Using time error differential measurement in protection applications

Numerous problems in power system protection have led to ongoing work for protection engineers to properly configure relays and other devices. These problems include power swing blocking, power swing tripping, and islanding detection. Traditional detection of these conditions using voltage and current have led to complex algorithms and setting guidelines. Distributed generation has complicated issues by making system models more extensive while large interarea power sales and load flows have made older setting guidelines suspect. Time error (TE) has been used as a basis for generation dispatch for years. Using a difference between "real time" and "system time" measured to tenths or even hundredths of a second, system frequency was adjusted and generation levels raised or lowered. Modern Intelligent Electronic Devices (IEDs) have the capability of measuring TE to fractions of a millisecond. This level of accuracy and resolution introduces the capability of a new input to wide-area control: Time Error Differential (TED). This paper discusses the basis of TED for use in special protection schemes such as islanding detection, generation dropping on loss of load, power swing detection, and system disturbance detection for automatic load preservation. System conditions leading to TED and comparison with alternate measurement methodologies for special protection schemes are presented. Because TED has never been available for use, practical considerations to its application are presented. These considerations are based on both the measurement unit and the communications system available. Both high-speed control algorithms and visualization systems for human intervention are presented as possible applications. Advances in both measurement and communications is expanding the efficiency and stability of the overall power system. The use of TED provides new tools and methods to continue to maximize the use of generation and transmission grid assets.