Propagation and Electrical Phasing
Propagation and Electrical Phasing
In this article we will look at more advanced, practical examples of how electrical networks propagate phase in an unbalanced distribution system. If you aren’t already familiar with how propagation works, please read the Explore attribute propagation and attribute substitution article.
Because the only way to directly observe propagated values is through the fields maintained by running Update Subnetwork, we will start by looking at how that process enforces propagation.
Subnetworks
As you saw in the previous article, the utility network will propagate phasing values as it walks the network. When a feature has valid phasing it will become part of the subnetwork, otherwise it will be de-energized. The examples shown in the previous article were simple linear examples, but the implementation of propagation also manages branching paths and loops. This means that if individual phases split and meet up downstream, the system can propagate the combined phases.
Splitting and combining phases can lead to individual phases in an electric line going in different directions, causing the line to become looped and have indeterminate flow.
Features that fail to propagate a value are called propagation barriers and are treated as de-energized. Propagation barriers are different from other barriers because propagation barriers are not included in the subnetwork regardless of the Include Barriers Feature setting of the trace.
Propagation barriers, and the features downstream of them, are not part of the subnetwork. This is an important form of quality assurance since it allows you to quickly identify features with an invalid phasing as de-energized.
Another important part of quality assurance is to look for features that are only partially energized, also sometimes referred to as being under phased. These are features that have one or more phase that is not energized. These features will still belong to a subnetwork but features downstream of them may become de-energized. You can identify an under phased feature by comparing the Phases field on the equipment to the Phases Energized field.
Now that we have seen how phasing and update subnetwork behaves with simple features, let us look at some examples of how it behaves with a device that has terminals.
Terminals
Tracing, barriers, and propagation behave differently when they pass through a device with terminals. This means that an open switch or the phasing of a transformer will only affect the trace when it passes through the device.
This is why you can draw a single-phase transformer in-line with a medium voltage conductor. The phasing of a single-phase distribution transformer does not affect a medium voltage three-phase conductor because it connects to the high side of the transformer. The phasing on the low voltage conductor is determined by the phasing of the transformer because it only receives the phasing that passes between the high-side and low-side terminals.
This situation works well for transformers, but it is something to consider with other devices that use terminals. There are several ways to represent protective equipment for a tap line. The recommended way is to place the device offset from the main line, along the tap line so the map clearly shows which line is protected. However, you can draw the device at the intersection of the main line and tap line if the device has terminals and the terminals are connected properly. In cases where a single-phase device is protecting a tap line, the main line should connect to one terminal with the tap line connected to the other terminal. If we revisit the example above with a single-phase switch on a three-phase line and use terminals to manage the different connections with the main line and tap line, we can see phasing is now correct.
What do you do if your switch or protective device does not have terminals and you still want to have it not restrict the phasing? The Subnetwork Tap network category can be assigned to a device or junction asset type to accomplish this. Assigning the Subnetwork Tap network category to a device or junction asset type, those features will no longer restrict phasing when drawn midspan on a line. However, it also means that those features must always be midspan on at least one line. Below is an example of a tap line connected to a main line using a junction feature that is a subnetwork tap.
Looking at the example above we can see that subnetwork taps offer a way to represent the equipment for isolating or protecting a tap line when the equipment doesn’t have terminals, or you don’t want to split the main line. This is done by adding a subnetwork tap on the main line, then placing the device on the tap line as shown in the example below.
Let us use this understanding of how propagation respects terminals, subnetwork taps, and is capable of splitting and recombining phases to solve the following problem: how do you model a single-phase device, like a recloser or regulator, installed in-line on a three-phase line? In this case you model the jumpers that bypass the device in the field to ensure that all three phases are available downstream of the equipment. You do this by creating subnetwork taps on either end of the device, then letting the two unprotected phases bypass the protection equipment while letting the protected phase trace through the device.
Boundary Devices
Another interesting situation to consider is how to calculate the energized phases when a device exists between two circuits? In this case each circuit will propagate its phasing then the shared features receive the combined phasing from each circuit.
The most common example of this is a three-phase open device between two circuits. A less common, but equally valid example, is to have a single-phase device between two circuits with distinct phases. A device that connects distinct phases from adjacent circuits is not common, but the utility network does model it correctly.
A similar issue arises when a customer connects to two transformers that belong to different circuits. In this case the customer, low-voltage conductor, and the transformers will all appear as belonging to multiple circuits. The utility network supports connecting a customer, or subset of each subnetwork, to multiple subnetworks but it is more likely to be bad data than a deliberate engineering decision.
If you keep an eye on your subnetwork name field, and if you see a conductor or device that is not a tie device that belongs to more than one circuit you should investigate!
Conclusion
If you’re interested in learning more about tracing and analysis with ArcGIS Utility Network, you should visit the Analysis and Tracing with ArcGIS Utility Network learning series. This series contains a collection of articles, videos, and tutorials to help familiarize you with tracing, subnetworks, and ArcGIS Utility Network.
If you have specific questions about how to solve different workflows, please visit us on the ArcGIS Utility Network channel on the Esri Community site. This is an active community with thousands of active members.
