HT Motor Direction of Rotation (DOR) Changed

Electrical engineering root cause analysis (RCA) related to considered not possible HT motors’ Direction of Rotation (DOR) changed.

Note: This root cause analysis (RCA) is from real-time scenarios that happened in industries during the tenure of two or three decades ago. These articles will help you to improve your troubleshooting skills and knowledge.

HT Motor Direction of Rotation (DOR)

Why Direction of Rotation (DOR) arrows?

Large motors’ come with backward-curved fans (below figure). They deliver max air-flows at marked Direction of Rotation (DOR) and very little in the opposite DOR.

Consequently, the winding temperature could go a lot higher than permitted. It could shorten winding lives even lead to burnouts. This is especially serious, as most motors have no winding temperature indicators (at that time). Hence, DOR marks.

However, one can change DOR to suit the driven machine thus:

1. swap the left and right internal axial fans (IAF above-figure)
2. Substitute the existing External Radial Fan (ERF) with a purchased or homemade opposite curved vanes fan
3. Fix a new DOR indicating arrow
4. Interchange the two electrical leads as usual

Benefits of the RCA learned know-how

The plant used surplus motors gainfully and saved purchase costs for new applications.

Author: S. Raghava Chari

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