Pole Mounted Sub-Stations

I was going around town, with a colleague, we came across a structure which by the roadside that my friend was quick to refer to as transformer. I quickly corrected him that its actual name is not a transformer as many might call it, rather it’s called a Pole Mounted Sub-Station.

A Pole Mounted Sub-station is a large, free standing, outdoor electrical equipment that is mostly located in residential places. Its main purpose is to step-down the lethal 11kV to 415/240V for light, commercial and residential loads (consumers)...

The 11kV line is connected to the Step-Down Transformer (11kV/415V) though a gang isolator and fuses. The lighting arrestors are installed on the H.T side to protect the Sub-Station from lightening strokes. The transformer steps down the 11kV to 415V, 3phase, 4-wire supply. The voltage between any two lines is 415V, and between any line and a phase is 240V. The Oil Circuit Breaker (O.C.B), installed on the L.T side automatically isolates the transformer from the consumers in case of any fault. The Pole Mounted Sub-stations are generally used for transformer capacity up to 200kVA
They should be periodically checked for dielectric strength of oil in the transformer and (OCB)
In case of repair the transformer or (O.C.B) both the Gang Isolators and (O.C.B) should be shut off.
This equipment is very expensive leading to the reason why people vandalize them. The Step-Down Transformer is oil cooled and its this oil that people steal. This costs the distribution company millions of 
Shillings annually. Please be warned that the current flowing through the transformer is deadly, it would kill you in seconds. Stealing that oil means that the transformer will overheat, reduce its efficiency and 
possible explode under normal circumstances. In case you spot any one 
vandalizing the equipment please call The Kenya Power and Lighting Co. Limited: www.kplc.co.ke.
See the image below of a Pole Mounted Sub-Station.