ML19329A810
| ML19329A810 | |
| Person / Time | |
|---|---|
| Site: | Davis Besse  |
| Issue date: | 03/30/1977 |
| From: | TOLEDO EDISON CO. |
| To: | |
| Shared Package | |
| ML19329A811 | List: |
| References | |
| NUDOCS 8001150706 | |
| Download: ML19329A810 (61) | |
Text
{{#Wiki_filter:-- ..
,4k Caps
- 5
*)
gegulatcry 63 UY
} ]1 *4l[ 11 7
, 1h The Toledo Edison Cospany Final Report On , Davis-Besse Nuclear Power Station Unit 1 r Condcit Separation Test Program 8 i March 30, 1977 l
e -, Table of Contents I ! I. Introduction II. Program Description & Criteria III. Tests
- 1. Overload Current Test and Results
- 2. Sustained Arc Tests and Results
- 3. EMI Tests IV. Conclusions Appendices Appendix A - January 31, 1977, Letter from Mr. L. E. Roe of TECo to
' Mr. J. F. Stolz of NRC 6 4 f
~ . - -. ..
LIST OF FIGURES AND TABLES AS THEY APPEAR IN TEST REPORT Fiaure/ Table 4 Title l Figure II-8 Typical Electrical Schematic of 600 A Current Supply and Control Table 11-1 Summary of Maximum Temperatures with 600 A Fault Currents Figure II-11 Temperature vs. Time History for 3/C #8 AWG Cable with 600 A Fault Current Figure 11-12 Temperature vs. Time History for 3 1/C #2 AWG Cables with 600 A Fault Current Table II-2 Summary of Maximum Temperatures with Fault Currents of 4 Less than 600 A Figure II-13 Temperature vs. Time History for a 3/C #6 AWG Cable with 300 A Current Figure II-15 Maximum Conduit Temperatures as Function of Current Load Figure II-7 Conduit Support Configuration Table II-3 Sumcary of Heat Transfer. Tests Table II-3 (cont) Sumnary of Heat Transfer Tests - Figure II-14 Temperature vs. Time Histories for Adjacent 1-1/2 Inch Conduits with One Conduit Heated Figure II-16 Target Conduit Temperature vs. Source Conduit Temperature Figure IV-8 Arcing Fault Test Set Up Table IV-1 Sunmary of Sustained Arc Tests Figure III Current Source and Receptor Configuration Figure III-8 Oscilloscope Traces, No Conduit - No Separation + Figure III-9 Oscilloscope Traces, No Conduit - No Separation Figure III-17 Oscilloscope Traces, Steel Conduit - Both Circuits - 3 Inch Separation
\
Figure III-18 Oscilloscope Traces, Steel Conduit - Both Circuits - 1 Inch Separation l l Figure III-19 Oscilloscope Traces, Steel Conduit - Both Circuits - (, Conduits Touching Figure III-20 Oscilloscope Traces,-Source Cable in Steel Conduit - l Target Bare - Separation Zero
- Table III-2 Maximum Observed Target Cable Voltage (Peak-to-Peak)
e , i l Part I: INTRODUCTION s'ha purpose of this Final Report is to present an overall view of the Conduit Separation Program as undertaken by the Toledo Edison Company, December - 1976 through March - 1977. Highlights of the Interim Test Report (January 12, 1977) and the Summary Test Report (February 17, 1977) will be used to describe the results achieved through the program conducted by the Franklin Institute Research Laboratories (FIRL); cor-relating these with the concurrent efforts conducted by the field con-struction forces and the Design Engineering team to provide clear justi-fication to where less than one inch conduit separation can be allowed. As stated in che previous reports, the purpose of the program was not to prove the adequacy of one inch separation as described in IEEE 384-1974 and Regulatory Guide 1.75, Revision 1, but instead to sub-stantiate where less than one inch is acceftable, a I t 4
Part II: PROGRAM DESCRIPTION & CRITERIA IEEE 384-1974 provides a basis for separation of redundant Class IE circuits where external hazards are not limiting. Section 5.1.1.2 further states that (...where the damage potential is limited to failures or faults internal to the electrical equipment or circuits, the minimum separation distance can be established by analysis of the proposed cable installation.) Without this analysis, 1 inch minimum separation would be used between redundant conduits. Since Davis-Besse Nuclear Power Station Unit I was substantially designed and constructs 1 Trior to the advent of either IEEE 384 or Regulatory Guide 1.75, the 1 inch separation was not necessarily im-plemented into the dasign of the exposed conduit installations. In addressing this issue, it was felt that ample conservatism existed La , the present design to warrant entering a test program which would then provide actual data to be used in the analysis approach mentioned in Section 5.1.1.2 of IEEE 384-1974. To our knowledge, no previous applicant had attempted to conduct such a program, therefore it was first necessary to develop guidelines for conducting the test. Neither IEEE 384 nor Regulatory Guide 1.75 give any guidance an the bases for conduc' ting a test; joint discussions between 7/Co and t1e NRC were held to develop a basis for conducting the test pragram. The conditions established were as follows:
- a. The cable or equipment in the circuit develops a fault that is not c3aared due to failure of the primary prctective device (breaker) and is just below the long-term trip point of the backup device. This causes long-term heating of the cable which may go unnoticed by the operators. For instance, using
r , th.is requirement on a motor control center circuit would mean that the backup protective device on the load center feeding the motor control center would allow any amount of current up to 600 amps on the circuit for a continuous period of time.
- b. After the long-term heating, a fault is developed that would be cleared by the backup device which could introduce EMI.
- c. In addition arcing faults are to be considered.
Implementaion of these three conditions into specific worst case criteria resulted in the 15 items listed below: TEST CRITERIA The criteria established to define the worst case condition that will be used as a basis for analyzing less than 1 inch conduit sep-aration is defined as follows:
- 1) A fault occurs in the cable or device and the primary protective device (breaker) fails to clear.
- 2) The fault has such a resistance associated with it as to produce just enough current to reach, but not exceed, the rating of the backup protective device. A lower level of current is assumed if it generates a greater amount of heating.
- 3) The resistanca of the fault is variable and adjusts itself auto-matically during rising conductor temperature so as to maintain constant current from the source.
- 4) There are no other loads running on the motor control centers supplied by the same load center breaker that might prevent the circuit from reaching its full 600 amp capability on the fault.
- 3) The adjacent circuit.less than 1 inch away contains the redundant circuit of the other channel to the faulted circuit itsalf.
- 6) Long-term continuous heating in this case is assumed t) mean any cable that can last longer than one' hour before the conductors melt. Where tests demonstrate that cables fail within one hour, this time period will be taken into consideration in the evaluation process. .
- 7) The overloaded cable can maintain the contincus overheated status without the operator being aware of the condition.
- 8) That if the redundant circuit is failed by the overloadad cable less than 1 inch away, the operator is unaware of this occurrence also. ,
- 9) That the failures of the redundant circuits cccur either before a LOCA without the operator's knowledge, or simultaneously with a
~
LOCA.
- 10) The impedances associated with the cable and circuit devices up-stream of the fault locations are assumed to be negligible, thus not limiting the energy available at the fault location.
- 11) The overloads installed within the starters on Class IE circuits !
l
-are assumed not to trigger an a'l arm that would warn the operator of l
the overloaded condition.
- 12) For separation at cross-over points, the fault is assumed to occur ~
in the conduit line at precisely the point of r as-over.
- 13) Separation is predicated strictly on an internal fault of the conduit affecting an adjacent conduit, not a common external hazard.
1
- 14) That the source of faulted conduit is directly underneath the l
target conduit. l l 1
- 15) That the IEEE 384 and Regulatory Guide 1.75 requirement of 1 inch applies for conduit with any type cable installed, that is they could be conduits with unshielded, untwisted pair instrument wire rated 75 C operation.
It should be noted that these circumstances when evaluated jointly, are very conservative. To inplement the above test criteria for this test program, meant taking a typical motor control center circuit and first subjecting it to high current overloads, up to 600 amps current which is the largest be.ckup breaker protection for a motor control center to determine the long-term heating effects. After determining the heating effects, the tests were also to evaluate point faalts and electro-magnetic interferences. Even though the point fault and electro-magnetic interference appeared to be the more conceivable events, the long-term heating proved to be the more limiting case and hence used as the basis for the sub-sequent evaluations. l l
. i BACKGROUND To provide a meaningful data base on'which to make meaningful analysis, a test program was prepared jointly with the Franklin In-stitute Research Laboratories (FIRL). At the same time, a review of the number of circuits involved at Davis-Besse Unit I was made by the design engineering team. It was found that there were about 30-40 circuits fed either from Class IE-4.16 KV buses or 480 volt load centers and thac most of these were run as embedded conduits. Since there were so few circuits, and.the test-program criteria discussed above would have required a testing capability of 2,000 amps, which was far in excess of the capability of FIRL, it was decided to merely rework these conduits where necessary. This decision allowed the test program to be con-centrated on power circuits fed from motor control centers or below, control circuits, and instrumentation circuits.
Early in the test program at FIRL, it became readily apparent that 3 with the rigid steel conduit useo on Davis-Besse. Unit 1, there were no internal faults that could be generated in cable of No. 12 AWG or smaller that could generate enough heat or discharge encugh energy to have any detrimental effects on the thick, rigid steel conduit walls thus affect-ing adjacent circuits. No instances of rupturin;;, bowing or dislocation of conduits occurred during any of these tests except in one test where a condulet fitting cracked due to excessive hsating caused by artifically holding fault current high and creating the high temperature. This fact 4
.alone was significant since this represents over 90% of the 3,000 Class IE circuits of Davis-Besse, allowing the program to really concentrate son the power circuits that may .cnceivably be a greater source of trouble.
.,y, y-.- --- . - , . ..-r e-- - s m- -u v +-w
l o ,
'l At this point in the program, the field had inspected existing l installations and had documented 2,100 cases where Class IE conduit of one channel come within 1 inch of the redundant channel or within 1 inch of a non-class IE conduit that may (bridge) the other channel.
Part III: TESTS The investigation was undertaken to study three safety-related aspects of electrict.1 spacing in a nuclear power generating station, as they pertain to common mode failures among redundant Class IE circuits:
- 1. Heat transfer from an electrically overloaded.(600 amp max-imum) conduit (the " source") to an adjacent conduit (the
" target") containing a redundant circuit.
- 2. Energy transfer from a sustained arcing fault in a source conduit to an adjacent targst conduit.
- 3. Electro-magnetic interference between adjacent conduits as a consequence of high power transients in one of them.
Tests were conducted with instrumentation, control and power cables in conduits of different sizes and configurations :o ' determine maximum credible temperature and electro-magnetic effects for adjacent conduits when physically touching, when separated by the thickness of pipe straps
~
and up to 1 inch of separation. The cable and configuration were the same as those used on the Davis-Besse project with the exception of the electro-magnetic inteference tests. The test program was conduct *d in three sections. They were: III-1. Overload Current Test Program Part A - Phase A 600 A Tests Part A - Phase B Less than 600* A Tests Part B Heat Transfer Test's III-2. Sustained Arc Test Program
- III-3. Effect of conduit spacing on electro-magnetic coupling from power cable faults.
