The anticipated changes in customer behavior and electricity demand on the low-voltage (LV) network, coupled with the objective to reduce the carbon footprint associated with the electrification of heat, pose significant challenges with transport and electricity generation for distribution network operators. Historically, distribution network operators have used traditional reinforcement to address the problems created by low-carbon technologies, but this option must change because of the high cost and associated disruption to supplies.
The substantial increase in new electricity load from low-carbon technologies such as heat pumps, electric vehicles and micro-generation has created thermal and voltage challenges for network management. Distribution network operators must connect the new low-carbon technologies to facilitate the customers’ transition to a low-carbon future, while maintaining statutory voltages, managing power quality and reducing network losses to minimize customers’ energy bills.
In November 2013, the UK’s Office for Gas and Electricity Markets (Ofgem) awarded Electricity North West funding from the Low Carbon Networks Fund for a project designed to use the latest advanced technology developed for LV network management. The £11.5 million Smart Street innovation project, which began in 2014 and will be completed in April 2018, aims to demonstrate how to optimize high-voltage (HV) and LV networks in real time.
The Smart Street project involves the application of three key incremental steps:
• Coordinated voltage control using distribution transformers fitted with on-load tap changers (OLTCs) and capacitors on HV and LV networks
• Interconnecting the existing radial LV circuits and arranging the control of these networks within the control room
• Real-time coordinated configuration and voltage optimization of HV and LV networks.
The Smart Street project is designed to quantify benefits arising from the installation of new technologies as well as the automated operational facilities available to control HV and LV networks, with extensive customer engagement provided throughout the project. Specifically, the project will determine the following:
• The capacity and voltage headroom released and the quantities of new low-carbon technologies that can be connected, together with the economic justification and carbon benefits
• Optimization algorithm settings to deliver loss and energy reduction from a decrease in the feeder voltage, that is, conservation voltage reduction (CVR)
• Customers’ energy reduction from the application of the CVR methodology and the variation in customers’ consumption reduction 24/7 throughout the year
• Reduction in HV and LV network losses
• Safety benefits associated with the introduction of automated LV equipment, thus removing the need for manual operation of live LV equipment
• Reduction in fault-response costs arising from the introduction of in-built fault detection and localization facilities.
Electricity North West selected six trial areas for the project, each centered on primary substations. Following the collation of the utility’s planning software, databases and codes of practice were subject to detailed network modeling using interactive power system analysis. Each of the selected circuits was modeled by interactive power system analysis from the source primary substation down to the LV feeders.
Several scenarios were applied to each circuit to study a variety of interventions over a wide range of demand and generation levels. These included operating with the HV loops open and closed, interconnecting LV feeders, installing HV and LV capacitors at different points on the network, and installing OLTCs on the distribution transformers in the HV/LV distribution substations.
The project circuit modeling yielded the following results:
• The Green Street/Caunce Road LV feeder circuit is 321 m (1053 ft) and has a photovoltaic (PV) penetration of around 40%, with 91 out of 226 customers having PV installations averaging 2.28 kW. The studies confirmed, with nil and maximum PV penetration, voltage levels varied between being below and above the statutory voltage limits. However, by meshing the LV feeder with an adjacent substation, the voltage profile remained within statutory limits. The installation of various-rated capacitors at different points on the LV feeder confirmed the optimum arrangement was to install a 100-kVAR capacitor halfway down the LV feeder.
• The Hindley Green/Walmer Road LV feeder measures 543 m (1782 ft) to the end node and has a PV penetration of around 20%, with 45 out of 255 customers having PV installations averaging 2.35 kW. The studies confirmed problems with the voltage levels depending on the percentage of PV in the circuit, irrespective of the position of the off-load tapping on the HV/LV distribution transformer. The optimum solution was the installation of a 150-kVAR capacitor positioned two-thirds down the feeder.
• The Denton East/Pendle Road LV feeder measures 513 m (1683 ft), and the circuit has a PV penetration of 10%, with PV installations averaging 2.4 kW. Studies showed meshing the LV feeder with an LV feeder from an adjacent substation resulted in an overall voltage profile within statutory limits. However, the optimum solution in terms of voltage profiles and voltage losses was to install a 100-kVAR capacitor halfway down the LV feeder.
• The Fallowfield/Lindleywood Road LV feeder measures 437 m (1434 ft) and has no PV penetration. However, to comply with the statutory voltage limits, the studies confirmed installing a 100-kVAR capacitor halfway down the feeder would provide the optimum voltage profile.
• The Wigton/Western Bank LV feeder has a PV penetration of less than 10%, with an average PV installation of 3.08 kW. The total length of the feeder to the end node is 422 m (1385 ft). Similarly, the range of studies confirmed a 100-kVAR capacitor positioned halfway down the feeder offered the optimum solution.
The addition of capacitors on the LV network increases the voltage measured at the distribution substation busbars. Each selected LV feeder was modeled to simulate the effects of placing multiple 100-kVAR capacitors on different LV feeders. Results showed, irrespective of the distribution transformer off-load tap position, the magnitude of the voltage rise is dependent on the transformer impedance and, hence, the rating of the HV/LV transformer.
