronic circuits. Additionally, heat caused by lack of airflow within poorly ventilated cabinets or through accumulation of dust can also drastically reduce drive life, allowing internal temperatures to remain high for extended periods, putting components under duress. The graphs (left) represent the temper- ature changes inside two drive cabinets as measured by ERIKS to help prevent future failure.
Over the course of time, mechanical vibration and heat cycles can also lead to faulty power connections resulting in electrical arcing that, in some cases, will cause catastrophic component or drive failure with the risk of personal injury.
When to repair or replace It is inevitable that at some point drive components will fail, either due to the causes listed above or simply through natural degradation. But with good maintenance practices and appropri- ate repairs, the life expectancy of drives can be more than doubled and simple repairs can be a fraction of the cost of a new unit. It is, however, important to know when it is and isn't economical to repair rather than replace an existing unit.
The break point for an economical Design Solutions 1971-2011 OCTOBER 2011
repair of a standard AC drive is typically between 4.0 and 5.5kW, and above this point the cost of overhaul- ing an existing unit can be up to half the amount of purchasing a new unit. For smaller low cost units which are often commodity products it is gener- ally more economical to replace the complete unit with a new device; at the other extreme, much larger drives tend to be modular in construction, so complete modules can easily be swapped and are frequently covered by third party maintenance contracts. A similar situation applies with servo drives, although as servos tend to command higher prices the break point at the lower end of the scale is slightly lower.
It is worth noting that, unlike fitting a replacement unit, a drive repair can also allow the root cause of failure to be identified, especially if the problem lies outside the drive unit. This makes it possible to avoid recurring and unidentified faults, thereby saving considerable time and expense. A final benefit of repairs is that they can result in improved drive performance and functionality though the use of newer components or upgrades to software.
Minimising downtime
Drive maintenance need not be ardu- ous. Regularly planned inspections to check for hot spots, dust build-up or even moisture and condensation on components such as circuit boards, are easy to carry out and will prolong the life of the servo device and improve machine uptime. Basic ventilation faults can also be quickly remedied to improve airflow and lower ambient temperatures. This can coincide with a planned shutdown for other routine maintenance to minimise downtime.
Condition monitoring
Condition monitoring using simple hand held vibration, thermal or ultra- sonic analysers can play an important role in determining when a drive is likely to fail. This can easily be carried out without taking devices offline and when used in conjunction with a planned approach to drive repair will reduce maintenance and capital costs and help to save energy to give a more sustainable approach. ERIKS UK T: 0121 508 6219
www.eriks.co.uk
Enter 236 31
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88 |
Page 89 |
Page 90 |
Page 91 |
Page 92 |
Page 93 |
Page 94 |
Page 95 |
Page 96