This technology report begins by reviewing the technologies needed to build a secure and energy sustainable city from the standpoint of electrical distribution and ends by presenting a demonstration project of such technology in the city of Jerez de la Frontera currently under development by ENDESA.
The solution adopted is based on the following points:
- Business needs: Nowadays, electricity is equivalent to comfort and prosperity. It is therefore necessary to optimise the quality/price ratio and the quality of supply at the minimum price.
- Strategy: The network must be reliable, predictive, efficient and safe. To achieve this it is necessary to have generators as close as possible to consumers. This requires providing intelligence to the network through integration.
- Tactics: Using emerging technologies. DER, ADA, V2G, AMI … and especially ICT.
The fundamental key of the concept of a smart grid can be summarised as obtaining a secure, efficient and self-healing grid. This will require the intercommunication of all electrical infrastructures through communications with the appropriate levels of reliability and bandwidth. It is ideal to reuse the existing electrical infrastructure as much as possible, including lines of the distribution grid and associated installations.
The main challenge in distributing electric power is that it is difficult to store. Therefore the generation infrastructures are highly inefficient because they must be sized to operate at certain moments at the maximum power consumption. This is particularly relevant in the case of renewable energy generation, which can be erratic. The following sections will demonstrate that smart grid technologies provide a solution to these challenges. Demand is balanced with generation and the electrical industry infrastructures are used in an optimal way. From an electrical point of view, the concept of smart grid is supported by the following three key concepts: AMI, DER and ADA, outlined in the following figure:
AMI: Advanced Metering Infrastructure. The efficient usage of electricity needs first of all to modify consumer habits, thus flattening the load curve of customers. This is equivalent in some ways to energy storage at the point of consumption.
DER: Distributed Energy Resources.
a) By having generators close to consumers, it is possible to minimise technical losses due to transmission and distribution. By diversifying and increasing the number of generators, the criticality of each of the individual generators is reduced. Thus redundancy in generation is maximised.
b) By diversifying, the effect of intermittent sources of generation is reduced because they can be combined in a balanced and statistical multitude of diverse sources of generation.
c) Energy storage: Due to the increase in renewable sources of generation, it is essential to be able to store energy that can be generated in those moments in which there is no consumption. The expected increase in electric vehicles could provide an extraordinary capacity for storage.
- ADA: Advanced Distribution Automation. The increasing complexity and criticality of the electric grid is going to require advanced methods of protection and control in order to maximise its efficiency. It will be necessary to automate more than the telecontrol of the topology, maintenance, and prediction capabilities. It will also be necessary to expand protection schemes and implement adaptive mechanisms of self-adjusting devices on the network in real time.
This basic core is going to need the support of large decentralised information systems (OMS, DMS, EMS, MBC, AGC, Advanced Simulation). And, of course, as a fundamental, a powerful telecommunications system will be necessary to interconnect all these systems in order to maximise the safety and efficiency of the grid.
The core of the system is communication, on top of which AMI, ADI and DER is deployed. And finally, several ICT systems will be necessary for control, supervision and maintenance of the system.
The creation of a smart city is a great technological advancement, promoting sustainable development and facilitating and providing solutions to future societies and individual clients.
The new technologies and initiatives that are going to be described represent a new structure of a distribution network within a metropolitan-scale, optimising all its parts in order to create a network with the following features :
- Self healing and Adaptive
- Interactive with consumers and markets
- Optimised to make best use of resources and equipment
- Predictive rather than reactive
- Distributed geographically and organisationally
- Integrated in systems and services
- Safe against physical and cyber attacks
Only an integrated approach will allow coexistence between the various components in a harmonised way.
The ultimate purpose from a business point of view can be summarised as follows: “Maximise the quality of service while minimising costs”. These needs should now be translated into concrete objectives:
Optimise the usage of the electric infrastructure:
- Minimising energy dependence.
- Maximising sustainability.
- Minimising the costs.
Optimise the quality of supply:
- Maximising power quality.
- Maximising reliability and availability.
Create value-added services:
- Demand response.
- Real-time pricing.
We know that the defined objectives at the top of the pyramid are ambitious and complex. This approach will need a longterm vision in order to make the adopted solutions viable, stable and sustainable. In the long term we get the paradoxical combination of two different worlds. Indeed, electronics and communications devices differ greatly compared with power electricity devices in terms of MTBF, life cycle, maintenance, cost and security.