I
- - m-
f Each part is described in the following manner: The test description andprocedures used for the test. Test data. Observations. Results from tests. 5 l b 9
- -- , -, c- -, ...-. ,,,
. l l
III-1.0 OVERLOAD CURRENT TEST PROGRAM For the overload circuit tests, it was assumed that the primary j protective device (braaker) failed to operate and that the current overload was slightly below the long term 600 amp trip level of the l l backup protective device. Therefore, the tests were conducted with several overload currents, up to values exceeding those chac would normally trip the primary circuit breaker; but they were maintained continuously until steady conditions were obtained or a malfunction occurred. Furthermore, although the current overload caused the temp-trature and therefore the resistance of the conductor to increase, which 1 wo,Td normally cause the current to increase, the overload current was kept at a constant level during the test. 1.1 600-A CURRENT SUPPLY A 30, 600 amp variable current supply was provided using a stack of three 10 auto-transformers (480 volt) connected to 3 prirs of 10 step-down transformers as illustrated in Figure II-8. The maximum power available, approximately 30 KVA, was sized to provide 600 amp initially in approximately 7 f t of 3/C #12 AWG cable (connected in wye f. ,hion). The currents were monitored using standard, instrument-type current transformers and ammeters. In addition, two legs of the 30 current uere instrumented with current transducers (in series with the ammetars), and their output was recorded on a 2-channel contin ~ us strip-chart recorder. The voltage between the three phases was monitored by means of a 3-position selector switch and a digital multimeter.
~
( . C ( TRANSFORMERS e = RECORDER TRANSFORf ERS TRANSDUCER
"^""
e : N O. 1
- : u-
~
.g. DRAIN CONDUCTOR
[3
= -
o = q__--.__ _ _._____ ____ y : = N " ,.
=
^
0 8 " '
- E e e <- : A _____ _____L ._________
-TEST CONDUCTORS XFMRS TEST CONDUlT C
=
5.
- RECORDER CURRENT 8
A TRANSDUCER-CHANNEL
<%. _ - i N O. 2
=
=
_ o , s FIGURE 11-8 Typical Electrical Schemat:c of good current supply and control 1 9 *
~
t III-1.2 TEMPERATURE MEASUREME.VIS All temperature measurements were made using type K (chrome 1/alumel) Land type T (copper /constantan) thermocoupins. Measurement of conductor , 4 temperatures was accomplished using an 0.063 inch diameter Inconel- . ~ sheathed ungrounded thermocouple. Measurement of the jacket temper-atures was performed using twisted and silver-soldered thermocouple j unctions. Measurement of conduit temperatures was accomplished using thermocouple wires electrically welded (for type K) or silver-soldered (for type T) directly to the conduit surface. The galvanized coating s-was previously removed in the vicinity of the thermocouple. The output of.the thermocouple was recorded. III-1.3 TEST PROCEDURES
^
The following general procedures were used to prnvide results for
. phases A and B of Part A tests:
- a. Thermocouples'(usually.11 in number) were attiched to the cable conductor, the cable jacket and the cotduit., A twelfth a
thermocouple was usually used to monitor the ambient air temperature in the flama test room. t i
- b. The conduit containing the thermocouples and test cable was
. positioned in the flame test room. .
t
- c. The test cable was attached to the energizing circuit and the
- voltmeter was attached to the connection by alligator clips. l d.- The instrumentation (that is, temperature recorders and current meters were checked to insure proper functioning.)
- e. The cable current was quickly brought up to the required level (for example, 600 amps) by manual control of the auto-trans-
' former stack while monitoring the current. Since perfect
, ,- ._.:._;...,__, . , . . _ _ _ , - _ _ _ _ _ _ _ ..a . _ . . .
balance of current between the three phases was not pe - ible with this arrangement, the auto'-transformer stack was adjusted manually to provide currents whose average value approximated the required level.
- f. Simultaneously with application of the current, an elapsed time clock was started. The strip chart recorders were started before the currents were applied.
- g. Periodically during the tests, selected temperatures and observations of special interest were recorded on a data log sheet. The script charts on the recorders were also annotated with chart speeds and elapsed times.
- h. The tests were terminated when either the cable failed (as evidenced by loss of cable current) or the ' temperatures stabi-lized or started to decrease.
- i. The cable conduit was removed from the flame test room and inspected v4.sually.
III-1.4 CONDUIT SUPPORT STRUCTURES The horizontal portion of the test conduits were supported at heights of 45 to 80 inches above the floor in the flame test room. Pipe stands with a saddle at the top were used to support the conduits for ' the Part A~ tests. A double thickness of abestos paper insulated the conduits from the pipe saddles. Conduits used in Part B heat-transfer tests were supported by standard Usistrut pipe-straps and short sections of Unitstrut channels. The channels, 'in turn, were -fastened either to vertical pipe stands or to a special box-like frame for the crossing conduit configuration. _ _ , , , - - _,% , ,,, , -_-- ,- y- -%e , - - - . - - - - - -
III-1.5 MEASUREMENT OF CONDUIT TEMPERATURES WITH 600-Amp FAULT CURRENTS TO DETERMINE MAXIMUM CONDUIT TEMPERATURE OF FAULTED CONDUIT (Part A - Phase A Tests) < The cable and conduit sizes listed in Table II-1 (together with summarized results) were assembled into six foot horizontal configura-tions and L-shaped configurations (horizontal legs). The ends of the conductors located in the conduit pull box (condulet) were connected together; at the other end of the conduit, the three conductors were terminated at a wye-connected, current-transformer bank, which supplied a 600 amp, 30 current. The temperatures of the cable conductors, cable jackets and conduit surface were measured using thermocouples and strip chart recorders. 4
Cable Corutu t t ihm* to ( . Test 5tte No. (AWG1 Sire fla.1 failure fotn) f* n f aum fe- e tuem f'r) wrwust Jacart Lonouc tur Renerks . Nortrontal Tests Al 1 3/C s12 3/4 so.5 96 300 519 Currents peaked 9 610 660 A then decayed to 9 3 min 9 3 200-250 A. One phased failed 9 so.3 min. 0.5 min 0.46 min Anotnce fatted a so.45 min. Conductors failed outside of outlet bon near energtrinej cnnnectlens. A1 2 3/C 78 1 1/2 s1.0 120 236 662 Cccay of current started a 4.7 min. Current was 9 520-540 A 9 0:9 min. Conductor fatted outside of
, 2.5 min outlet boa as in Test Al 1 above.
Al 3 3/C f6 1-1/2 s2.2 115 260 726 Currents tecame erratic and varied between 500 and
. 9 9 630 A. Conductor failed outside of outlet boa as 7.4 min 2.4 min in Test Al-l above.
Al-3C 3/C e6 1-1/2 14.9 192 775 800 After peaking 0 600 A. currents allowed to decay (see 3 9 9 naturally (i.e.. current controls were not remarks) 13.5 min 13.5 min 13.3 min readjusted). Ttee hn h i 0 !I ii ' 10 i 13 ! 13.5 i Current ( A): I 603 Tato ;350125) +310 ifrritici 3 Conductors failed outside of outlet box as in Test Al-1 above. Al 5 3 fic #2 1-1/2 s24.7 416 605 880
~
One phase fatted 0 23.5 min anJ other phase ! 9 9 9 currents decreased to 160 250 A. Test stoo;co ' 25.5 min 22.5 min 23.2 min 3 s24.7 min. Conductors fattes witntn eendatt. Al-6 3 1/C #4.0 3 s175 187 266 32S Test stopped 9 175 min. No condactor failure. 6 Cable jacket intact but shrunt in length on 138 to one conductor leaving a gaa of 3/4 in, at the 175 min midpoint of tne cenductor Jacket. The insula-tion was intact. No cucuctor fatture. I t-Skaced Co eutt Tests A3 1 3/C #12 3/4 1.1 110 197 587 Currents ;;: Pad 9 465-505 A then decrease'd t t! 9 9 9 rapidly to 253 A $ 0.*! sia. Cne smase fatted 2.0 min 2.0 min 0.7 min 7 0.65 min. Another chata maintas..:e 140 A s' , until 1.1 min. Corductor failure possibly
%}J r
6 occurred at point of ther-occuple insertion Into cable jacket (inside tr.e condutt). l.* i i*
.. . A3 2 3/C #8 1-1/2 s1.4 152 240 642 Current decreased starting 9 0.45 min. Current 6
9 9 9 was a10-430 4 ) 1.0 min. One pMase failed 1.6 mfn 4.4 min 1.5 min 3 s1.2 min. I.nother phase failed 3 1.5 min, j 5pecific point of cable failure was not dater-mined. i
}r A3-3 3/C #6 1-1/2 2.2 141 260 749 Current decreased starting 9 1.75 min. Current 9 .# 3 520-540 A G 2.0 min. One phase failed 0 2.2 m'r.
, p 4.0 min 4.0 min 2.25 min Another pnase failed 0 2.3 min. Cable jacket
,. swollen throughost and ruptured in two locattort.
. Cable failed within conduit, t
. . A3-5 31/C #2 1-1/2 20.5 304 480 802 Two phases failed 919.7 min. Condulet fitting
! cracked. Could not remove cable from conduit for inspection. Cable probably fatted within condutt.
A3 6 .1 1/C #4/0 3 220 142 274 305 Test stopped 9 220 min. Cable did rot fall. 0 165 to Cable jacket shrunk in lenntn leaving gaps
- 220 min 1/4 to 1/2 in, wide in jacaet in several places.
The insulatton was intact. l l l ., TABLE 11 -1 i Summary of maximum temperatures with good fault current temperature vs. time v history, for 3/C #8 AWG cable- \ j - wi* .
,, _ ~ - ^* ^'
III-1.6 RESULTS OF TESTS WITH 600 AMP CURRENTS (Part A - Phase A) The strip chart records were examined together with manually re-corded data logs. Thermocouple channels which indicated the highest temperatures (for the conductors, cable jackets and conduit) were selected for further evaluation. The temperature history of these selected thermocouples were then plotted for each test in the manner of Figures II-11 and 12, with annotatione of other observed events such as loss of current (a conductor failure). The results were resummarized and are presented in Table II-1. The highest conduit temperature observed with 600 amp currents was 416 C, which occurred with a 3/C #2 AWG cable in a 1 inch conduit (Test No. Al-5). It should be noted that the temperatures reported are subject to a
+ 8 C instrument tolerance.
The ambient air temperatures in the flame test room were usually well below 50 C (120 F).* These temperatures were measured at a hori-zontal distance greater than 3 ft from the test conduit. m
*Two test results tht; indicated room temperature of 50 C and 86 C were considered anomalous. It was always possib1? to step into the flame tr t room without discomfort from the heat. ,Part of the heat waa gan-erated by 300 to 600 watts of incandescent lighting, contained in the room.
FISURE 11-0 With 600 A fault current temperature vs. tlEe history for 31/C #2 AWG cables 1000 . ;
\d -
i TEST NO: Al-2
. LEG EtJ D
' CONDUlT: i2l" Itl.
O CONOUlT (TC2) 3-
~l-
- CABLE ** 3C d. 8 "
'--- O CABLE JACKET (TC 7) '
900 -
. --O CAOLE CONOUCTOR (TC RED). . CURRENT:GOOA ,
.. .. . . . - ORIEN TATIOil; .
i
; ... i j.. :: -
T
. . . . ..r. .
'. . . .HO.RIZONTAL.
.)
i t . : * ..;.. .. .. 8; .1. . e
. 4. . . ! ..
- l.
- s 4 . .g :.
, . -. .".l- :.;. ;}.
800 - . .;..... . ..
. . . . : : -.'. : . . . . . . . -. . - t .- .
-..-.--;---. ' -.i.
i.>. ..i :
- g. .. . . 3.. .l. . . .
..tg ,.c.'", : .. T """ j ..': .t.'. , .
g
. 8 . . .
l'.
. " "'..-; .*l'...
. . 3l .
,. ;[!. . ; .'
.tU.. ; ' ;.:
i . e
- 3. . ' , . .
...g e
~~.' *
. .: a + . . ~. !:9.'"'."
& . g .
. .s 700 - . . . .~. . . . .; - .'- .;--. . . . . . . : . .
L = . W.:.
