Ups System Component That May Fail

Ups System Component That May Fail



UPS Systems – Components That May Fail
Maintenance
An uninterruptible power supply is​ a​ complex electronic device with a​ number of​ components that deteriorate with age and​ use .​
It is​ therefore in​ the​ client's interest to​ have regular maintenance carried out on the​ UPS to​ ensure that it​ is​ working correctly and​ that the​ components that are known to​ deteriorate with age and​ use are monitored.
On analogue designed UPS systems it​ is​ necessary to​ regularly monitor and​ adjust the​ operating parameters of​ the​ control circuitry to​ ensure that the​ UPS is​ operating in​ its most efficient mode .​
With the​ digital designed UPS systems there are fewer adjustments to​ be made as; unlike their analogue counterpart the​ circuits do not alter with the​ aging of​ their components .​
However, in​ addition to​ the​ batteries and​ fans there are a​ number of​ components in​ the​ power circuits that need to​ be monitored and​ replaced on a​ regular basis .​
a​ Maintenance contract with a​ reputable company specializing in​ power protection is​ strongly advised especially when you may require 24-7 callout 365 days of​ the​ year.
All the​ components mentioned here have a​ recognised design life dependent upon their operating conditions .​
Normal operating conditions would assume that the​ UPS and​ its battery is​ installed in​ a​ clean, dry environment with a​ constant ambient temperature not exceeding 20 ? C .​
Also it​ is​ generally accepted that it​ is​ more prudent to​ operate the​ UPS at​ a​ load not exceeding 80% of​ its kW rating.
Batteries
Battery life, it​ should be noted that UPS systems generally use the​ sealed valve regulated lead acid battery, is​ determined by the​ manufacturer and​ is​ generally quoted with the​ expectation that the​ battery will be operated in​ an​ ambient temperature of​ 20C and​ not exceeding 25C .​
The design life of​ the​ battery by the​ manufacturer will be quoted in​ terms of​ 3-5 year life or​ 7-10 year life, in​ exceptional cases it​ can be as​ much as​ 10-12 years .​
The lower figure quoted normally takes into account both the​ ac ripple on the​ dc charging current of​ larger UPS systems and​ also the​ fact that on smaller systems the​ battery has less airflow round it.
It is​ possible to​ monitor the​ life of​ the​ battery by carrying out a​ regular (every six to​ twelve months) controlled battery discharge, checking each bloc on float (normal operation) and​ after a​ set discharge time .​
This can identify any blocs that may be prematurely failing, equally, as​ a​ matter of​ ‘good practice', one should not patch a​ 3-5 year life battery string on year 3 as​ the​ new bloc will tend to​ cause further problems.
An alternative method of​ monitoring batteries is​ to​ carry out impedance testing and​ monitor the​ figures over a​ period of​ time against the​ recommended values set by the​ battery manufacturer.
During the​ course of​ its life the​ valve regulated sealed lead acid battery will give up hydrogen due to​ the​ chemical activity experienced by; discharges (controlled and​ mains failures) and​ the​ ripple current supplied by many UPS systems on the​ dc bus .​
This hydrogen is​ irreplaceable and​ as​ a​ result over a​ period of​ time the​ AH that the​ bloc can support falls, if​ the​ battery is​ continually used beyond its design life the​ risk of​ fire can become very real .​
This is​ due to​ the​ fact that the​ battery can no longer support the​ current demand generated by its internal chemical reaction and​ will overheat; possibly entering a​ thermal runaway situation where the​ chemical reaction cannot be stopped with the​ result of​ uncontrolled fire.
When the​ time arrives for​ replacement of​ batteries, use a​ company that will both remove the​ batteries and​ replace them at​ the​ same time, to​ avoid any disputation to​ your mission critical load.
Fans
generally these have an​ operating life of​ 3 – 5 years dependent upon the​ manufacture .​
These fans are used for​ cooling the​ heat sinks of​ the​ power components as​ well as​ extracting excessive heat from the​ wound components such as​ transformers from the​ enclosure .​
Any failure will cause a​ rapid increase in​ temperature resulting in​ the​ inverter or​ rectifier/charger switching off due to​ the​ over temperature alarm and​ the​ load transferring to​ the​ utility mains (reserve supply) via the​ static switch .​
The load will now be unprotected from any utility mains fluctuations.
Some UPS manufacturers will build fan redundancy into the​ design of​ their uninterruptible power supplies, providing indication of​ the​ fan failure without compromising the​ load due to​ inverter shut down .​
a​ regular replacement routine during maintenance visits will allow this work to​ be carried out under controlled conditions rather than waiting for​ failure and​ the​ resulting loss in​ the​ protection of​ the​ load.
DC Capacitors; as​ mentioned above they have a​ smoothing effect on the​ battery charging current, also they provide a​ reservoir of​ instantaneous power for​ the​ inverter switching devices (thyristors, transistors or​ IGBT's) .​
With time they become less effective and​ two things can occur; one is​ that the​ battery ripple current increases, the​ other is​ that the​ inverter can fail to​ operate under load as​ it​ cannot derive sufficient current from the​ rectifier/charger to​ supply the​ switched mode waveform that makes up the​ sinusoidal output waveform .​
In extreme cases the​ chemical reaction can become so fierce that the​ safety valves will open, in​ some cases just leaking, in​ others causing a​ fire .​
Interestingly enough the​ inverter will often transfer the​ load to​ reserve without interruption, of​ course there is​ the​ cost of​ the​ fire brigade's attendance and​ the​ refill costs of​ the​ extinguishant .​
The normal design life for​ dc capacitors is​ similar to​ the​ battery being approximately 5 years, this can be monitored by checking the​ ac ripple current during regular maintenance of​ your uninterruptible power supplies .
AC Capacitors; the​ ac capacitors act as​ a​ filter to​ ensure that the​ UPS output waveform is​ sinusoidal within a​ close tolerance, also they act as​ a​ reservoir for​ out of​ phase loads.
Again the​ capacitors are similar in​ some respects to​ the​ dc capacitors as​ to​ what damage they can cause if​ neglected .​
They should be checked on a​ regular basis similar to​ the​ dc capacitors, this time for​ balanced currents in​ the​ case of​ a​ three phase output UPS system, case temperature and​ ‘purity' of​ the​ ac output waveform .​
In the​ event of​ failure the​ result is​ more dramatic, not only do the​ fire brigade arrive on site but the​ load is​ also lost.
PowerContinuity Means Business Continuity
For further information regarding uninterruptible power supplies please visit our website at​ www.powercontinuity.co.uk




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