TRANSFORMER NOISE

[hawkeye23]

We came across a 3phase 480v 120/208 trasformer that started making noise inside that was never there before. We loto the trans and looked inside for lose connections or something out of the normal . The circuit for this unit came from below with the conductors being open coming through the cement floor without any conduit just a 4" long nipple sitting in the hole in the floor with the wiring going into the bottom of the trans with no machancal connection to the trans. It did have a egc going to the frame, with h1 h2 h3 being primary connection.
I have no idea why the nipple was there, it did not connect to either end , maybe they though it was protecting the conductors. This trans has been in service for years.

When a transformer is feed from a MCC is the xo bonded in trans or first panel ?

The second 3 phase panel will have 5 conductors,
3 phase 1 neutral and egc. [ 75 kva ]
If there is something you can add to this as to why the raddling noise inside or about the installation we will appreciate any input.

 

[broadgage]

Do not overlook the obvious ! transformer noise is often caused by by a small nut, washer or bolt that has fallen into the unit and is vibrating due to the magnetic field.
If nothing can be seen to be out of place, vaccuum cleaning may help.

Another cause of noise can be loose fixings in the cover or screens, check and tighten.

It is possible that the transformer has developed some internal fault, but these usually progress fairly rapidly to complete failure and do not persist for long.

Most internal faults result in extra loses and can sometimes be detected by measuring the primary current whith no secondary load. Compare with manufactuerers data or with a known good transformer.

 

[Smart $]

...

When a transformer is feed from a MCC is the xo bonded in trans or first panel ?

...

MCC has no bearing on the matter. You can install the "system bonding jumper" in either the xfmr or secondary disconnect enclosure. This has to be the same location where you run your GEC.

 

[Haji]

MCC has no bearing on the matter. You can install the "system bonding jumper" in either the xfmr or secondary disconnect enclosure. This has to be the same location where you run your GEC.

I think the OP is asking about the bonding of the neutral on the primary side for a Y-Y transformer for which bonding of primary neutral , transformer body and secondary neutral at the transformer to ground may be appropriate.

 

[kwired]

I think the OP is asking about the bonding of the neutral on the primary side for a Y-Y transformer for which bonding of primary neutral , transformer body and secondary neutral at the transformer to ground may be appropriate.

I think the OP's transformer has delta primary with no neutral connection at all.

 

[kingpb]

Transformer noise is caused by the mechanical movement of individual lamination of the core under magnetization. The pulsation causes air disturbance (audible noise) and physical vibration of the core structure and everything attached to it.

The loading on the transformer will have no affect on the amount of noise, in general only about 1 to 2 dB change. As transformers age the individual lamination may vibrate more.

It is likely the transformer vibration is being transferred to another piece of equipment or enclosure through non-flexible connections.

 

[kwired]

One thing I have seen before is increased noise as a result of an increase in input voltage. At my own home I could hear utility transformer across the yard one time when POCO had a voltage regulator failure and voltage levels were high. Increased saturation of the coil. Output voltages of a 120/240 single phase transformer were around 137/274 during that event, surprisingly I don't recall having any equipment failures from this event.

 

[steve66]

So what is under the floor? Just open conductors?

Any chance there is a conduit down there being supported by the wires only, and the wires are transmitting vibrations to the loose conduit?

 

[templdl]

Do not overlook the obvious ! transformer noise is often caused by by a small nut, washer or bolt that has fallen into the unit and is vibrating due to the magnetic field.
If nothing can be seen to be out of place, vaccuum cleaning may help.

Another cause of noise can be loose fixings in the cover or screens, check and tighten.

It is possible that the transformer has developed some internal fault, but these usually progress fairly rapidly to complete failure and do not persist for long.

Most internal faults result in extra loses and can sometimes be detected by measuring the primary current whith no secondary load. Compare with manufactuerers data or with a known good transformer.

Ditto, this is an excellent starting point.

 

[eutaw42]

Harmonic loading on transformer?

Harmonic loading on transformer?

I have seen transformers that had no problems -- then started humming & vibrating -- cause? -- simple answer -- customer added a lot of variable speed HVAC equipment