. ..=-
.' . ! . *. . ' f .*.
.' .. . ...t.
. .g
... . .....,...........S.
. . $ E . . 8.....l.. .
1 2 g
.-. s. . ..... .
~ *
. . . . . . . . . . . . ..e.... . 4
- t. .
. t
. i .t . -* .
. . ... *. ...* 1:_' !, .
...e,,,,,,,,,,7,,,,.,,.. .g i
,,,j,.. . . , , , , . . , , , ,
L. . , t
.1 ..
600 -- .-. g
. . -.-.-.a
. . .j . . . .. . ..
..'f'. . . .g : . "... M . ". !' ". .".'. g..:::*. g..:: ' ' . .?*.* \* . - . . I. .
,U , .. . .
- f'.*. .
4* w gg
-. ..*; .g
, - , .j
; . j.; ..' '-' ;-.
.- .-...' 6 g . . ,f :::- - ~
---l- !" -
3 500 ,. .
.-.a.-.....~.
.f..... .. *
*...- .j.g ; - . ,1 g . . ( !. ... . . . . . .... .
g . ..
......3 .o r .;. . T .:.. . i y
G. . . . . .= : I:.
". ..'**t.* .' . *.[*
.-.-.8'.-....
. ! ' . . . . j *.
. .;Jj';:. ' . ..'*g ' . .*
3 - Id .. . . - . .. '..g ' ... .;. .; ..; . . .. . . . . ,.. .. 1". . . . , . . .,'
. .t.
Y .. .......... . e 400 --
% ....^....:..=.-..-...;.=...........=.,..=".-
*. . . .." .g
- ..- ... ./ ..6 . . . '. .! . . ... ........ ... .. -. .. . .. . . .. .. ... -. . . .** . ~ .
. . . .. 1 .. -
i .
. . . . . . . ........'s.!".
., . ! . .! .-...I.. ..
* :. ~< .
- 3. : ; !. .i
..e. 4 1
300 I...,...;-.=...-==-..--.u.-..;....
. - - . . ..... g ;. ,. . .
. . . .1.. . . .*8. . . . . . . .....f
. . . . . 't s 1
- 8'
. . . . ,.' . . g . .. .
.. . .. .. y : . .. . . . . .. -.
.-...g.g.~. t
- s. . . . . . .
. f.
j .' .
;,,. E)- = =.= = -(*j
. . . . .. .. .. . , ... , .. ..g.....,.,.. ...,. . .
O, , t
,I . -...i-
": .. .. ..sa. .,D, g.s.-. . u - . . .. .: - .. . . .: . . . . . .: .
I ... . . . . . . .
. ;..e. ,
j [* ig') 10 0 - .
, .i.
.-. .-- - . . . . .. . .--.; a.
s .. , .
,/ .
f . .
/ L s .
- t l
, o
/ . .,/ . . . .
......t.-.
. .s a . .
. =. , ' . .
. I ,
=
O 0 0.5 I 1.0 I 1.5 I 2.0 I f 2.5
;p -3.2 ELAPSED T!t.tE(MIN)
FIGURE ll-12 - With 600 A fault current su m ary of maximum temperatures with fault ' current of
- g. '
1000 - t:rt .il .
" 6 .v.ir.on. us:mL:
. . . . i.. >
8 W. . L. ' TEST NO: A3-5
.. . 1..:: ; + j l j ' . ~- - CONDUlT: 1 , ..
- LEGEND . 7 "O CONDuti(TC 8) !" * * ". - CABLE: 3-l/C#2 .
900 -
---O CABLE JACKET (TCl2) ' - , CURRENT
- 600 A '
. .:---O., . . .. . .CABLE CONDUCTOR .. . (TC. GREEN)' .s
. .. ORI.E.NTATION
- L.
. ... .S.H APED
...:.. . . _. .. ..... _. .. .. .. ...r...... ..... .. . -.. ..- .
. .. .. .. ._....i _
.1 . . .
. . . o. .
.. .. . . e. ... ,
. . . .. .... . . .. i .. ..
800 . . _ . . - . . .. ..:.
...a.. . ._. . _.. . . . _ . . _ . _ _ _ . .
a
. ............ .... ... .. .._ . . ...........f.
........i.. ..............r.
..... .i . .
. ... ...... ...... ... ... ...... .. . . ..s........ . . .
. . . . . .. ..r ..... .,.,.. ..... ........
..:. . . ...r... . . .
. .. . __. _ r 700 . . . .
. . . . . , . . .... ............. .... .. . . . . . . s.....
.r. .. . . . . . . . . . . . . .. .r.. ..-.. . .. .
- a. .
.......T. ....._._-..
..!... . . . . . .......I..........
s .!..
. . . . . . . . . . . . . . ....g.....:_..
.. s.....- ,..
.. g.
600 u.-
...l .
. 1 pm.
O . 4 . ._ --
.. =. . . . _ . _ = _ . . . . . . . . . .
%=*
^ .
. E =
....-I. .. . ..... .i.:
$' . ;. . . . . d. . .. .
l....i..'...
. . ... .f. . . . . . . .. .........i g st aaV .
. _ . _ - - - .. =.
. . . t. . , . . . , . . .. .. . . . .. . . . ....
.t
..l.... ......_.!. . . -. . ,. . . . . . ...... ...! . . . .. . .. ,.. .. ... .. . .
. . . . . . .p./. .
I. 4 .. .
. . .. . . . . s.
. . . ..1...,. ... . .
. . . ... . . . . . .g . .
, 8 -
. .. . ... ..... . ... . . . . . . . . ..../...1... .....
. . . . .. .. . . ..i.
. . . . . . .. .( ..
400 . . . . . . . .. .
.. . . . . . - 1. . .
6 . .. .
- . .. .. .. ..f,.....
e
. . . . . . ... .....4.......
. . . . s. .
./ .. .!..
._....t.... . . . . . . _ . . -
, . .. . .... .....a.s...,.
...s
. . . , . ..... .. . .t,-
.. j.
.s. .... . . . .; . . . . .....s
. 300 _....
..-t .. .
. . . . ..t.... . . . . . , . . .
./..... . . .
t
. . . .3... . . l / .. .
,4
.!.... /.
... .. .. . ... . .... ... . . .. ....... .....s.. ...../. .
. . . ..4..
.. .p...o . .. ...
.1..
..t
.f........L.... .
00 a. .. . . . . . - . .._. .
. /. . . ..
....I...
. ..... .I .,._!......!......... ..(. ..
. /.. . ... . . .
. . . ... .. . . . ....a.... ... .. .. . ... . .
. . l . .. .
t...... . t.
. . . ... ./. .
- 6. , .===...-.-.-
- s. . . . . . . . , . . . 4
.p
.1. . ..
.. .. . .... . . ...t... . . .. . + .....t. ..
'.,.1..
~
. -/. . ...
. .l *: s
. ./ ..,,/.....'...... ... . . . . . ... -.. . . . ..
10 0
- 4. .
. . . ,. t
./ -
./
,.,,o..
y
/ .. ;
- s .
/ j ,e ...
.. _ . ' .. ' *. .. e-- . . .. .f. '. '_ .
- i. . .
cr ,!. a , ._ . r
, s - . ;
O I I I I ' ! 0 5 10 15 20 25 ELAPSED TIME (MIN)
III-1.7 ' DISCUSSION OF FAULT-CURRENT TEST The results of these experiments, which are summarized in Table II-
- 1 are consistent with the hypothesis that the maximum conduit temper- I sture is dependent primarily on the energy dissipated within the conduit.
For a steady current through a 3/C cable, the energy dissipated per unit 2 length of cable is 3I Rt, where I is the current through each conductor, and R'the resistance per unit length of conductor and t the time that 4 the current is maintained. In the experiments under consideration, R 1 was an increasing function of time because of the heating of the con-ductor; and it was subject to local variations where a fault developed i in the conductor. Therefore, a quantitative correlation of conduit temperature with energy dissipation was not attempted. Qualitatively, however, looking first at the results of experiments with horizontal conduits, we see that the temperature rise of the conduit was relatively low when the experiment was of short duration (approximately 1 minute) because of early cable failure (tests Al-1, Al-2 and Al-3). In Test Al-
- 3C, which lasted about 15 minutes, the maximum conduit temperature was observed was significantly higher (192 C) even though the current was allowed to decay as a consequence of increasing conductor resistance, !
instead of being kept at the nominal value of 600 Amps by manual circuit I adj ustment. A comparable conduit te . rature (187 C) was attained in Test Al-6, which lasted a longer time (175 minutes), but in which the conductor was-larger and, therefore, had a lower resistance per foot. ! In.the aforementioned tests, the conductor either did not fail or failed l
.outside the conduit.- In Test Al-5, the conductor failed within the conduit and the maximum conduit temperature observed (416 C) was higher I than in any'of the'other tests in the same. series. This ireplies that i i l l
l [ w . - -- ... -- --
l I 7 the rate _of energy dissipation in the vicinity of the fault was greater than the rate along the rest of the cable.
~
The results obtained with L-shaped conduits were not significantly different from those obtained with horizontal conduits. The small 1 differences that may be noted are probably related to variations in the
, nature of the faults, and their location relative to the thermocouples.
Since the conduit thermocouples were approximately 18 to 36 inches apart, a fault within the conduit could be located up to 9 to 18 inches from the nearest thermocouple. It is interesting to note that the highcst conductor temperature observed in the phase B tests was 973 C approaching within 100 C of the melting point of copper, 1,050 C. It can also be noted that the cable jacket temperatures were gen-erally intermediate between the conduit and conductor temperatures, as would be expected. However, a quantitative analysis is difficult: for one matter, the method of attaching thermocouples to the conductor and jackets was subject to considerably greater variation than was the case with the conduit thermocouples. Also, after the cables were drawn-through the conduit there was no way of knowing the exact location of a thermocouple junction within' the cross-section (for example, between the jacket and the bottom of the conduit, near the canter of the cross-section or exposed to an air space). Matters such as these, however, were of relatively little importance in terms of the objective of the investigation. It was the conduit temperatures that were of greatest importance, because these determine the rate of heat transfer to ad-jacent circuits; and these were not subject to the problems associated with the measurement of. conductor and jacket temperatures.
?
5 e+ e tw,--,v--r--,-e--, e e, , -
,m,g - -
The most meaningful outcome of this first series of experiments was the descastration that maximum conduit heating was not necessarily accociated with maximum overload current. Conduit heating depends not only on the rate of energy dissipation within it but also on time; con-sequently, if a circuit is so highly overloaded that the cable fails very quickly, there is less conduit heating than that which occurs when the circuit load is reduced but is maintained for a longer period. d f 6 e 4
III-1.8 DETERMINATION OF MAXIMUM CREDIBLE CONDUIT TEMPERATURES FROM FAULT CURRENTS OF LESS THAN 600, AMPS. (Part A - Phase B Tests) TO DETERMINE MAXIMUM TEMPERATURE OF FAULTED CONDUIT Since the Part A - Phase A teatr and a few expsrimental tests with exposed cables (that is, not installed in conduits), indicated that 600 Amp currents in some cases resulted in cable failure before high conduit
. temperatures were realized, a series of tests were run with fault currents less than 600 Amps to determine whether conduit temperatures higher than those achieved with 600 Amp fault currents could be developed.
The cable / conduit configurations and the test currents that were tried are listed in Table II-2. The test arrangemants are illustrated
- in Figure II-8. The temperatures were recorded using thermocouples and strip chart recorders.
a i h I t
& - n- m w -
xtt- Csir 7.9:wnhv .Mitripitwla Cati ETg;_f itST. Stif Sllt CWti Ult iTC NO. ,(y) ' {d (A) f r sp) ' CO*:::UIT I Jf.CALT I CC3M,f R fitf' ARKS Horitojn al,T,e_s_ti t MreT""" e TK ,12 r., i50 -3 : 235 not rcLinary test tu select currin't To7feTt-to Csadult Conduit 14easured Al-13. Cabic coiled on ficor. Jacset Al-10 ruptured s30 in. f rom energizcJ end.
