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A b s t r a c t : Achievable g e n e r a t o r r e a c t i v e c a p a b i l i t y (GRC) i s g e n e r a l l y much less t h a n i n d i c a t e d by m a n u f a c t u r e r s ' r e a c t i v e c a p a b i l i t y c u r v e s , due t o c o n s t r a i n t s imposed by p l a n t a u x i l i a r i e s and t h e power system i t s e l f .The n a t u r e of t h e s e cons t r a i n t s i s e x p l a i n e d and a method f o r c a l c u l a t i n g them i s provided and v e r i f i e d by f i e l d tests on a u n i t a t h i g h and low system v o l t a g e l e v e l s . S e v e r a l recommend a t i o n s are made t o enhance t h e GRC of t h e tested u n i t .Keywordo:overexcitation,underexcitation, r e a c t i v e c a p a b i l i t y , g e n e r a t o r overheati n g , e x c i t a t i o n l i m i t a t i o n , r e a c t i v e requirement.INTRODUCTION t a n c e i s used.The g e n e r a t o r i s assumed t o b e connected t o an i n f i n i t e bus 111.For a g i v e n t e r m i n a l v o l t a g e V and c u r r e n t I, a t phase a n g l e @ ( i . e . , f o r a g i v e n MVA o u t p u t ) t h e emf E i s o b t a i n e d by adding armature r e a c t i o n I,Xd t o V a t 90" to I,.For c o n s t a n t MVA o u t p u t , I, i s c o n s t a n t and i t s l o c u s i s a c i r c l e w i t h c e n t e r on t h e end of t h e v o l t a g e phasor V. Constant e x c i t a t i o n i m p l i e s t h a t t h e l o c u s of E i s a l s o a c i r c l e w i t h c e n t e r 0.The a n g l e between E and V is t h e power a n g l e 6. I t c a n b e s e e n t h a t g e n e r a t o r ' s MW o u t p u t , V*I,*cos@, i s e q u a l t o :(V*E/Xd) * s i n 6.The g e n e r a t o r r e a c t i v e c a p a b i l i t y (GRC) For 6 = goo t h e limit of s t a b i l i t y c u r v e s f u r n i s h e d by manufacturers a n d u s e d is reached, so that t h e horizontal line g r e a t e r range t h a n can be r e a l i z e d d u r i n g a c t u a l o p e r a t i o n . G e n e r a l l y , t h e s e GRC c u r v e s are s t r i c t l y a f u n c t i o n of t h e synchronous machine d e s i g n parameters and do n o t c o n s i d e r p l a n t and system o p e r a t i n g concern o v e r GRC h a s been heightened by i n c r e a s i n g need f o r r e a c t i v e power t o p r o v i d e v o l t a g e s u p p o r t f o r l a r g e b l o c k s of power t r a n s f e r . i n o p e r a t i o n p l a n n i n g t y p i c a l l y have a through 0 r e p r e s e n t s t h i s l i m i t . c o n d i t i o n s a s l i m i t i n g f a c t o r s . Recently / P T h i s paper, d e s c r i b e s a method f o r d e t e rmining t h e r e a c t i v e c a p a b i l i t y l i m i t a t i o n of synchronous machines under p l a n t and system o p e r a t i n g c o n d i t i o n s . The methodology is tested and v e r i f i e d on a l a r g e g e n e r a t o r . Then s e v e r a l recommendations are made t o enhance t h e GRC of t h e u n i t . BACKGROUND 1. The Phasor Diasram The basis f o r g e n e r a t o r r e a c t i v e c a p a b i l it y (GRC) c u r v e s i s shown i n F i ...

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