[PDF] TESTS OF ARC-WELDING-RELATED EMI EFFECTS ON STARTUP

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41187_730032401.pdf TESTS OF ARC-WELDING-RELATED EMI EFFECTS ON STARTUP INSTRUMENTATION T . QIAN , W . KALECHSTEIN , D . COSGROVE* , U . MONDAL* * AECL , Chal k Rive r Laboratories , Chal k River , Ontario , Canad a KO J 1J 0 *Darlingto n Nuclea r Generatin g Station , Bowmanville , Ontario , Canad a L1 C 3W 2 **Pickerin g Nuclea r Generatin g Station , Pickering , Ontario , 0-<"""fc»-i~

1V 5

ABSTRAC

T CA990013 2 The tests described in this paper were conducted to characterize the effects that electromagnetic interference

(EMI),from arc welding, has on startup instrumentation (SUI). This paper reviews the results of a literature search on EMI

resulting from arc welding and gives the objective and scope of the tests conducted and describes the test equipment and setting, and test procedure and results. Arc-welding-related EMI levels in an SUI system were measured to determine the dominant source of interference, the coupling path and the susceptible part of the SUI system. The effectiveness of easily implemented improvements in reducing the level of EMI in the SUI system were also tested.

Recommendations

are provided on how to eliminate or reduce the EMI effects on sensitive nuclear instruments.1. INTRODUCTION A n investigatio n int o electromagneti c interferenc e (EMI ) wit h CANDU® 1 plan t startu p instrumentatio n (SUI ) from ar c weldin g ha s bee n initiate d i n respons e t o a reques t from a CAND U station . Startu p instrumentatio n i s use d fo r monitorin g neutro n flu x durin g reacto r shutdow n an d startu p period s whe n th e neutro n flu x i s belo w th e measuremen t rang e o f th e norma l neutroni c instrumentation . Th e proble m o f EM I wit h SU I ha s resulte d i n spuriou strips of safety systems on several occasions at a number of CANDU units [1]. A recen t surve y o n SU I i n domesti c CAND U station s [1 ] ha s reveale d tha t ar c weldin g activitie s hav e cause d a numbe r o f spuriou s reacto r trip s an d a numbe r o f significan t even t report s hav e bee n filed o n thes e events . Th

egeneral practice in CANDU stations is to avoid arc welding near the SUI and other sensitive equipment and cabling,

an d t o us e direc t curren t wher e weldin g nea r sensitiv e equipmen t canno t b e avoided . Us e o f high-frequenc y alternatin g curren t t o generat e o r stabiliz e th e ar c i s generall y avoide d becaus e ar c weldin g i s though t t o b e mor elikely to cause EMI when operating in this mode. A literatur e searc h an d communicatio n wit h statio n personne l an d EM I consultant s hav e show n that , a s i n Canada , th e genera l approac h t o problem s o f EM I cause d b y ar c welding , adopte d b y U S nuclea r utilities , i s t o avoi d ar c weldin g nea r potentiall y sensitiv e equipmen t [2-5 ] an d (Meininger , R. , CHA R SERVICE , INC. , persona lcommunication, 1995 June 12; Shankar, R., EPRINDE Center, personal communication, 1995 August 10;

Chiarella,

J. , Connecticu t Yanke e Atomi c Powe r Co. , persona l communication , 199
5 Septembe r 13) . Th e Electri c Powe r Researc h Institut e (EPRI ) advise s tha t th e administrativ e an d procedura l control s o n ar c weldin g b e used . EPR I als o advise s tha t wher e ar c weldin g i s necessar y i n room s containin g in-servic e EM I sensitiv e safet

yequipment, the welding must be contained in shielded enclosures [2,5]. However, the authors of the EPRI reports

coul d no t identif y an y plant s tha t hav e applie d shieldin g t o ar c weldin g operations , no r an y wor k t o identif y th e weldin g interferenc e couplin g path . 1 CANDU ® i s a registere d trademar k o f Atomi c Energ y o f Canad a Limite d (AECL) . 1

A search for information on EMI resulting from arc welding in other industries has revealed that, as in the nuclear

industry , ar c weldin g nea r sensitiv e equipmen t i s avoide d wher e practical . However , researcher s a t th e NAS A Lewi s

Researc

h Center , wh o wer e face d wit h th e proble m o f weldin g nea r sensitiv e electroni c equipmen t (qualifie d fo r EM I immunit y t o MEL-STD-461 A requirements) , hav e applie d standar d EM I contro l technique s t o reduc e welde r emission s t o a leve l compatibl e wit h th e equipment . Th e NAS A researcher s foun d tha t EM I emission s wer e mainl y fro m cable s an d tha t majo r benefit s i n reducin g emissio n wer e obtaine d b y (i ) providin g a goo d groun d retur n connectio n clos e t o th e wel d site , (ii ) usin g shor t groun d an d electrod e cables , an d (iii ) twistin g th e groun d an d electrod e cable s togethe r [6] . Th e weldin g equipmen t use d wa s a n orbita l ar c welder , whic h i s a roboti c welde r designe d fo r makin g circumferentia l weld s o n tubing . Th e uni t include s a shiel d aroun d th e ar c tha t i s provide d primaril y a s visio n protectio n fo r nearb y personnel , bu t ma y als o hav e provide d electromagneti c shieldin g fo r radiate d emission s fro m th e ar c (Sargent , N. , NAS A Lewi s Researc h Center , persona l communication , 199
5 Oct . 16) .

