recommendations please

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hardworkingstiff

Senior Member
Location
Wilmington, NC
Scenario:

120/240-volt service feeds an 800-amp panel. Panel feeds the boat slips. Each slip has an independent electronic meter and counter to monitor the individual boat power usage.

Problem:

Power company usage is much higher than the combined usage of the boats (worst month was boat meter readings = 2,000KW and PoCo readings were 4,000KW).



Customer owns the wiring from the transformer to the panel. CT's are in the (underground) transformer with the meter off to the side. I want to monitor power consumption at the MB of the panel for a month and compare it to the power company readings and the boat meter totals. (Our next course of action will be determined after these readings are analyzed).

Looking for recommendations of the best place to rent the equipment I need and what equipment you have had good experience with.

Thanks,
 

topgone

Senior Member
Power Usage

Power Usage

You didn't mean KW, did you?
What I know is power usage is expressed in kWHr. FWIW, the problem maybe due to different metering points. PoCo meters energy at a point before the line and trafo while the owner metered at the secondary side, hence the line and trafo losses were not metered by the owner. Suggest to owner to transfer metering point to the primary side of the transformer. It will also help if you can take a look at the metering CT's and PT's.
My 2?.
 

gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
090320-1141 EST

hardworkingstiff:

I just obtained a low cost power monitoring unit called "TED" wich might be of value as a test tool.

Your total power consumption by either of your figures does not seem like peak load would come close to 800 A.

The TED unit I have is good for 200 A and the current transformers can accept a wire up to 1" OD. A limited test indicates that this system does measure the real power component. Accuracy appears good. With their software option you can collect data over varying periods. The 200 A system with software is about $200 but obviously does not include a laptop to collect data.

Their current transformers saturate some where above 200 A and maybe the electronics as well. If your total peak loads did not exceed this very long it should not produce any great error.

At least you could use TED as a means of checking each of the individual KWH meters.

You really do not need TED or to monitor over a whole month to spot the kind of disparity you have indicated. Pick some one hour period of light load. At the beginning record the reading of each KWH meter and also at the end of the period. Take the difference of each. Sum the differences from the individual meters, and compare this total of the individual meters to the power company meter difference. Then pick some other hour with high load, and do the same kind of comparison.

The TED device looks to be a useful troubleshooting tool, especially with the software option. It provides instantaneous power consumption averaged over 1 second, and the display is updated each second. Cummulative power consumption (KWH) is updated each second as well. Long term collection of data at the 1 second quantizing level means the data needs to be saved maybe each day. I am not sure if within the monitoring program you can extend this beyond 1 day. But longer averages can be collected less often. Whatever collection computer is used needs to be on a UPS. When you collect data at the 1 second rate files get large quickly.

The TED device does not have two voltage channels. It would be nice if it did. Then it would be useful to quickly monitor and compare the voltages on both sides of neutral simultaneously.

.
 

wawireguy

Senior Member
2000KW and 4000KW readings scream ratio problem of some kind on your side to me. I doubt the POCO is off on their readings, could happen though. I'd look at how your meters are connected and make sure everything is set correctly.
 

chris kennedy

Senior Member
Location
Miami Fla.
Occupation
60 yr old tool twisting electrician
I just obtained a low cost power monitoring unit called "TED" wich might be of value as a test tool.

I also have recent experience with TED and agree it looks like a good value. But how would one use the small clamp around CT's to monitor a service with parallel 500's?
 

cadpoint

Senior Member
Location
Durham, NC
I'd be all over every part of the Dock service, and all of what they own.

Did I miss that you megger'd it ... ?

The CT's out of the box new have a test sheet issued with it, this is a ratio reading/rating of the correctness of the CT.
MO, you could also include some research into the CT themself's.
I looked and couldn't find the photo's right off that I took, Duh

I would also look at the connection of the CT that are correctly attached and what Larry said also.

I'll never forget when they terminated to the wires on my last Granda Service, (old story) they walked up with a hook bill in the CT and opened of the circuit in the CT only to attach a hex head screw to the CT's wire and drill it into the feeders...

33 or 88, was next, I was to stunded to ask ... :roll: ...
 

gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
090320-1921 EST

chris:

For $50 more TED has a big brother with 2 sets of current transformers, and two modules that the current transformers connect to, but only one monitor display. This is classified as their 400 A unit. Obviously this is not useful for 400 A because the current transformers are 200 A units.

Therefore, I do not think it should be classified as a 400 A unit, but rather as a dual 200 A unit with summing of the power on the display. It would provide for a second 120 voltage reading, but I do not know if this second reading is used or displayed. The second 120 V voltage input is of no use for power measurement unless it is associated with the current of that phase.

.
 

netaguy

Member
Location
Providence, RI
Scenario:


Looking for recommendations of the best place to rent the equipment I need and what equipment you have had good experience with.

Thanks,

I have had great luck using Megger's AVO PA9 power demand monitor on main service.

Check out Electrorent. $72 per day or $1100 month plus shipping. 3PH flex CT's up to 6000A.

Monitor during monthly billing period and compare.

Good luck.
 

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
PE (Retired) - Power Systems
First I would check the set up of the customers meter.
Then I would be spend my efforts on the customer's CT's and their wiring and the voltage connections.

Most inexpensive to moderate CT's cannot handle very much burden (load on the CT) before they reach saturation (a point where they max out their output). In systems with electronic metering, the leads (length and gauge) are usually the predominant burden. Clamp-on and split core CT's are particularly susceptible to lead issues.
 
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