Oper A T In G Tim - Hitachi H20-T Technical Notes

(i) t h e iron core of t h e electr om a gn et is da m a ged by a st r on g sh ock, a n d th e fat igu e of molded par ts a n d pr essed
p a r t s becom es gr ea t er , wit h t h e r es u lt t h a t t h e m ech a n ica l en d u r a n ce of t h e con t a ct or is s h or t en ed by
a pproxima t ely 50%.
(ii) th e con ta ct incr easin gly ju mps du e t o t he str on g sh ock a n d t h ere is a possibilit y of a bn or m al wear an d
con t act weldin g du e t o ma kin g a nd br eak in g of st ar t in g cur r en t of t h e mot or .
(2) Wh er e t h e power sou r ce volt a ge is lower t h a n t he r a t ed volt a ge
Wh en t h e power sou rce volta ge is low, it nea rs t h e closin g volt a ge (lower t ha n 85% of t he r a ted volt a ge) of t h e con-
t a ctor. As a r esu lt, a ca se occur s wher ein t h e elect r om agn et is n ot at tr a cted t o t he fu llest ext en t beca use of va ria t ion
of volt a ge, volt a ge dr op du e t o r ush cu rr en t of coil, a nd t h e lik e, so t h a t t he con t act flut t ers a n d t r ou bles ma y be
ca u sed in clu din g a bn or m a l con t a ct wea r a n d con t a ct weldin g, or bu r n in g of coil (beca u se t h e r u sh cu r r en t of coil
flows for a lon g t im e).
Mor eover, t h e mot or m a y in cur fa ilur es su ch as bu r n in g cau sed by cont in u ous flow of st a r tin g cu r ren t.
Th e st ar t in g cu r ren t of t h e m ot or ca u ses volt a ge dr op if t he wir e of t h e m a in cir cu it is lon g or fine, so t h e volt age of
coil becom es lower t h a n 85% of t h e r a t ed volt a ge, a n d t h e sam e ph en om en on as a bove m a y t a k e pla ce ; a t ten t ion
sh ou ld be pa id t o t h is poin t. Th e ca uses of volt a ge drop of power sou r ce a t closin g ar e sh own in Table 11 , so t h a t
t h ey sh ou ld be in vest igat ed a nd m easu res a ga inst t hem t ak en.
Cla ss
Ma in cir cu it
Oper a tin g cir cu it
P ower sour ce
2-3-2 Oper at in g Tim e
Cit ed below a re t he items to wh ich a t ten t ion shou ld be pa id when h a ndlin g th e closin g a n d r eleasin g t imes of t h e
con t act or .
(1) Closin g a n d r eleasin g t im e
Th e closin g a n d r eleasin g tim es of t h e cont a ct or va r y from 10 to 50 ms as sh own in t h e ca t a log. Th is is du e to t h e
ph a se a nd valu e of volta ge applied to t h e coil a nd t h e frict ion of t h e mech a n ica l section . E xam ples of t hese var iat ions
a r e as shown in F ig. 14.
Wh er e it is not desir ed t h a t two elect rica l sign a ls a re sequ en t ially la pped, t he cont a ct or is pla ced in t h e ot h er cir cu it
t o crea t e a t im e la g. However, t h is tim e la g is not a st rict t im e differen ce, but on e wh ich is used as a ppr opr iat e wh en
a n a pproxim at e t im e la g is wa n ted.
Wh ile, if t his closin g or releasin g t im e is used in pla ce of a t im er t o get t h e a ccu r at e t im e la g, n o degr ee of a ccu r a cy
ca n be expect ed beca u se of t h e a bove-m en t ion ed va r ia t ion fr om 10 t o 50 m s. At t en t ion , t h er efor e, sh ou ld be pa id
t o t h is point .
Ta ble 11. Ca uses of volt a ge dr op of coil power sou rce
･ Th e wir e of m a in cir cu it is fin e, so t h e volt a ge is dr opped by t h e st a r tin g cu r ren t
of t h e mot or .
･ Th e wir e of m a in cir cu it is lon g, so t he volt a ge is dr opped by t h e st ar t in g cur r ent
of t h e mot or .
･ Th e wir e of oper a t in g cir cu it is fin e, so t h e volt a ge is dr opped by t he r u sh cur r ent
of t h e coil.
･ Th e wir e of oper a t in g cir cu it is lon g, so t he volt a ge is dr opped by t he r u sh cur r ent
of t h e coil.
･ Th e capa cit y of power sour ce tr a n sfor mer for opera t in g cir cu it is shor t, so th e
volt a ge is dr opped by t he r u sh cur r en t of t he coil.
･ Th e volt a ge r egu lat ion of power sou r ce is la r ge.
Ca u ses
14