Market view: Monitoring LV networks

A Thames Valley trial conducted by Scottish and Southern Electricity Networks sought to identify the difficulties and benefits of real-time monitoring of distribution networks. The results were revealing.

As the low-carbon energy market continues to develop, network owners and operators will need to know more about what is happening on their systems. New Thames Valley Vision (NTVV), a Low Carbon Networks Fund (LCNF) project led by Scottish and Southern Electricity Networks, has been looking at how this can be done. NTVV has shown that intelligent network monitoring can deliver positive benefits to end customers. The enhanced insight can help distribution network operators (DNOs) prevent faults before they occur and avoid unnecessary expense when upgrading their networks.

It is vital that DNOs know as much about their networks as possible, especially the low-voltage (LV) network that feeds customers’ meters. DNOs have converged on a design that provides good value to the end customer in terms of reliability at the lowest cost. To achieve their economic goals, it has become custom for simple and practical LV networks to be built without any form of feeder-level monitoring. This approach has been justified by their relatively high reliability.

This philosophy is considered successful because:

1. Power has flowed from the top of the LV network to the customer.
2. DNOs understand the typical daily usage patterns of various customer types.
3. DNOs have learnt to quantify the diversity of customer demand and how this typically reduces peak demand from its theoretical maximum. This allows them to install efficiently sized cables and develop an economic overall network design.

However, if customers start using electricity in less diverse ways or exporting power to the network, then the success of the traditional LV network design is undermined.

Customers who fit solar panels, install electricity storage or buy an electric vehicle do not need consent from the DNO beforehand. If only a few households do this, it is unlikely to overload or cause serious voltage deviations on the local feeder. But it is becoming clear that non-diverse devices, such as domestic solar, and large loads, such as electric vehicles, are being connected in volumes, so changes may be needed to traditional design assumptions.

The NTVV project trialled a range of network-monitoring techniques. The project demanded an understanding of electricity usage patterns and information on the power flow of LV feeders in the trial area. This justified the development of an LV network monitoring system, involving the fitting of monitors in substations and customers’ properties.

As well as the real-time visibility benefits, NTVV indicated that significant value was found in storing this information for later analysis because it would provide planning teams with a more robust basis on which to forecast network flows and usage, which will be key to efficiently planning and operating LV networks in the future.

However, monitoring of the LV network created a lot of data. To leverage the full value of this data required a smart system to take it from the field and make it available to many diverse users. Within NTVV, the data was extensively presented in Scottish and Southern Electricity Networks’ distribution management system for operational users, and stored for accessibility by planning teams.

A key learning was that there is unlikely to be a one-size-fits-all solution in the short term and installers may need to find the sweet spot between maximum relevant data, accessibility and overall cost.

Retrofitting is challenging

Traditional LV systems were never designed with telemetry in mind. As a result, NTVV had to establish ways to fit them into legacy LV feeder pillars without the need for interruptions or compromising engineer safety.

Monitoring equipment used during the trial provided both half-hourly and real-time streamed data. The trials showed that streamed data may only be justified when used for the control of smart devices. In mainstream business-as-usual operation, all monitors fitted should be able to stream data, but this would only be enabled where appropriate.

NTVV focused on monitoring substations and users in the urban area in and around Bracknell. Because of the general prevalence of cellular networks in the area, the project was able to take advantage of the plug-and-play nature of data networks. However, in some trial areas, access to cellular networks was more challenging. In these cases, it was found that communication and connection rate could be improved by fitting a flexible antenna mounting arrangement.

The trials demonstrated real, practical ways in which operational staff can benefit from access to real-time network data. As a direct result, previously unknown network faults and issues were discovered which led to better operational decision making.

An example of this was the identification of an evolving main cable phase-to-phase fault. This problem was, at the time, not noticeable to any customer yet was flagged as an abnormality. This prompted an on-site investigation and repair before the fault could develop into a failure with a large number of customers being off supply.

The data availability from the distribution management system was also assisted managers who co-ordinate fault restoration. For example, the data allows fault response managers to direct staff to the likely fault location.

There are still hurdles to be overcome before the monitoring methodology trialled in NTVV can fully achieve its potential. In particular, these challenges relate to the accessibility of data, especially in more remote rural areas. That said, the NTVV trials have delivered many useful lessons on how this can be done effectively.

However, in order for this to be a truly cost-effective solution, there will need to be a larger and targeted application of a standardised monitoring solution across the DNO area. This will allow the economies of scale, which can then comprehensively bring efficiency and cost reduction to the DNO, and ultimately benefit all customers connected to the network.