Assertion: rotor's speed | /r/HasProperty | required
Facets:
Source sentences:
text: In the fractional horsepower range, most synchronous motors are used where precise constant speed is required.
text: These motors are expensive and are used where precise constant speed is required.
text: usually, synchronous motors are used for applications where precise and constant speed is required.
text: An alternate design, called the wound rotor, is used when variable speed is required.