Load Study

Ainsley Whyte

Senior Member
Location
Jamaica
Occupation
Senior Electrical Engineer
Can anyone share how they conduct a load study what are the lessons learnt. I have a load study to do and would like some ideas
 

paulengr

Senior Member
Can anyone share how they conduct a load study what are the lessons learnt. I have a load study to do and would like some ideas
You want to capture the peak throughout the period. With some customers that’s easy to do because their load is very consistent. With others you pretty much have to set up a test to make it happen. At least with industrial customers for this reason you don’t really need the full time span NEC requires.

One interesting “load study” occurred because of COVID-19. Dominion Power rate schedule GS-11 has a massive charge for demand and a tiny kwhr usage charge not reflective of reality. During the “lockdown” some customers went black but had maintenance crews start everything for a few minutes once a week. They were very surprised that their power bills were almost the same as normal production.
 

Ainsley Whyte

Senior Member
Location
Jamaica
Occupation
Senior Electrical Engineer
You want to capture the peak throughout the period. With some customers that’s easy to do because their load is very consistent. With others you pretty much have to set up a test to make it happen. At least with industrial customers for this reason you don’t really need the full time span NEC requires.

One interesting “load study” occurred because of COVID-19. Dominion Power rate schedule GS-11 has a massive charge for demand and a tiny kwhr usage charge not reflective of reality. During the “lockdown” some customers went black but had maintenance crews start everything for a few minutes once a week. They were very surprised that their power bills were almost the same as normal production.
Do you use any particular software when doing this load study ?
 

Flicker Index

Member
Location
Pac NW
Occupation
Lights
In a lot of the places in United States, it's a matter of just logging into the account and looking at the smart meter log. Industrial/commercial customers of many utilities have access to the kWh usage broken down into 15 minute interval, which is the demand.
 

paulengr

Senior Member
Do you use any particular software when doing this load study ?
Starting at the top, think about what you are actually looking for. There are two pieces of information from a load study. The first one is average load. But that’s not good enough. You often have to look closely to determine the peak of the averages. For instance an office may peak at 2-4 PM M-F (peak AC cycle) and may only be truly valid data if you collect it both winter and summer over the coldest and hottest weeks if you just passively collect data. Otherwise imagine if you are say ERCOT in Texas looking at average data for the whole year or only averages in August without considering cold snaps...oops! This is where judgement comes in. This data is useful for sizing cabling, distribution, etc. Usually you just capture readings say once a minute over a long period of time or if it will do it, 10 minute averages (like the utility). Either built in software or Excel is plenty.

Second is the peaks. Need this for sizing transformers for voltage dips. In this case you only need say the top dozen peaks. The power meter is going to produce event records...snapshots of high resolution data (sub millisecond) for once per second. No general purpose software is good for this and except COMTRADE files there is no generic file format so you are usually using whatever software the meter comes with. Looking at the raw data with Excel is pointless.

This is where you need to do a little hands on. Get demo units and try them out before you buy. You will quickly realize for instance Dranetz is inexpensive and very good but needs lots of auxiliary hardware (PTs, CTs). Fluke sucks overall. So so meter, lousy software. Diris, powerlogic, Shark fall in the middle. Decent all around but not very portable. SEL is very high end but very nice to use and software is free. It’s designed as a permanent meter but they sell it in a suitcase version.

Full disclosure my company is a distributor for SEL, Diris, Powerlogic. I’m just a service engineer though so whatever the company has is what I work with.
 

Hv&Lv

Senior Member
Location
-
Occupation
Engineer/Technician
Starting at the top, think about what you are actually looking for. There are two pieces of information from a load study. The first one is average load. But that’s not good enough. You often have to look closely to determine the peak of the averages. For instance an office may peak at 2-4 PM M-F (peak AC cycle) and may only be truly valid data if you collect it both winter and summer over the coldest and hottest weeks if you just passively collect data. Otherwise imagine if you are say ERCOT in Texas looking at average data for the whole year or only averages in August without considering cold snaps...oops! This is where judgement comes in. This data is useful for sizing cabling, distribution, etc. Usually you just capture readings say once a minute over a long period of time or if it will do it, 10 minute averages (like the utility). Either built in software or Excel is plenty.

Second is the peaks. Need this for sizing transformers for voltage dips. In this case you only need say the top dozen peaks. The power meter is going to produce event records...snapshots of high resolution data (sub millisecond) for once per second. No general purpose software is good for this and except COMTRADE files there is no generic file format so you are usually using whatever software the meter comes with. Looking at the raw data with Excel is pointless.

