This paper presents the results of a study that analyzes the relationship between the excitation system of a synchronous machine and the settings of the loss-of-excitation (LOE) relay applied to protect this machine. A complete generation system taking into account all the physical components was modeled in a real-time digital simulator, including a new excitation system model (ST7B). By considering a method to protect the generator against partial and total LOE, the settings of the LOE protection were made taking into account the technical data of the synchronous machine. A hardware-in-the-loop simulation using a numeric relay was implemented in a laboratory. Thus, several tests were performed in order to evaluate the coordination between the protective relay and the limits of the modeled excitation system during underexcited operation.

The installation and settings of protection devices and excitation control systems require experience since a failure can cause damage to the synchronous generator and negative impact on the power grid. A test bed implemented in a real-time digital simulator (RTDS) is presented in this paper as an alternative for the training and learning process that involves the knowledge of an effective coordination between such protection and control systems of synchronous generators. A complete generation system is implemented in a RTDS, including an excitation system model with its limiters. These limiters are coordinated with the protection functions implemented in a physical relay. The contributions of this work are the demonstration of the importance of this type of study (i.e., real-time simulations results through hardware-in-the-loop tests), the consolidation of the impedance (R-X) and admittance (G-B) planes as the more appropriate ones to analyze the coordination between the ANSI 40 function and the underexcitation limiter, and the presentation of a study focused on hydrogenerators (including novel settings for the ANSI 40 protection).

A test-bed implemented in a real time digital simulation environment is presented in this paper to perform coordination studies between protection functions and excitation limiters of automatic voltage regulators (AVRs) of synchronous generators. A hardware-in-the-loop (HIL) simulation is implemented in laboratory to test and evaluate several protection schemes during under-excited and over-excited events. The interactions among the underexcitation and overexcitation limiters (UEL and OEL) with these protection functions are investigated and the best settings for their coordination are proposed. This paper increases the scope of [1] and [2] by including the interactions among the protection functions ANSI 24 (V/Hz), ANSI 59 (overvoltage) and ANSI 81 (under and over-frequency) with the OEL and the interactions among the protection functions ANSI 21 (distance) and ANSI 27 (undervoltage) with the UEL in addition to the coordination between the protection function ANSI 40 (loss of excitation) and the UEL. So, the appropriate settings for these protection and controls are proposed for the excitation system developed. The main results are presented and discussed.

The performance of salient-pole synchronous generators protection is of great importance for the stability of power systems, as they are present in large hydropower plants, subject to various abnormal operating conditions such as three-phase or two-phase faults, electromechanical disturbances and loss-of-excitation. In this context, this work proposes a testing philosophy of salient-pole synchronous generators, in order to define more accurately the setting of the protections and controls of this asset. Thus, in the developed methodology, the admittance plan (G-B) proves applicable to analyze the coordination between the loss-of-excitation protection and the underexcitation limiter, as an alternative to the power (P-Q) and impedance (R-X) planes, normally employed in literature. In modeling the problem, real data for both the hydrogenerators and the electrical network are used. The simulations were performed in a hardware-in-the loop scheme integrated by a Real Time Digital Simulator and a physical relay. Thus, analyzes are made for situations of stable power swing and partial and total loss-of-excitation. The results are useful to prove, through the monitoring of relevant variables of the hydrogenerators, the feasibility and accuracy of the G-B plane in the coordination between the protection and the control of the synchronous machine.