W O R K E R S
By J. V . ALFRIEND, JR.
General Engineer
Westinghouse Electric & Manufacturing Co.
East Pittsburgh, Pa.
s h o r t c irc u its o f 10,000 a n d 2 0 ,0 0 0 am p . o n 4 4 0 v o lts w ith o u t s e ttin g fire to a b s o rb e n t c o tto n w ith w h ic h th e case w a s w ra p p e d f o r th e e x p e rim e n t. T h e sw itc h is sh o w n in a n a c c o m p a n y in g illu stra tio n .
A n d th e f a th e r o f th e m all is th e ty p e U D e-io n c ir c u it b re a k e r. D iffe re n t in a p p e a ra n c e a n d c o n s tru c tio n
— th e sa m e in p rin c ip le o f a r c e x tin c tio n , th e se c irc u it b r e a k e rs o p e n p o w e r f a u lts o f 5 0 0,000 to 1,000,000 a r c k v a . in less th a n 3 cycles a f t e r th e o c c u rre n c e o f th e f a u lt. W i t h n o oil to th r o w d u r in g th e tre m e n d o u s e le c tric a l s tr e s s e s in v o lv e d th e re is n o p o ssib ility o f s e t
tin g fire to th e s ta tio n .
T h e n u m b e r o f e le c tro c u tio n s in chem ical p la n ts fro m o p e r a to rs a n d la b o re rs c o m in g in c o n ta c t w ith liv e c ir c u its is b e y o n d e s tim a tio n . T h is ty p e o f h a z a rd fa lls in to tw o c l a s s e s : A c c id e n ta l c o n ta c t w ith k n o w n live c irc u its ; a n d c o n ta c t w ith su p p o se d ly d e a d c irc u it.
T h e firs t fo rm o f h a z a r d is e n tire ly e lim in a te d b y th e u se o f “ d e a d f r o n t ” c o n tro l a n d sw itc h b o a rd s. A ll p o w e r c irc u its a r e b e h in d th e b o a rd — all o p e ra tin g h a n d le s a r e
“ d e a d .” N o t ev e n d e lib e ra te su ic id e is p o ssib le f r o m th e f r o n t o f th e b o a rd .
T h e s u p p o s e d ly d e a d c irc u it m a y be p ro te c te d a g a in s t b y o n e o f th e f o rm s o f m e ta l clad s w itc h g e a r k n o w n as
“ l i f t u p ” o r “ ro ll o u t.” I n th e f o rm e r th e c irc u it b r e a k e r is lo w e re d f r o m e n g a g e m e n t w ith s ta tio n a ry c o n ta c ts ( o n ly p o ssib le w ith th e c irc u it b r e a k e r in th e o p en p o s i
tio n ) a n d th e u n it re m o v e d f r o m its c o m p a rtm e n t w h e re it m a y be w o rk e d o n w ith all p o ssib le s a fe ty . N o one c a n clo se th e s e d is c o n n e c tin g sw itc h e s w h ile th e o p e r a to r is w o rk in g on th e b re a k e r f o r th e sw itc h e s a r e th e t e r m in a ls o f th e b re a k e r. T h e ro ll o u t e q u ip m e n t is sim i
la r e x c e p t th a t a s th e te rm im p lies th e m o v e m e n t o f th e u n it to d is e n g a g e th e s ta tio n a r y c o n ta c ts is h o riz o n ta l in s te a d o f v e rtic a l.
T h e lia b ility o f tr a n s f o r m e r fire s r e s u ltin g f ro m lig h tn in g d is tu rb a n c e s h a s re c e n tly b ee n re d u c e d to th e m in im u m by th e d e v e lo p m e n t o f th e s u r g e p r o o f t r a n s f o r m e r . T h is d e s ig n is c a p a b le o f w ith s ta n d in g d ire c t s tr o k e s o f lig h tn in g w ith o u t p u n c tu rin g th e in su la tio n .
I n th is d esig n th e in su la tio n o f th e w in d in g s is c o rre la te d w ith th e in su la tion o f th e te rm in a l b u sh in g o r w ith a special fo rm o f lig h tn in g a r r e s te r in th e tr a n s f o r m e r so th a t th e su rg e w ill ju m p a c ro ss th e te rm in a l b u sh in g to g ro u n d o r ac ro ss th e a r r e s te r b e
f o re it w ill p u n c tu re th e in su latio n . I n o r d e r to im p ro v e th e tr a n s f o r m e r in su la tio n to th is e x te n t cre ep ag e p a th s h ad p ra c tic a lly to be e lim in a te d b ecause s tra n g e a s it m a y seem in c re a se d c re ep ag e d istan c e does n o t in c re a se th e re sis ta n c e to s u rg e v o lt
a g e in a n y th in g like th e ra tio e n c o u n te re d in th e less ste ep w ave f ro n ts o f 6 0 cycle v oltages.