Althoug

h th e welde r use d i s differen t fro m thos e use d i n CAND U station s s o tha t th e NAS A experienc e ma y no t b e directl y applicabl e t o CAND U stations , th e NAS A wor k i s a usefu l referenc e fo r th e genera l proble m o f reducin g arc-welding-relate d EMI . Th e pape r i s arrange d a s follows . Sectio n 2 give s th e objective s an d th e scop e o f th e tests , Sectio n 3 describe s th e tes t equipment an d tes t setups , an d Sectio n 4 provide s tes t results . Sectio n 5 provide s conclusion s an d recommendation s o n eliminatin g o r reducin g EM I fro m ar c weldin g o n th e basi s o f th e tes t result s obtained . 2 OBJECTIVE S AN D SCOP E Th e objective s o f th e investigatio n ar e t o characteriz e th e EM I effect s o n SU I fro m ar c weldin g an d t o develo p recommendation s fo r eliminatin g o r reducin g EM I fro m ar c welding . I n th e investigation , a n SU I instrumentatio n channe l wa s expose d t o ar c welde r emissions , an d th e EM I effect s wer e carefull y observe d usin g a n oscilloscope . Electromagneti c interferenc e effect s wer e characterize d fo r th e followin g variables : • typ e o f welding :

Tungste

n Iner t Ga s (TIG ) weldin g o r Shielde d Meta l Ar c Weldin g (SMAW) , als o know n a s stic k welding , • welde r setup : - Hig h Frequenc y switc h O N o r OFF , - a c o r d c curren t mode , - straigh t o r revers e polarity , • configuratio n o f th e groun d an d electrod e cables , i.e. , - locatio n an d qualit y o f th e connectio n o f th e groun d cabl e t o th e work , - groun d an d electrod e cable s lai d loos e o n th e floo r o r twiste d together , • locatio n o f th e SU I detecto r an d cabl e wit h respec t t o th e wel d site , an d • degre e o f electromagneti c shieldin g provide d fo r th e SU I detecto r an d cabl e an d th e processin g electronics . Ar c welde r emission s wer e no t measure d i n thi s investigation . Ar c welde r emission s hav e bee n measure d i n a relate d investigatio n an d will b e reporte d separatel y [7] .

3. TEST EQUIPMENT AND SETUP

Th e followin g equipmen t wa s use d (se e Figure s 1 an d 2) : Ar c weldin g machine : Mille r Electri c Manufacturin g Co . Mode l Syncrowav e 300
. SU I an d puls e generator : Th e SU I include s a Boro n Trifluorid e (BF3 ) neutro n detector , a pre-amplifier , a hig h voltag e (HV ) d c supply , a shapin g amplifier , a singl e channe l analyze r (SCA) , a dual counter/timer , an d a linear/lo g rat e meter . A puls e generato r i s include d t o ai d i n setu p o f th e SUI . Wit h th e exceptio n o f th e detecto r an d pre-amplifier , th e abov e ar e nuclea r instrumentatio n module s (NIM ) mounte d i n a NI M Bin complet e wit h powe r supply . Fo r th e tests , th e NI M Bin wa s house d i n a smal l stee l cabine t (0. 5 m high) . Th e mode l o f th e abov e equipmen t ar e liste d i n Tabl e 1 . A schemati c bloc k diagra m showin g th e signa l flo w i n th e SU I i s presente d i n Figur e 1 .

Measurin

g instrument s fo r monitorin g EM I levels :

Measurin

g instrument s include d a digita l storag e oscilloscop e (20 0 MH z bandwidth) , a plotte r an d a powe r lin e monitor . Th e measurin g instrument s ar e liste d i n Tabl e 2 . EM I suppressio n equipment :

Electromagneti

c shieldin g an d nois e filterin g wer e applie d t o preven t couplin g arc-weldin g emission s t o th e SU I detector , detecto r cabl e an d NI M Bin .

Improve

d shieldin g wa s provide d b y mountin g aluminu m shieldin g panels securel y bonde d t o th e SU I cabine t t o cove r th e ope n fron t an d bac k o f th e cabinet . Cable s penetratin g th e cabine t provid e a possibl e pat h fo r conductin g interferenc e int o th e cabinet . T o brea k thi s couplin g path , nois e couplin g t o th e SU I cabine t wa s suppresse d b y wirin g low-pas s filter s int o th e powe r lin e fo r th e SU I NI M Bin an d th e cabl e connectin g th e rat e mete r outpu t t o th e oscilloscope . Th e filter s wer e o f th e fee d throug h typ e an d wer e installe d i n on e o f th e shieldin g panels . Nois e filterin g wa s no t applie d t o th e detecto r cabl e becaus e o f th e larg e bandwidt h o f th e detecto r signal . However , nois e pick-u p o n thi s cabl e coul d b e reduce d b y placin g th e detecto r an d cabl e insid e th e SU I cabinet . I n addition , isolatio n transformer s wer e availabl e fo r powerin g th e NI M Bin an d measurin g instruments . Excep t wher e note d otherwise , th e shieldin g panel s wer e no t mounte d o n th e cabinet , th e powe r lin e an d signa l lin e filter s wer e bypassed , th e detecto r an d cabl e wer e no t place d insid e th e cabine t an d th e isolatio n transformer s wer e no t used . Th e availabl e EM I suppressio n equipmen t i s liste d i n Tabl e 3 . Th e SU I wa s setu p usin g a puls e generato r i n plac e o f th e neutro n source . Th e SU I setu p wa s typica l o f tha t a t CAND U stations . Reader s ma y refe r t o [8 ] fo r detail s o f th e tes t procedure . Th e SU I setting s an d measure d signal s wer e a s liste d i n Tabl e 4 an d Tabl e 5 , respectively . Th e setu p use d i n measurement s o f EM I level s i n th e SU I resultin g fro m ar c welde r operatio n i s a s show n i n Figur e 2 , whic h show s th e relativ e location s o f th e ar c welder , th e stee l weldin g table , th e carbo n stee l pip e tha t serve d a s th e wor k piece , th e wel d site , th e SU I detecto r an d th e SU I cabinet . Th e ar c welde r use d a s th e EM I sourc e i s th e mode l Syncrowav e 30
0 fro m Mille r Electri c Mfg . Th e machin e wa s connecte d t o a dedicate d singl e phas e 55
0 V 6 0 H z supply . Th e ar c welde r wa s initiall y configure d fo r TI G welding , bu t th e SMA W process , als o know n a s stic k welding , wa s als o used . Thes e weldin g processe s diffe r i n th e electrod e an d electrod e cabl e use d an d i n requirement s fo r ga s flo w an d coolin g water .

