Three Plane Motor Balancing: Do i Need it or Not

Rotor balancing is an essential part of ensuring proper motor operation. While typical specifications (API 541, API 684, MIL-STD-167-1A) require a multi-plane balance for rotors which go through the first bending critical, the details of how the balance should be performed and to what limits, is sparse. This paper will establish the best practices for when multi-plane balancing is beneficial, what the procedure should look like, as well as how to determine acceptance criteria for such a rotor. Additionally, it will be presented that a rotor could be designed such that it requires only 2-plane balancing even when operating above the first bending critical.A case study that explores the downside of not implementing multi-plane balancing techniques will be examined. Specifically, it will demonstrate how improving the balance of a flexible shaft rotor at operating speed caused the vibration to intensify at the critical speed.The described best practices combined with a fundamental understanding of the requirements for rotor balancing and proper applications will help manufacturers, system packagers and end users to be confident that their rotating machine has a quality balance throughout the entire speed range (including variable frequency drive operation) and will provide years of service.