Transformer primary and secondary

[EEpowerOK]

Is there a rule of thumb for the primary and secondary?

For example is the transformer is 12.5/34.5 KV, is the primary the highest KV or just the one on the left?

12.5/34.5 KV

Primary/Secondary ??

 

[RBsai]

Its usually on the left hand side rating of the xfmr.

 

[EEpowerOK]

Just seemed strange on this problem since the Primary was the low side of the transformer.

Is the Primary always connected to the source and the load is on the secondary?

 

[daw4888]

A transformer can go from high to low, or low to high. In a typical power system it goes

Generator > Step UP transformer > Transmission > Step Down transformer > Distribution > Step down transformer > Customer.

So you see, they have to go both ways. A generator might be 4-6kv, and your transmission might be 138kv. So you you are using a 4kv/138kv to step up the voltage. When you want to go back down to distribution you would use a step down like 139kv/12.47kv.

 

[knight1fox3]

Not always. The transformer isn't always high-to-low or step-down. There are plenty of low-to-high or step-up transformers as well.

For instance, for a certain combustion turbine power plant (natural gas), the voltage coming out of the turbine generator is 13.8 kV. But to convert that voltage for transmission, the voltage must be stepped up to 138 kV in this case. And a GSU (generator step-up) transformer would be required for that purpose.

 

[daw4888]

139kv/12.47kv should be 138/12.47

Just seemed strange on this problem since the Primary was the low side of the transformer.

Is the Primary always connected to the source and the load is on the secondary?

This I would say is typically how you see it, but I don't know if that's actually a rule. If they give you a problem, then I would assume its Primary/Secondary, Unless otherwise specified.

 

[EEpowerOK]

Thanks