KWh usage

Jezz

Member
Join Date
Dec 2002
Location
Kendal
Posts
399

Hi,
we are wanting to monitor electrical usage of our panels ,so I was thinking of using a current transducer feeding 4-20mA into a ML1100 so I can calculate the KWh's from there.I was wondering of any one else has done some thing similar and if so how did you do it the cheapest current transducer I've found so far is £72.
Thanks
 
Assuming that you are talking about an AC supply there is absolutely no way you can get anything like a good estimate of KWH from just a current transducer. You would need to use an estimated voltage, which might not be too difficult, and an estimated power factor, which will probably be impossible to guess at reliably. You can, however, buy multi function energy meters at quite reasonable prices these days and avoid all of the guesswork. I would go for one with a Modbus port but this would cost me around £250.00 (Merlin Gerin PM710) but if you only need KWH's then a cheaper model with a simple pulse output would suffice. You would also get a display of all of the normal electrical parameters plus information on maximum demands, THD and other information which might be useful.

Andybr
 
What are the sizes of your panels ie amperage and what is voltage and phasing ie single or 3 phase.

What is your purpose in doing this?
What is going to be the payoff from doing this work?

Why is using the utility metering for the whole plant not adequate?

Check with your utility to see if they have an energy conservation program. They may be willing to sell rent or maybe even loan instrumentation to meet your needs.

As previously said power = I x E. You have to measure both. In the case of three phase it changes to P = I x E x 1.73 x PF (power factor)

Dan Bentler
 
We have done similar work on site as part of an energy management system.

the meters i have used are Socomec Diris A20 units with an option for a pulse output module, they are quite cheap about £140 for the meter and £15 for the pulse module, as mentioned above you gat lots of other useful information doing it this way like maximum demand, maximum current drawn etc.
 
Looking into this a bit further, it looks like we are going to have to get a unit designed for the job ,in an ideal world we would like it to have ethernet coms via modbus/TCP.
 
Via Modbus TCP you might struggle to find anything, Modbus Serial the PM710 will do it or as already sugested the Socomec's (I prefer the PM710 myself), if you want to put either over TCP look at the Merlin Gerin EGX100MG
 
Im with andybr here. although you can use a cheaper pm200 (not alot cheaper) from Merlin Gerin meter. Gives you a pulse for every kwh. You can get most of ur readings, pf. voltage, current, real power etc. And it costs about 190 pounds. That roughly converted from our RANDS.
Using the pulse you dont need comms. Just a digital input
 
Doing the calcualtion ain't for the faint hearted either. Buy a meter or pulse output unit of some kind and count them. Lot easier than having to calculate all the variables across 3 phases. There are cheaper ones out there than Schneider - Rudolph, heaps of them.
 
Allan Bradley do a power monitor these are very good they have ethernet & a built in web page.
If you use RSpower32 in conjunction with RSView then you have a complete monitoring system.
I installed 12 of these on an existing RSV32 Scada but they are not cheap.
 
Jezz said:
Looking into this a bit further, it looks like we are going to have to get a unit designed for the job ,in an ideal world we would like it to have ethernet coms via modbus/TCP.

I quoted for one late last year, modbus / ethernet (I think) comms from power montiors on each substation (each macine has its own substation) all fed back to a Redlion G308 for datalogging the KWh, KVAr, Amps, Volts etc etc to a server. Job hasnt come off yet but the monitors i quoted for were from Nortonics Foxtam (uk based) cant remember the part number although they were dearer than £72! Around £250 - £300 from memory.
 
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