Dry-Type Distribution Transformers

Dear Mr. Sunilji,

I have used the compact bus extensively, for 1600 kVA, 1250 kVA, 2 mVA transformers for distribution of power for industries as well as IT buildings which are more than seven storied buildings. With the result the losses can be minimised. Please order only reputed makes of compact bus.

Regards

Shaw Sumanam. J. L.

Consultant

Clearances,

Don't forget you will have to tap off of the bus on both sides, Provide adequate space to be able to do this. The bus is compact but the equipment being tapped off of it is not. Also pay close attention to your conversion boxes (cable to bus etc.)

Dear Sunilji,

I have been doing this for more than a 1/4 century.Please go ahead without any worry.

In 1982/83,I was the electrical project engineer for a big ( >3,000,000 SQ FT 5-storey podium block of shopping area and on top of it, 2 tower blocks of 14-storey offices and apartment residences plus 3 basement levels of car parkings) mixed development in a city centre.14 units + 2 units of additional order of package substations totalling 23 MVA were installed in the complex. 4 pss in basement 2, 2 pss on level 1 and the rest on 5th floor .Each package substation (8ftx9ftx12ft ventilated mild steel epoxy powder coated IP20 enclosure) contained 11kv LBS-VCB ring main unit,one cast resin transformer ( 500,800,1000,1250,1500,2000KVA 11/0.433kv Dyn11) and Lv 415V ACB panel.Tx in the middle.Soon after we designed and manufactured more compact substations reducing the dimensions.We were first to do that in the country then and we were excited and anxious.These 11kv substations are still working fine today.

Kindly specify accurately the type of "dry transformer" i.e.HV coil & LV coils fully casted in vacuum with epoxy resin or HV epoxy resin casted coil with LV coil resin prepregnated,oven cured,the second type is cheaper and usable.11KV Paper insulated with varnish dip Dry type Tx is not suitable for humid enviroment,especially after switching off for maintenance.The cold TX will have water condensation that cause insulation failures upon re-energising.

Please note that while cast resin transformers,CRT are very reliable and trouble free,it is not suitable for enviroment that has salt spray,carbon / iron dust ( tyre factory and steel mill),textile fibre etc as these will cause surface tracking of the high voltage.

1 MVA CRT is about 4600 Kg each with IP20 enclosure and it has to be protected from water from the top and splasing of water from the side.Check floor loading and civil engineering and structural costs.

I suggest that you place one transformer on 4th or 3rd floor just next to the 415V main switchboard (in line with MSB or behind the main ACB in the same switchroom or the next TX room) where the main load is located.You can eliminate at least one length of the more expensive busbar trunking.

The termination of LV busbar trunking on the TX LV terminals is best via a short length of flexible conductor ( or flat retangular bars with 2 right angle bends ) to prevent the vibration of the TX from transmiting to the trunking.If the humming of the transformer affects lower/same floor,you can use neoprene vibration pads to reduce the noise. Not much from 1 MVA CRT ( less than 57 dB ).

I will be able to help you in case you encouter any technical problem.I am quite free.

Regards,

Khor.