Static
Switch Application Overview
Power distribution reliability comes down to
having two sources of power. The two sources can be utility and battery as in a
UPS, utility and generator, dual utility feeds into a building or dual UPS
systems in a facility. The last two examples can benefit by the use of a static
switch to allow transfer of power to the critical load from either source. The
transfer is designed to take place in .004 seconds which is quick enough to be
invisible to sensitive electronic and computer load.
Success in application of static switches
depends upon 1) the quality of the static switch, 2) the reliability of the two
sources feeding the UPS and 3) the independence of the two sources from each
other, if the two sources are totally independent.
If the two sources are totally independent
sources, i.e. dual utility feeds from separate utility companies, in different
geographical areas and different transmission routes and each were 98% reliable,
the resulting reliability of power to the critical load would be 99.96%. If the
source loads are 99.5% reliable and independent, the resulting critical load
reliability would be 99.997%. The latter would be a reduction from 43.8 hours
per year to 15.7 minutes per year. The use of two independent UPS systems as the
source where each were 99.99% reliable (four 9s) would mean the load reliability
becomes 99.999999% reliability (eight 9s). Four 9s is less than one hour per
year without power, eight 9s is 0.5 seconds per year without power. Equipment
reliability has been utilized at 100% in this analysis so figures will reduce.
However the point is that static switches can greatly increase the theoretical
reliability numbers.
To satisfy the needs of our customers, we offer the PDI static switch product. PDI is the
manufacturer that developed the static switch into the high integrity and
reliability product configurations. Multiple firsts have come from PDI,
including being the first to develop the static switch and obtain UL listing as a static
switch (others were labeled but surprisingly not as static switches) and for significant factory testing and customer witnessing of testing at
their Virginia factory.
Efficiency of static switches versus
traditional UPS can result in significant operational cost savings. A load of
800 amps at power factor of 0.8, electric rate of 8 cents per kw-hr and air
conditioning cost of 1.23 kw per ton results in a five year savings of $212,000 using static
switches . Efficiencies used are 99% for the static switch and 92%
for the UPS.