GEK-49848A
CONSTRUCT I ON
The JB C rel ays co n s i st of a di recti o n al uni t, a TOC ( ti me o vercurrent) uni t, a
cup type I OC (i ns tantaneous o vercurrent ) un i t and two tar get s eal - i n un i ts mounted
i n a l ar ge doubl e-ended drawo ut ( L2 ) case . A DC o perated auxi l i ary tel e phone rel ay
un i t and an add i ti onal I OC un i t ( h i nged armature type ) are added to certai n model s
as s hown by aste ri sk notes i n Ta bl e 1.
The d i recti onal un i t i s mounted a t t he bottom o f the c a s e, the TOC un i t i n the
m i d dl e, and the cup type IOC uni t i n the top .
D I RE CT I ONAL UNIT
The d i recti onal un i t i s o f the i nducti on- cyl i nder cons tructi on wi th a l am i nated
s tator havi ng ei ght pol es projecti n g i nward and arran ged symmetri c al l y around a
stati onary central core . The cupl i ke al umi num i nducti on rotor i s free to o perate i n
the annul ar ai r ga p between the pol es and the core .
The pol es are fi tted
al terna tel y wi th current o perat i ng co i l s and potenti al pol ar i zi ng co i l s .
The pri n ci pl e by w h i c h torque i s devel o ped i s the s ame as that of a n i nducti on
d i sk rel ay wi th a watt- metri c el ement, al though, i n arran gemen t of pa rts, the un i t
i s more l i ke a s pl i t- ph ase i nduc ti on moto r .
The i nducti o n-cyl i nder co nstructi o n
pro v i de s h i gher torque and l ower rotor i nert i a than the i nducti on-di sk cons tructi on,
resul ti n g i n a fas ter and more s e n s i ti ve rel ay .
LOW GRADI ENT CONTACT
The d i recti onal un i t contacts ( l eft front ) , w h i ch control t he t i me
o vercurrent uni t are s hown i n Fi g . 1 9.
They are of the
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ow gra di ent type
s peci al l y cons tructed to m i n i m i ze the e ffects o f v i brati on .
Bot h the
stati onary and mo vi ng co nta ct brus hes are made of
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ow gra di ent mate ri al whi ch,
when s ubjected to v i bra t i on, tend to fol l ow one another, hen ce, t hey re s i st
conta ct se parati on .
The contact d i al ( A) s upports the s tati onary contact brus h ( B ) on whi ch i s
mounted a co n i c al co nta ct ti p ( C ) .
The mo vi ng co nta ct a rm ( D ) supports the
movi ng contact brus h ( E) on whi ch i s mounted a butto n contact ti p ( F) . The end
of the movi ng contact brus h bears a ga i nst t he i nner face o f the mov i ng contact
brush reta i ner (G) . Si m i l arl y, the. end of the s ta ti on ary co ntact brush bea rs
a ga i nst the i nner face o f the s tati onary contact brus h retai ner
(H).
The
s ta ti onary conta ct support ( K ) and the co nta ct di al are ass em bl ed to gether by
means o f a mounti ng s crew ( L) a n d two l ockn uts ( M ) .
BARREL CONTACT
The
d i recti onal
un i t contacts
( ri gh t
rear ),
whi ch control
the
i nstantaneous o vercurrent uni t, a re s hown i n Fi g . 2 0 .
They are s peci al l y
constructed to suppress bo un c i ng .
The stati onary contact ( G ) i s mounted o n a
fl at s pi ral s pri ng ( F) backed up by a thi n di a phra gm ( C ) .
Th ese are both
mounted i n a s l i gh tl y i ncl i ned tube ( A) . A stai nl ess steel bal l (B) i s pl aced
i n the tube befo re the d i a phra gm i s a s s embl ed .
When the mo v i n g co ntact hi ts
the s tati onary contact, the energy o f the former i s i mparted to the
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atter and
thence to the bal l , whi c h i s free to rol l up the i n cl i ned tube . Thus, the
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