# Zero sequence current transformer for single phase supply

#### moonlystar1111

Joined Feb 1, 2024
57
Hello.
I tried to simulate a circuit which requires a zero sequence current transformer (zct) having N no of turns (lets say is 1000). Zct has line and neutral of power supply as primary winding and gives current differential of line and neutral. The secondary has 1000 no of turns and will step down the differential current. During normal condition, the net current at primary of zct is zero, therefore the secondary has zero current. During fault, suppose line current is 10A, and neutral current is 10.005A, the current differential is 0.005 A. The secondary of zct will step down the current by the factor of 1000 and gives 5 micro Amp.

#### BobTPH

Joined Jun 5, 2013
8,996

#### MisterBill2

Joined Jan 23, 2018
18,568
Really trying to understand, it is confusing to me.
Probably an explanation of the intended results will be helpful to our understanding.

#### Alec_t

Joined Sep 17, 2013
14,329
What do you want your circuit to do with those 5uA?

#### MisterBill2

Joined Jan 23, 2018
18,568
Hello.
I tried to simulate a circuit which requires a zero sequence current transformer (zct) having N no of turns (lets say is 1000). Zct has line and neutral of power supply as primary winding and gives current differential of line and neutral. The secondary has 1000 no of turns and will step down the differential current. During normal condition, the net current at primary of zct is zero, therefore the secondary has zero current. During fault, suppose line current is 10A, and neutral current is 10.005A, the current differential is 0.005 A. The secondary of zct will step down the current by the factor of 1000 and gives 5 micro Amp.
This description seems like a GFCI input circuit. And while it seems a bit like there would be a current step down, the result aI have experienced is 100% destruction of the GFCI assembly when there is a down stream short circuit.
AND, the transformer would normally be called a differential current transformer, meaning that the secondary voltage is proportional to the difference in current between the two primary conductors.
That is exactly the function of a ground-fault detector. It detects a few milliamps, while a short circuit to ground of mains power results in a current spike far greater than the protective device can instantly interrupt. This assures destruction of wahtever device is connected to the secondary of the transformer.

#### moonlystar1111

Joined Feb 1, 2024
57
This description seems like a GFCI input circuit. And while it seems a bit like there would be a current step down, the result aI have experienced is 100% destruction of the GFCI assembly when there is a down stream short circuit.
AND, the transformer would normally be called a differential current transformer, meaning that the secondary voltage is proportional to the difference in current between the two primary conductors.
That is exactly the function of a ground-fault detector. It detects a few milliamps, while a short circuit to ground of mains power results in a current spike far greater than the protective device can instantly interrupt. This assures destruction of wahtever device is connected to the secondary of the transformer.
Thanks for your reply. Yes it is a GFCI circuit. I'll attach the schematic part which i want to simulate.

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#### moonlystar1111

Joined Feb 1, 2024
57
What do you want your circuit to do with those 5uA?
5 uA current is the output current of sense transformer. It is then input to an IC which includes current to voltage converter. This voltage is then input to 2 window comparator circuit which has high and low threshold.

#### moonlystar1111

Joined Feb 1, 2024
57
I dont have link to transformer but i have GFCI model , RV4145 which i want to run.

#### Alec_t

Joined Sep 17, 2013
14,329
LTspice has all the components you need to run a sim of the RV4145 IC function and a GFCI application, as per Fig.1 and Fig.2 of the pdf. Post your .asc file and we can help you to get round any problem you have with the sim. You can just assume a 5uA AC current for the sim input.

#### MisterBill2

Joined Jan 23, 2018
18,568
Probably to make a simulation work you will need to change the transformer to a single, not differential, type.
Differential transformers had some interesting control applications back in 1958 That was not my project. My dad was a controls engineer also.