"Vibrating Neutral??

[JERRY01]

120\240 3ph 4 wire service. Service Conductors are par. 500 MCM for 2 phases and par. 250 MCM for the "wild leg". The amp readings are 460 amp on phase 1, 365 amps on phase 2, 100 amp on the "wild" leg and 60 amp on the neutral. Thre lighting for the building is mostly fluorescent. The 3 phase load consist of an elevator motor and various kitchen loads.The lineman that were upgrading the transformers reported a vibrating neutral conductor at the service drop.
Any thoughts as to what is causing the "vibration"???

 

[jbartos]

Suggestion: The vibration may be caused by electromagnetic forces related to unbalanced loading of the transformer.

 

[busbar]

Use of a portable instrument to provide a current (or voltage) ‘harmonic recipe’ in power systems is becoming almost essential these days.

 

[busbar]

Simpler yet may be a true-RMS ammeter that will also display DC-peak readings, allowing crest factor to be calculated. This could help to initially decide how much effort should be committed to studying/resolving the problem.

 

[jbartos]

Suggestion: It could also be caused by inadequate fastening of conductors while the electromagnetic forces due to transformer unbalance load, harmonics, etc. are within the safe or rated range.