Granular T&D Topology Identification
Bryce Johanneck
Principal Consultant, Advisory Services
Due to circumstances that are well understood and accepted, we’re amid the greatest transition and arguably the largest and most complex machine the world has ever experienced. As we continue to deploy variable generation at increasingly distributed locations while simultaneously electrifying new end uses, there’s a growing need to focus on granular visibility and control of our Transmission and Distribution infrastructure. Setting aside control for a moment, granular visibility is best discussed if unpacked into a few important components, specifically – nodal granularity, temporal granularity, and latency. I’ll address these below and begin to chart a path forward.
First, let’s address nodal granularity which refers to the intersections in our T&D grids – many of which are not presently monitored. At transmission voltages, these nodes often look like manual switch structures along a transmission route between two substations. As we know, in distribution the quantity of nodes increases significantly as does the variety of nodal hardware. Here we might have manually operated overhead switches, fused cutouts, overhead jumpers, primary URD switches/junction boxes, pad mount transformers etc. In the T&D Topology Identification realm, one question then is…how many nodes do we need to define the state (opened/closed) of?
Temporal granularity is simply a reference to the frequency at which the state of the aforementioned network nodes should be determined. Should temporal granularity be defined in milliseconds, seconds, minutes, hours, or days? Finally, latency, which is simply a metric measuring the time allowable to determine node state. Again, should latency be measured in milliseconds, seconds, minutes, hours, or days?
To put it simply, the last two paragraphs raise these three questions:
- As a percentage of the whole, how many nodes do we need to determine the state of?
- How frequently should we make these nodal determinations?
- How much time do we have to make said nodal determinations?
Now that I’ve set the stage for what it is that we’re trying to define, let’s consider a few knowns that might serve as helpful input.
- The frequency at which our system operates
- The duration required to reach physical constraint violation
- The consideration that network nodes introduce the opportunity for thermal constraints to change (due to differing conductor sizes, for example)
Lastly, before answering – it’s important to consider both the economic and technical value that we intend to extract via any future T&D Topology Identification efforts. This consideration leads us right back to the “control” term in ‘granular visibility and control of our T&D infrastructure’ found in the first paragraph. Without topology identification of granularity and latency high enough to impact T&D control decisions, we’re left trying to extract economic value from things like post-event analysis, after the fact model validations, etc. These are certainly valuable efforts, although they carry less financial impact – even if as analytical folks, we’d like to see otherwise.
Now to the fun part, where do we go from here? I’ll make it short:
- 100% nodal determination
- Millisecond granularity
- Millisecond latency
First and foremost, I’m aware of the scope of these proclamations. Second, the solutions to this outcome aren’t well defined, and will likely look very different in distribution than they do in transmission. This difference in solutions is driven by a few things, notably the quantity of network nodes at distribution voltage levels as well as the accuracy of distribution system models. Monitoring every node in the transmission network has a high likelihood of being technically and economically feasible. Conversely, the same isn’t true in distribution as the quantity of distribution hardware without provisions for PT’s and CT’s alone is simply too great – and that’s setting aside the fact that medium voltage live line work practices exist. Day in and day out, crews of skilled tradespeople reconfigure the distribution network for both planned and unplanned purposes. With some changes eventually returning to prior configuration, and others taking a “permanent” (a term used loosely…) place and state in network connectivity.
My intent here is to illustrate that our T&D infrastructure is a living and breathing thing. This monstrous machine that we love is a true network with an indeterminate state at necessary granularity. There’s no longer a static system state. Regarding actual system topology, we often go from Configuration A to Configuration B, to Configuration C, then we might revert to Configuration B except for a (or multiple) permanent change(s)…so now we’re really at new Configuration D. At which point, we might never see Configuration A again. Yet in this hypothetical, Configuration A may very well be what’s in various static planning models that exist at our utility.
One question that I always ask is, how many Distribution Switching Orders did your utility have last year? That’s often (and understandably) an unquantifiable number…a metric that isn’t tracked today. Yet all utilities and multiple departments within utilities are facing various issues that have a common theme, and that theme is Granular Topology Identification. Everything from System Operations to Protection Engineering, Capacity Planning to Rate Making, and from Generation through to Load Control/Demand Response is adversely impacted by a lack of situational awareness.
Fortunately, Topology Identification has become a topic of discussion at North American Synchrophasor Initiative (NASPI). To this end, the Distribution Task Team at NASPI just released a report (link below) that serves as a good primer for thoughts on granular T&D Topology Identification.
https://www.naspi.org/node/851
Quanta Technology offers advisory services related to the areas mentioned above. If you’re interested in exploring our service offerings, check out our Enterprise Integration and Field Area Communications and Monitoring web pages.
For more information please don’t hesitate to reply below or reach out to me directly at [email protected]