~
Al-18 3/C ell J/i IGO 14.5 194 290 5% Current was erratic e 9 & 10 rain. One pn.c.. 9 13.5 failed 914.0 aiin and another phase failed min 14.1 min. Canle failed in outlet t,oa and conduit. Al-lG 3/C ell 3/4 10 & 65 114 230 'not Nct catained consuit trrperatures o:WO'C wit-FeasureJ t*4asur-d 10 A af ter t;5 ein. Current then increased 85 A. fable failed 0114 min outside of cc:- delt. Prel. 3/G e4 :.a . 303 $5.3 ho ZJZ. 540
~
brcliminary test to select current for Test to Conduit Conduit A1 20. Cable coiled on sheet of transite. Al-28 Jacket ruptured in several pieces. A1-25 3/G #3 1 - 1,2 ZGO 2J.3 137 3d 575"~"~% C.O.as erratic d 10.6 and 21.5 man. O 9 16.5 ' 9 16 >% se failed @ s24.0 ein. Ar.other failed J min min 24.7 min. Cable failed instae and outside the conduit. Al-ZC 3/G s3 6-1/2 153 & 175 55 291 Not t;ct Getanceo conduit temeratures of 165'C wits reasured rassured I!J A af ter 65 min. Current tt:en increased to 175 A. Test stoppeo 9 95 min af ter te a. levelled off. Cable did not (411. Prel. 3/C e5 ..) 300 15.7 f.J *ot
. .;2 t Preliminary test to select currc1t for Test
? to Condait Conduit l'tasured tuasi. red Al 33. Cable Jacket ruptured 3 8.7 min.
Al-38 One phase failed 016.1 min. Another pnase
. fille ? 16.5 ein.
Al-38 3/C e5 1-1/2 JC0 20.5 222 563 5C7 iCarrent was erratic 0 sl9.6 cin. Ore puse 9 16 9 15.5 3 16 fatted ) 18.5 min. Another failed @ 20.e : ein min min Conductors reited at location outside of co
. hit.
Al-331 3/C e5 !.cne 450 4.1 t.o 255 I41 'Cicle jaciet rwturto J 2.5 min. One pnase Conduit 0 5.5 9 4.3 failed 0 W.4 min. Another ; nase failed 3 min min 4.6 min. Al-33 3/G s5 1 1/2 250 .M . 5 326 f.a t .o t %11 prsses failed 0 sM.5 min. Fire occurr-
. Measured Paasured at energized erd of cable. Ccnductors burn b -
. a.ay. Cable insida ccnduit not inspected.
Al-55 3-1/C f 2 -i-l/2 5CJ & 550 125 480 ' ta t sst *0ttained c:e:ut t tentrature of 418'C witn
. Measured reasured 503 A af ter 70 min. Current 'Jen increase:
to 553 A. One phase fallec 0110 min. Tes'
. r.4* D stcored 0125 mir tecause temerature was
-{ ,
, falling. One cond ctor melted at location outsica of condult. Cable nct inspected.
.U -
p Vertical Test f Al-5 3-IsG #2 1-1/2 5GJ 23.4 275 355 555 Test stcppeo 0 23.8 mn due to excessive
- p. 92S 9 23 scots frca cable. Cable not ins;ected.
,c; sin min
- 3 .
I*
/ L-Shared Tests .
4
-is. '
A3 15 3/C al2 .t. 4 100 14.4 laa 245 405 Current was erratic @ 10 min and recovereo g 9 10 9 11.2 '3 11 min. One pnase *:tled 314.0 rin. i ain min Anettier phase failed 314.5 min. Conduct:rt ( failed in cutlet box. ( ., AJ 25 J/C e5 1-Is 2 460 31.5 110 243 i 452 ;,rrent ceakea at 352-375 A and tnen stem 9 18.5 9 12.5 ' 3 23 3 200-210 A u..til 10.7 riin =nen currents to !~ sin min min care erratte. Erratt: also 3 23 and 25 r.ia. i Lost one snase at 26 min. Other two ocates o l_ q. , currents were 200-120 A 3 31.5 min unen tett [
- ended. Failure occurred witnin concult.
i .- A3-35 3/G #5 1-142 J00 14.5 231 27J 97J - ho concuctors f ailed at 14.5 mn. Ctacuctav
..: f ailed within condult.
l fABLEIl-2:
~
% Less' than 600 A temperature vs. time history for a 3/C #C AWG cable 4.
[ w ,. -,-
U III-1.9 RESULTS OF TESTS WITH CURRENTS LESS THAN 600 AMPS (Part A - Phase B) The tests data were processed in the same manner as for Phase A tests (Section 4.1). The results are summarized in Table II-2 and a typical plot is illustrated in Figure II-13. The highest measured conduit temperature was 480 C and occurred with 3 1/C #2 AWG cables in a lls inch conduit ' carrying 550 Amps (Test Al-53). S e W e-f i l-
FIGURE 11-13 With 300 A Current 1000 . TE. ST N. O . Al 38 LEGEND . - CONDUIT: II /2IIJ-
. O CONDUlT(TC2) l. .
CABLE: 3/C # 6 900 -
;---O CASLE- JACKET (TC7) p. CURRENT
- 3OO A
/* bs.
- -O CA8LE CONDUCTOR (TC RED) -
ORIENTATION:
. .e. ! HORIZONTAL
- ..:._.a.a
. . ......: ;_!.....t.. . :. .. g .
, _: .. g r. .. : -.r. -
.. . p .
.g ...g.
.. \.. .
800
.3' . V .. ! .. ! : : : . *!- I '!: S -
*. .I
-- ....---.-c.f' - , . . .
~~~~~~~;.t..:--
\. -
m .
.--~~.."
l
*.. . ;' - ' . . . . . . . . .l... .t. l..... # . . . . . .
4
*l:
8 L. , ;" i.. g. ;. ' '
. 3.
. . .. ...";'.*.?.. ! ,j.. . ,!.! .
g t.
'. !. -I i . 3...". ..!.i;. : . . :. . . .-. ..a ....r.-+.
*I
.. ... . .. . . .. . . . . . . .. .. ... ... .....,... .. '...$. . g.' ,.. . . .
s t
.p
- e. -.I .
. . . . .....g ..
9
. . e..
7QQ ,
. . . . _ . . ..','..* . * * .. A. ..
.' . . . . g
(....g.......;...~.J-. '
;&" ..j;
. ;$ * ~*.. * . *. * ...f- .!
. !!.;;.s. L. ';;; L .; " .. . . ' . .
; . n. .
j: R4 -
..b"- *
.. ' ! .......;...~.
t
.h ;
.. ./ ,
..I:;._'" ...3 . .:; .. . l
. L. .1. . . g..
.L.. . . , .
j ; .
. _ _ - .. .: -. a . .:. . . n :.._.. .. . ..; i; .m. . . . .n .l.. ...:....r...... :
O , .- -m g!:
.. *e. .t . , M .. n
..-;'t.. ' ;Ci . ;.'.e " . . f ;. ;;*, . S" *. , . :. ' f :
* * . i 600 I... ll 4 gj
. . . ... U l
.. t
, .. ,.a,..., .....g..
. ..l. ,. .. . I 1
....:..-...... . . . . .. . . . . . . . . . ~ . . i.-
. . . . , , ., ,g g ; g , , .; . . . . . . . . . . - . . . . . . . . . . . . . . .
e
, g i
. . . . . . .s .-.,......
. ._ .rp.. ~ . .. %, . .. g
- i- r-
. t. ... ..: . t. .:.
- m. .- :
w .
. . . .. m ... .
..-.g ga,)
- 6.
, .;.. I ;
g . ..
. .....,..,.l.-.. . . . . . . . .
- 2. .
;....e....
. e.
.. t i. .
- m......,...'.
- /. . -.. . .l.- ...(
g . .
)-
3 .
..a
>- $00 -
a .. r 4 - - -- ...."....'.:... . - .: ./ - .t- -
...,..-.,'-.L . -. - .-- . . . - . - - . ~ - -
E y . . . . . . . g. I. L. . ; . ' ' /
.;.. J'.*I....
\.\
.!.
- f .., . t . .
- n. - "
w.... E .... . ., ..
-.... . . . r . . .. . \
...1;....".. 1. . .. .
- O,
. . . .. . . . . . .. .. .. .. .. . . . . . .. . / - . .. *. ' . . .. . . ..! .. *.'.'
ta.) . .
.... .... . : . L. . ...p....
I" r . ... :
. ... ; .!'. ... ....-.4...
; . ; * * ;*l .. .' .. .. ,; ".'. ." e.
. ..! .". . * ; .....J. * ; r. 4. ; ."" .
.*..8 I". .. .. "'.* *l .......7.;.. 1. * ' .
400
- '-i = + - -%-- .i. . . . . ~ ~ . . ' .' ;I * ' _ i. . -- - . e - -- ...&., r -- t -- '. . .
.i.
. i. . .
. . , . . . . . . .. . . .... . ... .. .. .. ... f.....
. . , . . g......p.......,..Le ... -
. ., , , g ( .y . . . . . .
. . . .. .... . ..t..
g . ,
. , , . ..; ., .. . .. j . , #.
.....7...
.l
./.
. . ....p . . .. . . .
. . .I
. .; ; g . ,. . - . , . . 7 .;.,.,-.- .7 .. l ..t....
g ~ ~~ ~ . . . , . .;..; .. . . p . . o..-.
^ .' A. [.....
$QQ . . ..
. ~ " . . .. ." O
...,.,e.. . . . . ...' . ... . . . ...t. ,. .
I. . .
... "t. ..
- /
...........s, . . . . . . . .
.. i- ;
- e. .s
. . ,. ..r..s... . . .. t. .
. . . . . . . ...t.... . .
o . . .
... .. .. . .. *p. .. . -
.. * . s.
.........../..
..l..... ....
. . . .'t N* .
... . .. t.
s . ,e : . .: !' -Q ,
.I
- - -r-' - - - - : - - - - - - - -
t 200 - -
.. . . * . . - - d -- -- --
./. / * . .. .-. ....l.. . ..*
( 4, .
. . 2.
. . ..g. ..., .
. ,s . - .
./. a.
- ...-. .: . s. ~ ... . . . . . ., . : t. : ;
. f . .J. .p....
{** ..l.: . ,...... . . . . . . .
. .: .. ... 1; . . t...
?./ "!
,/ ..i.
,,O : .*
- 10 0 -
- . .n .. ~e
- f. , .- , -. ..,.g. ! . . .E....F-42. a, . :. . . .. : . . .-- . .
... , . . .g..
/
- g. .
- f. . ,
- .' j,f. . .i ~ . _ . ... . . . . . . . . . . ....
/- '
i
/ ,/ . . ... ... . . . . . . . . .. . . .I v ..;.
..i.