T h e m o st fo o l-p ro o f e q u ip m en t th a t th e m a n u fa c tu r e r can dev ise can be m a d e d e a th tra p s b y th o u g h tle ss o r ca rele ss in sta lla tio n . M a n y a co n tro l b o a rd h as been in stalled on th e ro ta tio n a l c e n te r-lin e o f th e d riv in g o r d riv e n e q u ip m e n t o r w h e re a b ro k e n belt m ig h t kill o r in ju r e th e o p e ra to r. O p e r a tin g a n d c o n tro l sta tio n s sh o u ld be placed in th e m o st se cu re o f p o sitio n s co n sid e rin g th e m echanical, electrical a n d fire h a z a rd . In o th e r w o rd s, th e c o n tro l e q u ip m e n t sh o u ld be located a t a place w h e re m en in d a n g e r w ill n a tu ra lly r u n to r a th e r th a n ru n fro m . T h is is m a d e p ossible only w ith
ABI De-ion switch has opened short circuits of 10,000 and 20,000 amp. on 440 volts without setting fire to ab
sorbent cotton with which the case was wrapped for the experiment
O cto b er, 1933 — C h em ical & M eta llu rg ica l E n gin eerin g 533
Adequate illum ination re
duces accidents. By installa
tion of a lighting control unit it may he maintained constant regardless of varia
tion in natural illumination
Gases escaping after an ex
plosion within this m otor in an oil refinery must escape through the bearings or through the ground metal fit of the brackets to the frame. The cooling thus ob
tained prevents ignition of the atmosphere outside of
the motor e le c tric a lly o p e ra te d d ev ice s su c h as c irc u it b r e a k e r s a n d
c o n ta c to rs . M a in c irc u its m u s t be k e p t clo se to th e e q u ip m e n t, b u t c o n tro l c irc u its f o r th e o p e ra tio n o f th e se d ev ice s m a y be c o n v e n ie n tly a n d ec o n o m ic a lly r u n al m o st a n y w h e re . T h e u se o f a m u ltip lic ity o f s to p s ta tio n s is m o st a d v a n ta g e o u s.
A fo o t- o r b o d y -o p e ra te d e m e rg e n c y s to p p u s h -b u tto n sh o u ld be lo c ate d a t a m a c h in e w h ic h is lia b le to e n ta n g le a n o p e r a to r ’s h a n d s . A se c o n d s to p s ta tio n sh o u ld b e clo se b y th e m a c h in e b u t s a fe f ro m it. A th ir d s to p s ta tio n sh o u ld be lo c a te d a t th e s u p e r v is o r ’s d e sk w h ich sh o u ld be p ro te c te d fro m th e o p e ra tin g ro o m by s a fe ty g la ss. H e r e also sh o u ld be lo c a te d a n e m e rg e n c y sw itc h to s h u t d o w n th e e n tir e p la n t.
E n t i r e C o n t r o l in S e p a r a t e R o o m
I n so m e r a r e in sta n c e s it is n e c e s s a ry to p la c e th e e n tir e c o n tro l in a ro o m s e p a ra te f ro m a n d p r o te c te d fro m th e h a z a r d s o f th e o p e ra tin g ro o m . S u c h a c o n tro l s ta tio n m u s t h a v e a c le a r v ie w o f all o p e r a tin g e q u ip m e n t a n d m u s t be c a p ab le o f c o m p le te c o n tro l o f each in d iv id u a l item .