A comparison of results between open and closed HV ring scenarios produced less of a voltage change on the LV networks than expected. However, control of the HV open points will be optimized by the Spectrum Power software from Siemens. During a fault condition, this software will need to be switched out and the network should return to normal operation. The fault will be isolated until repaired and only then will the optimization software be energized. This software is expected to switch out the capacitors under heavy PV penetration at times of maximum generation with minimum demand.
Background and Techniques
The Smart Street project makes provision for the use of capacitors on the HV and LV networks as well as the application of distribution transformers equipped with OLTCs. This will enable the customer supply voltage to be sustained at the optimum level for energy-efficient operation of appliances, reducing the energy consumed by customers and on the HV network, thereby simultaneously reducing network losses.
Existing LV networks were not designed to cope with the variable power flows caused by the introduction of low-carbon technologies, such as vehicle charging and generation. Interconnection of LV networks is one way in which the voltage, thermal and harmonic problems created by low-carbon technology loads and generation connected to LV networks can be reduced significantly.
The project will use intelligent switching devices that can be controlled remotely. Sensing feeder load flows offer the opportunity for dynamic reconfiguration of the LV network. This will transform radial networks safely into interconnected networks, providing a centralized LV network management and automation system.
Smart Street will be able to optimize the network configuration and voltage profiles in real time as well as alter both interconnected configurations and voltage profiles across HV and LV networks. Software will be used to compare and balance network losses and customers’ energy consumption.
CVR on a distribution network is defined as a reduction in energy consumption resulting from a decrease in the feeder voltage. The project will use CVR by installing OLTCs on distribution transformers in conjunction with shunt capacitors to optimize the voltage profile. The OLTC distribution transformer will regulate the sending end voltage on the feeder; the capacitor will produce a voltage boost at the end of the circuit. This will result in a flatter voltage profile and enable a reduced, more uniform voltage within statutory limits at the customer’s point of supply.
Smart Street Equipment
The following equipment is being used in the Smart Street project:
• The Weezap — a retrofit-design LV vacuum circuit breaker, supplied by Kelvatek — can be installed onto existing LV fuse boards, replacing the traditional high-rupturing-capacity fuses. The Weezap is installed in conjunction with the Kelvatek Gateway device, which communicates with Electricity North West’s supervisory control and data acquisition system as well as relays various controls and monitoring to and from the Weezap devices. The Gateway also acts as the on-site user interface for installation, configuration and control. Each Gateway can manage up to 15 devices; and as two Gateways can be installed in a single substation, a maximum of 30 devices can be installed at any one site.
• The Lynx vacuum switch, manufactured by Kelvatek, is designed to fit into an existing standard underground link box, with a modified bell housing surround to prevent water ingress. The Lynx enables the interconnection of LV circuits as well as advanced monitoring capabilities. It is designed to open and close LV circuits at the link box either manually or remotely. The Lynx communicates with the Gateway device, providing a remote connection to the installed devices, which enables remote monitoring and control by the network management system.
• The project includes the installation of 84 LV capacitors manufactured by ABB. Five units are installed in distribution substations, and the remaining 79 are installed on the LV feeders to apply voltage boosts. The project also includes the installation of six capacitors, three ground-mounted units and three pole-mounted units on the HV network for reactive compensation. The capacitor banks are designed with reactors in series to lower the resonance below critical order harmonics.
• Five HV/LV substations are equipped with Efacec distribution transformers fitted with Maschinenfabrik Reinhausen OLTCs that operate by an automatic voltage control relay. The Spectrum optimization software communicates with the automatic voltage control relay and alters the voltage set points to enable the transformer tap-changer to switch to the optimum tap setting.
• Monitoring units are installed at the remote end of all radial LV feeders, the point of the highest calculated voltage drop. These record voltage measurements for optimization purposes.
• Spectrum Power 5, developed by Siemens, includes optimization software that will manage and control the various devices based on the calculated load flow analysis. Spectrum also will optimize operation of the LV and HV networks in terms of voltage optimization and network configuration.
• Remote terminal units from CG Power and Industrial Solutions Ltd. act as a data concentrator and router, collating the information from the Weezap, Lynx, end point monitors, and HV and LV capacitor banks, passing it on to Spectrum Power 5 and the control room management system, as appropriate.
• Electricity North West’s existing network management system and control room management system communicate with the optimization software through an inter-control communications protocol that was developed specifically for the project. This enables all network configuration commands and alarms to be controlled by the network management system, which is overseen by trained control engineers.
Since the funding was awarded in November 2013, Electricity North West and its Smart Street partners have followed a strict timetable. From mid-2015 to January 2016, all the new technology equipment designed and specified for the project was installed and commissioned, a total of 775 new installations. The Smart Street project was commissioned and in operation in January 2016 for the trial period, which goes through January 2018.
Project Partners Key
The technologies installed were identified and investigated prior to the project bid submission; therefore, the requirements and specifications for the equipment were defined at a high level. This provided direction for the project delivery team to procure the necessary technologies to realize Smart Street.
The relationship between Electricity North West and its Smart Street partners has been key to meeting project milestones and further developing the new technologies involved. The commitment and buy-in from project partners has been essential to the successful implementation of Smart Street.
Electricity North West now expects to continue working with its project partners and manufacturers to further develop the technologies deployed throughout the project life. ♦
Check out the January 2018 issue for more articles, news and commentary.