-46 .
g O ' I I I I O 5 10 15 20 25
%/ ELAPSED Tif.1E(MIN)
These tests showed that the 4/0 cables were large enough to sustain 600 Amps current loads for several hours without failing, and that the peak conduit tempeature levels reached during this time were less than the peak temperaures reached when smaller cables (conductor sizes 2, 6, 8 and 12 AWG) were tested. With one exception, the few experiments conducted with L-shaped conduits and the one with a vertical conduit yielded maximum conduit temperatures that were lower than the maximum conduit temperature obtained with a single horizontal section of conduit with the same cable and current overload. This can be seen in Figure II-15. An exception occurred with a test involving conductor size #6, in which the peak condait temperature was 231 F in the test with an L-shaped conduit and 222 F with the horizontal conduit. The tests with vertical and L-shaped conduits were not pursued further because it seemed that they would not yield conduit temperatures exceeding those observed in tests with hori-zontal conduits. This series of tests served to establish the highest conduit temp-eratures that are likely to occur with the circuits under consideration. The next step in the program was to investigate how the conduits heated by an overloaded cabic (that is, the faulted conduit) could affect an adjacent (that is, target) conduit. - The next step in the program was to determine the circuit loading conditions that would lead to the highest conduit temperatures. The data of tests conducted to determine the current loading that would 3ead to the highest conduit temperature to each type of cable are summarized in Table II-2 and plotted in Figure 11-15.
, w -
500 - (-. '
/,0, 450
/#'!' I \
\
\
/ #2 'g o
b 400 -
\. -
g 350 - y+ < L 9 E ,/ O h o#2 "L" g 300 - O #8
/A s
W- - I t-
@250
- / lL \
~
\ .
#12 l O # 6 " L" lk 0 g
2 200 - f i i N - [6 E {
# 12 \ O # 8 "L" 15 0 -
l #8 O # 6 " L" [ O # 8 "L" # 12 " L" r 10 0 - A ! 50 - l 0 0 10 0 200 300 400 500 600 700 l CONOUCTOR CURRENT (A) FIGURE ll-15 llaximum conduit temperat:;res as function of current load 1
If we look at the curves for conductor sizes 2, 6, 8 and 12 in Figure II-15, we note the following pattern: For a given conductor size, the range of current load within which the peak conduit temper-ature occurs, is relatively narrow; and the conduit temperature drops substantially when the load current' deviates by only 10 to 15 percent from the value that gives the peak conduit temperature. As the con-ductor size is increased, the peak conduit temperature also increases; similarly, the current load associated with the peak conduit temperature also increases as the' conductor size is increased. This pattern is consistent with the hypothesis that the maximum total energy dissipation (I Rt) increases as the conductor size' increases; although the value of R decreases as the conductor size is increased, the increase in I (current at peak conduit temperature) and t (time to failure) appear to be the dominant factors. The trend of rising peak conduit temperature with increasing con-ductor size did not continue beyond the range represented in Figure II-15, that is, conductor sizes 2 through 12 AWG. Two tests with #4/0 cable'(Tests Al-6 and A3-6), with sustained 600 Amp fault currents, produced maximum conduit temperatures no higher than 187 C after approxi-mately 3 hours, at which time temperatures had stablizied and there was no outward indication of impending cable failure. There was some slight smoke and some liquid dripping from the outlet box-during the time interval cf 45 to 112 minutes elapsed time. This-is probably the result of the heat removing the volatile ingre-dients of the insulation and jacket. (See also the remarks column of Table II-2.) 4
+-, ,-- ,
s , , - - - - . - , , - ,
III-1.10 MEASUREMENT OF HEAT TRUISFER BETWEEN ADJACE$T CONDUITS (Part B Tests) TO DETERMINE MAXIMUM TEMPERATURE OF TARGET CONDUIT The following general procedures were used in the Part B Tests:
- a. Thermocouples were attached to the source conduit and the target conduit. Because of the temperatures ranges (up to 500 C on the source conduit and up to 200 C on the target conduit), type K thermocouples were used on the source conduit and type T on the target conduit. (The type T thermocouple systems provided better temperature accuracy at " low" temp-eratures, but the recorder was limited to 260 C maximum.)
- b. The conduits, with thermocouples attached, were assembled in the flame test room into the required configuration. (See Table II-3). The heaters for ths source conduit were connected to the energizing and control circuits. Thermocouples were connected to their recorders and tested for proper functioning.
- c. Upon application of power to the source conduit heaters, an elapsed time clock was started. Temperature recorders were previously started. The temperature of the source conduit was increased to the first temperature level of 150 C and main-tained while monitoring and recording the temperature of the target cotJuit(s). When the target temperature appeared to be stabilizing (for example, less than a 3 C change in 5 minutes),
the source temperature was increased to the next level (for example, 200 C), and so on. The test was performed at source temperatures of 150, 200, 300, 400 and 500 C. The average period of dwell at each temperature level was 20 to 30 minutes.
- d. Thhsame.conduitsandthermoccup[eswereusedinteststhat differed only in the separation of the conduits. The conduits were allowed to cool well below 100 C before they were readjusted to a different separation distance, and retested.
h e w- -- y-r - = - -+ v +4V-e--- 9 ,ww-ye .-9v. v - g - 1 e W e- er - *=P"'- -
-e ,
III-1.11 SOURCE CONDUIT HEATERS The source conduit for the Part B, heat-transfer test was heated by the following methods:
- a. For the 3/4 inch source conduit, resistive heating was achieved by passing a controlled current directly through the steel wall of the conduit.
- b. The 1 inch sourts conduit was heated by three 3.0-kW Calrod resistance heaters (approximately 6 ft long), which were assembled inside the conduit and in close proximity to the conduit walls. The power input to the heaters was controlled using a stack of three 10 auto-transformars* which were wye connected for 30 power control of the heaters.
The temperature of the source conduits was menitored by use of thermocouples. The temperature was controlled by manual adjustment of the auto-transformers.*
*The auto-transformers were the same ones used in Part A tests.
1 l l 1 l l
Conduits of 3/4, lh and 3 inches sizes were arranged in configura-tions simulating field installations (that is, side by side, over and under in parallel runs, and over and under in perpendicular crossings) as summarized in Table II-3. The conduits were held in place with " Uni-strut" pipe straps and sections of " Uni-strut" structural channel. The free air space between conduits was varied between 0 and 1 inch in the crossover configuration and 1/8 inch (with pipe straps touching) to 1 1/8 inches in the parallel configurations.
"Touching" is defined as that condition where two adjacent conduits are installed as close as possible using the existing support details for the Davis-Besse project. As shown in Figure II-7, this represents physical contact at support clips only, with an air gap of approximately 1/3 to k inch between the conduits.
To prevent end effects from having a significant effect on the test results, a conduit length to diameter (L/D) ratio of 10 was considered adequate. The conduit length of 6 ft that was used gave (L/D) ratios that considerably exceed this requirement; the L/D ratios were 96, 48 and 24 for the 3/4, 1 and 3 inch conduits respectively. In each test, a conduit designated as the source or faulted conduit was heated internally to temperatures of 150, 200, 300, 400 and 500 C and held at each temperature successively while the temperature of the adjacent target conduit (s) was measured. These temperatures were based on the preceding tests.
l (tT ' T
- i '-*. f ; 1 -
gg7 y,,, , d. *r, .' . '. .'I, Ct.....
. . . . . f*'.81*:'t! I?- J f Ilftt:1.I'O'. ( *C 1 '
s1, se t ! l ?'* e r n r; ti,, }
- L ( *+: M * * - (l.N WIU8 f et Lf' !?.9 to:F8 18 "'I fi f H f 4 p.,, i , fcT7 g ..,...C
*1Tr$
~
-Cver and t* *cr-n;est,-u\ 4 S-1 3/4 3/4 Teu:r.f ng U1
( ,, , a[.7y . 95 - - .
' 5(parati.he-*,7 52-1 1-1/2 3/4 - Tca: ting h 53 72 116 153 207 B2-4 Con.fuit .
1-1/2 3/4 - 1/2 - 73
- 101 137 179 32-5 1-1/2 - 3/4 ' toxP.teg 57 85 125 171 82 6 1-I/2 -
3/4 1/2 . 44
. 62 90 126 Pfre Strud tMt Shown B2 2 1-i/2 3/4 3/4 .1/8 62 68 112 157 218
$2 2A See Note 3
- 84 121 163- 2C.3 (7) 82-3 1 1/2 3/4 1/4 1
- 49 63 88 116 150 of re Strm t:st %own 83-1 1-1/2 1-1/2 -
Toc:afng 60 86 128 176 I 234 ' 83 2A(O 1-1/2 l11/2 1/8 O 62 82
, 119 163 222 B3-3 1-1/2 1-1/2 -
1/2 52 69 103 146 193 814 1-1/2 1-1/ 2 - 1 56 71 101 132 177 Pf tw Stetis 'et The-n B3-5 1 1/2 1-1/2 1-1/2 1/3 67 83 122 171 220 83-6 1-1/2 11/2 1 1/2 1/2
\' 83 7 1-1/2 1-1/2
@ $7 72 106 142 190 (7)
- 1 1/2 1 50 @ 67 97 sie, $tries est 9e n 131 165 sp 82-7 3 1 1/2 - Touening -
68 133 193 252
! 82 7A1III 2 1-1/2 -
1/3(5) - 72 107 143 195 B2 7A2(5)
\ -
3 1-1/2 - 1/3 h - - - - 186 82-78 3 1-1/2 - 1/2 97 127 162 82 7C 3 1-1/2 - 1 114 182
** # fee Straes Est the s Notes: Cca t'd T
. (1) Conduit snariti:n were in ceitset ir. tre distance tet-een oire strus as illustrated in Figure it' er:1 ctrer. Te;
!!-7.
"Touching* m ans the strans greater than tre ts. tratica te:-een stra;s. free air s.are between ccndults (in parallel arrange: ents) was 1/8* to 1/4*
* (2) "I" desigistes tar;et c:*catt.
*5* destgiates ss.rce ::ftdJit. .
.. (3) 82 2A mas a repest of Tes* 62 2 to frerease the stablitraticn tire at each source temperature .
. (4)and 83-2 testwas rer.n as aterted
$3-ZA. af ter 15 ein when it was noted that wrer.g ccaduit separation was used. ~
5eparation was corrected
. ;- (5) Test 82 7Al was rer n as 82-7A2 when it was r.oted that the actual separatien distance (6) Avenge source te ;eratare was 137'C trstead of notinal 150'::. .
. (7) 14;er target ter; erat:,re.
i Te perat:.re of lowr target conduit was lower. TABl.E 11-3 l. Summary of heat transfer tests e o e
s'..
'r rt: CCtW.UIT
'* * *' b* #I '
- I'* I TC$T r w elf 5t7tt in )
UI t:st.s rs*! . .; . .s. . r r ' '. t* . .: ' e i rc). 7a. . . . I .< . a fin.)III rit**rt f.: fMT!Off 4. u L ~.. s ' 7C'
'. - . " 'i . u C
$$-1 1-1/2 1-1/2 touchini) 81 37 67 'N IJ6
$5 2 1-1/2 1-1/2 1/8 41 4 'J G8 92 127 85-3 1-1/2 1-1/2 1/2' 33 41 59 04 117 !
85-4 1-1/2 1-1/2 1 Pipe Straps Not Shxn - (t) . - 106 Date 21 3/4
- 42 L2 76 105 '154
- 84 1-1/2 1-1/2 Toucning 43' 54 81 157 218 (h te 3) 3 61 79 120 165 232 3/4 39 47 69 93 123
. 84-2 1-1/2 1-1/2 1/8 39 48
** 71 99 133 (mate 3) 3 b 40 43 68 95 127 i
3 6 s 9
-. .. 3/4 38 46 65 83 121 fio Pipe Straps 84-3 1-1/2 1-1/2 1/2 (hate 3) 38 48 69 94 131 (mate 3)
'3 37 47 67 92 127 3/4 37 46 63 83 112
( . 84-4 1-1/2 1-1/2 1 (Note )) 38 48 67 89 121 3 36 46 64 86 119
- 1. , Notest
!** *#- (1) *T* designates target conduit.
i '5' designates source condult. f (2) Conduit separaticn is the distance between cipe straps as illustrated in Figure !!-7. "Toucning* means tne straps were in ccatact with each other. 1he tree air space betacen conduits (in parallal arranger.ents) was
.. .. 1/8* to 1/4' greater taan the separacion betwen straps.
