Injection-Based Generator Stator Ground Protection Advancements

IET Generation, Transmission & Distribution, 2007

Here, a comprehensive characterisation of the performance of voltage relays, focusing on their capability to detect islanding of embedded synchronous generators is presented. Such characterisation is done by using the performance curves and the concept of critical reactive power imbalance, which allows a systematic analysis of voltage relays considering a wide range of system operating points. The impacts of important factors on the relay performance are evaluated, such as the presence of voltage-dependent loads and the generator exciter control mode. Moreover, a graphical approach that allows protection engineers to adjust voltage relays to reach two objectives simultaneously: (i) to be sensitive enough to detect islanding efficiently and (ii) to satisfy the protection requirements against abnormal voltage variation is proposed. Results can be quite attractive to understand voltage relays behaviour and limitations and thus, they can be adjusted more efficiently.

IEEE Transactions on Industry Applications, 2004

This paper discusses typical grounding practices and ground fault protection methods for medium-voltage generator stators, highlighting their merits and drawbacks. Particular attention is given to applications of multiple generators connected to a single bus. The paper also provides an overview of the generator damage mechanism during stator ground faults. Problem areas associated with each type of grounding are identified and solutions are discussed. The paper also provides a list of references on the topic. The paper is intended as a guide to aid engineers in selecting adequate grounding and ground fault protection schemes for medium-voltage industrial and commercial generators for new installations, for evaluating existing systems, and for future expansion of facilities, to minimize generator damage from stator ground faults. These topics are presented in four separate parts, Parts 1-4. Part 1 covers scope, introduction, user examples of stator ground failure, and theoretical basis for the problem. Part 2 discusses various grounding methods used in industrial applications. Part 3 describes protection methods for the various types of grounding and Part 4 provides a conclusion and bibliography of additional resource material.

IEEE Transactions on Power Delivery, 2004

Disturbance is an inherent part of any power system during the transition from one steady-state operating condition to the next. Protective relays may experience abnormal operating conditions during this transient period. This paper reviews various control actions that play a part during the transition and provides technical guidance to the industry on the application and setting of generator protective relays that can operate during major system disturbances.

2020

Nowadays, there are still many high capacity generators have not yet protected completely from their internal ground faults. They still rely on differential and over current relays. It is seen that this relay will reduce their sensitivities when applied to generators with high impedance grounding systems. To overcome such problem, a combination protection scheme of the neutral overvoltage (59N) and neutral undervoltage third harmonics (27N3) is developed. This paper aims to design the protection scheme for high capacity generators. This paper demonstrates the designing of neutral grounding transformer (NGT) system, the relay settings and reviewing of their sensitivities. To clarify the concepts this study uses a generator 802 MVA, 22.8 kV as object. The results show that the protection scheme is very effective to protect 100% of generator stator with relays overlapping of 31.5%. It needs NGT transformer with capacity of only 28.33 kVA, 15000/240 V, and the secondary resistor of 0.38...

2015

In this paper, 100% stator ground fault protection by application of low frequency (20 Hz) injection for 6.6/132 KV alternators have been investigated. Here, different types of faults of alternators and possible protections by conventional means have been discussed. It is shown why conventional method by differential relay protection is not adequate. Modern approach of alternator fault protection is reviewed and effective methods of 100% stator ground fault protection of alternators have been applied. In this work, it is focused protection of alternators based on sub-harmonic injection method using low frequency band pass filter. The design of stator ground fault protection consists of 20 Hz signal generator, band pass filter, 20 Hz current relay and protection system model includes alternator, total capacitance to ground of stator winding, grounding transformer turns ratio, and neutral resistor. PSPICE simulation of the protection scheme is performed and analyzed. Keywords—Alternat...

Because of stator winding construction, an insulation failure is more likely to result in a winding-to-ground fault than in a phase-to-phase fault. Other failures, such as a broken conductor or turn-to-turn fault, may not be detected until the fault develops into a winding-to-ground fault. Consequently, stator ground fault protection is one of the indispensable schemes for protecting a generator stator winding. Dedicated stator ground fault protection is required for high-impedance-grounded machines.

2006

In this article a methodology for setting up generator out-of-step protective relay, to be applied in any generator of Colombian Power System is presented. A comparison between settings proposed in research articles and a manufacturer was carried out. The application of the methodology required information as generator direct-axis transient reactance, transformer reactance, power system impedance and critical time for setting up protective relay. The proposed methodology for setting up generator out-of-step protective relay was applied in the Salvajina and Alto Anchicaya power plants, improving the selectivity with new settings approaches.

This paper reviews the protection requirements for generators during periods of off-nominal frequency operation. It investigates the behavior of instrument transformers during these periods as well as the impact of frequency on the accuracy of protection operating quantities. Traditional methods for frequency tracking and compensation are reviewed. A novel approach, which provides excellent performance for very significant frequency deviations and can accommodate multiple frequency islands, is presented.

In this paper, 100% stator ground fault protection by application of low frequency (20 Hz) injection for 6.6/132 KV alternators have been investigated. Here, different types of faults of alternators and possible protections by conventional means have been discussed. It is shown why conventional method by differential relay protection is not adequate. Modern approach of alternator fault protection is reviewed and effective methods of 100% stator ground fault protection of alternators have been applied. In this work, it is focused protection of alternators based on sub-harmonic injection method using low frequency band pass filter. The design of stator ground fault protection consists of 20 Hz signal generator, band pass filter, 20 Hz current relay and protection system model includes alternator, total capacitance to ground of stator winding, grounding transformer turns ratio, and neutral resistor. PSPICE simulation of the protection scheme is performed and analyzed.

2018

Typical 100 percent stator ground protection for a single high-impedance grounded generating unit involves using a neutral overvoltage element in conjunction with a third-harmonic or injection scheme. Both of the latter schemes face reliability challenges when applied to multiple high-impedance grounded generators that share a common bus or generator step-up winding. Third-harmonic schemes cannot be applied to protect the neutral end due to the possibility of circulating third-harmonic contributions from the paralleled units. In addition, the change in the impedance network when units share a bus can result in thirdharmonic scheme misoperation. This paper presents a method that secures the third-harmonic scheme when misoperation is a possibility. When injection schemes are applied, the paralleled units appear as a ground fault to the protected unit. Addressing this requires desensitizing the element and thereby making it ineffective. This paper discusses a method to account for the ...