T h e u se o f su c h sim p le c o n triv a n c e s a s d o o r sw itc h e s se em s h a rd ly w o rth m e n tio n in g , y e t I d o u b t if th e r e is a p la n t in th e c o u n try w h e r e o n e o r m o re co u ld n o t be u se d to e lim in a te a s e rio u s h a z a r d . A n y se c tio n , c o m p a r tm e n t o r b in w h e re ele c tric a l p o w e r m u s t b e r e m o v e d f o r th e o p e r a to r ’s s a f e ty sh o u ld n o t be p r o te c te d by d isc o n n e c t sw itc h e s a n d a s ig n w a r n in g a g a in s t th e c lo su re o f th e sw itc h . T h e d o o r to su c h a n e n c lo su re sh o u ld be w ire d w ith a lo w -v o lta g e c o n tro l c irc u it so th a t w h ile th a t d o o r is o p en no c irc u it b r e a k e r o r lin e - s ta r t e r o r o th e r sw itc h m a y be clo sed , a n d th a t d o o r m a y n o t be closed w ith o u t th e k e y w h ic h is in th e p o s se ssio n o f th e m a n w h o is in th a t c o m p a rtm e n t. T h e r e a r e m a n y ty p e s o f th is s o rt o f p ro te c tio n . I n th e C o re y I n te rlo c k th e k ey is k e p t in th e lo c k o f th e c irc u it b re a k e r, w h ic h c a n n o t be closed u n le s s th e k e y is in place, a n d th e k e y c a n n o t be e x tra c te d u n le ss th e c irc u it b r e a k e r is o p e n . T h e sa m e k e y is th e n u se d to u n lo c k
th e d o o r— w h ich d o o r c a n n o t a g a in b e lo ck ed w ith o u t th e sa m e k e y . T h is s o u n d s c o m p lic a te d , b u t it is w o r th a life.
J u s t a s it is th e u n lo a d e d p isto l th a t d o es th e m o s t d a m a g e , so a lso is it th e d e a d c irc u it t h a t c a u se s th e m o st d e a th s . In p la n ts w ith h u n d r e d s o f fe e d e rs in one o f th e m a n y f o rm s o f n e tw o r k s to im p ro v e re g u la tio n it is d ifficult in d e e d to p r e v e n t s n e a k c irc u its w ith c e r ta in c o m b in a tio n s o f o p e n a n d clo sed sw itc h e s. S a d to r e la te th e u n lu c k y c o m b in a tio n d o es n o t a lw a y s o c c u r on th e te s t a t th e c o m p le tio n o f th e n ew in s ta lla tio n . T o av o id th is th e r e is o n ly one re c o u rs e — c a r e f u l w ir in g d ia g ra m s , c a r e f u lly ch e c k e d , a n d c a r e fu l w o rk m a n s h ip . A n aid to th is e n d is th e p u r c h a s e o f f a c to r y a s se m b le d c o m b in a tio n s o f c o n tro l. O n e ty p e o f c a b in e t c o n ta in s th e c o n tro l a n d f e e d e r c irc u it sw itc h e s f o r se v e n m o to r s o f a n in d u s tria l fu rn a c e . T h e o n ly w ir in g n e c e s sa ry in th e field is th e c o n n e c tio n o f th e p o w e r le a d s to th e in c o m in g t e r m in a l b lo c k a n d th e c o n n e c tio n o f th e se v e n m o to rs to th e te rm in a ls p ro v id e d th e r e f o r e . F o r tu n a te ly th e s a v in g s m a d e in sp a c e a n d in s ta lla tio n c o s t a r e m o re th a n sufficient to p a y f o r th e in c re a se d p u r c h a s e p ric e o f such u n its .
534 C h em ica l & M e ta llu rg ica l E n g in e e r in g— Vol.40.TSo.10
A roll out carbon circuit breaker installation. It will be noticed that these compartments are of the
dead front type
a n d th e tu b e c u ttin g off th e illu m in a tio n th e p h o to -tu b e - p la te c u r r e n t c h a n g es a n d th e c irc u it o p e ra te s to open c irc u it b re a k e rs o r m o to r s ta rte r s , to ap p ly b ra k e s o r to so u n d w a rn in g signals.
A so m e w h a t sim ila r p ro te c tiv e device p ay s d iv id e n d s in ad d itio n to sa v in g lives. R e c o rd s hav e p ro v e n th a t a d e q u a te illu m in a tio n re d u c e s a c cid en ts, d ec reases sp o il
ag e a n d in c re ase s p ro d u c tio n . B u t a d e q u a te artific ia l illu m in a tio n c o sts m o n e y in elec tric p o w e r consum ed, in rep la c e m e n t o f b u lb s a n d in su p e rv isio n . B y th e in sta lla tio n o f a lig h tin g c o n tro l u n it th e illu m in atio n m a y be m a in ta in e d p ra c tic a lly c o n s ta n t re g a rd le ss o f th e v a ria tio n s in n a tu ra l illu m in a tio n . T h e p h o to tu b e in th e c o n tro l u n its re sp o n d s to th e illu m in a tio n a t th e w o rk in g level. I f th is is deficien t th e elec tric lig h ts a re tu rn e d o n — if ex c essiv e th e y a re tu rn e d off.