- 1, -
-(3) conduit seoaration ror tests 84-i enrou;n 84-4 is ene distance det een ene io er cone a it .aii and tne uoper crossing conduit. Pire straps co not enter into the :4in neat trar.srer cecnanism ror tnis configuration.
y
'I .
t . TABLE il-3(Cont) - t Summary of' heat transfer. test temper.ature vs. time historices for adjacent
~
i
;: 1-1/2 .in. s
- i
? ' l l / l-Op h
, , _ , ~ - - - -*,
(-i , 9- .
, x FIGURE ll-7 Conduit support configuration CONDUlT COUPLING
\ .
A
, CONDillTS PIPE STRAPS
_ / 8
. /
/
isi
% ' /
/ 8 8 \ / / :1 pV 1 1
A PPROXIM ATELY . -UNISTRUT 1/8 - l/4 IN. AIR SPACE IN CONTACT POINT 'V'
" TOUCHING" CONDITION O
III-1.12 HEAT TRANSFER TEST RESL7TS (Part B) The test data were processed in the'same manner as for Phase A l 1 i tests (Section 4.1) except that the analys'is was limited to source-and- l
~
target-conduit temperatures only. A typical plot of a temperature l history is presented in Figure II-14. The results are further summa- j rized and presented as Table II-3. It should be noted that the source-conduit temperatures are the highest temperatures ceasured at the thermo-couple locations. 5 l l 1 l l t 1 1 1 1 9
. (
c - FIGURE 11-14 a CONDUlTS WITH ONE CONDUlT HEATED
.g.... . , . ; . .-
i . 4
- a. .
..:.......- l. .i. .:: ; i LEGEND ! . . _g_":
J ;. . , !,TEST NO . 83 - 2 A 2 y[. : Q TCv 'ARGET CONDUlT i. ~ ~5 g a - T HEAT TR ANSFER TESI"
- Q GREEN-SOURCE i s - .
.: . BETWEEN STRAPS
,i.,
S ;d : -
--:;: .-...a
.c: - - . . .::
I" i 12 . . .; ; .g...-
;' . ..i . ."!,;:
. . ; i "i
-i 1000
--a: !
- - g: ai-- h.
- t. - . ; ,- '--i: - - - -< ; -
/,
. :: .i.. .!. ,.- ,;
-l ...:.. , .
.j.
..;.,; :. : q ,; i..*;;:
. ; ,, . !.. ;3;;;p ,,pg ;.,.q .
- .3 :. , A pg.g;9._4 . - -
500 900 . -s.. . . .
~' . c' . . -
_J 800 F '.
.l i :ti.. . - A '
- l . : :..j .-
--i - -. -e-- - - - -
i
- I: . .: p:**>.r-
. I.{' i*
s- .- ! ...? g i .r:
,,.. ;.; . .: . A . 0--O-- -
l.-
.....i-, .1' i :'.l i-- -
400
,, 700
- - i.. ;: e: h: ;--. ,....',:
; ' :. . =. : t-- . ..:.: !:;. ...:---
i.a.:.
.-,.,---.,a..
.i :
- -.- u g , ,
c- ' : . ' ' w j
- i.. O' . .
a +
- c:
. 4
- ./ .
Q 600 -- j -. - . . . - g'. : :/ . . .. L. . : a ' l . : -- - ;;- . . - . . . . e. . - .. :: ,- .g.. c: ! R y n, .
.f $ Ay---0-- 0 ' I. -
4 l.... . I .: . - .
- 1. - ..:I .- .. i : :' . .
.t....
i*:.
- 6. .g.
3004 (g c.
;c : ' ! i : . ! . j. j-. :
. l- : i.: ! .~?
w
- ^- 5 0 0 -- - - - - - . , - --- T -
c-u .
.l- ,! .- -
n s -
] . . -
w 400 - . p O 4-.4._ .
.g g-9--OS-G-3 -O-O--O '-
.- 200
. / ,. : .
300 - ,f.H)-g--g .--. g a
. d -- fi. . :a- .h... .,. i ..;
h !, ..,..!ad: C. -.!- .- - J ,- - . , -
.: .:q ----.
g ., . .;. ,
.,. c.l g. _; .. . - .
200 - 1 -i . ! .: ..
.1. . . . .
10 0
,00r _-co-oeoeg . -
!...:1,....; :
.It..".a.i(
i . 7.
; i -! -
].
. e. .l,
. l- ; . . I-, .. i . 1. - .
o I f f I I s I i I e. 1-o 0 20 40 60 80 10 0 12 0 14 0 16 0 18 0 200 EL APSED TIME (MIN)
e we III-1.13' HEAT TR.CSFER TESTS - Selected results of tests to investigate the effect of heat trans-for from an overheated, source conduit to an adjacent, target conduit are summarized in Table II-3 and plotted in Figure II-16. It is readily apparent from Figure II-16 that the influence of the source conduit oa the target conduit is approxinately the same in the side-by-side and crossover conduit configuratins as long as there was some free air space between them, while the configuration of a target conduit above the source conduit leads, as had been expected, to significantly greater influence of the source on the target. For a given configuration, the influence decreased with increased separation between the conduits. As can be seen from the curve for the crossover configuration with the conduits in contact, the absence of any free air space greatly enhances
, the heat transfer between conduits. In the case of parallel conduits, the conduit support straps prevented contact between conduits in the tests conducted.
e
FIGURE 11-16 Target conduit temperature vs. source conduit temperature 240 LEGEND
%J 225 - SYMBOL SEPARATION TEST CONFIGURATION /,/ t T "
- - - -- O TOUCHING B 3-1 g ,
----- 4 I INCH 83-4 S Sl70 ,/
---O TouCHING B4-1 1!" y 3" [/
1/8 INCH SIZE /# 200 ---X B4-2 Sl$E7 '
---O I INCH B4-4 b S S
[ y TOUCHING B5-1 ' g _2f." SI Z E / A ilNCH B5-4 ,/ 175 -
/
[ / U ,
/ O '
L / i w 8 /
/
i
/
D 150 Y
, / l i
/ !/ ,
h W /
/ /
/
n ,/ / g/ '! 0 I25 - ' f' *
,/
l y
$ 100 -
/
/ .l
, ,s O'
/l/ '
u
// , , //'/
. j
/ fl t -l25 -
,s
' , ^,/ l .
9- - V/./ ' ,/. 4 1 . 50 - l f g/g .--#12 MAXIMUM CONOUli TEMPERATURES FOR FAULT CURRENTS
-#8 46 #2-l " l "l " l i "
l 30 15 0 200 250 300 350 400 450 500 , SOURCE CONDUlT TEMPERATURE ('C) l I l
l a III-1.14 GENERAL OBSERVATIONS l Smoke Generation - Considerable smoking of the cables, accompanied by a noxious odor, was observed when they became heated by overload currents. The smoke was visible from exposed sections of cable, and i also noticed leaking out of conduit joints (at the condulet on one end and the junction box at the other end). The smoking usually started well before a fault occurred. The smoke generated by the heated cables is a potential visual and olfactory indication of malfunction. Discoloration of the Conduits - The steel conduits became dis-colored as they were heated by the overloaded cables (or the heater simulating overloaded cables). The surface first turned brown in color and as the temperature continued to increase, it then turned a greyish white. Along with the discoloration, a slight smoking of the surface was sometimes visible. The discoloration and smoking were probably j caused by the heating of the galvanized surface or of compounds left on the surface during the manufacturing process. As with the smoke generated by the cables, the discoloration and
~
slight smoking of the conduits are potential visual indications of malfunction. Effect of Ventilation - In one test (No. B3-2A), the exhaust blower in the test room was turned off for 20 minutes to check whether the level of ventilation used during the tests had a significant effect.
-This was conducted while the source conduit temperature was being main-tained at 500 C. It was found that the conduit temperatures increased by 2 to'3 C while the blower was off, but this rise appeared to be a continuation of the normal temperature stabilization. Based on this e
observation, it appears that the low level of ventilation that was necessary to exhaust the smoke generated during the tests did not have a significant influence on the conduit temperatures. Accordingly, the test conditions may be regarded as being representative of those that apply in unventilated areas inside a plant. e e b
+ .- . . . - . , ..,_y __- y
III-2.0 SUSTAINED ARC TESTS l To investigate the effects of sustained arcs on a conduit system a test configuration was set up to place an intentional fault internal to a conduit with the conduit wall being part of the fault circuit. Temper-ature rise of the conduit surface was observed to determine if this test was,a.tounding condition on separation. The equipment used . I circuit configuration was as shown on Figure IV-8. The test description is regarded as notes to the data sheet Table IV-1. III-2.1 DISCUSSION OF SUSTAINED ARC TEST RESULTS After repeated attempts it became apparent that sustained arcing faults could not be maintined. Once the arc was established, it vaporized the conductor material at the point of fault. All faults were completely contained within the rigid steel conduit and therefore would not directly affect another conduit. Temperature rise of the faulted conduit did not exceed 55 C in the worst case recorded and, due to the nature of the test, was a transient 4 effect.
FIGURE IV-8 Arcing fault test serup TO 480 V. LOAD CENTER. 9 t t taggg gye5 USED FOR. ' PROOOClMG HIGH CURREMTS U FOR CABLt' TESTIN(.m ico ArnP
\- .s. FUSE _
- - '$ s7.E E CONT ACTOR
/ \
g g o.2.n./ usu 7 R = 0.0 7.b/L
- r. g i
- R t40 R9tuC= e
- AIAM E7EG, A
{ g TEST CAELE
- 3/C #12. OR 1 t/c trl*L O
I"R5G THERtTOCOUPLE [- - - -. _ _. w ./ n ., su DETAIL EELOW 1
^
3, CouN EC7 tO N TO e - CONQUIT WhLL. I _ Co' t . CONQUlT r - SPREAD STRAt<CS
~~~9
[ CAOLE
. OF cot & DOCTOR.
} PREPARC
, AS RECD.
. A FAULT LO C AT I O N O L7 At t
'FI GU R E
- - w b
( -
\ -
\m/ ,
e 73 0 . llA).! i CABl.E CF !!;CUCTOR IMX. CtP FUSE TEST VISUAL TEST SIZE C0!;C!;iGRS INE CU Z IT TE,!ir USED CONFIGURATICil t.0. A 7. tsD (101 A) B te 11 ft.ote 2) RESULTS ARC (tbre 4) RISi I '.n t a 2) Ct"AT!M (M ( *: ' ; I 3/C #12 I El.5 YES Conductor touching Conductor strands tiote 3 160 sit inside of conduit, burned off to con-ductor insulation. 100 A fuse did, not
, open.
2 3/C 112 1 ELs YES same as for Test 1. sace as for Test 1 Note 3 240 W
. except fuse opened.
3 3/C 712 3 in ELS YES Conductors twisted Approxirately ft of *; parallel I;ote 3 520
~ together and bent conducters I,urnt of f Into U-shape with on bend *.5cre they bottom of U touching were touching the the Inside of the ccnduit. The fuse conduit. c;eneo .
