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
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
Do you use any particular software when doing this load study ?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 ?
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.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 didn't think that kWh usage for a 15 minute window was the same as kW demand for that 15 minute window.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.
^ all of which you can most likely get from historical data already available for viewing by logging into the power bill account.
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..
Your right.. problem is my laptop also has full remote access with all permissions. SCADA, Windmill modeling software, billing software, remote metering disconnect, etc....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.
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?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?
You on a TOU rate? That’s where the kWh usage in a specific 15 or 30 minute window may come into play.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.
Kwhr or usage is just that. You can determine monthly averages from it but NEC ampacity is based on 3 hour averages.
From a load study point of view demand isn’t very important for equipment sizing .
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.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
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.