CT's and PT's connected to a power analyzer
CT's and PT's connected to a power analyzer
(OP)
I am using a power analyzer to monitor a 480V wye system. I have both CT's and Voltage inputs that come with the monitor which I will connect to the equipment. Because of the access to the service I am going to hook the CT's directly around the secondary of CT's and hook the voltage leads to the secondary of PT's.
My question is, the PT's are a 480:120V ration arranged in a corner grounded open delta arrangement. I was concerned that if I hooked up the PT's and CT's as described above then I might get false power readings because of a possible phase shift or wrond phase angle resulting from using the open delta PT arrangment.
Because the CT's are direclty on the wye system, I would think that thier phase angles would be referenced L-N. The PT's would have thier phase anlges referenced at L-L angles therefore the voltage phasors would be:
V a-b = 480V @ -330deg
V b-c = 480V @ -90deg
V c-a = 480V @ -210deg
Would this 30deg phase shift from L-N to L-L phase angles for the voltage give false current readings since the currents would be referenced at L-N angles?
To use the meter to monitor PT's you have to set it up for a delta system configuration and I was concerned about false readings as described above.
My question is, the PT's are a 480:120V ration arranged in a corner grounded open delta arrangement. I was concerned that if I hooked up the PT's and CT's as described above then I might get false power readings because of a possible phase shift or wrond phase angle resulting from using the open delta PT arrangment.
Because the CT's are direclty on the wye system, I would think that thier phase angles would be referenced L-N. The PT's would have thier phase anlges referenced at L-L angles therefore the voltage phasors would be:
V a-b = 480V @ -330deg
V b-c = 480V @ -90deg
V c-a = 480V @ -210deg
Would this 30deg phase shift from L-N to L-L phase angles for the voltage give false current readings since the currents would be referenced at L-N angles?
To use the meter to monitor PT's you have to set it up for a delta system configuration and I was concerned about false readings as described above.






RE: CT's and PT's connected to a power analyzer
Analyzer/meter is (should be) designed to calculate phase angles on its own for metering, as long as polarity (CTs) and phasing (A to a , B to b and C to c) are correct.
If in doubt measure a known load and see it matches the reading.
As for the reference, it for the display for user's convenience. There will be only one reference for I and V quantities in all phases. It should also be selectable, normally as Van or Vab.
RE: CT's and PT's connected to a power analyzer
Harmonics? Up to what order?
RE: CT's and PT's connected to a power analyzer
I am actually just trying to take power readings and was thinking about the various connections.
If I connect the meter to a three phase 4-wire wye system and I put the CT's and PT's on each phase + neutral then I'm guessing that the power meter will read both L-L phase angles and L-N phase angles. I guess it will always use the L-L phase angles when calculating power?
Is all line current measured in regards to the phase angle difference between current and L-N voltages for determining power factor. In other words for a power factor of .76 the phase angle between current and voltage is 40deg. This 40 deg is referenced between current phasor and L-N phasor not L-L phasor. Therefore when refering to current phase angle it may be represented as 70deg if the L-L phase angle is given as 0deg.
So i guess my other question is how line curren phase angles are typically represented. Are they represented by the difference between L-N or L-L voltage phase angles when displayed?
When watts are calculated then I'm guessint that the current has to be referenced to the L-N voltage to get correct power in watts? Is this correct?
RE: CT's and PT's connected to a power analyzer
The meter will coorectly calculate the power. It is true when one says pf is .76, the 40 degree phase angle is between each phase (L-N) and its current as you mention.
Just by selecting a different reference, the relationship with betwen any two vectors on the same system do not change.