INTRODUCTION
The digital processors for power system protection have been widely
used for the last fifteen yuus, and many techniques for digital power
system protection have been developed and implemented since then
[5,6,71.
Kalman filtering is one of these techniques which has found many
applications in power sstem protection [1,7,8] and is well-known
twhni ue to many wnvo r and communication engineers, and it can be
used ?or estimating phasors from noisy measurements. The Kalman filter
is a recursive filter whose output depends on the resent inputs as
well as all previous inputs [El. Also, The an filter gain
coefficients vary with time, the gain are non-stationaty.