MadSci Network: Engineering

Re: What kind of equipment is located in a power Substation

Date: Sat May 26 12:43:21 2001
Posted By: Donald Howard, Staff, Nuclear Engineering, Retired
Area of science: Engineering
ID: 987783025.Eg

A substation is basically a power switching facility.  Transmission lines 
coming from generating stations or other substations are connecter to 
switches called "circuit breakers" or just "breakers." The substation 
design usually includes a bus system, either in a parallel or ring 
configuration.  A bus is just a solid stiff wire that looks like a pipe, 
but it is connected to its support structure by brown, tapered and ribbed 
insulators.  The length of the insulators is dependent on the voltage 
involved.  The higher the voltage, the longer the insulator.

As you look at a substation, you should see the incoming and outgoing 
transmission lines in groups of three because the power is three-phase 
AC.  There is a small wire at the top of the transmission tower above the 
center of the three main conductors.  This is called a "telemetering 
line," and it is the line that is usually hit by lightening, so if you 
follow it into the sub station you will find it is connected to a very 
long brown insulator that is not tapered called a "lightening arrestor."  
It's job is to shunt any lightening that doesn't go to ground through the 
transmission tower steel away from the main conductors. 

Some substations will have transformers if there is a need to change 
voltage.  The need to change voltage depends on customer needs, and in 
some cases, is required to connect a new higher voltage transmission 
system to an older, lower voltage one. 

Transformers are usually large and have cooling pipes and sometimes fans 
on the outside.  They will have six insulators on top connected to the 
incoming and outgoing transmission lines or to the buses, but breakers 
also have six insulators.  The breakers are smaller and the insulators are 
all the same length.  The transformer insulators are different lengths 
depending on the voltage.

Older substations may have a building used to contain controls for the 
breakers and instrumentation to monitor the conditions of the insulating 
oil within the tanks housing the transformers and breakers.  Newer 
technology has reduced the size of that equipment to a small box mounted 
directly on the transformers and breakers that sends the information to a 
central control station usually the System Operating Center. 

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