Our strategic approach can be summarised as the harmonisation of both worlds: The electrical aspect and the communications and electronic devices aspect. This approach will allow us to solve the problem completely in the long term and requires the following strategy:
- End-to-end communication. Homogenised data models will lead us to a comprehensive solution by minimising the number of necessary equipment, gateways and translators. Data must be self-descriptive in origin and allow for the usage of the data in a transparent way until final destinations.
- Using a distributed architecture. This solution does not necessarily mean that operationally it cannot be centrally managed.
- Building an integrated solution: Planning the coexistence of all the involved services, reusing the involved infrastructure and avoiding duplication – thus minimising the overall resources required to assume the required goals.
The final solutions must be studied and designed according to different sectors in order to adapt the technology to the client profile.
AMI, DER and ADA cannot be considered separately since they are going to share the same infrastructures and are intimately related. It is necessary to expand the concepts of network automation not just to control the secondary distribution network, but also to include the new protection schemes and the automation of micro generators that are going to be incorporated into the system. The obtained information about instant consumption and quality of service for end-users will also be very useful in driving the distribution network.
Basically, the most radical changes that appear on the new network of our smart city are:
- A large increase in the complexity of the secondary distribution network
- An expected increase in the number of mini-generators connected to the secondary distribution network (25 kV)
- The emergence of multiple generators connected to the lowvoltage grid that will have to operate in a coordinated manner
- The emergence of smart meters for demand response.
The first two points already exist. We are going to have a network that will require much more complex, efficient and safe control mechanisms. The third point is probably the greatest novelty and will require a special design from the perspective of stability, security and operation. The last point will also allow real-time. Its massive attributes will also require the use of special techniques for maintenance and communications.
FROM THE COMMUNICATIONS AND SYSTEMS POINT OF VIEW
As a matter of justification for the chosen solution, it would be convenient to make a small historical review of the classical solutions used till now in similar systems.
One of the first used solutions was the independent design of systems and the interconnection between them at the end (as an “afterthought”), mainly through the massive use of gateways, and translators as these connections were needed. This process quickly proved to be too expensive and costly in terms of maintenance.
As a second immediate approach, centralised solutions were frequently designed through the use of large repositories of data to make the data exchange. Again, such systems are proving to be too inefficient to meet the new needs.
Finally, from these previous experiences, it seems that an integrated approach is the use of a data bus, where all clients can share information and applications that can grow horizontally without affecting the applications already running.
Again in this chapter we’ll distinguish between primary equipment (those related to the power infrastructure), and secondary equipment (those related to electronic devices for control and associated communications), and information systems necessary for the coordinated control of both worlds. Although those three subsystems deal with different worlds, we will pay particular attention to keeping these worlds harmonised all the time.
The primary infrastructure equipment is that equipment directly related to power equipment (including power meters). Emerging technologies related to generation can be summarised in the following figure.
It makes sense that the distribution network of the future will consist of a combination of many generators, together with many storage elements using some of these technologies and others that will appear in the future. All these sources of energy will have to be treated statistically.
AMI: Advanced Meter Infrastructure
A smart meter is an electronic device that will replace in the coming years the existing electromechanical meters. This device participates in the functions of DER, AMI, and ADA. The main reason for these devices is to cause a change in the habits of consumers. The special feature of this technology is its volume in terms of the number of devices (millions) and also in terms of the amount of information to be processed. Special care must be taken regarding operation and maintenance procedures.
The simple fact of the installation of these devices involves the functionality of the consumer portal explained in the next section about secondary equipment. This feature involves the installation of a device in the transformation centres (called a smart meters concentrator).
DER: Distributed Energy Resources and storage
This is undoubtedly one of the key pieces of our smart city: Multiple small generators geographically distributed so that consumption is balanced where it occurs. In fact, V2G (vehicles to grid) and storage techniques can be seen as resources of distributed generation.
We will distinguish two different types of generators according to the level of tension in the network where they are connected.
