I’ve spent most of my career working on protection and automation systems for electric utility distribution systems, writes Chris McCarthy, Managing Director, S&C Electric UK Holdings.
When involved in new-product development, I’ve typically been one to champion advanced sensing and communication for all new products.
Communication can add a new dimension to a distribution circuit device. Getting timely data from field operations opens a new realm of possibilities for new products and services, and it can improve utility operations.
In near real time, network operators are rapidly informed of outages, errors, or routine maintenance needs. The distribution system becomes visible to them. After service cuts have happened, they can more easily retrieve historical log files to reconstruct events and switching actions that have occurred in the field.
When distribution system devices can communicate directly with each other, network operators can automate the decision-making and switching actions to rapidly minimise outages.
Communication comes at a non-trivial cost
Network operators must configure, modify, and maintain the communication devices over time. Batteries need replacing and electronic components become obsolete, so the utility needs a proactive maintenance programme to keep the communication system running.
We hear about data-driven solutions in all industries, so the question is, what will be done with the data from the distribution system?
I’ve heard utilities say they’ll collect it all and decide what to do with it later. This point of view only makes sense if utilities actually analyse the data and make that analysis part of their broad operational and planning practices. Just collecting endless streams of data and getting SCADA alerts that devices are operating in the field is nothing more than noise unless a utility puts the data to work.
So, the idea of collecting data and giving remote operational commands starts with a physical protection or switching device. A utility then adds a communication system layer and then a data-analytics layer. Each additional layer has an incremental cost and requires a different set of personnel skills.
To give a sense of the scale of the data overload problem, the IET published in its 2013 report “Electricity Network, Handling a Shock to the System” that the number of distribution network automatic controls on the Great Britain system is expected to increase from 10,000 devices today to 900,000 devices in 2030.
Additionally, automatic controls in homes will go from none to 15 million in the same time frame. The control centres that I’ve visited already seem busy with today’s level of communicating devices, so this signals massive changes are needed if the automation predictions come true.
The case for communication: fault-passage indicators
Let’s start with fault-passage indicators (FPIs). Their main purpose is to signal the location of faults to the network operators. Some models work without communication, but they require a restoration crew to drive to an FPI location and to inspect it to determine whether it has registered a recent fault event.
There may be many thousands of these devices on the system, and some may be enclosed within housings, obscured so they aren’t easily seen, or difficult to reach.
A case can be made that fault-passage indicators become much more useful if a utility can automatically route the information to the control centre as soon as a fault event happens. This reduces patrol time significantly, which means communication is enhancing the device’s main function.
Three-phase overcurrent protection: To connect or not?
In another example, three-phase overcurrent protection devices on the main feeder lines are critical devices for fault clearing and restoration crew response. A case can be made that these devices should have communication capability:
- Their population is relatively small because there are usually between one and four overcurrent protection devices per circuit, but the data set can be very rich with details regarding the electrical system.
- The typical design of these fault interrupters or switches already includes a means for utilities to power the controls from the distribution line, so it’s only a small additional draw for a communication device.
- The cost of a cellular or radio communication option is small relative to the overall price of three-phase protection devices with an electronic control, perhaps 2%-10%.
If the device’s main purpose is overcurrent protection for single-phase distribution spurs with fewer than 50 customers, then the decision whether to add communication is not as clear.
BlockQuote“Utilities need to determine which distribution items should have communication capability, and which should not”
A utility could have many thousands of overcurrent-protection devices on the system, so the cost per device will be heavily scrutinised. The cost to add communication becomes a larger percentage of the overall installation, perhaps adding another 30%.
Utilities will need to monitor, maintain, and upgrade at regular intervals thousands of batteries and communication devices spread across the countryside, requiring physical visits to each device every few years. They can avoid batteries if the device is self-powered, but then the devices stop communicating when the steady-state line current drops below a certain threshold, which may look like false loss-of-communication alarms to the control centre.
Is the utility control centre ready to deal with a myriad of alarms when batteries start to fail or the communication signal fades in and out? And after all that work to enable the communication system, the data set and extent of operational commands for simple devices will not match the rich data set and operational flexibility of three-phase devices. So, is it really worth it?
A better functional and economic solution can result from letting protection devices perform protection functions while other devices, such as communicating FPIs, do the sensing and communication functions as desired.
In conclusion, adding communication functions to the right devices can give network operators real-time and historical visibility of their distribution system, which leads to reduced outage times and more efficient operation.
However, they should use caution against jumping to the conclusion that all devices should have communication. In the case of a low-cost protection device, adding communication for sensing and monitoring purposes could greatly increase both the initial cost and ongoing maintenance costs, and the perceived benefits of data collection may never be realised.