It all starts at the generating station. In this case, It is coal fired. The generators generate electric at 13.8 thousand volts (13.8kv). As the power leaves the building, it goes in to a transformer that steps up the voltage up to 138 thousand volts (138kv). It then goes to a substation where it is sent out over several lines that take it to other substations. Some of the power in that first substation is also put through another transformer that steps up the voltage to 345 thousand volts (345kv) for long distance transmission. Higher voltages are used for longer distance transmission since you can get by with smaller wires.
A large 345kv to 138kv transformer
These substations contain breakers just like you have in your house only much larger to protect the system in case of a problem. Each circuit coming in and going out of any substation will have at least one breaker on it for protection.
Here is a 345kv breaker.
So, the electric leaves the generation station substation and travels down the wires at 138kv. It enters another substation where it goes in to a transformer where it is stepped down to 69kv and is divided in to several circuits.
If we follow one of the 69kv circuits, it will then either go to another location within this substation or it will travel down the wires to a smaller substation. For the purposes of this explanation, we will assume that it goes to another smaller substation. When it gets there, it goes in to another transformer that steps it down to 12.5kv. That voltage is then sent to a switch gear with breakers where it is divided up in to more circuits.
These 12.5kv circuits then go out to provide power to a neighborhood. Once it gets there, it will go to several small transformers that are either hanging on a pole with the overhead wires or a transformer on the ground if the wires are run underground. These small transformers will feed several homes and step the voltage down to 2 legs with 120 volts each for a total of 240 volts. This voltage goes into your home at the circuit breaker panel and more breakers and is distributed throughout your home.
A large 345kv to 138kv transformer
These substations contain breakers just like you have in your house only much larger to protect the system in case of a problem. Each circuit coming in and going out of any substation will have at least one breaker on it for protection.
Here is a 345kv breaker.
So, the electric leaves the generation station substation and travels down the wires at 138kv. It enters another substation where it goes in to a transformer where it is stepped down to 69kv and is divided in to several circuits.
If we follow one of the 69kv circuits, it will then either go to another location within this substation or it will travel down the wires to a smaller substation. For the purposes of this explanation, we will assume that it goes to another smaller substation. When it gets there, it goes in to another transformer that steps it down to 12.5kv. That voltage is then sent to a switch gear with breakers where it is divided up in to more circuits.
These 12.5kv circuits then go out to provide power to a neighborhood. Once it gets there, it will go to several small transformers that are either hanging on a pole with the overhead wires or a transformer on the ground if the wires are run underground. These small transformers will feed several homes and step the voltage down to 2 legs with 120 volts each for a total of 240 volts. This voltage goes into your home at the circuit breaker panel and more breakers and is distributed throughout your home.
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