Abstract
Voltage and current time-synchronized measurements, better known as synchrophasors, use an absolute time reference and can provide information of the state of the power system in real time. So far, typical synchrophasor applications have been limited to visualization and post-mortem analysis. This dissertation proposes four efficient and reliable synchrophasor-based protection and control applications for detecting ground faults in power lines and preventing power system disruptions. The work begins by recommending the quadrature demodulation method for estimating synchrophasors suitable for detecting power oscillations.
The first proposed application is a system integrity protection scheme (SIPS) for automatic generation shedding based on estimation of the voltage angle difference between two areas of the power system. The proposed scheme combines phasor measurements, phasor data concentration, and control functionality in a single device to minimize components within a system and increase its reliability.
The second application is a synchrophasor-based line differential protection scheme that complements primary distance protection schemes, provides backup protection, and does not require voltage information. A negative-sequence current differential element, together with total current faulted phase identification, detects high-resistance faults without compromising phase selectivity. An additional important benefit of this proposed approach is that communication channel delay asymmetry does not affect differential element operation resulting from use of time-stamped measurements.
The third application proposes a power system dynamics monitor that includes out-of-step detection, power swing detection, and predictive out-of-step tripping algorithms. These synchrophasor-based algorithms allow the implementation of a SIPS that requires minimum network topology information and automatically adapts to changing operating conditions of the power system.
The fourth application proposes a SIPS that performs modal analysis in real time, identifies inter-area power oscillations within the frequency band of interest, and takes remedial action if the signal amplitude exceeds a predefined threshold and the damping ratio is less than a predefined threshold for a predefined time. The proposed SIPS has proven effective in a field application and has prevented power system collapse on multiple occasions when inter-area power oscillations occurred.
Throughout all four SIPSs this work proposes components have been kept to a minimum. This reduction in complexity makes these schemes more reliable.