The concept of reliability became important in the
mid-1940s when the complexity of systems began to increase rapidly as the
electronic content grew. The development of advanced weapons systems and the
early work on electronic computers stimulated the study of reliability. More
recently, with the application of complex electrical and electronic systems
in the telecommunications, nuclear and space industries, a complete new
science of reliability has emerged.
The reliability expectations of power distribution
systems have increased because of the critical nature of some of the systems
supplied and the high costs associated with failures. For example loss of
power to an air traffic control installation or a medical system could be
life threatening and it is common for such sites to have a standby supply of
some sort. Power loss to a computer data processing system can incur high
costs due to loss of data and long recovery periods. The larger the computer
system, the longer will be the recovery period after a power supply
disruption and, for some of the larger installations, this can be 7 hours or
more.
Data processing installations are now extremely
important to commerce and industry and consequently feature strongly in the
examples and illustrations given here. This is not meant to imply that they
are the only important types of installation; production processes are also
badly affected by power failure resulting in waste of raw materials, lost
production time and wage costs. However, since computer systems are now
central to almost every enterprise, they are used as an example to which
most managers and engineers will easily relate.
Computer systems are notoriously sensitive to poor
quality mains supplies and the Electric Data Processing (EDP) supply
specification is much tighter than any mains supply specification.
Tolerances for durations of less than 10ms are typically: -
| Voltage |
± 5% |
|
| Frequency |
50Hz ± 1% |
i.e. 49.5 to
50.5Hz |
For personal computer systems the requirements are:
-
| No deviation or
break |
> 15ms |
| Spike free |
> 1kV |
| Total harmonic
voltage distortion |
< 10% |
| Voltage, steady
state |
± 1% |
| Frequency, dynamic |
± 1% |
| Slew rate (Rate of
change of frequency) |
< 0.5Hz/s |
| Neutral-earth
potential difference |
< 5V |
No electricity supplier could provide a public
supply meeting these specifications at an economic price level, so the user
must install suitable power conditioning and distribution equipment to
provide the required level of security. Of course, the extra equipment will
contribute an unreliability of its own which must be taken into account.
We have more than 10 years experience in improving
customer's site electricity reliabilities. We offer wide varieties of
equipment starting from Servo-control Autotransformer Power Conditioner for
industrial application to sophisticated Un-interruptible Power Supply for
delicate computer system
