NASA Technical Reports Server (NTRS) 19940024208: Evaluation of pyrolysis and arc tracking on candidate wire insulation designs for space applications

16 Pages·0.27 MB·English

by  NASA Technical Reports Server (NTRS)

EVALUATION OF PYROLYSIS AND ARC TRACKING ON CANDIDATE
WIRE INSULATION DESIGNS FOR SPACE APPLICATIONS
Thomas J. Stueber N94- 28711
Sverdrup Technology, Inc.
Lewis Research Center Group
Brook Park, Ohio
and
Kenneth Hrovat
Cleveland State University
Cleveland, Ohio
NHB B060.10 Comparison
Apparatus
Sampte Descrlptlon
Procedure
ResuLts
Discussion
ConcLusions
Future Plans
NHB B060.1C (Aprl[ 1991)
Flammability, Odor, O??gassin _ and
Compatlbltlty Requlremen±s and Test
Procedures ?or Haterla[s in
Environments thQ± Support Combustion.
O??lce oF Sa?ety and Nlssion Quality
Section 4.18 Arc Tracking (Test 18)
PI_IdDII)ING PAGE BLANK NOT FILMED 131
PURPOSE
Determine abltlty oF wlre
insulation materials and
constructions to resist
arc tracking,
Assess damage caused by
initial arcing and restrike
events,
TEST CRITERIA;
NHB 8060.10
Arc propagatlon on either Inltlal appllcatlon
oF power or on reappLlcatlon o? power Is
considered a test Failure,
Tests conducted on samples o? worst-case
use Insulation thickness and wlre gauge, and
in the worst-case envlronmen±.
Wiring For Space Appllcatlons Programa
All candidate space application Insulation
constructions arc track,
Worst case Insulation, prepyro[Ized polylmlde
wire Insulation,
Results oF Arc Tracking Initiation,
Self Extinguish (Best scenario),
- No loss In wire bund[e performance,
- Charred Insulation.
Conductors Lose Insutatlon (exposed conductors)
- Safety h_z_rd.
- Short-circuit risks
- No loss In wire bundle perForl_clnce.
Severed Conductor.
- Lost use oF _ wlre palr within the bundle,
- No loss In remainder oF wlre bundle performance.
- No loss in wlre bundle performance,
FL_shover Severs All _/Ires. (_/orst scenario)
132
Best and Worst Case DiF?erences
Voltage diFFerence between two conductors.
- High enough to break down the dielectric
strength oF the charred mnterlo[.
- Not high enough to break down the dielectric
strength oF the charred material (sew ext.)
Curren± Ftow,
- High enough, such that Joule heating will con±lnue
to pyrotlze neighboring Insulation.
- Not high enough, such that Joule heating will
continue to pyroUze neighboring Insulation.
- Self Extinguish
- GLow (Ike a carbon Filament tight bulb
(Vacuum case)
Proper[y Insulated Wire,
(Rated For task requirements)
_/ILI not Arc Track due to voltage
diFFerence between conductors.
_/IU not Arc Track due to typical Joule
heating From current In conductors.
Be£ectlvely Insulated Wire,
May momentarily short-clrcult
- Arc generated heat nay char the
Insutatlon.
- Charred Insulation towers the
dielectric strength.
n # oF momentary short-circuits before
sustaining an arc.
_/orst state oF Insulation.
- Pyrotlzed to the point oR sustained
arc tracking,
- Restrlke possible.
dielectric strength.
133
Necessary Res±rike
MIn. Voltage and MIn Current
= EQUALS =
Mln. Voltage and Min, Current
Necessary to Pyrollze the Insulatlon
To The Polnt o? Sus±alned Arc Tracking
Arc Tracklng Circul±.
[ ] Arc Voltage
I]
I C°Mputer I
It t Arc Current II
t;
11
II
#C
+ - I II
Power
Suppty
/ Sampte
wire,
Non-short-clrcult
is, => r':Z4_rOi.'.._ 4;;-_
potential between Hax :_P-:or i:- ::it-;- u{_
conductors.
Supply Return
+
Terminal Strlp
j
Twlsl_rd life p_lr
with space =ppUc_tlon
¢_hd_date _suJ.(_tlon
A|u_lnu_ cud
