This paper describes a new artificial neural network (ANN) based digital differential protection scheme for generator stator winding protection. The scheme includes two feedforward neural networks (FNNs). One ANN is used for fault detection and the other is used for internal fault classification. This design uses current samples from the line-side and the neutral-end in addition to samples from the field current. Fundamental and/or second harmonic present in the field current during a fault help the ANN, used for fault detection, to differentiate between generator states (normal, external fault and internal fault states). Results showing the performance of the protection scheme are presented and indicate that it is fast and reliable.

An artificial neural network based digital differential protection scheme for synchronous generator stator winding protection

A method and system for estimating phasors and tracking the frequency of a signal is provided. The method uses a variable N-point DFT to compute one or more phasors based on data acquired from one or more sampled signals. At each sampling interval the change in phasor angle between the current sampling interval and the previous sampling interval is determined and used to estimate the instantaneous frequency of the signal. Instantaneous frequencies are averaged over a cycle of the signal. In addition, a number of discrete frequencies and corresponding DFT windows based on a fixed sampling rate and a predetermined fundamental frequency of the signal are defined and used in estimating the instantaneous frequency. Once the average cycle frequency is determined the DFT window is adjusted by setting it equal to the DFT window corresponding to the discrete frequency closest to the average cycle frequency.

System and method for phasor estimation and frequency tracking in digital protection systems

This paper introduces a new differential protection scheme based on zero-sequence voltages with 100% coverage for generator stator ground faults. Analysis shows that the Delta-fundamental zero-sequence voltages and the Delta-third-harmonic voltages at the generator neutral and the terminals will change simultaneously, and they present some similar characteristics. According to that, the new scheme that exploits the fault information of both the zero-sequence fundamental voltage and the third-harmonic voltage is described. As it combines the information of the zero-sequence fundamental voltage and the third-harmonic voltage, the scheme can detect the ground fault with high sensitivity in 100% coverage winding. Simulation and field test results show that the proposed scheme can obtain higher sensitivity than the traditional schemes

Differential Protection Based on Zero-Sequence Voltages for Generator Stator Ground Fault

A method and apparatus for over current backup protection is provided. The method generates a set of root mean square (rms) values from samples that are taken from the system current. Several rms current values are averaged to generate an estimated rms over current value. The estimated over current value is compared with a predetermined threshold value. If the estimated current is above the predetermined threshold value, a fault protection mechanism, such as opening a circuit breaker, is activated. A generator protection unit having digital signal processing capabilities executes the inventive method to provide protection from over current episodes.

System and method for rms overcurrent backup function

A digital technique for stator winding protection of synchronous generators

The authors provide the specifications and characteristics of a digital relay for synchronous generators that performs seven protection functions. They also present preliminary performance results, following installation on one of the units at the Carillon generating station in the Hydro-Quebec power system. During a period of four months, although no fault was recorded in the unit, the relay watchdog system and self-monitoring routines functioned flawlessly. The prototype provides the basis for a new standard protection system for Hydro-Quebec's future and existing generating stations. >

S. Barceloux

Papers

Field experience with a digital relay for synchronous generators