The 23-kV low-voltage secondary substation showing the high-voltage switchgear and the wallmounted Schneider Electric T200 unit.
Economic growth and an increasing population translate into an increasing demand for energy. This situation, coupled with strict regulations on the quality and security of supply, increases pressure on distribution network operators (DNOs) to maintain the integrity of the network. While huge investments are already being made in replacing aging infrastructure to minimize the probability of equipment failure, the chances of failure cannot be completely eliminated. Therefore, when network faults occur, it is necessary for DNOs to minimize the impact by reducing the outage time and number of customers without supply.
To minimize the fault outage time, the Dutch DNO Stedin has started a project to introduce automation to its distribution network. The first phase of the project consists of installing intelligent fault passage indicators, while the next two phases use more advanced techniques such as remote-controlled ring main units (RMUs) and a completely self-healing distribution feeder.
In the Netherlands, the distribution network consists of underground cables, which means permanent faults can occur that cannot be resolved by stand-alone automatic reclosers. Stedin developed a self-healing network pilot based on a software restoration routine that employs several remote terminal units (RTUs). The RTUs communicate through a general packet radio service (GPRS) network to identify the fault location, isolate and restore (FLIR) supplies in steps automatically.
Automatic FLIR schemes can be implemented with several different architectures. A fully centralized architecture uses a distribution management system (DMS) that has a complete picture of the network topology. Local, centralized architecture uses intelligent master controllers, each of which communicates with a limited number of slave devices.
The architecture installed by Stedin is fully decentralized, where the intelligence is distributed between several nodes. The FLIR algorithm uses messages passed between numbers of RTUs. Therefore, the communications architecture mirrors the electrical network, which makes it easy to add and remove nodes.