- MV: Generators connected to the medium-voltage grid. (Typically 25 kV.) They are generators with power greater than 0.1 MW. They need a protection infrastructure similar to that used in the MV network. They are going to share communication infrastructures and must interact with smart devices installed within that network. Their primary purpose is to provide power to the segment of MV where they are connected. Usually these generators produce all the available energy (as it is renewable). There is not usually a significant amount in each segment of MV (0 <10). Today, they are automatically disconnected from the network the moment there is a voltage gap in the main feeding line.
- LV: Generators connected to the low-voltage grid (230 V). They are generators with power smaller than a few kW. They need protections adapted to the LV grid and share communication infrastructures with the smart meters. Their primary purpose is to provide power to the segment of LV. The main feature of these generators is that we can have a significant amount in each segment of LV (0 <100). The optimal situation is when the generator’s installed power matches the required power of consumers.
The first aspect to consider in a generation system is the control of the generated power. Active and reactive power is the result of regulation. But the regulatory system should take into account other parameters such as the availability of generators and price.
Another very important aspect to consider is synchronisation. A generator must meet the following conditions if it is to be attached to the network:
- Same frequency
- Same phase
- Same voltage.
Otherwise a short circuit could be caused. There are several synchronisation mechanisms for each type of generation in order to guarantee the fulfilment of these conditions. However, in the proposed generation scheme an additional problem appears: Who is the master of synchronisation? Under normal circumstances, the master of synchronisation is the distribution network itself. However, what happens when the main distribution grid power disappears? Is it possible to govern such a system in islanding mode? In our approach, we have decided to follow an anti-islanding approach. This means that the main power grid voltage acts as a synchronisation reference and when it disappears, all generators must be disconnected from the network. The goal is always to minimise the power consumed within the main feeder.
We define every connection from a controllable load, a storage device or a generator with the electrical grid as an energy spot. It can produce or it can consume energy. It will have an associated electronic controller and is modelled with:
- Autonomy: Maximum energy that it can provide/consume per unit of time
- Power: Instant power that it can generate/consume as a function of time
- Availability: as a function of time (planning)
- Cost: According to per hour basis and type of generation
- Type of regulation: on/off, active power set point or reactive power set point. In this system, we name the controllers installed within the lowvoltage grid as iNode.LV. These devices communicate by PLC with the upper level controllers (iNode.MV), and these in turn communicate with controllers at the header feeders (iNode.HV).
Case MV: The secondary distribution network is typically composed of rings connected to two primary distribution substations with some ramifications. It is radially operated. This means that there is always an intermediate switch normally opened – the so-called border point. If there has been any self-healing operation this opened switch can be changed and so can any other. That is, to increase the automation of the network can be a potential problem because the network topology can change easily. That means that the number of generators/consumers connected in a section is not constant.
A typical model of the network of secondary distribution, then, consists of a cluster of automated switching elements (which will enable the auto healing to be coordinated with the automatic reclosers in the header feeder).
The generators connected to the grid have a limited capacity of regulation or no capacity at all. For this reason they are controlled using on-off commands. Towards the primary distribution grid, the transformer can be seen occasionally as a generator with some capacity of regulation. At this level, it can accept a set point command for active and reactive power that locally controlled will optimise the number and type of generators used.
The new concept for MV network automation can be defined as the traditional MV concept plus “minimising the power supplied within the HV feeder”, ensuring the constant integrity and stability of the network and minimising the cost.
- The controller within the HV feeder (iNode.HV) controls the generators, storage and consumers in order to minimise the delivered power. Losses are minimised by not supplying energy back through the HV/MT transformer.
- The devices to control are generators, storage points connected within the MV grid, and the feeders of the lowvoltage grid with an iNode.MV.
- It includes functions of AMI, ADA, and DER.
- Case BT: In the scenario of low-voltage micro-generation, transformers can become casual generators. In this case, it may have a certain regulating capacity globally through regulatory mechanisms of connection/disconnection of individual generators.
As can be seen in the previous figure, we can connect to our network of secondary distribution, consumer groups, generators or other users, who will act as generators or as consumers depending on each case.
In the same way, the low-voltage distribution network can be modelled as a star of buses of loads and individual generators.
In a similar way, the new concept for LV network automation can be defined as the smart meters reading and demand side management concept:
- The controller within the MV feeder (iNode.MV) controls the generators, storage and consumers in order to minimise the delivered power.