The welder setup was changed during testing to study the effect of various welder operating modes. The welder

setup s ar e summarize d i n Tabl e 6 . Fo r eac h aspec t o f th e welde r setup , th e tabl e list s bot h th e option s use d an d th e initia l setup . I n th e discussio n o f tes t results , th e welde r setu p i s describe d i n term s o f difference s fro m th e initia l setu p liste d i n Tabl e 6 .

Severa

l configuration s o f th e welde r groun d connectio n wer e used . I n th e initia l configuration , th e welde r groun d cabl e wa s clampe d a t th e fa r en d o f th e pipe , abou t 3 m fro m th e wel d site , a s show n i n Figur e 2 . T o stud y th e effec t o f poore r groun d connections , th e welde r groun d cabl e wa s late r clampe d t o a nearb y le g o f th e stee l weldin g tabl e an d change s wer e mad e i n th e electrica l contac t betwee n th e pip e an d weldin g table . Fo r som e tests , th e pip e wa s lai d directl y o n th e table , s o ther e wa s electrica l contac t alon g th e entir e lengt h o f th e table . Fo r som e othe r tests , electrica l contac t betwee n th e pip e an d th e weldin g tabl e wa s severel y restricte d b y layin g th e pip e o n a n insulatin g suppor t place d nea r th e wel d site , an d acros s a n aluminu m block , abou t 1-c m squar e an d 10-c m long , nea r th e othe r en d o f th e table . Thi s force d th e weldin g curren t t o flo w th e lengt h o f th e pip e an d throug h a smal l contac t are a betwee n th e pip e an d aluminu m block . Th e contac t pressur e applie d wa s jus t tha t resultin g fro m th e weigh t o f th e pipe . I n mos t o f th e tests , th e configuratio n o f th e groun d cabl e an d electrod e cabl e wa s uncontrolled . Som e lengt h o f th e electrod e cabl e wa s coile d an d hun g nea r th e welder . Th e remainin g lengt h o f th e electrod e cabl e an d entir e lengt h o f th e groun d cable , whic h wa s shorter , wa s lai d o n th e floo r i n rando m fashion . Fo r som e o f th e tests , th e electrod e an d groun d cable s wer e twiste d togethe r a s thi s ma y b e expecte d t o reduc e magneti c field emissions . 4 . TES T PROCEDUR E AN D RESULT S

Electromagneti

c interferenc e measurement s wer e conducte d a s consecutivel y numbere d test s fo r variou s welde r operatin g condition s an d configuration s o f EM I suppressio n equipment . A summar y o f th e test s i s provide d i n Tabl e 7 o f thi s paper . A mor e detaile d descriptio n o f th e result s i s provide d i n [8] . Th e setu p use d fo r th e test s i s a s show n i n Figur e 2 . Durin g testing , th e configuratio n o f th e SU I wa s a s liste d i n Tabl e 4 . Th e setu p o f th e ar c welde r i s describe d fo r eac h tes t i n term s o f th e differenc e fro m th e initia l setup , a s liste d i n Tabl e 6 , o r th e setu p fo r a previou s test . Th e SU I detecto r wa s initiall y place d o n th e weldin g table , abou t 0. 5 m fro m th e carbo n stee l pip e an d abou t 1 m fro m th e locatio n o f th e arc . A n ar c wa s struc k briefl y durin g eac h test , a t th e locatio n indicate d i n Figur e 2 . Unles s otherwis e indicated , th e detecto r an d cabl e wer e place d a s above , an d a n ar c wa s presen t durin g testing . Th e oscilloscop e wa s use d i n analo g mod e t o carefull y inspec t signal s i n th e SUI . Th e norma l preamplifie r an d amplifie r outpu t signal s wer e serie s o f pulse s (du e t o th e signa l generator ) havin g amplitud e an d repetitio n rat e a s liste d i n Tabl e 5 . Th e presenc e o f othe r pulse s i n th e preamplifie r o r amplifie r output , o r a significan t deviatio n i n th e rat e mete r indicatio n o r outpu t fro m tha t liste d i n Tabl e 5 , wa s interprete d a s evidenc e o f EMI .

Electromagneti

c interferenc e wa s observe d a t th e preamplifie r an d amplifie r output s a s randoml y occurring , shor t pulse s havin g a duratio n similar t o tha t o f pulse s fro m th e puls e generator , bu t a lowe r amplitude . Swee p speed s nea r 1 us/divisio n wer e use d t o inspec t th e puls e shap e a s th e pulse s wer e severa l microsecond s wide . Becaus e o f th e lo w puls e rate , muc h slowe r swee p speeds , u p t o 5 ms/division , wer e use d t o estimat e th e averag e puls e rate . Th e characteristic s o f th e measure d wav e form s wer e recorde d i n th e tes t lo g an d for m th e basi s fo r th e descriptio n o f th e tes t results . T o obtai n plot s o f th e SU I wav e forms , th e oscilloscop e wa s use d i n it s digita l storag e mod e wit h it s RS-23 2 seria l por t connecte d t o th e plotter . Sampl e plot s obtaine d i n th e test s ar e show n i n Figure s 3 an d 4 . Th e vertica l sensitivit y (volts/division ) an d tim e bas e (seconds/division ) ar e show n a t th e botto m o f eac h plot . A complet e se t o f plot s i s provide d i n [8] . Th e powe r lin e monito r recorde d som e line-to-neutra l an d neutral-to-groun d hig h frequenc y nois e an d als o som e neutral-to-groun d RM S bursts . However , th e abov e powe r disturbance s produce d n o spuriou s pulse s a t th e preamplifie r o r amplifie r output , an d n o disturbanc e i n th e rate-mete r output .

