This paper presents experimental and theoretical analyses used to establish electrical features that can be utilized as indicators of armature winding, field winding or rectifier diode deterioration in brushless three-phase synchronous generators before the imperfection progresses to become a ground fault. The paper begins with the description of a 5 kVA synchronous generator specifically designed and constructed to allow for simulation of armature winding, field winding or rectifier diode deterioration in a brushless machine. Subsequently, a description of the experimental methodology and the results of experiments are presented. Specific features that can be used as indicators of the deterioration are described and a theoretical basis for them is provided. The proposed features can be obtained continuously during normal generator operation. As such, they can be used as a basis for both winding brushless and brush-fed synchronous generator health monitoring applications.

Condition Monitoring of Brushless Three-Phase Synchronous Generators With Stator Winding or Rotor Circuit Deterioration

A simple and economical technique for measuring voltage phase angles and generator shaft angles is reviewed. The principle is briefly exposed and its practical operation is illustrated by an experiment in a real power system. Due to the importance of accurate time for this application a short survey on time dissemination systems is included. The main part of the paper is devoted to the possible applications of phase angle measurements for the control and monitoring of power systems. The discussion deals with various topics and makes ample reference to available literature. The paper is intended as an information survey for assessing the practical significance of phase angle measurements

Phase Angle Measurements with Synchronized Clocks-Principle and Applications

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

The authors present an adaptive optimal control strategy for enhancement of the integrated AC/DC power system performance. The system modeling is general and applicable to large-scale power systems with an embedded HVDC link. The control algorithm incorporates the nonlinear power system dynamic equations. A novel feature of this development is the use of real-time system measurements as inputs to the optimal controller. The closed-loop optimal control law consists of both model and measurement-based terms. The effectiveness of the optimal control algorithm in damping the electrochemical oscillations is illustrated with the use of a nine-bus AC/DC system. >

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An adaptive optimal control strategy for dynamic stability enhancement of AC/DC power systems

A new internal fault detection and classification technique for the synchronous generators is presented. First, the presence of an abnormal/fault condition is detected based on the negative sequence component (NSC) of neutral end current. Thereafter, the internal fault and abnormal/external-fault conditions are discriminated by utilizing the instantaneous phase angle between the NSCs of the terminal voltage and current. Subsequently, the internal fault is classified based on phase angle between NSCs of terminal voltage and neutral end current along with the zero sequence component of the neutral end current. Efficacy of the proposed scheme has been verified on a phase domain synchronous machine model developed on the real time digital simulator (RTDS). The results derived from various fault datasets show that the proposed technique is able to effectively distinguish between internal and external faults including special cases, such as current transformer saturation, overloading, and unbalance condition. Further, it provides added capability of detecting and identifying inter-turn faults irrespective of the winding configuration of the generator. Comparative assessment of the proposed scheme in terms of detection time and incorporation of different types of faults with the existing techniques proves its superiority.

A New Internal Fault Detection and Classification Technique for Synchronous Generator

An on-line digital computer technique for the protection of a generator against internal asymmetrical faults is described in this paper. The proposed technique relies on the detection of a second harmonic component in the field current at the onset of a fault in the armature winding. Discrimination against external faults is achieved by monitoring the direction of the negative sequence power flow at the machine terminals. Tests have been conducted on a laboratory synchronous generator for various types of internal and external faults. Results show that the total time for internal fault detection and tripping is well within half a cycle of the 60 Hz signal. A simple extension to negative sequence relaying and loss of excitation relaying is proposed.

Fast generator protection against internal asymmetrical faults

This paper presents an on-line digital computer technique used for differential protection of a synchronous generator. It provides fault detection and tripping well within half a cycle and is also capable of discriminating between internal and external faults. In the latter case, sufficient restraint signals are generated to overcome maloperation. Further, the scheme is highly reliable even with CT saturation due to heavy through faults on the generating unit. On-line tests using a laboratory synchronous generator show the results for different types of internal and external faults with varying fault incidence inception.

Digital differential protection of a generating unit scheme and real-time test results

For a parallel ac-dc power system, the effect of a controlled dc link on system stability and damping depends on the system operating conditions.Thus a controller which improves stability at one operating condition may have a detrimental effect at other system operating conditions. Further, when the machine power angle to the ac line angle is high, improvement in stability is difficult to obtain solely by the control of a d.c. link. The variation with operating conditions of the influence of a dc link control on system performance indicates that a predictive or adaptive control mode would be needed to improve system stability over a wide range of system performance. The paper, therefore, examines both the conventionaI and optimal control of the link for large disturbance performance of a parallel ac-dc power system and digital simulation results show interesting features of optimal control. From a practical implementation point of view, full state optimal feedback law is suitably modified to be a linear combination of reduced state variables by an eigenvalue grouping technique and the performance of the actual nonlinear system with the suboptimal controller is quite encouraging.

O.P. Malik

Papers

Fast generator protection against internal asymmetrical faults

Digital differential protection of a generating unit scheme and real-time test results

Transient stability and optimal control of parallel A.C.-D.C. power systems