Stator Ground Fault Protection Research Articles

Adaptive 100% Injection-Based Generator Stator Ground Fault Protection With Real-Time Fault Location Capability

The paper presents a novel adaptive stator ground fault protection scheme with fault location capability for high-impedance grounded synchronous generators. The protection scheme uses already available neutral grounding signals in the existing subharmonic injection protection to obtain a Kalman adaptive filter (KAF) for real-time stator insulation parameter estimation. The KAF estimator yields a method of continuous tracking of stator insulation condition during healthy operations. This information is then used for real-time stator ground fault detection as well as fault location. The effectiveness of the proposed method is verified using extensive experiments performed on a lab-scale unit-connected generating station.

Modeling and Experimental Verification of a 100% Stator Ground Fault Protection Based on Adaptive Third-Harmonic Differential Voltage Scheme for Synchronous Generators

In this paper, a novel adaptive stator-ground fault protection scheme based on third-harmonic differential voltages is implemented on a lab scale synchronous generator. The lab scale generator is used to emulate the fault characteristics of industrial generators along the stator windings. Simulations based on finite element analysis methods were used to design and tune the laboratory testbed. Experimental results prove the expected fault characteristics as well as fault detection capability of the adaptive stator-ground fault protection scheme.

Advanced Generator Ground Fault Protections in Pulp and Paper Mill Applications

Ground faults in field/rotor and generator stator circuits are serious events that can lead to damage, costly repair, extended outages, and loss of revenue. This paper explores advances in field/rotor circuit ground fault and stator ground fault protection. These advanced protection strategies employ ac injection, ground differential protection, and the use of hybrid grounding to reduce both internal generator ground fault levels and facility ground levels in utility-paralleled operating modes.

Adaptive 100% Stator Ground Fault Protection Based on Third-Harmonic Differential Voltage Scheme

The paper presents a new adaptive 100% stator ground protection for high-impedance-grounded (HIG) synchronous generators. This is done by first examining reliability, that is, dependability and security of the most prominent conventional 3rd-harmonic voltage schemes. Using field data from various capacity industrial generators, it is shown that the conventional 3rd-harmonic differential voltage scheme, while being dependable, lacks security. Using the same field data, it is shown that the new adaptive scheme is a highly secure and sensitive scheme. Moreover, the new adaptive scheme is a zero-setting scheme which does not require any setting calculations, 3rd-harmonic voltage testings, or additional hardware.

PARALLEL UNIT-CONNECTED GENERATOR MODEL FOR THIRD HARMONIC STATOR GROUND FAULT PROTECTION

Conventional ground fault protection schemes can be applied for any generator terminal connection but it covers at most 95% of generator stator length. 100% protection for synchronous generator stator winding can be achieved by a combination of zero sequence and third harmonic protection schemes. The implementation of the third harmonic scheme on any generator is determined by magnitude of third harmonic voltage produced in the generator. The methods of connecting the generator terminal also influence the range of third harmonic voltage at the stator terminal and neutral. An investigation into the compatibility of particular generator configuration with the third harmonic scheme is important to prevent protection mal-operation since the scheme is hampered in performance by certain factors which include grounding method employed and generator terminal connection among others. In this paper, the modelling of parallel unit-connected generators of the second order is presented to study the influence of parallel unit-connected generators on third harmonic stator ground fault protection. Application of mesh analysis method to the circuit models produced ordinary non-linear algebraic equations. The equations were solved using Cramer’s rule. Simulations of the circuit models were performed for no-load, light load and full load conditions using MATLAB/SIMULINK to study the character of third harmonic voltage at stator neutral and terminal when a ground fault occurs to validate the results of the models. Introduction of a ground fault at the neutral point of the single generator showed that the third harmonic voltage decreased towards zero at the neutral but increased towards maximum at the terminal.

Wavelet ANN Based Stator Ground Fault Protection Scheme for Turbo Generators

This article proposes a protection scheme for turbo generators to detect stator ground faults in particular closer to neutral. The scheme considers total generated voltage of the machine and makes use of wavelet multi-resolution analysis. A fault index is defined in terms of peak and valley values of the highest-level wavelet decomposition, which is compared with a threshold value to discriminate from other transients, like sudden unbalance, in load. To identify the faulty coil, an ANN employing back propagation algorithm is used with the lowest level wavelet coefficients as inputs. The results of digital simulation are presented for different fault impedances and fault locations.

Wavelet-based directional stator ground fault protection for generator

This paper introduces a wavelet-based stator ground fault protection scheme with selectivity for generator. It is found that the WT results of the measured zero sequence current at the terminals, zero sequence voltages at the neutral and the terminals of a fault generator, especially the modulus maxima, contain important information. It can be used to discriminate the generator stator ground fault. By applying the zero sequence current, the proposed scheme can detect if the fault is in the internal generator or out of the generator. The effectiveness of the proposed scheme was verified both in the experiment and in the field. Investigation results show that the scheme can detect the ground fault with high sensitivity and selectivity during all operating conditions.