5. CONCLUSIONS AND RECOMMENDATIONS

A surve y o f th e genera l approache s adopte d b y nuclea r utilitie s an d othe r industrie s i n dealin g wit h EM I resultin g fro m ar c weldin g ha s bee n conducted . Th e surve y ha s reveale d tha t EM I resultin g fro m ar c weldin g i s a recurrin g problem , bu t tha t n o satisfactor y solutio n ha s bee n develope d withi n th e nuclea r powe r industr y t o protec t sensitiv e equipmen t from EM I resultin g from ar c welde r emissions . Administrativ e control s o n ar c weldin g hav e bee n use d i n th e nuclea r industr y t o avoi d exposur e o f sensitiv e equipmen t t o ar c welde r emissions . Technique s hav e bee n develope d b y NAS A t o minimiz e emission s from ar c welding , thu s avoidin g possibl e damag e t o sensitiv e electroni c equipmen t tha t canno t b e remove d from proximit y t o th e wel d site . Th e ke y element s o f th e NAS A techniqu e ar e t o provid e a lo w resistanc e groun d connection , kee p cable s shor t an d t o twis t th e groun d an d electrod e cable s together . Thes e precaution s ar e intende d t o avoi d retur n curren t flowing i n o r nea r th e possibl e victi m equipmen t an d t o minimiz e magneti c fiel d emission s from th e cables . A serie s o f test s aime d a t achievin g a bette r understandin g o f EM I resultin g from ar c weldin g i n th e SU I ha s bee n conducted . Th e test s mad e us e o f quantitativ e measurement s o f EM I level s i n th e SU I syste m t o evaluat e variou s welde r operatin g mode s an d severa l nois e reductio n measure s applie d t o th e welde r an d SU I system . Th e SU I syste m wa s monitore d fo r interferenc e effect s a t th e preamplifier , amplifie r an d rate-mete r outputs .

Conclusion

s regardin g th e characteristic s o f spuriou s signal s presen t i n th e SU I syste m becaus e o f ar c weldin g an d th e metho d o f interferenc e couplin g ar e a s follow s (se e als o summar y o f recommendation s i n Tabl e 8) :

Spuriou

s signal s du e t o ar c weldin g appea r a s impulsiv e nois e a t th e preamplifie r an d amplifie r outputs . A n exceptio n i s th e shor t (5- 7 JJ.S ) burst s o f decayin g oscillation s tha t appea r a t th e preamplifie r outpu t whe n high-frequenc y stabilizatio n i s switche d on . Th e SU I detecto r an d th e cabl e t o th e preamplifie r ar e th e part s o f th e SU I syste m tha t ar e mos t susceptibl e t o interferenc e from ar c welding . A s interferenc e i s reduce d b y increasin g th e separatio n from th e weldin g apparatu s and/o r providin g additiona l shielding , i t i s conclude d tha t interferenc e i s radiativel y coupled . N o evidenc e o f pick-u p o n SU I syste m cable s othe r tha n th e detecto r cabl e wa s note d i n th e tests . N o evidenc e o f interferenc e conducte d vi a th e powe r lin e wa s noted .

Spuriou

s pulse s ca n appea r a t th e preamplifie r an d amplifie r output s unde r al l welde r operatin g modes , bu t th e puls e amplitud e an d frequency o f occurrenc e depen d strongl y o n th e welde r operatin g mod e an d distanc e from th e SUI . Fo r certai n welde r operatin g modes , ther e i s n o evidenc e o f EM I a t th e rate-mete r output . Thi s i s becaus e th e amplitud e o f spuriou s pulse s a t th e SC A inpu t fall s belo w th e lowe r leve l discriminato r settin g (3. 0 V) , s o tha t spuriou s pulse s d o no t contribut e t o th e coun t rate . Not e tha t interferenc e effects , i.e. , th e presenc e o f spuriou s signal s a t th e preamplifie r an d amplifie r outputs , ar e no t considere d significan t unles s th e rate-mete r outpu t i s als o affected . Conclusion s regardin g th e severit y o f interferenc e effect s arisin g from variou s welde r operatin g mode s ar e a s follows : 1 . Tungsten-inert-ga s weldin g i n d c mod e withou t high-frequenc y stabilizatio n produce s n o significan t interferenc e effec t o n th e SUI , eve n whe n th e SU I detecto r an d detecto r cabl e ar e i n ver y clos e proximit y (< 1 m ) t o th e weldin g arc , weldin g electrod e an d groun d cables , an d structure s carryin g th e retur n current .

Althoug

h TI G weldin g ma y resul t i n som e spuriou s pulse s induce d i n th e detecto r and/o r detecto r cable , th e rate-mete r outpu t i s unaffected . Wher e ar c weldin g nea r SU I o r othe r sensitiv e equipmen t canno t b e avoided , TI G weldin g i s th e recommende d weldin g process . 2 . Shielde d Meta l Ar c Weldin g produce s greate r interferenc e effect s tha n TI G welding . Th e rate-mete r outpu t i s affecte d b y SMA W welding , excep t wher e a separatio n o f severa l metre s i s maintaine d betwee n th e wel d sit e an d th e detecto r an d detecto r cable .

Shielde

d Meta l Ar c Weldin g nea r sensitiv e equipment , suc h a s SUI , shoul d b e avoided .

3. Use of high-frequency stabilization can result in very strong interference effects. The interference source is the

weldin g machin e itsel f an d emission s ar e presen t eve n i f ther e i s n o weldin g curren t drawn . Th e interferenc e cause d b y high-frequenc y stabilizatio n i s reduce d substantiall y whe n th e SU I detecto r i s remove d mor e tha n 7 m awa y fro m th e weldin g machine . Th e interferenc e ma y b e reduce d belo w a significan t leve l b y additio n o f shieldin g fo r th e detecto r an d cable . I t i s no t necessar y tha t th e shiel d entirel y surroun d th e detecto r an d cabl e t o provid e a substantia l benefit .

