We have a panel that feeds 5 different machines and of those five the utility company would like to monitor 3 of those machines for 3 weeks using CT's. Our in house engineer trying to be conservation with cost says that we only need one 3 phase monitor for the line side coming into the panel. His belief is that if we run the load side wires of the equipment we don't want to monitor up through the CT's that it will null that particular machine draw via the CT. He supports this theory with the right hand rule, which makes sense but I am not convinced. Has anyone seen this done or even think this is plausible. Thanks.
Current Transformer application
- Thread starter kvl
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I'm not sure I understand the problem. If the utility wants to monitor why are you concerned with cost? I would assume they would pay for the installation. If you only install 1 set of CT's you will read all of the machines at the same time. You need the CT's on the circuit to each machine. It will not affect the operation of the machines.
The cost for each set of CT's is $500 per point hookup. This was initiated by our company for the utility to give our company an idea of expense associated with running the 3 particular machines, sorry if I caused some confusion. Again the idea is to get away with only having one hook up point and nullifying the loads we don't want recorded by routing those wires backward through the CT.
Re: Current Transformer application
Yes, that's right. I wouldn't worry about the right hand rule. Consider the magnetic field is porportional to the vector sum of the current through the CT. So, consider the panel feed A-phase going through the CT with power flow left-to-right. Now, install A-phase machine feeder also through the CT with power flow right-to-left. Vector sum of the current is:
I(total) = I(panel) - I(machine).
Works great as long as you want to monitor all three machines as one lump and not see the currents of the individual machines.
carl
kvl said:
Yes, that's right. I wouldn't worry about the right hand rule. Consider the magnetic field is porportional to the vector sum of the current through the CT. So, consider the panel feed A-phase going through the CT with power flow left-to-right. Now, install A-phase machine feeder also through the CT with power flow right-to-left. Vector sum of the current is:
I(total) = I(panel) - I(machine).
Works great as long as you want to monitor all three machines as one lump and not see the currents of the individual machines.
carl
kvl said:
If the loads are balanced, just use one CT, not three. No need to measure more than one phase - unless you need power factor.
If we get this down to the minimum information needed, maybe it costs very little - even nothing - if all it takes is a stopwatch and reading the nameplate :roll:
carl
This is a site that has power monitoring equipment. If needed you can get 3 clip-on CTs and PTs. You would only need to buy one. Move it to the other machines as needed. No wiring required. Its a handy device to have around the plant. There are other sites also. Do a google for power monitors.
http://www.emon.com/products_class2000.htm
http://www.emon.com/products_class2000.htm
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