This paper reviews the philosophy of the end-to-end relay testing using GPS-synchronized secondary injection in communication based protection schemes.
The paper describes an application case at a Distribution Division in Jalísco, Mexico, operated by the national utility CFE (Comisión Federal de Electricidad). The line protection scheme is special due to a tap derivation line in the middle of the line which has a normally open switch to feed a sensitive and important customer. In normal condition, the line differential relay (87L) is the main protection and the distance element (21 ) is an integrated back up protection. Following the discrete back up protection philosophy there is another relay which is used as phase comparison (67N ). In maintenance condition the line differential relay (87L) has to be disabled and the settings for the distance element must be changed remotely from the control center. All the above protections are Communication based Protection (Transfer Trip Schemes). The document will describe the purpose of the testing, the actual test scenarios, special tools needed, resources, and criteria for success.