High-frequenc

y stabilizatio n shoul d b e disable d wheneve r possible . I f i t i s necessar y t o us e high-frequenc y stabilization , ther e shoul d b e a t leas t 5- m separatio n betwee n th e SU I detector/cablin g an d th e weldin g machine . 4 . Weldin g i n d c mod e generate s les s interferenc e tha n weldin g i n a c mode . Weldin g i n a c mod e produce d significan t interferenc e effect s i n th e tests . Direc t curren t weldin g i s recommende d fo r maintenanc e an d repai r wor k nea r sensitiv e equipment . Th e polarit y shoul d b e se t t o STRAIGH T polarit y fo r TI G weldin g an d REVERS E polarit y fo r SMA W weldin g a s th e abov e setting s produc e superio r weld s an d les s interference . Th e weldin g electrod e i s a t a negativ e potentia l wit h respec t t o th e welde r groun d unde r STRAIGHT polarity , an d a t a positiv e potentia l unde r REVERS E polarity . I t i s norma l practic e t o us e REVERS E polarit y fo r SMA W welding , a s thi s yield s a bette r qualit y weld . (TI G weldin g i s alway s performe d i n STRAIGH T polarity. ) 5 . Transien t interferenc e ma y resul t whe n welde r switc h setting s ar e changed , eve n i n th e absenc e o f a n arc .

Transien

t interferenc e wa s note d severa l times durin g th e test s an d appeare d t o coincid e wit h changin g switc h settings . Transien t interferenc e appeare d t o b e cause d b y togglin g th e polarit y switc h fro m STRAIGH T t o

REVERSE

, bu t th e effec t di d no t occu r consistentl y an d coul d no t b e confirmed .

Changin

g welde r setting s shoul d b e avoide d whe n workin g nea r sensitiv e equipment . Th e welde r setu p shoul d b e complete d befor e th e welde r i s brough t int o proximit y t o SU I o r othe r sensitiv e equipment . 6 . A goo d groun d connectio n i s importan t i n minimizin g welde r emissions . Th e groun d connectio n shoul d b e mad e clos e t o th e wel d site , goo d electrica l contac t shoul d b e provide d betwee n th e wor k piec e an d welde r groun d cabl e an d th e welde r groun d cabl e shoul d b e kep t short .

Conclusion

s regardin g nois e reductio n measure s applie d t o th e welde r an d SU I syste m ar e a s follows : 7 . Additiona l shieldin g fo r th e SU I detecto r an d detecto r cabl e i s effectiv e i n reducin g EM I resultin g fro m ar c welding . Th e shieldin g doe s no t nee d t o completel y enclos e th e detecto r an d cabl e t o provid e a significan t benefit . A numbe r o f approache s ma y b e use d t o improv e shieldin g fo r th e detecto r cable , includin g dedicate d conduit , triaxia l cabl e o r Zippertubing . Zippertubin g i s potentiall y o f grea t benefi t a s i t ma y b e applie d quickl y i n existin g installations . A n evaluatio n o f Zippertubin g i s recommended . 8 . N o reductio n i n ar c welde r interferenc e wa s observe d a s a resul t o f twistin g th e welde r electrod e an d groun d cable s together . I n fact , interferenc e effect s wer e observe d t o becom e greate r a s a resul t o f twistin g th e cable s together . Thi s findin g contradict s finding s o f NAS A researchers , wh o foun d emission s t o b e reduce d a s a resul t o f twistin g groun d an d electrod e cable s together . Additiona l investigatio n i s recommended . 9 . I t wa s observe d i n th e test s tha t disturbin g th e detecto r cabl e coul d resul t i n generatio n o f significan t nois e i n th e SU I system . Car e shoul d therefor e b e take n t o avoi d mechanica l disturbanc e o f in-servic e SU I detecto r cabling . 10 . Th e SU I shapin g amplifie r act s a s a ban d pas s filte r fo r th e preamplifie r signal . Th e shapin g time constan t shoul d b e properl y adjuste d t o accommodat e th e coun t rat e an d achiev e bes t nois e reductio n results .

REFERENCES

1 . QIAN , T . an d LOPE Z A. , "Surve y o f Startu p Instrumentatio n i n Domesti c CAND U Stations" , COG-95 - 117
, Rev . 0 , 199
5 March . 2 . Cha r Services , Inc. , "Handboo k Fo r Electromagneti c Compatibilit y o f Digita l Equipmen t i n Powe r Plants , Volum e 2 : Implementatio n Guid e fo r EM I Control, " EPRITR-102400-V2 , 199
4 October . 3 . SHANKAR , R. , MOLLERUS , F.J. , "Result s o f a n EMI/RF I Plan t Survey" , Electromagneti c Interferenc e

Contro

l i n Digita l Instrumentatio n an d Contro l Upgrades , Baltimore , M D (Unite d States) , 199
2 Sep t 10 - 11 , EPRI-TR-102479 . 4 . STAR K A. , "Electromagneti c Interferenc e Poin t o f Installatio n Emission s Testing , Connecticu t Yankee, " Jun e 21
, 199
3 throug h Jun e 24
, 1993
, i n EM I Workin g Grou p Meeting , Phoenix , Arizona , 199
3 Sep t 23
- 24
. 5 . PUBLI C SERVIC E ELECTRI C & GAS , CHA R SERVICE , INC. , an d EPR I ND E CENTER , "Guideline s fo r Electromagneti c Interferenc e Testin g i n Powe r Plants, " EPR I TR-102323 , 199
4 Sept . 6 . NTI S Technica l Note , LEW-14480/TN , "Preventin g Ar c Weldin g fro m Damagin g Electronics : Appropriat e

Shielding

, Grounding , an d Cabl e Routin g Protec t Delicat e Parts" , 198
9 January . 7 . KALECHSTEIN , W. , COSGROVE , D. , "Measuremen t o f th e Radiate d Electromagneti c Fiel d Du e t o

Operatio

n o f a n Ar c Welde r o f a Typ e Use d a t CAND U Plants" , COG-96-148 , Re v PI , 199
6 March . 8 . QIAN , T. , KALECHSTEIN , W . an d MONDAL , U. , "Arc-Welding-Relate d Electromagneti c Interferenc e

Effect

s o n Startu p Instrumentation, " COG-96-126 , Re v P2 , 199
6 March . TABL E 1 . SU I EQUIPMEN T MODULE S SU I Equipmen t BF 3 Detecto r

