The electric power systems' PAC industry is moving into the 21st century by replacing the existing hard wires of the secondary circuits in the substations with fiber optic cables. The relay outputs and opto inputs disappear as well, replaced bycommunication ports and messages between the multifunctional IEDs.
This immediately creates a barrier that may be difficult to overcome. It can stop us from looking carefully and trying to find out if it really is so different and what we can apply from what we know to the new world we live in.
Many things are just a matter of perception. What is different is the technology that is being used to implement the same things that we can do with copper wires, but in a more efficient way. At the end of the day we still need analog and binary signals to provide the IEDs with the data that they need. But instead of closing a relay output of let's say a distance relay that will energize an input of another relay to initiate a breaker failure function, the first relay will send a GOOSE message indicating the operation of a Zone 1 distance element that will start the breaker failure function in the second IED. Everything else is the same. I assume that many of you are shaking you head and saying "Yeah, right! It is that simple."
Well, it is not that simple, but it is not that difficult either. One of the things that we need to solve is the fact that we are introducing a new range of devices in the substation – the ones that make the so called substation communications network. The ones responsible for delivering the messages from one IED to another, from a server to a client. So while it may not be that difficult to convince a protection engineer that the change of the value of a data attribute in a GOOSE message from False to True is equivalent to the closing of the output contact of a relay, it may not be that simple to explain the replacement of a few pairs of copper wires that go between the terminals of the relays with fiber cables and Ethernet switches.
To further complicate things we have the organizational challenges. In many cases the PAC specialists need to work with the IT departments, because the rules say that when they buy a switch, the IT people have to approve the specific switch for use in the company. And here we need to make a decision of what to do. We need to have a strategy. We have a couple of options.
The first one is to bring some smart IT people into the protection and control groups and make them part of our teams by educating them to the differences between the office and substation environment, between protection IEDs and printers.
The second option is to make the protection experts also IT specialists. This is not going to be easy, but it is a matter of interest in the new technology and desire to learn and solve problems. In this case in order to keep the IT people out of our way, we need to stop talking about switches in the substation, but rather about process and station bus devices. To achieve that we will also need the cooperation of the hardened switches manufacturers – they will have to change the devices' labels.
Once we solve these issues, we can focus on the architecture. We should always keep in mind that when we replace the copper wires and terminal blocks with fiber and communication ports, we need to think about the substation communications architecture. Like every protection and control system design, we cannot say that one architecture fits all applications. It will depend on the importance and size of the substation, the performance requirements, the protection philosophy, our budget, and many others that we cannot list here. The decisions will be based also on the requirements for reliability and availability. And here we can ask the question "What if something – for example an Ethernet switch - fails?". If we are using a single star architecture, we lose the complete protection system. This may sound horrible, but if you think about it, this is a very common design approach implemented in thousands of substations – the ones that have a single battery. If it fails – we lose the complete protection system and live with remote backup.
So to me the key is not to be afraid of the new technology – it is just another tool to apply our PAC knowledge in the 21st century. The same way that we changed from electromechanical to microprocessor based relays, we are changing from hardwired to communications based protection and control systems.
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