Why TVSS (MOV + Filter based technology) is required with UPS • Recen tly , there has been some conf usion regardin g the ‘Uni nterru ptib le Powe r Supp lies’ (UP S) role in transient protection. n fact, a UPS will not protect against the same types of disturbances as a !ransient "o ltage Surge Suppressor. (!"SS). Ty!ically !urchased to !ro"ide stand#by !ower to critical equi!$ent% a UPS will not !rotect against high energy transients& • #ften, manufacturers ad$ertise ha$ing surge protection integral to their UPS. n most cases, this built in protection consists of one or more Metal O'ide Va risto rs (MOVs) insta lled or the sole !ur!ose o!rotecting the sensiti"e control co$!onents within the UPS&%hile this does pro$ide some base le$el, &single shot protection', the electronic loads attached to the UPS are not properly protected. • ot only pro$iding lower clamping $oltages, the TVSS also has the ability to handle $ulti!le surges& nown as *ie ,ycle Surges-% the !"SS will clamp a minimum of ,*** surges without degrading. UPS $anuacturers do not !eror$ lie cycle testing& .. !he +#"s in the UPS are not rated nor tested for life e-pectancy. a$e a short life span. • !he only sol uti on to thi s pro ble m is to !ro"ide additional TVSS to the UPS syste$. !he nstitute of/lectrical and /lectronics /ngineers, nc. (/000) agrees with this solu tion& • !he following paragraph is ta0en directly out ///’s /merald boo0. * /t is reco$$ended !ractice that both the in!ut circuit to the UPS and the associated by!ass circuits (including the $anual by!ass circuit) be equi!!ed with eecti"e Transient V olta ge Surge Su!!ression (TVSS)& • !ypical UPS come e1uipped with either single or dual input terminals. For single in!ut syste$s it is only required to ha"e one TVSS on the line side othe UPS& 2ec ause dual in!ut syste$s consist otwo se!arate !ower sources%one that feeds the UPS and one that feeds the mainten ance bypas s circuit, it is required that two TVSS be utili1ed& (See 2iagra$ # 3 4 5) 33 !he +#"s do not protect the bypass line during transfer of static line. • 4iebert ta0es ///’s directi$e one5step further by also suggesting TVSS at the connected branch !anel% as shown in 2iagra$#6& igh5energy transien ts entering the electrical system through ser$ice entrance would be clamped at the UPS and then again at the branch !anelin order to pro$ide the best !rotection or the critical loads downstrea$& • The Metal O'ide Varistors (MOV7s) in the UPS ront end are unused and un$onitored. %e ne$er 0now when they failed unti l the UPS fails due to surg e prob lems . 6o u need a de"ice with !ro!er $onitoring o!tions either !hysical (02 indication) or so$e dry contacts& (7or 8udio 9 "isual indication) • The UPS is not tested to either /0, 83896#3 or isted to U399:#5 or insurance !ur!oses& 33 !he UPS is not considered as a lightning protection SP: for insurance purposes. ; TVSS and ightning arrestor are acce!table by the insurance underwriters& • !he !ransien ts ; oise created down stream of the UPS by any load are circulated to other down stream loads if no !"SS is placed in the last branch panel to pre$ent the circulation paths to other susceptible loads. • <eerences /nstitute o0lectrical 0ngineers% /nc& (3:::) /000 <eco$$ended Practice or Powering and =rounding 0lectronic 0qui!$ent&