Preamplifie

r Hig h Voltag e

Amplifie

r SC A Dua l Counter/Time r

Lin/Lo

g Rat e Mete r NJMBI N NJJ M BI N Powe r

Precisio

n Puls e Generato rManufacturer N . Woo d Counter s

Canberr

a

Canberr

a Orte c

Canberr

a

Canberr

a Orte c Orte c Powe r Desig n Inc . Orte cModel G-10- 8 200
6 310
2 48
5 203
1 2071
A 44
9 401
A

AEC-320-

3 41
9

TABLE 2. MEASURING INSTRUMENTS

Measurin

g Instrumen t Powe r lin e monito r

Oscilloscop

e

Plotte

r

Spectru

m Analyze r EM I Prob e Se t

Curren

t Prob eManufacturer BM I Joh n Fluk e Mfg . Co . In c

Hewlet

t Packar d

Hewlet

t Packar d

Electro-Metric

s Sola r Electronic sModel 480
0 PowerScop e

PM3392A

, 20 0 MH z 7475
A 4195
A

EHFP-3

0

9215-1

N TABL E 3 . EM I SUPPRESSIO N EQUIPMEN T EM I Suppressio n Equipmen t

Shieldin

g Cabine t Signa l Lin e Filte r Powe r Lin e Filte r

Isolatio

n Transforme rManufacturer CR L (retrofitted )

Spectru

m Contro l

Spectru

m Contro l Sola r Electronic sModel

SCI-2330-004

, DC940 2

SCI-6340-007

, DC944 0 7032-
1 TABL E 4 . SU I EQUIPMEN T SETTING S SU I Equipmen t Hig h Voltag e

Preamplifie

r

Amplifie

r SC A Dua l Counter/Time r Rat e Mete r Puls e Generato rSwitch/Knob Coars e Selectio n Switc h Fin e Selectio n Kno b Coars e Gai n Fin e Gai n PZTri m

Polarit

y Puls e Shap e Lowe r Leve l Windo w

Displa

y Selec t

Counte

r B Prese t

Thumbwhee

l

Countin

g Mode Rang e Tim e Constan t Zer o Suppressio n Puls e Repetitio n Rat e

Normaliz

e Puls e Heigh t Rela y Re f Voltag e

Polarit

y Ris e Tim e Outpu tSetting Options 0KV , 0.5KV , 1. 0 K V 1 0 Tur n Po t 2 1 to2 6 3. 0 t o 10. 0

POSorNE

G Uni - o r Bi-pola r 1 0 tur n po t 1 0 tur n po t Aor B 0.0 1 Se c o r 0.0 1 Mi n N , M , P Singl e o r Recycle 1 0 t o 1 0 i n 1-3-1 0 step s 0.0 3 t o 3 0 i n 1-3-1 0 step s 1 0 tur n po t 6 0 Hz , 7 0 H z 1 0 tur n po t 1 0 tur n po t A C Freq , Off , In t Os c Int , Ex t POS , NE G Min , 20 , 50
, 100
, 25
0

Direct

, Attenuate dSetting 1. 0 K V 8. 0

Defaul

t settin g 4 4. 5

Properl

y adjuste d PO S

Unipola

r 3. 0 V 10. 0 V A 0.0 1 Se c 1,0, 2 Singl e 10 2 H z 1 o r 3 sec . properl y adjuste d 6 0 H z 7.5 5 1.0 9 A C Fre q In t NE G Mi n Direc t TABLE 5. SIGNALS MEASURED IN VERIFICATION OF SUI SETUP

Signal

/ Indicatio n Puls e amplitud e a t th e outpu t o f th e puls e generato r Puls e amplitud e a t th e outpu t o f th e preamplifie r Puls e amplitud e a t th e outpu t o f th e amplifie r Puls e rat e a t th e puls e generato r outpu t

Rate-mete

r readin g (dial )

Rate-mete

r outpu t voltag eLevel -0.2 2 V 0.4 3 V 8. 5 V 6 0 H z 5 8 Hz * 6. 0 V (indicate s 6 0 Hz ) Th e observe d discrepanc y betwee n th e puls e repetitio n rat e settin g an d th e rate-mete r dia l readin g i s acceptable . TABL E 6 . SETU P O F TH E AR C WELDE R Ite m

Weldin

g proces s

Weldin

g wor k piec e Welde r high-frequenc y (HF ) stabilizatio n Welde r curren t mod e Welde r polarit y Star t curren t

Curren

t settin g

Weldin

g groun d connectio n

Electrod

e an d groun d cabl e configuratio nOptions t• TIG welding SMA W (stic k welding ) • Carbo n stee l pip e • Aluminu m plat e > Of f • Star t

Continuou

s > a c • 6 b • Straigh t (- ) > Revers e (+ ) Dia l setting : 0 t o 1 0 0 A t o 37
5 A i n tw o range s Fa r en d o f pip e Groun d cabl e clampe d t o tabl e leg , pip e lai d directl y o n tabl e Groun d cabl e clampe d t o tabl e leg , pip e i n restricte d electrica l contac t wit h tabl e • Untwiste d (normal ) • Twiste d togethe rInitial Setup TI G weldin g Carbo n stee l pip e (lai d o n stee l weldin g table ) Of f d c

