I’ve watch several Two-Wattmeter Method videos, including this series (3 parts starting with this one) and I have some questions to take the topic a bit farther and to better understand the vectors, specifically when CTs and PTs are in the mix. Furthermore, my confusion and frustration relates to an actual real-world meter application I have right now. Please reply if anyone has any whitepapers or info you can share for the full vector representation carrying thru from the primary to secondary side that could guide me.
PROBLEM: For a SCADA and meter checkout, I need to test thru the secondary test switch input connections to Form5 meter, using a 3-phase test set. I plan on setting up a spreadsheet with individual secondary input values; i.e. voltage and current magnitudes and angles for the technicians to setup in their Doble. There will be a minimum of eight (8) test to exercise the meter and note it’s readings; i.e. all four (4) quadrants (PF=.707) and the four (4) axes (+/- pure watt/vars). I want this spreadsheet to be universal for the technicians to use on future Form5 meter projects; i.e. enter system voltage, PT & CT ratios and then have spreadsheet calculate the correct real & reactive power and PF. Ideally I don’t want to hard code the angles in the spreadsheet. I’d like the technicians be able to change them and see calculated/predicted results. Unfortunately, I am getting hung up with the vector math in the spreadsheet (complex conjugate trap?) for the relative vector relationships (addition/subtraction of angles) between the voltage and currents. Also, I am wondering if the Y-connected CTs and Delta-connected PTs and their combined vector translation from Primary to Secondary may cause angle shifts and play another part in my spreadsheet woes. Lastly, I am struggling to understand if/how bonding of the B phase to ground on the secondary side may impact the vectors, too.
++++++++++++++++++++++ Info ++++++++++++++++++++++++++++++++++++++++
Please see attached PDF
1. The below SEL meter diagram which shows the ground connecting to the CT and PT circuits.
2. Also, SEL provided their version of the vector representation for the secondary inputs.
3. The table and screen shot below shows the results of a bench test with injected secondary voltages and currents starting out with their unity vectors and going thru all quadrants and axes.
4. Meter screen shot of calculated System vectors at unity
PROBLEM: For a SCADA and meter checkout, I need to test thru the secondary test switch input connections to Form5 meter, using a 3-phase test set. I plan on setting up a spreadsheet with individual secondary input values; i.e. voltage and current magnitudes and angles for the technicians to setup in their Doble. There will be a minimum of eight (8) test to exercise the meter and note it’s readings; i.e. all four (4) quadrants (PF=.707) and the four (4) axes (+/- pure watt/vars). I want this spreadsheet to be universal for the technicians to use on future Form5 meter projects; i.e. enter system voltage, PT & CT ratios and then have spreadsheet calculate the correct real & reactive power and PF. Ideally I don’t want to hard code the angles in the spreadsheet. I’d like the technicians be able to change them and see calculated/predicted results. Unfortunately, I am getting hung up with the vector math in the spreadsheet (complex conjugate trap?) for the relative vector relationships (addition/subtraction of angles) between the voltage and currents. Also, I am wondering if the Y-connected CTs and Delta-connected PTs and their combined vector translation from Primary to Secondary may cause angle shifts and play another part in my spreadsheet woes. Lastly, I am struggling to understand if/how bonding of the B phase to ground on the secondary side may impact the vectors, too.
++++++++++++++++++++++ Info ++++++++++++++++++++++++++++++++++++++++
Please see attached PDF
1. The below SEL meter diagram which shows the ground connecting to the CT and PT circuits.
2. Also, SEL provided their version of the vector representation for the secondary inputs.
3. The table and screen shot below shows the results of a bench test with injected secondary voltages and currents starting out with their unity vectors and going thru all quadrants and axes.
4. Meter screen shot of calculated System vectors at unity
