Mellanspänning

Mellanspänning, or medium voltage, is the portion of the electrical power system with nominal voltages higher than low voltage and lower than high voltage. The exact voltage range varies by country and standard, but it is commonly understood to cover roughly 1 kV to 35 kV. In practice, many distribution networks operate at 10 kV, 20 kV, 22 kV, or 33 kV, serving as the link between transmission systems and low‑voltage distribution to end customers.

Medium-voltage networks transport power from substations fed by high-voltage transmission to distribution substations that step the voltage down to low voltage, typically 0.4 kV. These networks can be implemented as overhead lines or underground cables and are used in both urban and rural settings. Key equipment includes MV switchgear, transformers (for example 10/0.4 kV or 20/0.4 kV), protection relays, surge arresters, disconnectors, and sectionalizers. Insulation coordination and proper clearances are essential due to higher voltages than low voltage, as are considerations for switching transients and lightning impulses.

Operation and safety in mellanspänning require trained personnel, appropriate personal protective equipment, and established procedures for safe work, lockout/tagout, and fault isolation. Utilities implement protection schemes such as overcurrent protection, distance protection, and automatic sectionalizing to minimize outage times and ensure reliability.

Standards and regulation for MV systems are set by national authorities and international bodies. IEC standards commonly govern equipment design, protection, and insulation coordination. Definitions and voltage bands can differ by country, so the exact boundary with low voltage and high voltage may vary in different grids.