The increase of distributed generation is a major challenge for Distribution System Operators (DSOs). Distributed generation integration not only impacts on DSO short-term costs but also involves new risk uncertainty regarding system reliability, security and network planning. Therefore, because DSO is mainly a regulated business, it is clear that new regulatory mechanisms should be designed.
Why is there a new role for DSO?
In the past, we had a passive network which included:
- Networks with unidirectional flows from transmission to final customer
Networks are predictable due to low distributed generation penetration
Low monitoring and control level at medium and low voltage levels
Fit and forget approach (most issues solves at the planning stage)-easy to solve and easy to understand
However, the role of the DSO will now have to change as the system has changed. It is no longer a passive network. Networks have become systems and there is a massive penetration of distributed generation.
Passive vs. Active approach
The problem is that the system is still being run with a passive approach, explains David Trebolle, Manager of Active networks and Control Systems, Gas Natural Fenosa, Spain. He points out that the passive network is becoming an active network which requires a coordinated, centralized and distributed control. The new system calls for distributed generation and demand side management to go hand in hand.
The DSOs role is to maintain system security and quality of service in distribution networks in order to serve network customers. They will also help with market facilitation, encourage transparent and non-discriminatory access, and ensure security of system and quality of service. This will all be done using active system management.
By carrying out system services, the Distribution Network Operator (DNO) becomes a DSO.
Active system management and the DSO
In the future, supervision control, simulation, analysis and Distributed Energy Resources (DER) management-systems will be active-not passive networks. The DSO will adopt a more active approach towards distribution network development, planning and connection.
Here are a list of new system responsibilities for the DSO:
Black start capability-This is to ensure national or zonal blackout recovery. Both the Transmission System Operator (TSO) and DSO will be responsible here.
Information exchanged-Allows DSO and TSO to supervise and monitor the electricity system. Both the TSO and DSO are responsible.
Anti-islanding operation-To avoid unsafe, unbalanced and poor quality distribution electric islands.
Islanding operation-To improve continuity of supply when higher voltage source is unavailable.
Security congestion-Operate the grid within security standards
Firm capacity management (long term)-For planning and efficiency of asset usage.
Voltage and power quality control-For a high quality of service, the DSO will participate in voltage control optimally
Congestion Management-DSO will need to manage congestion in its network to avoid security problems
The DSO business will involve-long term planning with regards to network planning, connection and access, operation and real time management
Mr Trebolle points out that various changes have to be made in order for the DSO business to work. He explains that distribution networks will need to evolve in to distribution systems, renewables will become real distributed generation, distributed generation connection will become distributed generation integration, passive demand will become active networks and there will be a move towards the coordination between network users and network operators.
A new regulatory framework
A new regulatory framework is key, says Mr Trebolle. He says that it should cover all the DER aspects. Roles and responsibilities must be clear in order to ensure security of supply and a decent quality of supply and quality of service. Within this framework, the following should be taken into account:
Distributed generation revenues and incentives
Access and connection model
System services with DER
DSO incentive schemes and revenues
DSOs have to alter their business focus in order to keep their business viable. By developing new business activities, diversifying the business model, and transforming operational philosophies from passive into active network management, DSOs will overcome the threats and challenges that the increase in distributed generation presents.