4 3/C #12 i ELS N0 same as for Tes t i l sc e as for Test 2. tute 3 360 s .; 5 3/C s12 3 In ELS 5.0 Concuctors twisted The tips of the con-parallel Note 3 176 si! together and bent ductors ralted. The to touch the inside fuse opened. 9f the conduit. 6 3/C 12 3 In ECS lio parallel sane as for Tes t 5. rd arc. ruse opened None 120 e too fast. 7 3/C 12 3 in ILS ';0 Repeat of Test 6 t.one reported except parallel tute 3 304 %I2 with ELS fuse. fuse ooened. 8 31/C 42 I ELS YIS one #2 conductor tene reported. Note 3 s184 4 g g 1, . , terminated with 3 s trands f ro.T. a #12 conductor. Strands whiskers arranged to t' ' touch inside of I " conduit. S 3-l/C 12 1 ELS YES Similar to Test S . rune reported. 7ote 3 S240 $9 10 3-l/C p2 1 ELS YES Similar to Tes t 8. Concc: tor strands rate 3 S464
$13 burned a.'4 In.
II 3-l/C #2 l !.0 ELS $imilar to Test 8. fune reported. Note 3 S206 s3
. NOTE $t *
- 1. !rductors were tw large scecial 'eurrent transfor aers connected in parallel. There was no Infornation on their impedance, no. of turns, etc. Their dirrensions are approxir ately 23 in. by 21 in, by I4 in.
thick with a central hole approximately 6 in, by 6 in. P 2. 78 (v The tests were designed asrt perforned by D. Schieman of Bechtel with FIRL support. The test description and results were proviced by Mr. Schienan. 3 The measure ent of are curation o.as limited by tre capability of the current record'er (Iten No.18-256) whose pen response is cescribed as " faster than 0 3 s for full scale response." Secause the current traces appeared be reportedasasinstantaneous less than 0.3 s:lics
- s. on the recorder chart traveling at 16 in./ min, the arc durations can only
- 4. The ruximum currents can te reported only as appromlnate values due to the transient nature of the currents and the recorder limitatior.s discussed in tiote 3 above.
- 5. The conduit was cavipped with a ther ocouole on the botto i and another on the top. tiaxienum conduit temoer-atore rise was deter tired by the dif ference in pre-test and post-test conduit temperaturcs recorded on item P4. 18-237 TABi.E IV-1 .
Summary of sustained ARC Tests
.w- =-
III-3.0 EFFECT OF CONDUIT SPACING ON EJCTR0 MAGNETIC COUPLING FROM POWER CABLE FAULTS INTRODUCTION In some power generating station applications, where electrical o conduits carrying instru=entation cables are in close proximity to other conduits carrying relatively high power electrical distribution cables, electromagnetic energy-from high current faults that may develop in the distribution cables nay be coupled to the instrumentation cables. A series of tests were performed by the Applied Physics Laboratory of FIRL to determine the cagnitude of the coupling and its dependence on conduit type and conduit separation. The tests and results are described below. III-3.1 CABLE LAYOUT, FAULT-CURRENT GENERATION AND MEASUREMENT INSIREMENTATION ( To produce a ceasurable value of EMI for comparative purposes, with separation of the conduits as the variable, it was necessary to rearrange the electrical circuit configuration from that installed at Davis-Besse. To increase fault current and. increase EMI, the impedance of the circuit was reduced by eliminating the conduit and/or ground conductor a; a fault path return. This vould also eliminate the cancellation effect (typically 80%; Rel. IEEE-68-TP90-PWR) on the strength of the magnetic field due to the return current traveling parallel to the faulte,d conductor. See Figure III-1 for the cable / conduit layout. e
From this arrangement several different configurations were tested. Included were both power cable (source) and instrument cable (target) with no conduit; and both cables in adjacent steel conduits. In all of the " conduit" configurations the general geometry of the cable layout was the same: the source cable (3 paralleled, twisted #8 copper wires) was arranged in a rectangle 30 ft by 20 ft, and the target cable (130 ft of s ielded twisted pair instrumentation cable supplied from plant site) was placed in a straight line close to a 20-ft side of the source cable rectangle. Measurenents of induced voltage in the target cable were made with source and target conduits "touching," and with 1 inch and 3 inch separations measured between conduit outer walls. For the tests without conduits, the source and target cables were taped together; for t'ests with the cables in touching conduits, the conduits were in contact in as many spots as possible. ( The source cable was powered (from the side of the rectangle 30 ft from the target cable) through a three-phase.contactor by two phases of a 480-V/30/60-Hz line. A 100 Amp delay fuse was inserted in series with _f the source cable. Closing the contactor produced fault currents of about 18,000 Amps for one to two power-line cycles. Both source and target waveforms were monitared by wide bandwidth (greater than 150 MHz) oscillosecpes.
=i
-ry9 y
,- n n ,
.(.
. , .. p.pui y
~
. f , g_ .
( i <#i 34 <aOy '
'{ SU PPLY NC CONTACTOR h CURRENT SPLlTTER
& CURRENT PROSE 800 AMP FUSE
,e
,i g "
, SOURCE LOOP I) wtRE ONLT(3# EwlRES IN PARALLEL) .
- 2) WIRES IN ALUMINUM CONDUIT 20' '
3),wlRES IN STEEL CONDUlf 30' . UNa5TRUT SUPPORTS & CLAMPS H OCONDulf
~
8 ALTERNATE l 8 INST RUME N T j g LOCATsON WSTRUMEpiT i.____., ,, .,
,, )
_n i, . LOCATION 3 y
,I :
10 0 , \ . l,
# RECEPTOR CABtf *
. 30 OF CABLE WITH NO CONDulT I) wire ONLY(2 CONDUCTOR WIS $HIELDED,Twl5TED PAlR) 21 W8RES IN ALUMINUM CONOUlf 31 wlRES IN STEEL CONDUlf Fl5URElil-1 -
, Current source and receptor configuration P
. m. -o. . , ,. . .: . .
The voltage induced in the target cable was ceasured three ways: ( wire to wire; wire to shield; and wire to wire-shorted-to-shield; the
.last of which is not a normal condition. This essentially is a voltage between the conductor and the shield. All measurements were performed with the far ends of the source and target cables both open and shorted.
Maximum voltages were recorded with the far end of' the target cable shorted and ceasurements made between wire and wire-shorted-to-shield. All further measurements were made using this configuration to obtain the highest noise levels possible. III-3.2 EXPERITTIAL RESULTS The oscilloscope triggering was arranged so that the fault-current monitoring scope was triggered by the first positive-going voltage appearing at the scope input. The induced-voltage monitoring oscil-loscope was triggered by the sweep of the fault-current monitoring k scope; thus both sweeps started at the same time. Although there was some variation of waveform due to fault in-cidence, the induced voltage was a rapidly dampened, high-frequency (about 3MHz) transient waveform with maximum amplitude of about 3 volts, peak to peak, over a time span of 3 to 5 micro seconds and decreasing exponentially on the order of 20 micro se,conds. See figures III-8, 9, 17, 18, 19, and 20. l t l k i
49 * ' , . ' .M85 6N #
~~ ~~ '
y
,' an-
', K
^
.) _.
1< ) a g T ' Y
, w
[ .. ,,
., ~- ,a .
-,- , a3
. ' 4 ,,
.s ~
,.. g -( .
4* :
. *. y-
,. m/.
g', .- A.
. ..- %'- w , , - .
- g- .e p -w,
. .: -d g - '.
.g=
-y . .
',, t 't *
' ['
s.- 3 .
. . - , . , , #, k ~ , '*' . ,
~ , . - -h- t e - t f -s
#$ r
*[ ,( . .- ,' ,
l._ . l . * . .
. n -
g g o. g v ._ ?, .c - _l
,y Y-Y$$ y h hje:
- h ., ;-
g ,_ g. u . , 4 ' l . 7 . .. 7 .
- 2
.~ . ,A. +
7" _ 4 :
*V
(.- * -
)
s - 4 . 9
*i - .,
g g . n
- x g
,..)
. .# 9
. e a
,L
.c f . .- -
e
.x
. .D N
j c a-e g: 6 -- % 9
, g
')'
+.
A * *-
e._
*D ,. + ... c
-4 .* - , .~ 'k .[, .
. . . ^
.' . . 6 .v $. ,.d. 5 .] #. #
I-mb1 6
..y h- y . ,
- g. . e ', , - g s' - "*-
, .g .;> ;
,4 '4 '
'-^'
,' ~
h ..
~ '
, , . . . ,. . s...
, .' s.)
j Q 4
- y , t , *
, . ' . ." (
o s. e . 1 ; . ,
. , ~ ~
^ '
( **
- N %h % k, '
4 4- .
' ' 4 >
*~ . .'-
- o. f -- ; y .V -
_e. t.*
,s
, ." j
, , %% '4'
. 6" .. . . .
+
e
,j
" . . $M . . ... k,* sj y.
r L
-45, ww4s4 din.,7 mn 14 et/4tv. ,y L.
.t s:, A7 4 . u l3; 4~ ?. t - 3O
...........7 e..
A . 4
. . . . . . .4. . . . , ..
3 . [.-... .:. n~ l, - , - - l *. J,
.w -. _ "
4, D u- . 9 h, hAAm W m4 f.'P
* { g y ;+ . E g.j 4 i
3
'g y}'- y-
__ ___.... l ,.. h.
. 1
) . j -
I s
*$- ( a
_ . ,_.f . -,...
;yfRK-
., r - , y
.(se .
g ,y . M , p-4 P , tsa
.ty, . t + '. . '
Md(:
* ., - . .. . . . . . . . . . . . . . . s
_ , f . ". .:._ s. p . y .
. - e ?,
- g. g . . -
O'
' . . , .e 3) .y . ar. - - W '- s
< 4' s-
- 4 )d-.' + ,; , Ak ""
... 9 '
4- L.
- f N* *
,J , #
[ T *[, c k.[.'t .
*- ~
~
,.. s%. *y
. . . , *i n n.,
s
.. . p
, , . j . . pi , - g -.
I f Y - ,a-c p, .
+ ., . : '
=
.s 1
. . ,[ .
- >2 . . . - - . g.-
n y
. . +. .
~ ' * *
.(. . ., - - s. -
- 3. .
s .. 2 n 9.5
.- 3 g,,
. . . j g ,f. . - .3 '+ '
. 'e tig, ' *
- s. +-
o; ,_ -
- ( y .:,, g#;
',' y n # s >>
, _ yy 4-
, i 4 - ,, ,
i .. , )
- 4, ,
p . . g .
- . y ~
r ,.' r 1 ', .
. &M s..' .4 . ,. r. ..- - 944
- i
' ~
.~ ,* . .
,~
. .*~
2 '. '
- l. 4q . p,
. g ,,
4 # . e.
.*~
s t-e a.4^+8 ~ .:r {, s - 7 ,. p- .. f e .< . < *
. ., . . . * . - ~
, ' ,, . . - g)
.i (,- >, i<- ,. 4 s
, ..* ' .' S 3
' d.
! . . ~
7, a e" 1 M. . -
' I '-
..g. . . . , ., ,_ s,_. . ;-
.._....g
3_ ,-g g y, h ..
* ~g , . s 4 , - ,
.g
"~., ' *
. . ' ' . ..' ' ) *
, 4 , 4 a-
., - y
.y z-
~
e _g
^
.-( ..
, y ' - x ,
g --+ . g .
- h. .
; a ;
~
~ . .
& .r _- '
s.
~
p. g + * ' i '
'e ,_ , ,
..,. ' O=f %$$MIT., #d Mj% ' t
* ~
~ b '* ' . .
a,.% s, .
. e. , g <
'l e
_.- r up -.any c-
.* N
, s~'-
O j , . f - t
..e + q~ ,
' .; )
4 a O, ,
n .
O'
, + -
'a
., 4-w k,
t . #., * * . p 3 m g, ,
) ,- ' '
. s. f )
. 4, t , < . e ..
g
' s _
a .
,Y ' .
",.~'
3, , ? _. (. ,
. 6g '
-- . i .
n.
