Line vs Load Side of Switches: Industry Standard Terminology

[elsag131]

My name is Elsa and I’m a new Engineer in the Distribution Operations Center for my company. Recently, my Distribution Ops Manager asked me to reach out to people in the electric utility field regarding terminology used within different organizations. Specifically, we’re looking for standard best practice in the industry with regards to referencing of switches in, and outside of, substations.

We have varying language used to describe the high and low side of a switch. For example:

In Sub Outside Sub
Bus / Line Line / Load

Source side of switch is referred to as Bus within the substation, and Line out on the feeder.
Load side of the switch is referred to as Line within the sub, and Load out on the feeder.

As you can see, there is room for miscommunication and misunderstanding and we are working toward the standardization of common terms used within our enterprise. Are any of you willing to share what terminology is used throughout your organization? I appreciate any input or comments you have to offer.

Thanks in advance for the input!

 

[mcgyvr]

in = line
out = load
No more complicated than that.
line/load in my opinion are ONLY to indicate which direction out of a switch/breaker,etc.. to go to find the power source (or the load)

 

[elsag131]

In our company though, terminology within a substation is currently referred to differently than on our distribution lines. The consensus I have received by contacting several utility companies directly is that on the distribution line, it is referred to as line/load. When we get into the sub, the terminology gets more skewed and is referred to in a variety of ways like bus, highside bank, etc. My understanding is that different companies refer to the "high" side of the switch within the sub based on the type of bus configuration they have. I'm just digging in different forums to either confirm my understanding, or to clarify it. Any thoughts or comments?

Thanks mcgyvr and anyone else who posts!

 

[dpc]

The terms are all ambiguous and depend on context. For simple radial system, line and load are generally clear. For transmission switching stations and substations, the term "load" really doesn't mean much in many cases, since power can flow in any direction. Synchronizing terminology has traditionally referred to bus and line, but these are not always the same, depending on what is being synchronized to what.

I understand the desire to standardize, but I wouldn't get your hopes up. The best tool is an accurate one-line diagram with bus, line, switch and breaker designations that everyone uses and refers to.

 

[stevenal]

For radial systems, why speak of line at all? As you state, it depends on where you are standing. And since you are likely communicating with someone standing elsewhere, you have no common understanding. Why say left when you can say north? Use source/load terminology for purely radial systems. But even systems run radially can be looped and distributed generation is increasing, so one still needs to take care.

For looped systems use bus/line terminology.

I find mixing them; ie line/load and source/bus problematic. The line side can be the load side and the source side can be the bus side.

 

[davidbeach]

Every switch should have a unique number. If it needs to be opened, it doesn't matter what's bus/line/load, nor if it needs to be closed. If it is necessary to check phasing across the switch you need to check phasing, again no worries about bus/line/load. Not sure why any terminology other than the switch number is necessary. Or, how anything other than a specific number could be less ambiguous.

 

[bacon4life]

In our transmission substations most circuit breakers have a BUS side disconnect and LINE side disconnect. On our distributions feeders, voltage regulators and reclosers sometimes have reference to SOURCE and LOAD because the controllers need to know the "normal" direction of power flow. Although our distribution is operated as radial, many sections can be picked up from alternate locations. As distributed generation becomes more common, the only appropriate use of source/load might be on UL listed low voltage components