There is no standard design for sub station. All sub station are design according to the apparatus and equipment installed, that need to control and distributed the power supply to the equipments or to the consumer.
Basically, there is no standard maintenance needed for the substation expect you need to keep the substation clear of obstruction of material and keep the sub station clean.
For equipments that install in the substation, it can only be service by a qualified charge-man that has license approval by the local electricity authorities.
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Management is just like a bunch of Monkey sitting on a tall tree. Some climb to the highest branch and some at the lowest branch. The highest Monkey look down and see a lot of happy faces but the lower Monkey looks up and see nothing but all the....