etec'l=rlc=t
blos wire
InsuLation ty-wr_ps
2M Of Inlulatlon s_rlpped _ rJ
AtueLt_ cup
Pl_tfor_ ,
ol_r_tor _lse
_nd |owcr
Portion A Position B
134
Insutatlon Construction Descrlp±lon
Champ[ore #i 2919 Kap_on (50%rIL)/Ex_ruded XL ETFE
Filote× PTFE Extruslon/616 KQpton (50% Mln OL)
/PTFE BlspersJon.
Thermatics #3 ModiFied PTFE Tape (50% rain OL)/TPT
Tape (50% MIn DL)/Mod PTFE Tape
(50% rain nL)/PTFE Dispersion.
Abl0revi&tions: 2919 Kapton => 0.5 mltFluoroc_rbon (PTFE), 1 ml[
Poiylmlde,0.5 M;[Fluorocarbon (PTFE).
GIG Kapton => 0.1mJLFtuoroc_rbon (FEP), I mJt
Potylmlde,0.1rollFiuorocorbon (FEP).
XL => CrossUnked,
ETFE => Ethytene Tetr_Fluoroethylene,
ilL => OverLap,
PTFE => Poty TetroFtuoroethytene.
1 roll => 25 micrometers.
PRDCEDURE:
i) Sampte Assembly and Installation,
2) Vacuum or Atmospherlc Air Pressure,
3) Arc Tracking Initiation,
4) Arc Tracking Restrlke,
ARC TRACKING INITIATION:
Bbjectlve= Manually initiate arc tracklng
on the wire sampte,
Procedure; Raise and tower platform untlU
arc tracking started.
Next Stepz Terminate power,
Reset power supplies to OV.
Test samptes ready For
res±rike tests,
135
ARCTRACKINGRESTRIKE
Objective, Ascer±aln minimumvoltage to
sustain an arc,
Procedure,
Increment voltage From O.
Results: Upon restrlke, terminate arc
by removing power.
Log Data, Open-Orcult-Voltage, and
employed current [Imlter.
Calculations: Potential Short-Circuit-Current
and, Volt • Amp product,
FUTURE INITIATION PLANS
Arc tracking did not Inltlateat onset oF First
momentary short-clrcult,
Number oF momentary arcs necessary to initiate
arc tracking may be dependant on the Intenslty
o? the arc,
QuantiFy the energy necessary to Initiate arc
tracking by summing the energy In each arc
during Initiation exercises,
Use computer to log the data.
Thls InFormation may determine which Insulation
type is least likely to start arc tracking,
FUTURE RESTRIKE PLANS
Monitor voltage and current charac±erlstlcs
oF an arc.
Obtain necessary pyrotysls energy,
To determine which Insulation ±ype is [east
tlkely to restrlke,
136
Champlain Arc Tracking Restrike
AWG 20, Vacuum
36O I
...'" ,. •.""
,....•'"
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0
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Short-Circuit Current (Amperes)
Filotex Arc Tracking Restrike
AWG 20, Vacuum
360 170.0 0 IIN
..... .....'" ....."
4.t
O
270 o.; ..d _ . 29.4 t_
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Short-Circuit Current (Amperes)
137
Teledyne Therm. Arc Tracking Restrike
AWG 20, Vacuum
360
.°" ,." .. .,,
t/J 0 •' I.'°
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>
270 • •." ...' 29.4 f)
ota0 ..8 # ." .• ..• .°.O" iii
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0
0 1 2 3 4 5 6 7 8
Short-Circuit Current (Amperes)
Champlain Arc Tracking Restrike
AWG 20, Air
360
t_
O
>,
270 29.4
im
ee
4.t ,°.,.,°'""
N
O 21.3 f_
>, 180
..,.,-"
.,.,.
o
Pw,q 90 _'"!
•- .g
! ..".0._
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O :..k:Si2:..-."
0,_" .....
0 1 2 3 4 5 6 7 8
Short-Circuit Current (Amperes)
138
Filotex Arc Tracking Restrike
AWG 20, Air
360 Bl.Of) 65.
0 .." ... .."
.." .. .° .°*' .°
270 , f' i.• 29.4_
.. .' ..."
M ." .0 .."
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0 1 2 3 4 5 6 7 8
Short-Circuit Current (Amperes)
Teledyne Therm. Arc Tracking Restrike
AWG 20, Air
360
¢,q
4..,t
O
270
29.4
4,.t
O 21.3 t_
>, 180
._..t
¢J
r..) 9O
!
l:h
O
0
0 1 2 3 4 5 6 7 8
Short-Circuit Current (Amperes)
139