31
3-3-4 In chin g a nd Plu ggin g Oper at ion
Sin ce fr equ ent in chin g a nd plu ggin g oper a tions a ct u a te t h e t h erm a l over loa d r ela y, con t in uou s oper at ion becom es
im possible .
In or der t o a void t h is, t h e set t in g va lu e of cur r ent of t h e t h er m a l over load r ela y m a y be incr eased over t h e r at ed
cu r r en t of m ot or ; h owever , it is n ot advisable t o pr otect t he m ot or .
In t h e ca se of in chin g a nd plu ggin g oper at ion, t h e st art in g cu r r en t flows int erm it t ent ly a n d t he self-coolin g effect
of t h e coolin g fa n decrea ses. In t h is st a t e t h e t em per a t u r e r ise is differ ent fr om t h at of n orm a l oper at ion.
Ta k in g in t o consider at ion t h e a bove, in or der t o prot ect th e m ot or wh en ca r r yin g ou t in ch in g a n d plu ggin g opera t ion s,
it is m ost su it a ble t o prot ect t h e m ot or dir ect ly det ect in g t h e t em per a t ur e by in cor por a tin g t he t herm ist or in t he
m ot or win din g.
In t h e case of slip-r in g m ot or, t h e rot or m ust be pr ot ect ed fr om bu r nt -out . In a ddit ion t o t h e t h erm ist or in cor por at ed
in t h e st a t or windin g, t he t h erm a l over loa d r ela y sh ou ld be concu rr en tly used for rest r a in t pr ot ect ion, t h us ensu rin g
perfect pr ot ect ion.
3-3-5 Wher e St a rt in g Tim e is Lon g
F or t h e fa n, press m ach in e, et c. whose m ech a n ica l in ert ia (GD
2
) of load is gr eat , t h e sta r t in g t ime is lon g.
If t h e st a r t in g t im e is lon g, it is ver y difficu lt t o a ch ieve com pa t ibilit y of pr even tion fr om m a lfu n ct ion wit h pr ot ection
of m ot or , so t h a t for pr act ica l pur poses, su ch a m et h od is adopt ed t h a t t he pr ot ect ive per form a n ce at r est r ain t is
som ewh a t lower ed (sin ce t h e pr obabilit y of r est ra in t tr ou bles is low).
Th e followin g t able classifies t he gen er a l cou n term easu r es.
Ta ble 23. Gen er a l cou nt er m easu re
St a rt in g t im e
Applica ble t her m a l
over load r ela y
Con n ect ion
Mer it
Dem erit
Appr ox. 5 t o
15 sec.
Th er ma l over loa d r ela y
wit h sa t ur a tion r eact or
(P lease consu lt wit h us)
Sa m e as st a n dar d
Simple cir cu it
In bot h st a r t in g a n d
r u n n in g t im es, t h e
pr otect ive perfor m-
a n ce a t r estr a in t is
in sufficient .
15 sec. or
lon ger
St a nda r d th erm a l
over load r ela y
Tim er a nd con t a ctor
a r e addit ion a lly u sed.
Refer to F ig. 28.
Th e pr otect ion
du r in g oper at ion
is cert a in.
Th e rest r a int
pr ot ect ion a t
st ar t in g ca n be
ca r r ied ou t t o
som e ext ent by
ch a n gin g t h e
set t in g of t he
t ime .
Th e cir cu it is
com plica t ed.
Summary of Contents for H100C
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