- Losses are minimised by not supplying energy back through the MV/LV transformer.
- The controlled devices are generators, storage points, consumers and electric vehicles connected to the low-voltage grid. All of them with an iNode.LV.
- It includes functions of AMI, ADA, and DER.
In the coming years, the fleet of electric vehicles (EV) and plug-in hybrid electric vehicles (PHEV) will increase with a direct impact on:
- Increased energy efficiency
- Reducing emissions of NOx and C02.
95% of the time, our vehicles are parked. During this time millions of batteries can be employed by the electricity grid (V2G) for use during high demand times, stabilising the network and increasing reliability, or can be recharged by the production excess of renewable energy sources. They can also be used at home (V2H) as a power supply system in case of emergencies due to lack of supply or to increase the power available for housing in certain hours.
The storage capacity of 600,000 cars is equivalent to all the hydroelectric pumping plants’ capacity in Germany. The idea is that users can limit the amount of energy they want to return to the network (ensuring a remaining range). The distributing company pays for this service (or offsets its electricity tariff) to owners of vehicles.
The key feature of this mechanism is its volume and mobility. The service is similar to that of smart meters, but in this case will require a system for local control and self-generation. The ability to deliver power to the grid off PHEV depends on several factors: where it is connected, the capacity of the connection, the amount of time you need to download the vehicle, the capacity of your battery, battery status, and the possibility of activating the engine combustion to produce electricity.
Reliable communication technologies are the cornerstone of coordinating this framework. Protection, control, regulation, and measuring devices must be interconnected within a hierarchical network with adequate levels of quality and reliability. To reuse the infrastructure and the topology of the power grid will also be an indispensable element of this approach.
It can be said that this new system should transform actual control systems typically centralised and poorly integrated in a highly distributed and integrated control system.
Finally, the complexity of the system makes it necessary to harmonise the data models that will be exchanged between the controlling devices, so that all the necessary information describing communicating values are available from the origin of the data until the consuming end, avoiding the use of translators or intermediate gateways.
The consumer portal is the window through which the distributor sees the consumer and sends two-way information , as shown in the following diagram
Protection and tele protection
Fortuitous accidents can occur at the lines of electric distribution, causing a short circuit of a different nature. For this reason it is essential to install within the distribution network some elements for automatic isolation in case of a short circuit in order to isolate the damaged segment and not damage in any way the rest of the network.
Techniques used to monitor different parameters (mostly intensity) and isolate the circuit when they are outside the boundaries of work are called protective devices and tele protection.
In coordination with the protections, automatic reclosers are usually installed to minimise the duration of sporadic outages.
PROJECT ‘SMART CITY: IMPLEMENTATION TECHNOLOGIES FOR A SMART GRID’
ENDESA is developing a practical demonstration of all these technologies and integration between all of them in the town of Jerez de la Frontera in the south of Spain. This project is scheduled for five years and has a budget of €25 million. ENDESA is also currently developing a theoretical project regarding new distribution technologies called DENISE . The Smart City project has essentially a practical approach and should use the theoretical results from project DENISE and be harmonised with that project.
The general vision of the project can be summarised thus: “The energy and environmental needs of the future will demand the optimisation of the electricity distribution infrastructure. For this reason the network structure must be reversed from a few huge generators to many small ones.”
This particular vision involves:
- Deploying an exemplary distribution network that includes a heterogeneous mixture of generation and consumption.
- Plug It Smart: not simply connecting but also integrating.
- Taking the most from the best experience and real equipment already in the market and concentrating on implementing only those parts that do not exist in the market. The real added value of the project is integration.
The main objectives of the project are:
- Validation and practical implementation of the conclusions from project DENISE.
- Inclusion of micro-generators and micro-storage within the LV network in order to minimise the power delivered through the LV feeders, optimising the usage of renewable energy sources.
- Inclusion of mini-generators and mini-storage within the MV network in order to minimise the power delivered through the MV feeders, optimising the usage of renewable energy.
- Active demand response through acting on loads and passive demand response through acting in consumer habits.
- Automation of the network.
At the end this period it is expected to demonstrate the feasibility of all the used technologies within an urban environment in an integrated and efficient way.