Relays have evolved in the last 50 years from electromechanical relays via solid state relays to today's intelligent electronic devices. While electromechanical relays were built for one function, today's devices have become truly multifunctional – not only in the relaying application calling for a multitude of individual settings by the customer – but also they often comprise additional features like synchrophasor measurement and precise time data. And modern relays have grown into veritable computers, calling for frequent software updates and subsequent adjustment of settings.
What has not changed is the current transformer (CT) that provides the relay with a secondary current circuit. It's at this point that analog electrical power meets the digital world of the relay. The current transformer (CT) is liable to saturation – a status that cannot be detected by the relay. Just so, it remains a matter of testing whether the relay responds correctly to the analog current provided to it. This is why secondary injection testing remains a core requirement of every maintenance schedule, despite all self-testing functions of modern relays.
Also, what has not changed is the requirement for commissioning testing and maintenance testing. Modern IEDs have become faster and more reliable. One should think that an electrical installation needs less change and maintenance. Unfortunately relays are now part of the digital world and have joined the cycle of technological acceleration. They are liable to software and security updates – each change calling for a new commissioning test cycle. Beyond the conventional secondary injection testing, test interfaces today are also used to access the relay after updates and cybersecurity improvements.
Lastly, what has not changed are the typical functional areas of relaying: distance protection, overcurrent protection, differential protection, line protection, motor protection, etc.. Generations of relaying specialists have worked on conventions and standards for setting up these relaying instances. With regards to test interfaces, e.g. the German engineering association VDE has set up a number of test blocks with configurations of 7, 14 and 19 poles, that match the current, voltage and signal requirements of each respective situation. Within most electrical utilities, standards and procedures exist using test blocks or test switches to deal with these relaying situations. If you have an existing standard or established usage of a test interface in your organization and would like to know how to solve that with a SecuControl product, please talk to us.