oil filled transformers 1

[Elec777]

Dears,
I want to ask whether it's better to ship the transformer filled completely with oil or empty?

 

[waross]

small transformers should be vacuum dried and filled at the factory.
Larger transformers it depends.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[prc]

It is better to transport with oil filling, if there are no transport weight limitations. Advantages- less chances for moisture ingress, less time for installation and processing at site.

 

[marks1080]

you might need to worry about environmental permits or something if you transport with the oil? I have no clue, but seems like a possibility in some regions.

 

[stevenal]

We let the hauler worry about the permits. If permits are needed to transport oil, I doubt it matters much whether it comes in a transformer or barrels.

 

[thermionic1]

As Waross said, it's really a matter of how big the unit is. Pad mount or smaller station class (~2500kVA) typically ship filled from the factory. I've seen larger (~40MVA) units shipped full, with only the radiators to install on site and about 300 gallons to top off.

For larger units, removing the oil reduces the transport weight, which may be an issue when moving on small roads to the final location.

 

[bacon4life]

For large transformers, is there any concern with oil sloshing potentially tipping the truck over?

All of the substation class transformer I have been involved with purchasing have been shipped with nitrogen instead of oil. I have seen full substation class transformers moved from one substation to another substation within the same region.

 

[stevenal]

Not a lot of room for sloshing. Oil is pumped from the radiators into the tank, filling the gas space, so the radiators can be removed. What doesn't fit into the tank goes into barrels.
And the trucks move slowly.

 

[prc]

When the main tank with active part is transported with oil filling, oil shall be filled with at least 10% of tank height empty. If you fill full, the oil can expand with ambient temperature variation and tank welding will crack with oil seeping out. Sloshing will not be a problem as the heavy trailers move at a very low speed. The trailer capacity and the route limitations decide whether to dispatch with oil filling. Oil filled transportation is also advantageous in case the transformer has to be stored say more than 6 months at site. Manufacturers normally insist to store under oil filling in case installation is delayed more than 6 months.

Nowadays transformers are transported under dry air instead of nitrogen, basically from safety angle. When sent in ships many liners insist to avoid nitrogen. At site also protocol demands nitrogen to be pumped out before commencing installation . By using dry air this process is also eliminated in installation process.

 

[waross]

Highway size and weight regulations vary greatly from place to place.
Most jurisdictions have cut-off points where more expensive protocols apply. More axles, pilot cars, daylight only, specified routes etc.
Many bridges have maximum weight limits. A transformer that may be transported fully assembled and filled with oil in one jurisdiction or route, may have to have the radiators removed due to weight and/or size limits and may have to have the oil drained due to weight restrictions.
Bushings are often removed but that may be because a bushing chipped by a tire thrown rock is more expensive than a cracked windshield.
The unloading equipment that is available on site may have an influence on shipping weight.
It depends.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[stevenal]

PRC,
I'm pretty sure out transformers are shipped with the nitrogen system active. I'll need to check next time. The relief valves would prevent over-pressurization anyway. The nitrogen is also plumbed into one or more of the ribs, increasing the volume available for expansion. I can see that conservator style systems may be different. When on-site, radiators are installed and valves are opened allowing the oil to drop and air displaces the oil. No extra ventilation has been necessary to get safe O2 readings.

Not sure I'd like the idea of using air for shipment. O2 will dissolve into the oil where it will stay, increasing oil oxidation.

 

[prc]

Of course my comments were for transformers with conservators. Even in case of transformers with nitrogen sealed system, if the unit is transported empty of oil, it is better to fill with dry air than nitrogen.
There is no question of excess oxygen getting dissolved in oil. At site transformer is finally oil filled after vacuuming the tank for several hours. Of course in service both nitrogen and oxygen will get dissolved in to oil. Nothing can be done about it, unless you go for nitrogen sealed system that has its own problems.
Middle of last century in some countries (eg UK) carbon dioxide (CO2) was the gas used for sealing transformers during transport. During those days vacuum pump effectiveness was poor or transformers were usually oil filled with out vacuuming the tank. Solubility of CO2 in oil is several fold more than that of air. Hence all air bubbles that stick to windings will get dissolved in to oil quickly, eliminating hazard from air bubbles in an energized transformer.

 

[FreddyNurk]

prc, can you advise the benefits or reasons why dry air is used over nitrogen when transporting transformers?

EDMS Australia

 

[prc]

Advantages of transporting with dry air :
- At site you need not remove gas(done by oil filling and draining or by vacuuming the tank) before conducting internal inspection or bushing fixing.(from safety angle)
- Shipping agencies object N2 filling esp if it cannot be kept over the deck
- Can be easily made at transformer factory using a small dehumidifying unit instead of buying N2 in cylinders.

 

[stevenal]

PRC,
You apply vacuum to a transformer that was shipped oil filled? In our case, it would only remove N2 that would be restored anyway.

Big difference between dissolved O2 and N2. One is an oxidizer, the other isn't.

 

[wroggent]

Transporting a new transformer and disposal of an old transformer would be considered differently. For ancient distribution transformers that I was involved in replacing we would frequently drain the oil due to the questionable integrity of the transformer tank. Where I am, an accident on a highway is the waste producers problem.

 

[prc]

stevenal-My comments were for units transported with out oil but with gas sealing only. In case of partially oil filled but with gas sealing at top case also I will recommend dry air (unless unit is of N2 sealed type). If N2 is used, then the same has to be flushed out at site before starting internal connection to bushing etc. Even with N2 filling case also, O2 will get in once free breathing starts.