Tests on XLPE-insulated cable arcing faults and arc-proofing

Abstract

I n s t i t u t d e r e c h e r c h e d'Hydro-Qusbec (IREQ) 1800 montee S a i n t e -J u l i e , Varennes, Quebec Canada JOL 2PO A b s t r a c t -An a r c f a u l t 011 a c a b l e or s p l i c e inevi t a b l y damages a f a i r l y l o n g s e c t i o n of t h e c a b l e a f f e c t e d and a l s o j e o p a r d i z e s t h e e n t i r e f e e d e r . Even more s e r i o u s , p e r h a p s , i s t h a t i f t h e f a u l t o c c u r s i n a manhole, a d j a c e n t equipment can a l s o be damaged by t h e t h e r m a l and m e c h a n i c a l e f f e c t s of t h e power a r c . I n view of t h e i n c r e a s i n g number of a r c f a u l t s on underground s y s t e m s u s i n g XLPE-insulated c a b l e s , q u e s t i o n s a b o u t t h e adequacy of a r c p r o o f i n g have a r i s e n . A l a r g e volume of tests a t a v a i l a b l e s h o r tc i r c u i t -c u r r e n t l e v e l s of 8 kA performed by IREQ a t t h e r e q u e s t of CEA l e d t o t h e c o n c l u s i o n t h a t a minimum s a f e d i s t a n c e of 50 cm s h o u l d be m a i n t a i n e d f o r nona r c p r o o f e d equipment.As f o r equipment p r o t e c t e d w i t h new a r c -r e s i s t a n t t a p e , t h i s d i s t a n c e would be s u b s t a nt i a l l y reduced. S t a n d a r d t e s t s based on t h e u s e of f a u l t e d XLPE c a b l e e n d s are proposed t o v e r i f y a r cp r o o f i n g e f f e c t i v e n e s s and t h e a r c -r e s i s t a n c e of materials.

Distance Protection of Cross-Bonded Transmission Cable-Systems

“…As the resistance increases, however, only a little current will flow to ground at the fault location and for a grounding resistance of 1, almost no current flows and the fault loop impedance is almost equal to that of a core-tosheath fault only. In real life, a time varying fault resistance is expected [3].…”

Online Location of Faults on AC Cables in Underground Transmission Systems

“…However, as the resistance increases, very little current will flow to ground at the fault location and for a grounding resistance of 1 Ω, almost no current flows and the fault loop impedance is almost equal to that of a core to sheath fault only. In real life, a time varying fault resistance is expected [6,88]. For fault location problems, this can be a potential problem, as a very high accuracy is needed for exact fault location.…”

“…Internal failures in these cables result from gradual deterioration of the insulation materials between core and sheath [6]. Voids and impurities in the insulation material or between boundaries of different material can initiate a process called treeing leading to insulation breakdown [7].…”