Lastströme

Lastströme, or load currents, are the electrical currents drawn by loads connected to a power supply or distribution network. They reflect the real-time and scheduled consumption of devices and systems, and they are a central consideration in the design, operation, and protection of electrical installations. Load currents depend on voltage level, impedance, and the power characteristics of connected equipment, and they may vary significantly over time due to changing demand or control strategies.

In practice, lastströme are modeled and measured to study power flow, voltage drop, and equipment loading. They are influenced by factors such as power factor, reactive power, inrush at start-up, and non-linear loads that introduce harmonics. Proper handling of load currents is essential for maintaining voltage quality, ensuring safe operation, and preventing overloading of conductors, transformers, and protection devices.

Calculation of load currents can be done from complex or real power data. For a single-phase load, I ≈ P/V when the load is purely resistive. In AC systems with reactive components, the complex power S = P + jQ relates to current by I = S*/V*. For three-phase systems, the relationship S_total = √3 V_line I_line holds for a balanced load, giving I_line = S_total / (√3 V_line). Per-phase currents follow similarly, with adjustments for phase balance and line voltages in the network.

Applications include planning conductor sizing, transformer loading, protection coordination, and demand forecasting. See also power factor, load management, and distribution network design.