6 Voltage transformer
6.2 VTRatio
Use the VTRatio test card to measure a voltage transformer’s ratio with injection on the VT’s primary side with up to 2 kV from AC OUTPUT.
It measures amplitude and phase angle of the voltage (atV1AC) and the current on the transformer’s secondary side, and calculates the actual ratio and the deviation from the nominal ratio.
Figure 6-2: Setup for testing ratio DANGER
Death or severe injury caused by high voltage or current
► Do not connect the CPC 100 output to the secondary side of the VT. This will cause hazardous voltages on the primary side.
A/H1
N/H2
n/X2 a/X1
VT
Burden
6.2.1 Test settings
Figure 6-3:VTRatio test card with test results
► Navigate to the parameter fields, and enter the values according to your test requirements:
Vprim: nominal primary voltage with the option "value x 1/√3"
Vsec: nominal secondary voltage with the options value x 1/√3
value x 1/3
Vtest: primary injection voltage.
By default, Vtest = Vprim (with option x 1/√3) if Vprim ≤ 2kV.
If Vprim > 2kV, Vtest = 2kV.
f: output frequency
Auto: select check box for automatic test (default), clear for manual test (refer to 6.2.3 "Automatic test vs. manual test" on page 144).
6.2.2 Measurements
Selecting the check box Manual input lets you enter the value for Vsec manually, for example when Vsec was measured with an external volt meter rather than at input V1 AC.
Vprim: actual output voltage at 2kV AC output that is injected into the voltage transformer’s primary side
Vsec: secondary voltage measured at V1 AC, and its phase angle relative to Vprim nominal Ratio: ratio Vprim /Vsec., here 10000.0/√3:100.43/√31
1. The value 100.43/√3 is calculated as follows:
Vsec act * (Vprim nom / Vprim act) * (1/√3 / 1/√3) = 20.087V * (10000V / 2kV) = 100.43/√3
and deviation of voltage ratio in %. Formula:
((Kn x Vsec - Vprim) / Vprim) x 100%2
((10000V / 100V * 20.087V - 2000V) / 2000V) x 100% = 0.431%
2. Kn = rated transformation value, here: 10000V / 100V
Polarity: displays the status of the polarity
OK = phaseVsec - phaseVprim = -45° < 0° < 45°
NOT OK = all other cases
6.2.3 Automatic test vs. manual test 1. Option "Manual input" clear
Automatic test
► Press the I/O (test start/stop) push-button to start the test.
► The test voltage increases from 0V to Vtest in a ramp characteristic within 1 second. Then Vtest is kept for a period of 2.4 seconds, and the measurements are taken. Next, the ramp decreases again within 0.3 seconds.
► The automatic test stops by itself, it can now be assessed.
► To repeat the test, first press Back to Top, if applicable, and then Clear Results.
Manual test
Clearing Auto lets you set the test voltage Vtest manually with the handwheel.
► Press the I/O (test start/stop) push-button to start the test. The focus is set onto the "V test:" entry field.
► Set the value of your choice either by turning the handwheel and/or by entering it with the numerical keys.
Note:A value set with the numerical keys needs to be fully entered and acknowledged by pressing either Enter or the handwheel before it is applied to the output. If needed, it can then be adjusted using the handwheel.
Values set by turning the handwheel are applied instantaneously.
► Now the measurements are taken and displayed.
► To save the measurement press Keep Results (pressing the I/O push-button has the same effect).
The last measured values are "frozen", the test can now be assessed.
► Stop the manual test by pressing the I/O (test start/stop).
► To repeat the test, first press Back to Top, if applicable, and then Clear Results.
2. Option "Manual input" selected
Note:Select Manual input prior to starting the test. If the test card still contains results, clear them by pressing Clear Results.
When Manual input is selected, there is no phase available. Consequently, neither the polarity nor the phase angle can be calculated.
Since an automatic test only lasts a very short period of time, and a manual measurement is rather difficult, an automatic test with a manual measurement is not useful. Therefore, this Reference Manual will not cover this subject.
Manual test
Clearing Auto lets you set the test voltage Vtest manually with the handwheel.
► Press the I/O (test start/stop) push-button to start the test. The focus is set onto the "V test:" entry field.
► Set the value of your choice either by turning the handwheel and/or by entering it with the numerical keys.
► A value set with the numerical keys needs to be fully entered and acknowledged by pressing either Enter or the handwheel before it is applied to the output. If needed, it can then be adjusted using the handwheel.
Values set by turning the handwheel are applied instantaneously.
► Vprim is measured and displayed.
► To save the measurement press Keep Results.
► Navigate to the "V sec" entry field.
► Enter the measured Vsec value either by turning the handwheel or by entering this value with the numerical keys, and press Enter or the handwheel to acknowledge your setting.
► The ratio is calculated and displayed.
► To stop the manual test, press the I/O (test start/stop). The test can now be assessed.
► Alternatively, it is possible to enter the manually measured value into the test card after the test was stopped (for example, if the measurement was carried out at a remote location).
► To repeat the test, first press Back to Top, if applicable, and then Clear Results.
To learn more about test assessment, refer to 10.1 "Test assessment" on page 268.