When it comes to excitation systems for synchronous alternators, one of the main choices concerns the type of power supply for the Automatic Voltage Regulator (AVR). The two most widespread solutions are the auxiliary winding and the PMG (Permanent Magnet Generator). Both ensure high performance, but they feature different characteristics, advantages, and limitations depending on the application.

PMG: Origin and Features

The PMG was introduced more than 30 years ago as a solution to the limitations of synchronous generators of the time, which were not able to provide permanent short-circuit current.
The principle is simple: a small permanent magnet generator, coaxially coupled to the alternator, supplies dedicated energy to the AVR under all conditions, even in the event of a fault or short circuit.

Today, the PMG is especially valued for:

• High immunity to non-linear loads (power electronics, UPS, converters, etc.)
• Stable excitation even under critical conditions
• Reliable support during the start-up of asynchronous motors

On the downside, the PMG involves higher costs, larger size, and greater construction complexity.

Auxiliary Winding: The Compact Alternative

The auxiliary winding, present in all Linz Electric alternators, uses high-strength enameled copper wire (the same used in inverter-fed motors, already tested to withstand very high voltage peaks) to provide the AVR with a dedicated and reliable power supply.

Its main advantages are:

• Permanent short-circuit current between 2.5 and 3.5 times the rated value
• Support for asynchronous motor starting without performance loss
• Immunity to harmonic disturbances from non-linear loads
• Optimized electromagnetic compatibility
• Compactness and cost reduction compared to PMG

In fact, this system is electrically equivalent to PMG, with the added benefit of simpler construction and a better performance-to-cost ratio.

In summary: the PMG was originally developed as a historical solution to a technological limitation, whereas the auxiliary winding today represents a modern, leaner, and more competitive alternative—without compromising on high-level performance.