Straigh

t Dia l se t a t 2 fo r al l test s 10 0 A (hig h range ) Fa r en d o f pip e

Untwiste

d

TABLE 7. SUMMARY OF TEST RESULTS

Tes t No . 1 2 3 4 5 6 7 8 9 1 0 1

1Welder Configuration

- Setting s pe r Tabl e 6 , excep t high-frequenc y (HF ) stabilizatio n se t t o CONTINUOUS . - Setting s pe r Tabl e 6 . - Curren t settin g a t 37
5 A . - Two ful l turn s o f detecto r cabl e woun d aroun d th e pipe . - Groun d cabl e clampe d t o tabl e le g abou t 3 m fro m th e wel d site . - Conductin g suppor t (aluminu m block ) place d unde r th e pip e 3 m fro m th e wel d sit e (nea r th e groun d connection) . - Non-conductin g suppor t place d unde r th e pip e nea r th e wel d site . Sam e a s Tes t 4 , except : - Extr a lengt h o f coaxia l cabl e adde d betwee n th e amplifie r an d th e SCA . - A longe r H V cabl e used . Sam e a s Tes t 4 , except : - Longe r cable s use d a s i n Tes t 5 - Polarit y se t t o REVERSE . Sam e a s Tes t 4 , except : - Welde r se t u p fo r SMA W welding . - Longe r cable s use d a s i n Tes t 5 - Polarit y se t t o REVERSE . Sam e a s Tes t 4 , except : - Welde r se t u p fo r SMA W welding . (Sam e a s Tes t 7 , except : straigh t polarity) . Sam e a s Tes t 4 , except : - Welde r se t u p fo r SMA W welding . - Ar c no t struck . - Polarit y se t t o REVERSE . - NI M Bi n temporaril y powere d throug h isolatio n transformer . - Welde r se t u p fo r SMA W welding . - Groun d cabl e clampe d t o tabl e le g abou t 3 m fro m th e wel d site . (Al l othe r setting s a s i n Tabl e 6) . - Welde r se t u p fo r SMA W welding . - Groun d cabl e clampe d t o tabl e le g abou t 3 m fro m th e wel d site . - Polarit y se t t o REVERSE . (Al l othe r setting s a s i n Tabl e 6) .Results - EM I effect s apparen t wit h an d withou t ar c struck . - Rate-mete r reading : 250
0 t o 300
0 Hz . N o evidenc e o f EMI . N o evidenc e o f EMI . - Low-amplitud e spuriou s pulse s observe d a t th e amplifie r output . - Rate-mete r readin g normal , i.e. , 6 0 Hz . - Sparkin g observe d occasionall y a t aluminu m pip e suppor t bloc k wa s correlate d wit h momentar y increase s i n rate-mete r reading . - Low-amplitud e spuriou s pulse s observe d a t th e amplifie r output . - Rate-mete r readin g normal , i.e. , 6 0 Hz . - A numbe r o f spuriou s pulse s observe d a t th e amplifie r output . - Rate-mete r reading : 24
0 Hz . - Mor e spuriou s pulse s observe d a t th e amplifie r output , compare d wit h Tes t 7 . Bipola r pulse s 2- 5 v p .- Rate-meter reading: >1100 Hz. - Transien t increas e i n rate-mete r reading , coinciden t wit h chang e i n polarit y setting . - Spurious , repetitiv e (12 0 Hz ) wav e for m i n preamplifie r output . - Amplifie r an d rate-mete r outpu t no t affected . - Low-amplitud e spuriou s pulse s observe d a t th e amplifie r output . - Rate-mete r readin g affecte d slightly . Sligh t variatio n i n readin g observed . - Low-amplitud e spuriou s pulse s observe d a t th e amplifie r output . Lowe r interferenc e tha n i n 10 . - Rate-mete r readin g wa s stabl e a t 6 0 Hz . 1 0

TABLE 7. SUMMARY OF TEST RESULTS, CONT'D

Tes t No . 1 2 1 3 1 4 1 5 1 6 1 7 1 8 1

9Welder Configuration

- Polarit y se t t o REVERSE . - Groun d cabl e clampe d t o tabl e le g abou t 3 m from th e wel d site . (Al l othe r setting s a s i n Tabl e 6) . - H F stabilizatio n se t t o CONTINUOU S an d use d wit h foo t peda l contro l - Polarit y se t t o REVERSE . (Al l othe r setting s a s i n Tabl e 6) . - Welde r se t u p fo r SMA W welding . - Polarit y se t t o REVERSE . (Al l othe r setting s a s i n Tabl e 6) .

Positio

n o f detecto r an d cabl e wa s varied . - Welde r se t u p fo r SMA W welding . - Weldin g groun d connecte d t o table . - Pip e lai d directl y o n table . - Detecto r place d o n to p o f oscilloscope , 2 m from th e en d o f th e pip e an d groun d connection , an d 4 m from th e wel d site . (Al l othe r setting s a s i n Tabl e 6) . - H F stabilizatio n se t t o CONTINUOU S - Detecto r an d cabl e location s varied . - N o weldin g arc . (Al l othe r setting s a s i n Tabl e 6) . - H F stabilizatio n se t t o CONTINUOUS . - SU I detecto r an d cabl e place d o n th e weldin g table . - Aluminu m shieldin g panel s mounte d o n SU I cabinet , bu t penetrate d b y th e detecto r cable . - N o weldin g arc . (Al l othe r setting s a s i n Tabl e 6) . - H F stabilizatio n se t t o CONTINUOU S - Detecto r an d cabl e insid e th e cabinet . - Shieldin g panel s electricall y connected , bu t no t mounte d o n th e SU I cabinet . - N o weldin g arc . (Al l othe r setting s a s i n Tabl e 6) . - Welde r se t u p fo r SMA W welding . - Groun d cabl e clampe d t o tabl e le g abou t 3 m from th e wel d site , a s i n Tes t 4 . - Detecto r an d cabl e lai d o n tabl e paralle l t o th e pip e (distanc e abou t 3 0 cm) . (Al l othe r setting s a s i n Tabl e 6) .Results N o evidenc e o f EMI .

Spuriou

s pulse s observe d a s i n Tes t 1 . - Detecto r an d cabl e place d insid e th e SU I cabinet : n o evidenc e o f EM I - Detecto r besid e th e pipe : spuriou s pulse s observe d i n amplifie r an d rat e mete r outputs , rate-mete r readin g wa s 7 0 Hz . - Detecto r cabl e wrappe d aroun d th e pipe : mor e interferenc e observed , rat e mete r readin g wa s 11 0 Hz . N o evidenc e o f EMI . - Detecto r an d cabl e place d o n aluminu m pane l tha t wa s electricall y connecte d t o th e cabine t b y shor t bondin g straps , bu t no t mounted : n o evidenc e o f EMI . - Detecto r an d cabl e move d towar d th e welde r machin e (fro m 2 m t o 1. 5 m separation) : lot s o f spuriou s pulse s observed . Rat e mete r readin g increase d t o 70
0 t o 100
0 Hz . - Spuriou s pulse s presen t a t th e amplifie r output . EM I radiate d b y welde r appear s t o b e couple d t o th e detecto r and/o r it s cable . N o evidenc e o f EM I wa s observe d a s th e cabine t wa s turne d s o tha t th e ope n front o f th e cabine t face d th e weldin g machine . - Nois e observe d i n amplifie r output . - Rate-mete r readin g wa s abou t 80
0 Hz . 1 1

