Use of Pad Mounted Distribution Transformers

A1) It depends upon the transformer general arrangement drawings, which cannot be seen from here.

A2) It depends upon the capabilities of the undefined "we", which are not known here.

I do not know what you mean by Pad mounted.But a 500 KVA can be placed on a foundtion of sufficient height to get required clearances and all other things like Isolating switch , Fuses can be on H pole.This is a common arrangement in India.

The term "pad mounted transformer" is normally used to describe a type of transformer designed in such a way that the primary and secondary conductors come up through a concretye "pad" base. They are self contained and protected from the elements by nature of their construction.

Whether or not you can use such a device... depends upon the local conditions and the points mentioned by PWSlack.

I'm not surprised you're having difficulty mounting a 500KVA transformer on poles. They're not the smallest of things.

A pad mount packaged unit normally incorporates both MV and LV switchgear in its own housing making them ideal for your application.

The MV end of a 800KVA packaged substation I had to re-supply.

The LV end.

Hi,

Gound mount distribution transformers are very common. We will put them in from 30kVA single phase for customers want to get away from overhead lines and transformers. Distribution transformers in urban areas are usually in the 300kVA to 1000kVA range: bigger than that and maintaining LV supplies during maintenance can be difficult. They all sit on concrete pads.

1. 11kV cable needs to be buried and enter the HV cubical from below. Local regulations here say 900mm, in proper bedding material. Please be aware of the bending radius of the cable as it transits from the horizontal to the vertical.

2. Use suitably qualified cable jointers, using correct kits, are required for making off terminations of the 11kV at the transformer and on the crucifix.

3. Foundation material of compacted AP25 (300mm deep) should be laid underneath pad when there is good ground conditions. With bad ground conditions a geotech engineer should be used. If a pad moves then stress is placed on the cable and the HV bushings.

4.Earth rings need to be established to control step/touch voltages. If I cannot get below 10ohms on the standard earth system then additional measures such as deep driven earths, gravel or asphalt can be laid around the transformer (1500mm away from pad) and fencing the transformer off from the public.

5. Equipotential bond the transformer cabinet.

6. LV cables should be ducted away from the LV cubicle with 100mm sweeps to get them outside the earth ring (at 600mm depth). This means that will be the least opportunity to damage the earth ring or foundation of the transformer pad.

7. Specifying transformers as having separate HV and LV cubicles (under different locks) as this is intrinsically safer.

8. If you are putting a LV distribution frame in the LV cubicle (as shown in a post above) then consider

a. MDI metering

b. Setting a LV pillar up for attaching a genset to.

c. Putting a 230V GPO in place (protected by a 10A MCB)

d. Having a switchable light inside the LV cabinet (protected by a 6A MCB).

e. Fused test points for each phase.

f. Make sure the frame is large enough to straddle the cable void in the concrete pad and able to be dynabolted to the pad without blowing out the concrete.

Simply, Yes. Look up Mini Sub stations.

See, for instance:

http://ufgscriteria.tpub.com/3_550_03/3_550_030052.htm