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Old October 11th, 2017, 11:40 AM   #1
Mark Snodgrass
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Switchgear and Transformer Loading

As we keep expanding, the demands on our electrical system keep increasing. I am trying to determine how close to maxed out we are. I have my power company coming to discuss our loading on the various transformers next week.

What I would like to know from you guys, is what do you typically use as the demand factor for your loads off the transformers and/or switchboards. If I was really conservative I would just add up the FLA of all the connected loads, but if I did that almost everything would be overloaded already (some may be).

As management wants to add equipment, I want to be able say whether I have the available power for it. So I am gathering load and supply information to determine where we are at.
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Old October 11th, 2017, 12:57 PM   #2
PBuchanan
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Hard to really add up FLA and tell you anything because in a plant not everything is running at once.

On night shift the admin offices are normally low load and such.

It would be best to add some monitoring gear to your mains on you switch gear feed for each utility transformer for a few days of normal plant running to get a better idea of your loading pattern.

Most utility companies have a Dranetz or something similar they will bring out and log for a few days for you free of charge to determine your needs or there are services online where you can rent them by the week.

You normally want to stay within 85-90% of your utility transformers load rating.

If you are above 85% average and plan to add a lot of equipment you may want to consider a larger utility transformer or better an additional utility transformer.

Utility companies normally have a max size transformer they stock on their local depot yard so you don't want any special order unit larger than that if you can help it because if it goes bang you have a more complicated issue
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Old October 11th, 2017, 12:59 PM   #3
cornbread
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Your best bet would be to measure the actual load. We installed power monitoring equipment in our subs and switch gear.. makes it real easy to keep tabs on the loading. Get a qualified electrical guy/gal and have them measure (clamp on) to see what you are actually running.
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Old October 11th, 2017, 02:12 PM   #4
Mark Snodgrass
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I have an Amprobe data logger that I am going to be using to collect data. The actual transformer loading is what I want to talk to our power company about. We are also trying to upgrade our system to be more arc flash compliant, so I do want to upgrade the switchboards we have and install switchboards where multiple MCCs are being fed from a single transformer. The data collection may be a little difficult on my end due to the arc flash concerns, but I will figure out a way.

Since I am the only qualified electrician, PLC tech, head chef, and bottle washer, I will be the one collecting all the data and sorting it out. Looks like a lot of work ahead of me.
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Old October 11th, 2017, 06:32 PM   #5
jraef
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Quote:
Originally Posted by Mark Snodgrass View Post
I have an Amprobe data logger that I am going to be using to collect data. The actual transformer loading is what I want to talk to our power company about. We are also trying to upgrade our system to be more arc flash compliant, so I do want to upgrade the switchboards we have and install switchboards where multiple MCCs are being fed from a single transformer. The data collection may be a little difficult on my end due to the arc flash concerns, but I will figure out a way.

Since I am the only qualified electrician, PLC tech, head chef, and bottle washer, I will be the one collecting all the data and sorting it out. Looks like a lot of work ahead of me.
Especially with the Arc Flash concerns, it might be something your employer should consider farming out as a Power Study to someone with the right metering and protective gear. An Amprobe alone is not going to give you everything you need, you should be monitoring kW, which implies power factor, etc..
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Old October 12th, 2017, 08:01 AM   #6
Mark Snodgrass
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Jraef, the Amprobe we have has voltage as well as current. It also records the data to be downloaded to a PC. It will record power (kW and kVA) and power factor, so I can get all the correct data I need. In almost every situation, I will have to come in to de-energize the equipment to attach the meter. For the few items I cannot do that I will have to see what action to take at that point.

One of the things I am also trying to do, is to minimize the places where there is no PPE that will protect you. We have a few of those that require the utility to shut the transformer off for us to access them safely.

Don,t worry, I like myself to much to take any chances on getting hurt.
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Old October 12th, 2017, 02:07 PM   #7
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We have a few older switchgears here at my plant that didn't have any load or voltage monitoring systems from when they were installed back in the day. I was able to research a company called "Flexcore" they make flexible split core clamps to fit around the primary or secondary busses so you don't have to physically disassemble any buss bars. Just size up the correct turns ratio for your CT's and add some gauges and you got yourself some real time load monitoring.
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Old October 13th, 2017, 03:19 AM   #8
Andybr
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I am not sure how things work with the supply companies in the USA but you may be surprised by the amount of data which they can provide without the need for any additional instrumentation. Our supplier in the UK provides half hourly consumption data broken down into active and reactive figures, min and max consumptions etc. This data is freely available on their web site once you have registered.
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Old October 13th, 2017, 06:39 AM   #9
Mark Snodgrass
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Thanks Andy, I will ask my account manager next week when I meet with him if they have this feature. I know they do collect a lot of info on their installed meters, just don't know if they have it available online.
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