Longhong Machinery & Electric explains the classification of generator excitation methods as follows:

According to the excitation method, generators can be divided into two categories: 

brushed excitation generators and brushless excitation generators.

Brushed excitation generators employ an externally excited method, 

while brushless excitation generators utilize a self-excited method. In externally excited generators, 

the rectification device is located on the stator of the generator. In self-excited generators, 

the rectification device is mounted on the rotor of the generator set.

The above content is compiled and published by the generator manufacturer—

Guangdong Longhong Power Machinery Equipment Co., Ltd. For more details, visit https://www.longhongpower.com.