Ct Phase Correction - Ametek TR-2100 Operation Manual

TR-2100 User Manual

CT Phase Correction

CT phase correction is not part of the calibrate program described above. Details are
included here to complete the adjustment of the input scaling parameters of a TR-2100 to
ensure maximum accuracy. The correction values are computed and set manually.
Inputs derived from interposing CTs and some other forms of transducer will normally
suffer from phase shift error. This will affect the accuracy of derived parameters like power
and impedance. This error can be corrected by adjusting the phase correction value in the
Analogue channel configuration in Display Station. For more details on how to set the
value, see the Display Station 32 manual.
To measure the phase shift for a particular input, first ensure that the phase correction value
is set to zero using Display Station. Next, apply 50 or 60 Hz signals to the voltage input and
interposing CT connected to a current input of the same phase. That is, inputs with the same
phase designation as set in the line and phase group definitions. These two signals must be in
phase. This requires a specialized test set that can generate voltage and current at the same
time. Now, use the real time display option in Display Station to show the voltage and
current vectors. The CT error can be seen by noting the difference between the voltage and
current angles. Another method is to show the power values in the real time display and to
compute the CT error from:
Where Q is the reactive power & S is the apparent power.
The CT phase correction value entered at Display Station is a phase lag. That is, if the
current signal is seen to lead the voltage, then the correction is negative. Enter the value and
Setup the TR-2100. Now, check that the angle difference is zero or that the reactive power
(Q) is zero using the method described above.
Unfortunately, CT phase error is not fixed and varies with current magnitude. To maximize
accuracy, the system should be phase corrected at a current value close to the normal
working value. For a protection CT with a 5A secondary, the interposing CT should be
calibrated at approximately 2 to 3A.
⎛
− Q
=
1
⎜
CTerror Sin
⎝
⎞
⎟
⎠
S
40