Final Thoughts

This is a question that many protection, automation and control specialists are asking themselves and their colleagues every day. And as usual the answer is - It Depends?

The first question that we need to ask ourselves is - What are we testing? In the past and still in many cases today the power system equipment is protected by electromechanical relays that have changing with time characteristics, hard wired interfaces and no intelligence that will support self-monitoring. As a result, the answer to the question in the title is definitely "Yes."
Testing is the only way to find out if the characteristics are still within the acceptable tolerances and that all interfaces are OK - that is why we do scheduled maintenance testing of such devices.

The situation is more or less the same with solid-state relays, so we are not going to spend any time on that.
Things change significantly with the introduction of intelligent, multifunctional electronic devices (IEDs). They have self-monitoring capabilities and since their characteristics are defined in numerical algorithms they don’t change over time. Such devices also have the ability to monitor their analog interfaces. However, when the interfaces with other IEDs are hardwired, they cannot be monitored.

As a result, the answer to the question in the title is - "It depends." If we are talking about an IED that does not give an alarm that it has a problem - we don’t have to test it. The only thing we need to test is the hardwired interfaces between the IEDs and the switchgear.

The transition to IEC 61850 based digital substations creates a unique environment in which all interfaces are digital, based on sampled values and GOOSE messages. The streaming sampled values and the GOOSE repetition mechanism, combined with the PRP and HSR redundant communications allow the monitoring of the complete substation protection, automation and control system. In this case the answer to the question is "No," until the condition monitoring system or any of the integrated IEDs indicate that there is a problem.

BeijingSifang June 2016