COMPARISON OF HOT STAND-BY AND PARALLEL REDUNDANCY Hot Standby This is generally a solution used with older technology. It works very well and comprises of one UPS (standby unit) connected in the static bypass of another unit (main unit). This means that the main unit carries the entire critical load continuously and only if something is wrong will it switch to bypass. At that instant, the standby unit experiences its first taste of load at a 100% load step. This is not ideal although if the unit is suitably rated in the first place it should handle the situation. Also, the hot standby configuration means that the main unit is doing all the work all the time and as a consequence its MTBF factors will be higher than the standby unit that is doing nothing for 99% of its life. Disadvantages of the Hot Standby configuration · It is an old technology solution. · Load is completely dependent on the reliability of the Primary units static bypass (this is effectively the single point of failure · Secondary unit is idle for 99% of its life so MTBF on primary unit is much lower than that of the secondary unit · If secondary unit is called on, it experiences a 100% load step as it takes over from the primary unit, which can severely stress components. · Battery 1 does all the “backing up” and consequently lasts for less time whilst battery 2 does not get “cycled” which also has a detrimental effect on its eventual performance True Parallel Redundant configuration. Here, two units, each rated at the actual maximum load rating are connected so that they share the output load all the time. Their actual running load is therefore less than 50 % at all times which means that the units are running well within their design parameters and their combined MTBF will be exponentially lower !!! If one unit does go faulty or requires attention the other unit only experiences about a 30 to 50 % load step (Not an 80 - 100% load step) and the transfer is absolutely seamless. Downside here is that the technology is understandably slightly more costly but the protection capability is twice as good. Hope this info is of some assistance. Advantages of a true parallel system · There is no single point of failure. · The system is ten times more reliable than hot standby · The two UPS’s share the load equally (within 5% for dynamic loads) at all times. · Both batteries support the critical load at all times, and the back-up time is effectively doubled. · If either UPS fails or does need attention, then the other immediately assumes the full load with no frequency or amplitude complications that would otherwise negatively affect the load. The MTBF (mean time between failure) of both units is substantially increased as the units are effectively operating at half load or less.
Posted on: Fri, 24 Oct 2014 18:18:16 +0000
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