1. With speed negative feedback automatically regulated, its speed rate of change: the first step: < 1.8% and the second step:n< 2.5%.

2. Without runaway area of speed with techogenerator gauging speed.

3. Stable adjustable operating speed and wide range of adjustable speed, reaching 10 : 1.

4. Good starting performance, smooth start and large moment.

5. Simple reliable structure and convenient maintenance.

6. Small power of controlling speed and easy to control in many ways.