Starting from the type of supply, electric power distribution grids or networks can also be distinguished according to their type of meshing. The following basic network configurations are distinguished:
• Radial networks
• Ringed networks
The spur-line-fed radial network is the most simple form. Its advantages lie in easy monitoring and protection as well as in fast fault localisation and simple operational management. When the expense is doubled, the outcome is a double-spur network. Every load centre can be reached via two different paths. Switching devices are only closed if required. If the requirements placed on supply reliability are high, each supply line can be fed from an independent supply network. Due to fact that the networks are independent from each other, a fault in one network will not affect the other one. In combination with a ring line as an extension of the spur network , a ringed network can be built up.
Difference between Radial networks & Ringed Network Configurations
- Dependent on the spatial structures, the investment to be made for an open-type ringed network can be lower or
higher than for a spur network. A spur network is advantageous if individual transformers shall handle low-voltage supply in a confined space. A ringed network can be favourable regarding costs of investment if supply is spread out over a larger area with several transformer centres.
- In terms of space requirements, power demand coverage, environmental friendliness and cable costs, the differences between the two network configurations are small. Although ringed networks more often come with shorter cable lengths, the cable cross section must be higher owing to the transmission of higher capacities from one ring endpoint to the other.
- With regard to the costs of power losses, the spur network and the open-type ringed network only differ insignificantly. There are minimal advantages if the ringed network is operated in the closed-type variant. However, protection of the closed ring requires circuit-breakers and line differential protection. These additional costs show up in investments.
- In case of a cable fault in an open-type ringed network, all stations downward of the fault location up to the normally open switch will fail. In case of low-voltage-side meshing of the ring stations, the failure of a large sub-ring could result in overload and disconnection of non-affected, still operable transformers. Whereas a cable fault in the spur network merely results in the failure of one station.
- Only with a closed-typed ringed network and appropriate protection expense could such a level of reliability be also attained in the ringed network. In addition to this, the closed-type ringed network provides an immediate reserve in case of cable faults, whereas the spur network merely offers a load transfer reserve. A single fault with transformer failure can be handled in both networks without interruption if (n-1) redundancy applies for the transformers.
- Furthermore, operating a ringed network always requires distributed switching operations which hamper ease of operation. Switching operations for fault localisation and actions to attain a defined switching condition in cases of defect are more complicated than with a radial network. Weather-dependent power feed-in of solar and wind power stations increasingly burdens grids owing to fluctuations which can inadequately be planned only. In line with this, safely connecting parts of the network into supply and likewise disconnecting these parts from supply together with a realisation of what is going on are becoming more and more important.