'l
?Yf ,
s. g
%~
__ y :? z + ,
^
, p. ' ' * - *
.a- ,'4 ;*'- '*
.. Y' .' h q a
Y' '
-
- hhh k@tt NI .
N"
~ ;'
4 ~ U -
+
4 '. i .,
+ .,
' +'
3 4
/t e
s w
. d
)F . ' ' '- -- ' . ,
. .): .
_ g
^
- j.. *a. . .
4
~
. ._ . n i
s .
- 5. ,
v 4'_ g - y.
^
?- -
s ,, e, . . e- ~
~- [ '
- h '
$ +., * '
l.
.. est SWed.. ts' .1 tacts agerettec v .'
.s .~'
. ' . _,g-
.+ -
4, . , -
-y .
~
g
, _ , y __
a , s,,. f y ., , ,
"% d e
* ~
w.
.. ,s .
.s. -
* - 0
+ '-
, ' , 9
. y . .A ,
.. . . .i _
~
,1,. q . , ' ,' * * * - - ' '
,, . q w- + - ,
,g' v "
M*
, y
. f .
~
e.-
',(
, g. ,
. )
3
*p 7 -
, .4 a gj 4 ,
I
,. y .
. - . e j
.',,{* ,g i - -
i 1 .' a .. x ,. & y., . c
./
S ' g,
,e-
, 4 .
$ 4 W. $ts/dIV., N MIWe '
M .. m
.g
'g7' . y
}
'p.-
.7".
, b g* v-
%="
- f: ,
~ .
.y
.. _. . . , . .. . _ , , . _ .4 ,
4
* + -
- . .. a 3
-. - g .. _
g .
,. %.~
' N i ,
+
- s. I -
- 6 .
. t . +
5 a o ; a ...
. - ~.
_ ). . g , , g' -
. t .
. .- FigurepsE pseinescome-Trentag Spine 4 condelt a ,
..p
- ,. .4 . . seek stydp . condutes .TempMag
'[ -
" b ,1 i1 '
4 +
$ ' 7 M YD g. ~ 9.g a' -
e, .;.r..'"
~ ~
. . . ,e ,
.- s.
%- +# * * ,
p W s ,. , I g -- - 4 y
,. . i
- y. I ;
- . - 1 l T. : .1 i ! I i i
( ff,-
- i. '
.. - O m- '- - - . . . , ,. ,
I(( l .f y
. f f y i j - .. .
4 4- 4 ., 4 e in . , u e- . . < r .*
, gg .
> n .
;. < , , , m ..
;9 4,,6*-
% s .
s.r ..
, . ~ ...
, "p. ..
+ . -
g g ,.1 , * . y .# .
.g,. ..
. g ; * .i .
.e , .
. . ,' % l O-* ' '
4 - i g .k f ..
. v.
.- .2,.,-
- e ',, :
l.
..~!- _
, - ,, ,, f , g
- k
; -^'
-j . -
. _ . . . .. ,. ' b( l V .
tk* -
.g ; - s y; y_. u
- 3.: , . . .
, , - .- u A .
g ,_ .- ;.- 4 1p . . ( , --
, ,g $ , .-
- v .
-- +. , s .:
.Ew - , - . . * , * . . _ , ,,
g, *' .
a III-3.3 ' DISCUSSION OF EMI TEST RESULTS At first glance the results of the tests may seem surprising since so little voltage was induced in the nearby target cable by an extremely high current change in the source cable. We must also take into con-sideration the fact that the layout of the test was designed to maximize the pickup by the parallel runs of target and source cables, and most impo[tantly the fact that the teats simulated a phase-to-phase or phase-co-ground fault that had a current return outside the source cable or conduit (pickup would be reduced otherwise, in that there would be magnetic field cancellation by the return current). The factors that must be taken into account to understand the results are: (1) the fact t' hat for any pcwer distribution network of large dimension the conductors themselves present an inductance that prevents extremely rapid current change - and it is pri=arily the rate i of current change that provides coupling to nearby cables; (2) the in-strumentation cable tested incorporates in its makeup the specific remedy for unwanted electromagnetic coupling - it is a tightly twisted pair within a fairly good conductive shield. It must be noted the characteristic response of the instrumentation cable was a damped sine wave having a frequency of about 3 MHz; this frequency is a direct result of the cable length of 120 ft. If a short electromagnetic disturbance is coupled to the line, the disturbance will
" rattle around in" or bounce from end to end of the line (assuming a line mismatched at each end, as our cable was) until it dissipates. The time between recurrences of the disturbance at one end of the line will be the time it takes the disturbance to travel to the other end of the line and back. In our case, this is about 2/3 (ft/ nanosecond) x 240 ft,
\
- ~~-
,n. - ,, -r
or approximately 0.36 us. This would result in a repetitive waveform with a frequency of 2.8 MHz. This approximate calculation agrees well with the observed frequency of approximately 3 MHz. Based on chis analysis, the actual frequency observed in a current-fault occurrence would be expected to be primarily datermined by the receptor cable length, and the amplitude to depend on the fault magni-tude and the source-to-target cable spacing and geometry. III-3.4
SUMMARY
AND CONCLUSIONS OF ELECTROMAGNETIC COUPLING From 131 fault-current coupling measurements, using fault currents between 13,000 and 18,500 Amps, and tests specifically configured to induce EMI, no induced voltages were obtained greater than 3 V peak-to-peak for longer than 20 micro seconds in a nearby instrumentation cable. The separation between the fault-current co'nductor, or its conduit, and the instrumentation cable, or its conduit,~was varied from 0 to 3 inches. Table III-2 lists the maximum voltage observed under each set of conditions. Although there are uncertainties in the da'ta, primarily due to our inability to-switch the source voltage at a controllable, repeatable instant, we believe the data demonstrate that the voltages coupled to instrumentation cables near fault currents of 18,500 Amps are in the order of 0.5 to 3V peak-to-peak; this was true for spacings of 0 to 3 inches. These specific conclusions hold only, for parallel runs of about the length investigated - about 20 ft. However, we can conclude that the spacing of from 0 to 3 inches should have little influence on the magnitude of the coupling, no matter what the length of the parallel cables.
I TABLE III-2. MAXIMIDI OBSERVED TARGET CABLE VOLTAGE (PEAK-TO-PEAK)
' Free Air Space (in.)
Configuration Zero 1 3 6 No conduit on source 2.75 _ _ or target cable 13 8 8 Both cables in 1-in 3.0 3.0 3.0 steel conduit 17 Source in steel 2.75 - - conduit - target bare . The circled numbers give the number of measurements obtained for each set of conditions. We feel compelled to state again that we were only able to get measurable induced voltages through a contrived conduit arrangement
- not typical of what exists at Davis-Besse. Therefore, the test evidence linking " target" cable length to frequency of the induced voltage is strictly academic. Again it must be noted that the tests were artificially ~ contrived by not taking credit for the cancellation effect of the return current in the conduit for the sole purpose of
- achievine measurable signals on the target cable. Where lower values of
- fault current are used and the conduit or cable ground conductor returns 1 the fault current, no measurable signals on the target cable could be recorded.
\
IV-
1.0 CONCLUSION
S A. From the results of the point fcult tests it is concluded that point faults in the Davis-Eesse conduit system
' 1. Do not propogate beyond their own conduit.
- 2. Do not elevate the temperatures significantly of the faulted conduit.
- 3. Are not a factor l'n separation criteria.
B. Frcm the results of the EMI tests and the noise rejection capability of the RPS and SEAS systems it is concluded that:
- 1. On the Davis-Besse conduit system, no EMI is introduced into the target cables that exceeds a 3 volt peak-to-peak signal for a longer duration than 20 micro seconds. The only safety systems that use low level analog signals that could be affected by this EMI are the RPS and SFAS systems. Since the RPS and SEAS bistables do not electronically seal-in for a signal less than 52 milliseconds and 15 milliseconds in duration respectively, the induced signal vill not cause the RPS or SEAS systems to trip. T. erefore the EMI produced will not adversely affect the safety functions of.these systems.
- 2. EMI in the Davis-Besse conduit system is not increased for separation less than one inch.
- 3. Conduits closer than one inch do not degrade other systems ,
because of EMI since separation is not a factor due to the shielding used on Davis-Besse instrumentation circuite
\
l [
-C. From the results of the heat transfer tests it was found: The maximum temperature of the faulted conduit carrying No. 12 AWG power cable was 230 C (test Al-1C) with 85 Amperes. Lower currents caused lower temperatures and higher currents, due to melting of conductor, and therefore shorter times, a.2o caused lower tem-paratures of the faulted conduit. Combining this vi:h the results of the B series of tests on #12 AWG which showed the vertical configuration with conduits touching to be the worst case, results in the first design criterion based on thermal considerations.
(Reference is made to Figure II-16.) Quotations from Appendix A.
"1. Conduits carrying control, instrumentation, or power cable (where the power' cable is limited to 480 volt or lower and No.
11 AWG or smaller) are allowed to touch each other." As it was not practical to seek another laboratory to do high power I testing, in the time frame involved, and relatively few conduits were involved (a dozen or so) the design criteria for conduit separation for . power cables 13.8, 4.16 KV and 480V load centers was based on Regulatory Guide 1.75 1.e., one inch separation. These tvc design criteria are:
"2. Conduit carrying essential class IE 4.16 KV power cables or 480 volt center power cables will have a 1-inch =inimum separa-tion from conduits carrying class IE circuits of a redundant channel."
"3. Conduit carrying non-essential 13.8 KV, 4.16 KV, or 480 volt load center power cables that bridge conduits carrying essential class IE circuits or redundant channels will be separated from conduit carrying circuits of the redundant channel to give a minimum separation of 1 inch."
4
- -- - e y
~
The 1 inch vertical configuration was shown to be the worst case f from the heat transfer tests (Test Al-5B ) and the maximum source conduit temperature was 480 C for conductors larger than #12. Using the worst temperature case of the faulted source conduits (Test Al-5B) and the vertical configuration, which is the most suscep-tible to heat transfer (i.e., the worst case) gives the curve and axis point to determine the worst target temperatures. From Figure II-16 this temperature is 167 C for the vertical configuration with 1 inch separation. Using the same figure for the horizontal-touching gives a maximum temperature of 127 C, and for crossing with 1/8 inch separation, a temperature of 120 C. Considering: 1. the cables used have been tested for 160 C for 13 hours LOCA conditions and, 2. the maximum temperature of 167 C could only be reached by manually adjusting the fault current to hold it constant to counteract the inherent increase in resistance due to temperature rise; The following design criteria are conservative and just . fied:
~
"4. Conduit carrying essential class IE power cable of 480 volt or lower voltage with conductor size larger than number 12 AWG, and not covered by 2. above, will meet the following criteria:
- a. Will have a minimum of 1/8-inch separation from the surface of any conduit crossing above which contains an essential class IE circuit of the redundant channel,
- b. Are allowed to touch conduits containing an essentAal class IE circuit of the redundant channel when installed in a horizontal, side-by-side configuration.
t
- c. Will have a mini =us separation of 1 inch from conduits
( containing an essential class IE circuit of the redundant channel mounted directly abova and running parallel." To control bridging of conduits it is necessary to impose a fifth design criterion relating back to the previously stated items therefore
, ,,"5 . Conduit carrying non-essential power cable 480 volt or lower voltage with conductor size larger than number 12 AWG, and not covered by 3. above, that bridge conduits carrying essential class IE circuits of redundant channels will be created as in
- 4. a. , b. and c. for proper separation from the redundant channel."
It is therefore concluded that conduits placed closer than 1 inch, but limited by the five criteria established above, creates no adverse impact to adjacent redundant channels of Class IE circuits. D l
.- - - .-- . - - - - - -}}