Testing Superimposed-Component and Traveling-Wave Line Protection
In the last few decades, our industry has witnessed the proliferation of traveling-wave-based, standalone fault locators and fast line protective relays using superimposed components. Today, some protective relays integrate traveling-wave fault locators. This field experience has led to new line protective relays that use traveling waves and very fast superimposed components for tripping. These relays also leverage the communications bandwidth available today and include sophisticated differential schemes that work on time-domain currents and voltages. How do we test these relays in the field? Do we need different test sets? Do we need to adjust our testing methodologies to accommodate these new relays? This paper addresses these and other key questions and reports on a joint activity between practitioners who specialize in relay testing and practitioners with hands-on experience designing these new relays. This paper explains the common characteristics of traveling-wave and superimposed-component protection principles. From there, we derive the desired characteristic of the test equipment and test tools and present a suggested testing methodology. The topics covered in this paper include traveling-wave and superimposed-component test signals, test set hardware requirements, end-to-end testing with satellite-synchronized test sets, generating test signals with the Electromagnetic Transient Program (EMTP), the feasibility and benefits of combining low-frequency injection with traveling-wave signals versus testing independently with low-frequency signals and traveling waves, special applications such as series-compensated lines, and lessons learned. Finally, we review and contrast the objectives of type (functional) testing and testing in the field when commissioning and provide recommendations for each scenario as it relates to traveling-wave and superimposed-component line protection. Most of the presented material applies to both testing protective relays and testing standalone fault locators or traveling-wave fault locators integrated in protective relays.