What is Unitised or Package or prefabricated or compact substation (CSS/USS) ? Single line diagram, area required and advantages?


Have you seen this (kindly see below picture) ?

This is a outdoor 11000/440 volt substation on double pole structure. Why you need this ? Obviously you need Low voltage or LT supply for the office, school or construction etc. or electric distribution companies make this type of outdoor substation to supply local area.

How many components you see above .

One is Transformer and second is Equipments ( HT isolator/switch, Fuse)

Apart from transformer and HT switches/ fuses, there will be a LT panel for distribution of LT loads.

Discussed above is a outdoor substation.

Many times indoor substations are made.

Where also there are 3 components .

HT panel + Transformer + LT panel

So three components are required usually to get the low voltage supply and takes lot of time to purchase these equipments and install and than testing and commissioning of the same.

Solution to this is Unitised Package substation( USS). It has all these 3 parts( HT side + Transformer+ LT side) in a single container.

Below is the picture of a 11000/440 volt package substation..

11 KV Compact prefabricated Package Unitised Substation (USS)
11 KV Package Substation

Unitised Substation (USS) or prefabricated substation or Compact Substation (CSS) are other names of package substation.

In This Package or Unitised substation, all the three equipments i.e. HT side breaker, Transformer and LT breaker with LT distribution are in a single container.

Single line diagram of this 11 KV package substation

Compact (prefabricated) Package unitised Substation (USS) SLD (single line diagram)

This Package substation has three parts placed each in a separate compartment in a single container.

  • HV switchgear: A Ring Main Unit(RMU) RMU has three switches i.e. 2 isolators or disconnectors as incomers to give two source of supply to package substation and one vaccum circuit breaker(VCB) as a outgoing to transformer.
  • A dry type transformer to convert 11000 volt into 440 volt.
  • LT compartment: a LT breaker(MCCB/ACB and feeders)
  • Package substations can also be made with inbuilt APFC (automatic power factor correction) feature to improve the power factor, if required.

Questions in Your Mind

  1. Up to what capacity, package substation is available?
  2. Area required for Installation
  3. Advantages of package substation

1. Package substation is available upto 33 KV and upto 2500 KVA(2.5 MVA).

2. Area required for installation: approx. 100 square feet (10’x10′).

3. Advantages of Package Substation:

  • Requires less space max. 100 sft (10’x10′) area.
  • Can be installed on roof top or basement or truck or on floor indoor/outdoor.
  • Easy installation
  • No need of cabling between HT breaker/switch to transformer and to LT side breaker/switch should be done at site as its already done in factory.
  • It is well suited for construction sites as a mobile substation.
  • Transportable
  • Safe(dry type transformer is used) and totally enclosed so not acces to live parts.
  • Requires very little maintenance


Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.

error: Content is protected !!