This is where you need to do a little hands on. Get demo units and try them out before you buy. You will quickly realize for instance Dranetz is inexpensive and very good but needs lots of auxiliary hardware (PTs, CTs). Fluke sucks overall. So so meter, lousy software. Diris, powerlogic, Shark fall in the middle. Decent all around but not very portable. SEL is very high end but very nice to use and software is free. It’s designed as a permanent meter but they sell it in a suitcase version.

Full disclosure my company is a distributor for SEL, Diris, Powerlogic. I’m just a service engineer though so whatever the company has is what I work with.
I assume your talking about the 734 in a suitcase style? We have a 734B as a cap controller. Don’t like it at all for that application.

I use a Dranetz HDPQ. Its OK and the data is good, although there is no battery life. I don’t like keeping up with the dongle and now many corporate IT depts are doing away with E drives, the computer sees the flash drive and won’t accept it, so getting the data to a laptop requires an unlocked computer. the touch screen is a little slow, and remote on an iPad isn't always reliable.
but the data is good..
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
In a lot of the places in United States, it's a matter of just logging into the account and looking at the smart meter log. Industrial/commercial customers of many utilities have access to the kWh usage broken down into 15 minute interval, which is the demand.
I didn't think that kWh usage for a 15 minute window was the same as kW demand for that 15 minute window.
My smart meter has registers for both the 15 minute usage and the 15 minute demand, but my utility only gives me access to the usage information and not the demand information.
 

paulengr

Senior Member
I assume your talking about the 734 in a suitcase style? We have a 734B as a cap controller. Don’t like it at all for that application.

I use a Dranetz HDPQ. Its OK and the data is good, although there is no battery life. I don’t like keeping up with the dongle and now many corporate IT depts are doing away with E drives, the computer sees the flash drive and won’t accept it, so getting the data to a laptop requires an unlocked computer. the touch screen is a little slow, and remote on an iPad isn't always reliable.
but the data is good..
You can’t honestly do service work with an encumbered laptop. Service laptops need to be off any domain controller, period. Just save all data to thumb drives and work from that. More than once I’ve used a vendor to sell me a “motor configuration tool” or “power meter reader”. I don’t care or want corporate network access. Yes you don’t have corporate IT backups, support, etc. That comes with strings.
 

Hv&Lv

Senior Member
Location
-
Occupation
Engineer/Technician
You can’t honestly do service work with an encumbered laptop. Service laptops need to be off any domain controller, period. Just save all data to thumb drives and work from that. More than once I’ve used a vendor to sell me a “motor configuration tool” or “power meter reader”. I don’t care or want corporate network access. Yes you don’t have corporate IT backups, support, etc. That comes with strings.
Your right.. problem is my laptop also has full remote access with all permissions. SCADA, Windmill modeling software, billing software, remote metering disconnect, etc....

I don’t want to carry two laptops, so I deal with it with Bluetooth and OneDrive..
 
I didn't think that kWh usage for a 15 minute window was the same as kW demand for that 15 minute window.
My smart meter has registers for both the 15 minute usage and the 15 minute demand, but my utility only gives me access to the usage information and not the demand information.
Interesting. I have seen "KW usage" on a POCO reports and assumed it was 15 minute demand. What is the difference betwen KW usage and demand/KW demand?
 

paulengr

Senior Member
Interesting. I have seen "KW usage" on a POCO reports and assumed it was 15 minute demand. What is the difference betwen KW usage and demand/KW demand?
Kwhr or usage is just that. You can determine monthly averages from it but NEC ampacity is based on 3 hour averages. If you get “detailed” usage like 10 or 15 minute averages you can calculate the 3 hour average.

Demand is a utility way of describing the “load”. In other words how big your service is. You have to look at the rate schedule for details how it is determined. There is no standard but for example they will take 10 minute rolling average kw. Out of any given billing cycle they take the three highest and average those together. On an industrial/commercIal bill you will see separate charges for demand and usage.

From a load study point of view demand isn’t very important for equipment sizing but it can have a dramatic effect on reducing costs. As an extreme example in the Southeastern US average costs are around $0.08-10/kwhr. But on Dominion Power rate GS-11 (the standard industrial/commercial schedule) they charge around $0.03/kwhr. The difference is the demand charge is dramatically higher. So during the Covid-19 lockdowns some businesses closed down completely but they still had maintenance crews come in on weekends and fire up the equipment and run it for 10-15 minutes before shutting it back down for maintenance purposes. They were quite shocked to see an electric bill that was virtually unchanged. It also matters a lot under Dominion when looking at energy efficiency projects because it reduces demand and usage. Across the line in Duke East (Progress Energy) stretching from North Carolina to Florida the demand rate is relatively small and the kwhr rates are around $0.08. Still if you have long startups and you can space out starting your biggest loads you can dramatically reduce the power bill with almost zero effort.

