Distance protection relays have changed dramatically in the last two decades from simple single function distance protection relays into multifunctional IEDs with primary transmission line protection functions based on classical or advanced operating principles. Testing of such devices requires the availability of a set of tools that will simplify the testing process, while at the same time will ensure the required high quality of that testing process.

Testing of distance protection relays and IEDs is one of the key requirements to ensure their correct operation under short circuit faults during abnormal system conditions. Since protection technology is becoming more and more complex, with protective relays evolving to multifunctional devices with integrated pre-programmed control logic and additional functions like metering, fault and disturbance recording, programmable scheme logic, etc., ensuring that they are properly configured and implemented requires adequate testing of their functionality. At the same time the operation of the transmission systems close to their stability limit requires significant reduction in the fault clearing times that can be only achieved by using the advanced logic schemes available in modern transmission protection relays. In this case verification of the relay operating times through testing is critical.

The relays are also used as a front end to the substation automation system and provide different logging functions for analysis of their operation or different power system events. That is why testing of such devices requires excellent understanding of the available protection and non-protection functions, as well as the operational logic of the different schemes that require testing.

The paper first analyzes the functionality of modern state-of-the-art distance protection relays. Several groups of functions are identified:

• Basic transmission line fault protection
• Advanced protection schemes
• Abnormal system conditions detection
• Automation
• Monitoring
• Recording
• Analysis

Considering the fact that there is a possibility for simultaneous occurrence of different types of abnormal system conditions, it is clear that it is necessary to be able to test the distance protection relay's operation under such conditions. The requirements for the testing of all above listed functions are presented in the paper.
 
Different methods for testing are described, with special attention being paid to the testing tools for advanced transmission line protection functions and schemes.