coloradog1
Mining
Hello guys,
I am hoping someone can help me understand zero sequence CT's (sometimes referred to as ground CT's) by answering a few examples for me. Any additional information someone can provide such as a reference or description would be appreciated.
1.0 If the zero sequence CT surrounds all three phase conductors and you have the following currents in each phase, what will the zero sequence CT read on the primary side?
Ia=100 A < 0 degrees
Ib=100 A < -120 degrees
Ic=95 A < +120 degrees
3I0=Ia+Ib+Ic=5 A < -60 degrees
In this example the CT would read 5A on the primary, correct? Mathematically can you add the currents in all three phases making sure to include phase angles in order to get the current the ground CT see's?
2.0 This example assumes the zero sequence CT surrounds all three phase conductors plus a neutral conductor.
2.1 If there is imbalance in the circuit due to line-to-neutral loads, would the zero sequence CT read zero amps? I would think that any imbalance in the three phases would be canceled out by the current in the neutral.
2.2 What about if there is a single-line-to-ground fault? Then the zero sequence CT would not read zero assuming the neutral is insulated from ground, correct?
2.3 What about if there is a line-to-line fault? Then what kind of currents would the CT read? I would assume it would read close to zero and you would rely on the phase protection.
3.0 If a neutral conductor is present, does the zero sequence CT typically surround this conductor in addition to the phase conductors? Are there any downsides to doing this? This kind of goes with question 2.
Thanks for the help guys.
coloradog1
I am hoping someone can help me understand zero sequence CT's (sometimes referred to as ground CT's) by answering a few examples for me. Any additional information someone can provide such as a reference or description would be appreciated.
1.0 If the zero sequence CT surrounds all three phase conductors and you have the following currents in each phase, what will the zero sequence CT read on the primary side?
Ia=100 A < 0 degrees
Ib=100 A < -120 degrees
Ic=95 A < +120 degrees
3I0=Ia+Ib+Ic=5 A < -60 degrees
In this example the CT would read 5A on the primary, correct? Mathematically can you add the currents in all three phases making sure to include phase angles in order to get the current the ground CT see's?
2.0 This example assumes the zero sequence CT surrounds all three phase conductors plus a neutral conductor.
2.1 If there is imbalance in the circuit due to line-to-neutral loads, would the zero sequence CT read zero amps? I would think that any imbalance in the three phases would be canceled out by the current in the neutral.
2.2 What about if there is a single-line-to-ground fault? Then the zero sequence CT would not read zero assuming the neutral is insulated from ground, correct?
2.3 What about if there is a line-to-line fault? Then what kind of currents would the CT read? I would assume it would read close to zero and you would rely on the phase protection.
3.0 If a neutral conductor is present, does the zero sequence CT typically surround this conductor in addition to the phase conductors? Are there any downsides to doing this? This kind of goes with question 2.
Thanks for the help guys.
coloradog1
