by Alex Apostolov, Editor-in-Chief

Testing in a brand-new world

So why is this issue of PAC World focused on testing? The answer is very simple - because we live in a brand-new world and we cannot anymore do things as we always did.

For more than a century we have been testing protection, automation and control systems in a world that we knew quite well - the world of electric power systems with large and small power plants delivering power to the load centers of a vast network of transmission lines, the world of significant short circuit currents and DC offset, the world of current transformers saturation and CCVT transients, the world of hard-wired electromechanical relays.
So, we have developed everything that we needed to test the protection in this world. We have the models of the transient behavior of the electric power system components, we have the simulation tools, we have the test devices that can apply the simulated currents and voltages to the tested protection relay and detect and measure its response time, we have the test switches that can isolate the test object from the energized substation when doing maintenance testing in a live substation.
Based on all of that we have established a testing process - every couple of years we send a testing crew to the substation with their test equipment, they isolate the relays that are scheduled for testing, connect the test equipment and run the tests using the tools available to them. We had to do this, because nobody new which characteristic has changed, and which terminal screw has loosened.

But now in the last few decades this world has been changing. Everything is changing - from the electric power grid to the protection and control systems and the testing technology. The large synchronous generators in nuclear or coal power stations are disappearing and being replaced by wind turbines and photovoltaic panels everywhere – at the transmission and distribution level in wind or solar farms and at the low voltage level as rooftop PV panels. This is all good for the environment, but it creates a problem for the protection and control systems – these distributed energy resources are not synchronous machines. They are connected to the electric power grid through inverters that do not produce fault current in case of a short circuit but behave in a way that depends on the algorithms implemented in the inverter controller by its design engineer. So many of the protection functions that we use may not work. And the testing tools that we have developed are not able to accurately simulate the behavior of the inverters under fault conditions.

Another major change is in communications technology and its impact on protection and control systems. First of all, we are not talking anymore about the testing of protection relays, but about testing of protection functions, schemes, distributed or centralized protection systems interfacing over IEC 61850 communications interfaces. They replace the copper wires with fiber thus eliminating another familiar tool - the test switch. So, we must come up with new methods and tools for functional isolation when doing maintenance testing in an energized substation.
The availability of optical and other non-conventional sensors also requires a different approach to the testing.

Now even that we have the problem of not being able to do testing as we always did, and we need to learn some new tricks, we need to look at the bright side. The IEDs are self-monitoring themselves and we can monitor all communications-based interfaces.
This means that when we monitor, and we don’t see anything abnormal - we don’t need to test. And if we need to test - we can do the functional isolation and run the testing tools from the comfort of our office, instead of having to drive to the substation to do it. On top of that, we need to test much less - just a function element instead of the complete IED. Which is all good! 

"As ironic as it seems, the challenge of a tester is to test as little as possible.
Test less but test smarter."
Federico Toledo

Power. Flexible. Easergy.
BeijingSifang June 2016