Hitachi H20-T Technical Notes page 42

5-2-3 Con nection of Th er m al Over load Rela y wit h CT
Wh en CT side is V-conn ect ed, 2 set of CT can m ak e 3-ph ase pr otection . Th en, in order t o ensu re corr ect oper a t ion ,
m ak e wir in g a s sh own in F ig. 33 a n d F ig. 34 by pa yin g a tten t ion to t h e m oun t in g dir ect ion a nd polar it y.
F ig. 33 Con nection dia gr a m
A cu rr en t flows to t h e 3 hea ters of t h e t herm a l over loa d r ela y a t 3-ph ase overloa d.
E ven if ph a se fa ilur e occu rs, cur r ent flows t o t h e 2 h eat ers with ou t pha se fa ilur e, rega r dless of t h e in ser tion ph ase of
CT; th e sam e oper at ion is m a de as t h e 3-ph ase t herm a l over load r ela y n ot usin g CT.
Wh er e 3sets of CT ar e u sed, in dividu a l CT's ar e con nected t o t h e r espective hea t er s of t h e t h er ma l over loa d r ela y as
sh own in Fig. 37 a n d F ig. 38.
Th en , even if t he CT pola r it ies a r e a rr a n ged u n ifor m ly, prot ection ca n be ensu r ed.
F ig. 34 Mou nt in g of CT a n d wir in g
F ig. 35
F ig. 36
38