“Diamond-shaped” distribution network: Shanghai model of strong and smart urban power grid

Not long ago, a large-scale power outage occurred in Manhattan, New York, affecting more than 70,000 users, which once again aroused the attention and thinking of all walks of life on the power safety of megacities. For Shanghai, which is building an outstanding global city, it not only needs sufficient and reliable power supply to ensure it, but also needs to plan ahead for the long-term development of the power grid. To this end, Shanghai is actively exploring the construction of a "diamond-shaped" distribution network, accelerating the formation of a power grid improvement model in the city center with a pioneering effect, and then creating a Shanghai model for the high-quality development of a strong and smart urban power grid.

(Text丨Correspondent Shen Xuan)

At present, State Grid Shanghai Electric Power Company is accelerating the construction of strong smart grid and ubiquitous power Internet of Things, further promoting the overall improvement of grid equipment, management, and operation and maintenance levels. The overall power supply reliability of the power grid has exceeded "4 9s" (above 99.99%), ranking first in the country.

On July 3, the Shanghai Municipal Government and State Grid Corporation of China signed a strategic cooperation agreement in Shanghai. Both parties clearly stated that they would accelerate the construction of "three types and two networks" and jointly build a world-class modern urban distribution network. Among them, exploring the construction of a "diamond-shaped" distribution network in the central urban area of ​​Shanghai is an important measure for State Grid Shanghai Electric to actively implement the content of this strategic cooperation.

The so-called "diamond-shaped" distribution network refers to the dual-ring network structure currently being built in Shanghai, which uses a 10 kV switch station as the core node, is powered by dual-side power supplies, and is equipped with self-healing functions. This model was first created by State Grid Shanghai Electric Power based on benchmarking advanced distribution networks at home and abroad. It has the characteristics of significantly improving power supply reliability and load transfer capabilities, while taking into account the economic efficiency of construction and transformation. The "diamond-shaped" distribution network is named because its network topology is similar to the shape of a diamond, and the image of "diamond" is also deeply in line with the development concept of the future power grid: the incomparable strength of diamonds is the core pursuit of power grid planning, the exquisite cutting process of diamonds is the best reference for power grid construction, and the eternal vitality of diamonds is the ultimate goal of power grid operation.

Diamond-grade rugged, reliable power supply

It is understood that compared with the conventional double-ring network structure adopted by most urban power grids in China, the "diamond-type" distribution network has the technical characteristics of "full interconnection, full cables, full circuit breakers, and full self-healing".

Specifically, Shanghai's "diamond-shaped" distribution network changes the traditional wiring mode centered on the ring station (load switch) to one centered on the switch station (circuit breaker), and replaces the traditional distribution automation system with the self-healing system developed by the State Grid Shanghai Electric Power Organization, which can collect information on-site and automatically execute self-healing strategies remotely, thereby compressing the fault handling time from minutes to seconds. At the same time, due to the use of dual-side power supply from different substations, its load transfer capacity reaches 100%. With this flexible and controllable load transfer performance, the "diamond-shaped" distribution network can meet the "N-1" safety verification under maintenance mode, thereby effectively reducing the planned maintenance and construction power outage time, and greatly improving the power supply reliability in the city center.

In the field of international benchmarking, the "diamond-shaped" distribution network is also significantly advanced. Compared with the "point-to-net" wiring method of the Tokyo power grid, the "diamond-shaped" distribution network not only has a similar power supply reliability level (average power outage time per household), but also has stronger inter-station load transfer and load balancing capabilities.

As a forward-looking exploration in the field of power grid planning, Shanghai's "diamond-shaped" distribution network concept has been transformed from a blueprint into reality and has achieved results in a series of pilot projects.

In 2018, State Grid Shanghai Electric Power planned and built 10 switch stations in response to the "six-zero-three guarantee" power supply guarantee target for the first CIIE, combined with the undergrounding project of overhead lines in the Xihongqiao area, and simultaneously configured self-healing systems to form four high-reliability "small diamonds", pushing the power supply reliability of the regional power grid to more than "five nines" (99.999%), successfully ensuring the smooth convening of the CIIE.