The other big hit in Dominion and Duke West (western NC, SC) for instance is power factor. Both of them gross you up to a 0.85 on the demand charge. On Dominion payback for adding capacitors to the largest motors is measured in weeks. In Duke West its months. In Duke East the return on investment is decades. The largest plant in Duke East with a $1.2 million dollar power bill had a $200 charge for low power factor if Duke/Dominion chose to charge for it but the cap bank was around $100k to do it.

So keep in mind load studies aren’t just for capacity and expansions. Often they pay for themselves. Compressed air and steam/chilled water are the other big areas that often get neglected.
 

Hv&Lv

Senior Member
Location
-
Occupation
Engineer/Technician
I didn't think that kWh usage for a 15 minute window was the same as kW demand for that 15 minute window.
My smart meter has registers for both the 15 minute usage and the 15 minute demand, but my utility only gives me access to the usage information and not the demand information.
You on a TOU rate? That’s where the kWh usage in a specific 15 or 30 minute window may come into play.
Also peak demand calcs
 
Kwhr or usage is just that. You can determine monthly averages from it but NEC ampacity is based on 3 hour averages.
Reread my post. It was not a typo. They have a field "KW usage". There is no H in it.

From a load study point of view demand isn’t very important for equipment sizing .
I think it depends in what we are doing a "load study" for. As a design/build electrical contractor, demand is what I need most of the time.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
You on a TOU rate? That’s where the kWh usage in a specific 15 or 30 minute window may come into play.
Also peak demand calcs
The last time I looked they let me download the 15 minute usage data, but when I looked just now, it is a 60 minute usage that they give me. They have something that call "power smart pricing" which is billed in 60 minute blocks so, what I can download not matches up with their time or day or time of use billing. Not sure if they had 15 minute block billing in the past when I was able to download the 15 minute data. I can go back to 1/12019 and download the 60 minute date in blocks that do not exceed 60 days if I want to look at that.

I am not on a TOU rate.
I have thought about the TOU, but that creates the same risk that resulted in the huge power bills in Texas as their tie the TOU rate to the wholesale market rate. When I looked the other day, the TOU rate was less than half of my fixed rate, but with the fixed rate at 4.3 cents per kWh, I don't think it is worth risk to change to the TOU.
 

Flicker Index

Member
Location
Pac NW
Occupation
Lights
I didn't think that kWh usage for a 15 minute window was the same as kW demand for that 15 minute window.
My smart meter has registers for both the 15 minute usage and the 15 minute demand, but my utility only gives me access to the usage information and not the demand information.
It's not the "same" direct reading, but it's essentially the same thing and easily deduced even though you may have to go through data manually if it's not computed for you. Your kW demand is based on the highest kWh accumulated energy during the 15/30/60 min period during the applicable period during a specific window of time. This is something defined by your schedule of service.

There is no reason to compute the demand if your schedule of service does not have a provision for demand, which is only present for commercial and industrial customers, or in some cases, in rural cooperatives.

For example, if you're charged for $8/month/kW on 15 minute time base for highest demand occurring during peak hours (we'll call it 3-8PM M-F summer only) per billing period (this could be longer than billing period as well. again, read the schedule of service)
Let's just say that you showered, then pre-heated the oven, all while drying clothes, and microwaving and cooking things on stove while charging an EV at level 2 and running A/C full blast causing you to accumulated 10kWh in 15 minute at the highest at 5PM by using 40kW for 1/4 hours. Your peak 15 minute demand is 40kW and now you're on the hook for $320 demand fee that month even if you only used 10kWh of energy during the whole billing cycle.

That $320 is the cost for your utilization of distribution resources. For billing purposes, 15 minute averaging period is common.
This is in addition to kWh (energy) used. if you used 80kW for 7 1/2 minutes, the demand is still only 40kW, because of the 15 minute time base.

So under the above schedule, if the maximum energy that flowed through the meter during 3-8PM M-F in 15 min was 1kW, your demand charge is only for 4kW. Whatever happens outside the defined time frame is billable. If what you're trying to do is generator/UPS sizing/voltage sag, then that's called maximum instantaneous demand.

To go deeper into TOU rate, the energy charge per kWh might not make sense, but sometimes, they waive the transmission and distribution charge for off-peak hours making the raw variable cost of kWh use just the energy charge.
 
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