T h is p a p e r s ta rte d o u t w ith th e p re v e n tio n o f fires a n d ex p lo sio n s— it is th e r e f o r e fittin g th a t it sh o u ld end w ith th e e x tin c tio n o f fires.
T h e sm oke d e te c to r also uses a p h o to tu b e f o r th e r e d u c tio n o f a h a z a rd . A slig h t w isp o f sm oke co m in g b etw e en th e lig h t so u rce a n d th e p h o to tu b e is sufficient to se t u p th e c irc u it f o r th e r in g in g o f a la rm s o r th e o p e ra tio n o f a s p rin k le r sy stem .
T h e sm o k e d e te c to r h a s o th e r in te re s ts f o r th e ch em i
cal en g in e e r. G en e ra lly , th e chem ical w o rk s is located w h e re it does n o t n ee d to c o n c ern itse lf w ith th e q u a n tity o f sm o k e em itte d , b u t th e sm oke re c o rd e r is n e v e rth e le ss v a lu a b le as a m e a n s f o r im p ro v in g a n d su sta in in g bo iler p la n t econom ies.
T r u l y it ca n be sa id th a t th e p h o to tu b e is th e s a fe ty e n g in e e r’s “ elec tric e y e” f o r d a n g e r ca sts its sh ad o w b e fo re a n in ju r y o cc u rs a n d th e sh a d o w fa llin g on th e p h o to tu b e can in s ta n tly set in m o tio n a la rm s o r c o rre c tiv e m e a su re s.
Panel hoard assembly of Nofuse switch units
M a n y h a z a r d s e x is t w h ich a r e n o t su b je c t to e lim in a tio n b y th e se lec tio n o f su ita b le e q u ip m e n t o r b y th e m o s t c a r e fu l in sta lla tio n . In o u r tr a n s f o r m e r te s t d e p a r t
m e n t w e w e re m e n a c e d b y th e d a n g e r o f m e n fa llin g o ff th e to p o f tr a n s f o r m e r s w h en m a k in g c o n n e ctio n f o r a te s t. S a f e ty b elts co u ld n o t be u se d . T h e sam e p ro b le m m a y be m e t w ith in m a n y p la n ts in th e c a re a n d m a in te n a n c e o f a n y la rg e tr a n s f o r m e r , ta n k o r bin.
W e so lv e d th e p ro b le m by b u ild in g a p o rta b le sectio n - alize d fen c e. T h e p o sts a r e held to th e t r a n s f o r m e r by m e a n s o f th e co v e r b o lts a n d th e s h o r t se c tio n s s u p p o rte d b y L -s h a p e d b o lts in th e p o sts. B y m a k in g th e se c tio n s o f o n e s ta n d a r d s h o r t le n g th th e eco n o m y o f d u p lic a tio n is o b ta in e d a n d th e a sse m b le d fe n c e fits a n y s h a p e o f t r a n s f o r m e r sufficien tly w ell to p re v e n t a n a c cid e n t.
S u c h a p o rta b le se c tio n a liz e d fen c e is sh o w n in th e illu s tr a tio n on p a g e 532.
W e c a n n o t p re v e n t a m a n fro m d e lib e ra te ly w a lk in g in to d a n g e r, n o r can sufficient g u a r d s alw a y s be e m p lo y e d to sa v e fin g e rs, h a n d s o r a rm s , b u t w e c a n d isc o n n e c t p o w e r a n d ap p ly b ra k e s w h e re a m a n a p p ro a c h e s o r e n te r s th e d a n g e r zone. T h e p h o to tu b e o r elec tric ey e h a s m a d e th is possib le, a n d th e d e v e lo p m e n t o f th e P h o to tr o lle r h a s m a d e it p ra c tic a l.
T h e P h o to tr o lle r is a s ta n d a r d device f o r th e co n tro l o f e le c tric c irc u its a t th e d e m a n d o f a b eam o f lig h t. S o lo n g a s th e p h o to tu b e is illu m in a te d n o th in g h a p p e n s.
T h e in s ta n t a n y th in g in te rv e n e s b etw e en th e lig h t so u rc e
O cto b er, 1933 — C h em ical & M e ta llu rg ica l E n gin eerin g 535