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| Test winding in zero sequence current transformers |
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| duak:
Red, Yes, the burden resistor will present a load to the test winding. |
| Red_Micro:
--- Quote from: floobydust on March 18, 2020, 07:19:21 am ---I would say you can't drive the test winding directly with an MCU unless its substrate diodes can withstand overload with CT saturation under an unbalanced fault, like a line-ground short at the load. The CT can then see >100's amps or more depending on the size/voltage of the system, until a breaker trips. So the test winding circuit can see a surprise. The two drive resistors do lessen the surge current but I'll add clamp diodes. Tri-stating the MCU outputs would work. The design I did used H-bridge '125 from 3.3V with 1k ohm drive to a 100:1 test winding around 4 ohms, I think giving around 3mApk drive but it was a high current trip test. --- End quote --- Do you have a reference schematic that you may want to share? |
| Red_Micro:
--- Quote from: Red_Micro on April 03, 2020, 10:22:34 pm --- --- Quote from: floobydust on March 18, 2020, 07:19:21 am ---I would say you can't drive the test winding directly with an MCU unless its substrate diodes can withstand overload with CT saturation under an unbalanced fault, like a line-ground short at the load. The CT can then see >100's amps or more depending on the size/voltage of the system, until a breaker trips. So the test winding circuit can see a surprise. The two drive resistors do lessen the surge current but I'll add clamp diodes. Tri-stating the MCU outputs would work. The design I did used H-bridge '125 from 3.3V with 1k ohm drive to a 100:1 test winding around 4 ohms, I think giving around 3mApk drive but it was a high current trip test. --- End quote --- Do you have a reference schematic that you may want to share? --- End quote --- Doing some research I found the circuit attached below. In that circuit they use a dual power supply, but I don't think I need dual. I just would need to feed this circuit with the signal coming from the micro. |
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