Phase rotation

Phase rotation describes the temporal shift between two or more alternating voltages or alternating currents of the same frequency. In electrical systems, it is a central concept for analyzing and controlling energy flows, particularly in transformers, three-phase systems and power electronics.

What does phase rotation mean?

In an alternating current system, voltage and current change direction periodically. If two signals do not reach their zero crossing or peak value at the same time, this is referred to as a phase shift or phase rotation. This is specified in degrees (°) or radians and can have positive (leading) or negative (lagging) values.

Phase rotation for transformers

Transformers transmit electrical energy by electromagnetic induction. This can result in a phase rotation between the primary side (input) and the secondary side (output) – depending on the type of winding and circuit:

Typical causes of phase rotation:

Winding arrangement: In a star-delta circuit or delta-star circuit, there is a phase rotation of ±30° between the primary and secondary voltage.

Transformer switching group: The so-called time-of-day switching group (e.g. Dyn11) indicates how much the secondary voltage is out of phase with the primary voltage.

Load behavior: Inductive or capacitive loads can cause additional phase shifts between current and voltage.

Why is phase rotation important?

Mains parallel operation: When interconnecting several transformers, the phase rotation must be taken into account in order to avoid short circuits or power feedback.

Power calculation: The active power depends directly on the phase angle between current and voltage.

System compatibility: Devices and systems must be matched to the phase position in order to avoid efficiency losses and faults.