The successful pilot of the "diamond-shaped" distribution network in Xihongqiao has also laid a solid physical foundation for promoting the integration of the ubiquitous power Internet of Things and the strong smart grid. This year, with the in-depth promotion and application of ubiquitous power Internet of Things technology, the reliability advantage of the "diamond-shaped" distribution network in Xihongqiao has been further highlighted, and the power supply reliability is comparable to that of international advanced cities such as Tokyo and Singapore, reaching world-class levels.

Diamond-like planning and implementation

Just as the value of a diamond comes from its exquisite design and cutting, the "diamond-shaped" distribution network has always been permeated with the connotation of "lean" from its concept to planning, design, construction and implementation. This is not only reflected in the fact that the "diamond-shaped" distribution network takes into account both economy and feasibility and has good construction adaptability, but also in its response to Shanghai's refined promotion of urban construction.

From the perspective of economic benchmarking with the current international advanced distribution network structure, the comprehensive cost of building a new "diamond-shaped" distribution network in a blank area is slightly lower than the "petal-shaped" distribution network (Singapore model), and about 9% lower than the estimated investment of the world's most advanced "double petal-shaped" distribution network. However, if the existing grid structure of Shanghai's distribution network is upgraded and transformed into a "diamond-shaped" distribution network, its comprehensive investment will save about 5% compared with the "petal-shaped" distribution network and 31% compared with the "double petal-shaped" distribution network. Even though the construction investment has increased compared to the conventional double-ring network structure, considering the benefits of improved reliability, balance, and flexibility, the "diamond-shaped" distribution network is still the preferred solution for building a strong and smart urban power grid in Shanghai in the future.

From the perspective of construction feasibility, the advantage of the "diamond-shaped" distribution network "adapting to local conditions" is more obvious. After nearly 20 years of multiple rounds of transformation, Shanghai's 10kV distribution network has gradually solidified the development model of "taking switch stations as core nodes" and formed a certain scale. Therefore, on this basis, it is only necessary to build or reconnect the lines between switch stations to achieve the upgrade to a "diamond-shaped" distribution network. Moreover, the scale of its newly built lines can be reduced by about 10% and 60% respectively compared with the "petal-shaped" and "double petal-shaped" distribution networks, thereby effectively saving line channels and power supply intervals of upper-level substations.

It is precisely because of this planning concept of extracting efficiency from limited spatial resources that it is more realistic to create a "diamond-shaped" distribution network in Shanghai's central urban area, where the spatial layout has been basically completed.

In 2018, State Grid Shanghai Electric Power fully combined the undergrounding of overhead lines and the consolidation of poles in the city center, and carefully designed a grid planning strategy in accordance with the "diamond-shaped" wiring principle. In the 100-kilometer road overhead line undergrounding project, 61 switch stations were newly built and renovated in a way of making full use of every available space and replacing old with new, and 18 sets of double-ring networks were constructed. By avoiding large-scale demolition and construction in this way, the "black pollution" above the center of Shanghai disappeared, and was replaced by an invisible "diamond-shaped" power grid underground. While the urban environment has been beautified, the distribution network has also been able to achieve a new round of transformation and upgrading, which can be regarded as a model of "one-shot win-win" in the refined management of the city.

Diamond-like sparkle leading demonstration

The "diamond-shaped" distribution network is an important direction for Shanghai to build a world-class urban power grid in the future, and it is bound to play a leading role in the planning and development of urban and even regional power grids.

In the next stage, State Grid Shanghai Electric will continue to combine the power supply supporting projects for newly built residential communities and non-residential business expansion projects, continue to promote the layout of core switch stations, and gradually form a "diamond-shaped" connection in the distribution network in the central urban area.