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In off-grid systems with Sunny Island, the stand-alone grid distributes the energy. AC loads draw energy from the stand-alone grid and AC sources (e.g. PV inverters) feed in energy. Distribution grids can be designed differently. The grid configuration of the distribution system determines how it is grounded.
This blog gives an overview of the following topics:
• Grid configurations of stand-alone grids with Sunny Island
• Ground electrode connection
• Required protective devices for personal protection
The information provided does not replace any locally applicable standards or directives.
Figure 1: Schematic diagram of a TN-S system A hybrid form is common in extended utility grids with the TN-C system being used from the source while the TN-S system is limited to the load system. This form is known as TN-C-S system (French: Terre Neutre Combiné Séparé). Advantages of the TN system: • Low-resistance protective connections allow for a reliable execution of simple protective measures under fault conditions. Circuit breakers automatically disconnect the voltage source from the distribution grid under fault conditions. • Only one ground electrode is required. The TN-S system is thus the preferred grid configuration for a new off-grid system.
If you require more information or are installing an Off-Grid system call us today and talk to our technical sales team. Check out the full range of SMA Sunny Islands at CCL
1 Grid Configurations in Off-Grid Systems with SMA Sunny Island
The grid configuration of the distribution system determines how it is grounded. Personal protection is the purpose of grounding in all grid configurations. Under fault conditions no dangerous voltages may occur on exposed components. A slight transition resistance from the ground electrode to ground is crucial in all grid configurations.TN System
The most common grid configuration is the TN system (French: Terre Neutre). Here, the neutral point of the source is grounded. The neutral conductor of the system is connected to this neutral point. The exposed conductive parts of the connected loads are connected with the grounded neutral point of the source via protective conductors. A distinction is made between the TN-C system (French: Terre Neutre Combiné) and the TN-S system (French: Terre Neutre Séparé). In the TN-C system the PEN conductor is a combination of the grounding conductor and the neutral conductor. In the TN-S system the neutral conductor and the grounding conductor are separate.
Figure 1: Schematic diagram of a TN-S system A hybrid form is common in extended utility grids with the TN-C system being used from the source while the TN-S system is limited to the load system. This form is known as TN-C-S system (French: Terre Neutre Combiné Séparé). Advantages of the TN system: • Low-resistance protective connections allow for a reliable execution of simple protective measures under fault conditions. Circuit breakers automatically disconnect the voltage source from the distribution grid under fault conditions. • Only one ground electrode is required. The TN-S system is thus the preferred grid configuration for a new off-grid system.
TT System
In a TT system (French: Terre Terre), the neutral point of the source is grounded, as it is in TN systems. However, the exposed conductive parts of the loads are connected to separate ground electrodes of the system using protective conductors. The neutral conductor must not be grounded in the load system. This grid configuration has no direct grounding conductor connection between the exposed conductive parts of the equipment and the neutral point of the source. This is only possible when connected to ground. The connection to ground cannot reliably trigger a circuit breaker under fault conditions. Therefore, residual-current devices are required in TT systems.Grid Configuration for Stand-Alone Grids
Stand-alone grids with Sunny Island can be designed as TN-S systems, TN-C-S systems or TT systems. At least one ground electrode must be present in all grid configurations. This is in any case necessary for the equipotential bonding of the electrical system.2 TN-S Off-Grid System without Generator
3 TN-S Off-Grid System with Generator
4 TT Off-Grid System without Generator
5 TT Off-Grid System with Generator
If you require more information or are installing an Off-Grid system call us today and talk to our technical sales team. Check out the full range of SMA Sunny Islands at CCL