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Department of E l e c t r i c a l Enginnering Indian I n s t i t u t e of Technology Kharagpur -721 302 I N D I A B b s t s a c t I. A knowledge-based d e c i s i o n ayfitem I s developed f o r EHV t r a n s m i~s i o n l i n e d i s t a n c e p r o t e c t i o n . This paper d e s c r i b e s t h e two major a s p e c t s of t h e system, ( I ) Knowledge represen tnt 5 on, ( 2 ) Logic p r o c e s s , f o r f a u l t difltance c a l c u l a t i o n . Dj f f e r e n t knowledgc r e p r e s e n t a t ion techniques a r e d i s c u s s e d with t h e i r r e l a t i v e performances. The developed flystern is shown t o be r e l i a b l e and s t a b l e under d i f f e r e n t fault, c o n d i t j o n . including z e r o f a u l t i n c e p t i o n a n g l e . Computing burden is q u i t e reasonable and u l t r a high speed (UHS) performance can be e a s i l y achieved with commerc: i a I m i c r o~r o c e s s o r s . Inf;rclducthn LThe need and s i g n i f i c a n c e o f UHS re1ayi.ng f o r EHV t r a n s m i s s i o n l i n e s are by now w e l l known'. I t improves power system r e l i a b i l i t y , t r a n s i e n t stability and reduce6 t h e damage caused t o t h e equipments.T h e r e a r e a p p a r e n t l y two d i s t j n c t approaches i n d i s t a n c e p r o t e c t i o n taken t o achieve high speed performance.One is based on f a s t e s t i m a t i o n of power f r e p e n c y components using Kglman f i l t e r s , , s y m m e t r i c . 3 1 components e t c . The o t h e r approach relie8 on t h e information c o n t e n t i n t h e high frequency p a r t of t h e f a u l t induced components. The l a t e r is p o p u l a r l y c a l l e d a6 t r a v 1 i n g wave (TW) based d i s t a n c e relaying"'-Both t h e schemes have t h e i r awn advantage and disadvan-t a a a s . The i n i t i a l p o s i t i o n of t h e f a u l t induced v o l t a g e and c u r r e n t s are h e a v i l y dominated by t r a v e l l i n a waves. So f o r t h e i n i t i a l p e r i o d o f a f e n m i l l i s e c o n d s , s i g n a l t o n o i s e r a t i o is h i g h e r f o r TW-based r e l a y i n g and lower f o r power frequency based r e l a y i n g . However, f o r n e a r z e r o -f a u l t i n c e p t i o n a n g l e s t h e magnitudes o f t h e t r a v e l l i n g waves a r e very 1 Q W and I t I s very d i f f i c u l t t o d e t e c t t h e s e f a u l t s u s i n g TW-based d i s t a n c e r e l a y i n g .The problem can be solved by combining both t h e methods wjth g r e a t e r compul;ing burden and algorithm complexity.A novel approach is presented h e r e t o s o l v e t h i s problem u s i n g knowledge-based system. The beauty o f t h i s system i s t h a t t h e wholespectrum of the information contained in the f a u I t induced s i g n a l s ( l i m i t e d by t h e sampling frequency] i s considered i n a very simple manner. The i d e a of t h e knowledge-based system came from the t h a t post f a u l t v o l t a g e and c u r r e n t waveforms are dependent on f a u l t d i s t a n c e . T...

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