Patent ID: 7199991
Filing Date: 2007-04-03
Classification: H02H

Abstract:
1. A protection relay for a power line system where current on a bus is provided to one or more power lines for receiving and generating power, and where associated with each of said power lines is a current transformer for providing a line signal representative of current flowing through a respective power line, and wherein said protection relay is operative for generating a fault trip signal in response to a detected power line fault, the protection relay comprising: a signal processor responsive to said line signals for generating a fault trip signal in response to a detected fault on any one of the power lines; means for summing said line signals, separately for each power line phase, for all power lines coupled to said bus and producing, means for deriving, means for deriving, means for determining the harmonic phase difference between said first and second harmonic signals; phase comparator means responsive to said harmonic phase difference for selectively generating a blocking signal for blocking said fault trip signal if said harmonic phase difference satisfies a first condition; and a trip signal generator means responsive to said first and second signals for generating a fault trip signal upon said first and second signals being beyond a defined bus differential characteristic conditioned upon the status of said blocking signal.