TABLE 7. SUMMARY OF TEST RESULTS, CONT'D

Tes t No . 2 0 2 1 2 2 2 3 2

4Welder Configuration

- Sam e a s Tes t 19 , bu t wit h th e groun d an d electrod e cable s twiste d together . Th e exces s lengt h o f electrod e cabl e wa s twiste d backward s wit h th e twiste d cabl e assembl y s o tha t th e tw o part s o f th e electrod e cabl e wer e hal f a tur n apart . (Al l othe r setting s a s i n Tabl e 6) . - Sam e a s Tes t 19 , bu t wit h th e groun d an d electrod e cable s twiste d together . Th e exces s lengt h o f electrod e cabl e wa s twiste d backward s wit h th e twiste d cabl e assembl y s o tha t th e tw o part s o f th e electrod e cabl e wer e adjacent . (Al l othe r setting s a s i n Tabl e 6) . Sam e a s Tes t 19 , excep t that : - Th e exces s lengt h o f th e electrod e cabl e wa s unwoun d an d lai d o n th e weldin g table . - Th e groun d cabl e wa s clampe d t o tabl e le g abou t 3 m fro m th e wel d site , a s i n Tes t 4 . Sam e a s Tes t 22
, excep t that : - Polarit y se t t o REVERSE .

Setting

s pe r Tabl e 6 , excep t that : - Welde r se t u p fo r SMA W welding . - Curren t mod e se t t o a c welding .Results - N o reductio n i n EMI . I n fact , th e rate-mete r readin g increase d t o abou t 200
0 Hz . - EM I leve l similar t o tha t i n Tes t 21
. Rate-mete r readin g wa s a t 200
0 Hz . - Changin g th e locatio n o f th e welde r groun d cabl e connectio n fro m th e tabl e le g o f th e weldin g tabl e t o th e pip e produce d n o chang e i n th e spuriou s coun t rate . Rate-mete r readin g wa s stil l a t 200
0 Hz . - Som e reductio n i n EM I observe d compare d wit h Test s 2 0 an d 21
. N o reductio n i n EM I compare d wit h Tes t 19 . - Rate-mete r readin g wa s a t 120
0 Hz . Spikin g towar d 200
0 H z wa s observe d briefl y once . - Reduce d leve l o f EM I observed , compare d wit h Test s 20 , 21
, an d 22
. - Rate-mete r readin g wa s a t abou t 20 0 Hz . - A significan t leve l o f EM I wa s observe d o n th e amplifie r output . - Rate-mete r readin g wa s aroun d 60
0 Hz . 1 2

TABLE 8. RECOMMENDATIONS

No . 1 . 2 . 3 . 4 . 5 . 6 . 7 . 8 . 9 . 10 .Recommendation

Tungsten-inert-ga

s weldin g i s recommende d fo r maintenanc e an d repai r wor k nea r sensitiv e SU I equipment .

Shielde

d Meta l Ar c (stick ) weldin g shoul d b e avoided .

High-frequenc

y stabilizatio n shoul d b e disable d wheneve r possible . (I f i t i s necessar y t o us e high-frequenc y stabilization , ther e shoul d b e a t leas t 5- m separatio n betwee n th e SU I detector/cablin g an d th e weldin g machine. ) Direc t curren t mod e weldin g i s recommende d fo r maintenanc e an d repai r wor k nea r sensitiv e equipment .

Changin

g welde r setting s shoul d b e avoide d whe n workin g nea r sensitiv e equipment . Th e welde r setu p shoul d b e complete d befor e th e welde r i s brough t int o proximit y o f SU I o r othe r sensitiv e equipment . Th e groun d connectio n shoul d b e mad e clos e t o th e wel d site . Goo d electrica l contac t shoul d b e provide d betwee n th e wor k piec e an d welde r groun d cabl e an d th e welde r groun d cabl e shoul d b e kep t short .

Provid

e additiona l shieldin g fo r th e detecto r cable : conduit , triaxia l cabl e o r Zippertubing . Zippertubin g i s potentially o f grea t benefi t a s i t ma y b e applie d quickl y i n existin g installations . A n evaluatio n o f

Zippertubin

g i s recommended .

Additiona

l investigatio n i s recommende d t o determin e i f twistin g welde r electrod e an d groun d cable s togethe r i s usefu l i n reducin g welde r emissions . Car e shoul d b e take n t o avoi d mechanica l disturbanc e o f in-servic e SU I detecto r cabling . Th e SU I shapin g amplifie r act s a s a ban d pas s filte r fo r th e preamplifie r signal . Th e shapin g time constan t shoul d b e properl y adjuste d t o accommodat e th e coun t rat e an d achiev e bes t nois e reductio n results . SU I

Detecto

r H V Suppl yPre-amp Puls e

Generato

rRmplifierSCRRate Meter Dua l Counter / Time r NIMBI N FIGUR E 1 . BLOC K DIAGRA M O F SU I SYSTE M SETU P 1 3

550 V 60 Hz

Singl e Phas e 1 Powe r Ba r 12 0 VA C

PM339PA

ch l HGUR E 3 . AMPLIFIE R OUTPU T I N TES T 1

PM3392A

ch lIJ.I.\ •- \ t [ - 1 1* - II\ t-.it im i.• > j: n J L/f 1 ] !i •. . . 5 . Yr fill1 ;• j j/ 1 i . 1 j •| i j ... . i .VJ,^ 4 f P,Qw?. ,i ! i j • * n " 1 • l r | j ii ! ! ! ... . 1.. . . c•< - - ! • - i J HGUR E 4 . PREAMPLIFIE R OUTPU T I N TES T 1 1 5

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