Review of Select Theoretical and Practical Aspects of the Generator Relay Protection Application
Abstract
Relay protection of synchronous generators of higher power regularly includes the application of a number of protection functions, some of which are intended for protection against faults, while others relate to protection against various abnormal operating conditions. The setting of the starting values and other parameters of the protection functions is regularly based on certain theoretical foundations, as well as some assumptions (which are very often tacitly adopted). In doing so, most of the applied protection functions must be coordinated with the settings of other protections in the system, as well as the settings of the controller and the generator operating map. Furthermore, there are several different ways of implementing certain protection functions (e.g. protection against generator loss of excitation), each of which has its own advantages and disadvantages. In addition, the application of protection functions is also based on certain practical aspects related to the generation of relay protection, the manufacturer of the relay device, the method of design and connection of the generator itself, and other aspects. This presentation aims to present the basic characteristics of the relay protection system of higher-power synchronous generators (with an emphasis on hydrogenerators), which depend, among other things, on the connection method and the choice of generator grounding. An overview of the calculation of generator short-circuit currents and the selection of current transformers for protection (class P) will be given. Some of the fundamental theoretical foundations behind some of the more important protection functions will then be presented (e.g. differential protection, 90% stator earth fault protection, protection against generator loss of synchronism). The intention is also to highlight certain practical aspects of the implementation of some of the protection functions, by comparing their implementations by different manufacturers, as well as to present recommendations for their adjustment and coordination. This review aims, first of all, to point out different ways of implementing and applying some of the basic generator protection functions, emphasizing their theoretical foundations, built-in assumptions, advantages and disadvantages.
