Primary vs. Secondary Distribution

[xptpcrewx]

Wondering if anyone has an official definition of "primary" and "secondary" distribution?

Some things to consider are:

• What are the voltages ranges that would apply to these terms?
• What if more than one transformer is used and multiple voltage levels are present?
• Does it makes a difference if the system is part of the premises wiring system or electric supply system?
• Do these terms also apply generally to sub-transmission and transmission applications or do they only apply in some simplified sub-transmission and transmission applications?

Thanks in advance!

 

[Hv&Lv]

Medium voltage (600V-69kV)for primary and low voltage for secondary? (50-600V)

substation level transmission (HV) is primary and distribution (medium voltage) is secondary.

as far as transmission primary transmission and secondary transmission your getting into EHV and UHV

interesting question. I just assumed C84.1 or transformer specifics would dictate it

 

[xptpcrewx]

Medium voltage (600V-69kV)for primary and low voltage for secondary? (50-600V)

substation level transmission (HV) is primary and distribution (medium voltage) is secondary.

as far as transmission primary transmission and secondary transmission your getting into EHV and UHV

interesting question. I just assumed C84.1 or transformer specifics would dictate it

Thanks for giving it a shot. Let me provide some additional context:

The Lineman’s and Cableman’s Handbook states, “All high-voltage distribution circuits greater than 600 volts up to 34,500 volts are often referred to as primaries by the lineman. The branch circuits that connect to the main- or express-feeder distribution circuits are properly called primary circuits or primaries”.

It also states,”The conductors originating at low-voltage secondary winding of a distribution transformer that extend along the rear lot lines, alleys, or streets past the customers’ premises are called secondaries”.

The concern with these two definitions, is that they seem to exclude anything which does not fit into these two classifications. I can think of a few systems I’ve encountered where it isn’t so clear (like 138-kV after the service point without a transformer).

 

[Hv&Lv]

Thanks for giving it a shot. Let me provide some additional context:

The Lineman’s and Cableman’s Handbook states, “All high-voltage distribution circuits greater than 600 volts up to 34,500 volts are often referred to as primaries by the lineman. The branch circuits that connect to the main- or express-feeder distribution circuits are properly called primary circuits or primaries”.

It also states,”The conductors originating at low-voltage secondary winding of a distribution transformer that extend along the rear lot lines, alleys, or streets past the customers’ premises are called secondaries”.

The concern with these two definitions, is that they seem to exclude anything which does not fit into these two classifications. I can think of a few systems I’ve encountered where it isn’t so clear (like 138-kV after the service point without a transformer).

I have that book and have read that also. There is a very nice chart in there with weights allowed on poles 8’ down by class.

Trust me when I say this, linemen definitions do not dictate nomenclature.

If you want to get technical about it primary vs secondary is determined which side of the XF your on.

Simply put, the primary winding is the coil that draws power from the source, whether is is step up or step down.

 

[xptpcrewx]

Simply put, the primary winding is the coil that draws power from the source, whether is is step up or step down.

True, however this distinction becomes somewhat meaningless with bi-directional systems like in a transmission network, or when dealing with transformers having tertiary windings.

 

[Hv&Lv]

True, however this distinction becomes somewhat meaningless with bi-directional systems like in a transmission network, or when dealing with transformers having tertiary windings.

but then we are getting into different areas altogether where one definition doesn’t suit all circumstances.

As long as the transformer is designed properly for bi-directional operation, there shouldn’t be an issue.
Forget “primary” and “secondary” and use ”high side” “low side”. Or Hv&Lv…

Utility class transformers should be able to handle bi-directional operation based on their construction. When you get into dry packs it shouldn’t be utilized bi-directional because of the lighter windings on the Hv side vs heavier windings on the Lv side.
Used backwards a winding will burn up rather quickly in relation to transformer life.

DER is getting so that Bi-directional is more important than it used to be.
Also with DER voltage regulation is going to be a bigger issue than bi-directional. If you get enough small scale DER to cause an issue with bi-directional the utilization voltage will be too high and something will have to shut down.

you know, if you think about it, all transformers are used bi-directional in everyday use now.
Vars one way, power the “correct” way…

 

[xptpcrewx]

but then we are getting into different areas altogether where one definition doesn’t suit all circumstances.

As long as the transformer is designed properly for bi-directional operation, there shouldn’t be an issue.
Forget “primary” and “secondary” and use ”high side” “low side”. Or Hv&Lv…

Utility class transformers should be able to handle bi-directional operation based on their construction. When you get into dry packs it shouldn’t be utilized bi-directional because of the lighter windings on the Hv side vs heavier windings on the Lv side.
Used backwards a winding will burn up rather quickly in relation to transformer life.

DER is getting so that Bi-directional is more important than it used to be.
Also with DER voltage regulation is going to be a bigger issue than bi-directional. If you get enough small scale DER to cause an issue with bi-directional the utilization voltage will be too high and something will have to shut down.

you know, if you think about it, all transformers are used bi-directional in everyday use now.
Vars one way, power the “correct” way…

I get what you’re saying. In Nevada electrical contractor licensing scope is based on this so called distinction between “Primary” and “Secondary” systems. It’s pretty inadequate and creates grey areas in my opinion. I think it would be better treated as “Electric Supply” and “Premises Wiring” systems, and if they really needed to, could further divide that into low-, medium, high-voltage classes.