Influence of Generator Load Conditions on Third-Harmonic Voltages in Generator Stator Winding

The influence of changes in load conditions of the generator-transformer unit on the operating conditions of the 100% ground-fault protection of the generator stator winding based on the third-harmonic voltages was analyzed. The analyzed stator ground-fault protection system is by ratio of the voltages third harmonic in generator neutral and at the generator terminals. The third-harmonic voltages were determined on the base of the experimental tests (measurements) run in real conditions at changes in active and reactive load conditions of the generator. It was found that mainly the generator active load influences the voltage feeding the measuring element of ground-fault protection. Therefore, determining operating conditions of ground-fault protection the influence of the generator active and reactive load should be deeply considered. This can ensure the proper operation of the ground-fault protection based on the voltage third harmonics in the whole range of the changes in generator load. Considering the influence of changes in generator load on the third-harmonic voltages (feeding measuring element of the protection system) will allow eliminating irregular generator tripping as a result of unselective operation of these protections.

Stator ground fault protection based on phase angle differential of delta third harmonic voltages

New stator ground fault protection principle is presented in this paper, which takes into account the phase angle comparison of the third-harmonic voltages at the generator terminals and the neutral. Analysis results show that the phase angle differential value of Δ-third-harmonic voltages under normal condition and fault condition will present greatly different, and this characteristic could not be influenced by the operation conditions. Thus, it can be used to detect the generator stator ground fault, which could ensure higher sensitivity because of cancellation of the pre-fault component. The start-up component is based on the wavelet transform (WT), its effects are also described. Experimental and field test results demonstrate that new scheme can obtain high sensitivity and reliability the generator relay required during different operation conditions.

Influence of Difference System Parameters on Operating Conditions of Third Harmonic Ground-Fault Protection System of Unit-Connected Generator

In the paper, the influence of unbalance of the measuring element of the unit-connected generator stator ground-fault protection system excited by the ratio of third harmonic voltage to ground in the generator neutral and at the generator terminals on the value of the voltage supplied to the measuring element during ground faults is analyzed. The analysis is made for currently used ground-fault protection systems in which the measuring element is balanced by an autotransformer voltage divider or an impedance bridge.

Wavelet-based ground fault protection scheme for generator stator winding

Abstract A new stator ground fault protection scheme is introduced in this paper. It is based on wavelet transform, particularly the multiresolution analysis (MRA) technique. The effectiveness of the proposed scheme was verified both in the experiment and in the field. Investigation results show that the scheme can detect the ground fault with high sensitivity and selectivity during all operating conditions.

A New Principle for 100% Stator Ground Fault Protection Using Wavelet Transform

A New Principle for 100% Stator Ground Fault Protection Using Wavelet Transform

Upgrading the protection of industrial-sized generators using digital technology

This paper presents the reasons why industrial generator owners should consider upgrading the electrical protection of their generators to meet today's standards. It specifically outlines the risks assumed in five functional areas where 20/sup +/-year-old generator protection is inadequate. These areas include negative sequence (unbalanced current) protection, sensitive stator ground-fault protection, sensitive overexcitation protection, inadvertent (accidental) generator energizing, and VT fuse loss protection. It also outlines the need to provide generator oscillographic monitoring. The paper discusses the advantages of digital versus conventional technology for such an upgrade program.

Adaptive ground fault protection schemes for turbogenerator based on third harmonic voltages

Equivalent circuits based on the actual connection of coil-groups of generators are used to study the characteristics of various generator stator ground fault protection schemes presented in the literature. The evaluation and the comparison of the characteristics of those schemes are given by means of protection coverage-critical resistance curves. Although these schemes are successful in practice, they suffer the disadvantage of low sensitivity, which is strongly related to generator operating conditions. To overcome this disadvantage, two adaptive stator ground fault protection schemes based on digital techniques are developed. Compared to conventional third-harmonic voltage schemes, they can automatically track the change of generator operating conditions before a ground fault occurs. Test results from a digital simulation show that they can keep high sensitivity during all operating conditions.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A Comparison of 100 Percent Stator Ground Fault Protection Schemes for Generator Stator Windings

A Comparison of 100 Percent Stator Ground Fault Protection Schemes for Generator Stator Windings

A Comparison of 100% Stator Ground Fault Protection Schemes for Generator Stator Windings

This paper describes three different schemes for detecting single-phase-to-ground faults in 100% of the generator stator winding. The operating theory, a setting example, and field measurements are provided for each of the three schemes. A chart comparing the significant application characteristics of the three schemes is presented.