Phasenreihen

Phasenreihen, also known as phase sequences or phase orders, are fundamental concepts in the study of rotating electrical machines, particularly three-phase systems. They describe the order in which the instantaneous voltages or currents of the three phases reach their maximum positive value. In a balanced three-phase system, the three phase waveforms are identical in magnitude and frequency but are displaced from each other in time by 120 electrical degrees. The phasenreihe dictates the specific sequence of these displacements.

There are two possible phasenreihen for a three-phase system: positive phase sequence and negative phase sequence. In a positive phase sequence, often denoted as ABC or L1-L2-L3, phase A reaches its maximum positive value first, followed by phase B, and then phase C. Conversely, in a negative phase sequence, denoted as ACB or L1-L3-L2, phase A reaches its maximum positive value first, followed by phase C, and then phase B. This reversal in the order of phases significantly impacts the direction of rotation of a three-phase motor.

The phasenreihe is crucial for the correct operation of many electrical devices. For instance, three-phase induction motors will rotate in one direction with a positive phase sequence and in the opposite direction with a negative phase sequence. Incorrectly connecting the phases can lead to motors running backward, which can be detrimental to the driven equipment. Power systems are designed to maintain a specific, usually positive, phasenreihe for reliable operation and predictable performance of connected loads. Generators and transformers are also designed with considerations for maintaining or converting phasenreihen as needed.