Fault loop impedance. Is there a formula to calculate the impedance?

Question

Hello all. I have read a bit about the short circuit loop impedance and I know that it can be measured with a meter. Is there a formula to calculate this impedance?

stomat · Answer

Are you going to measure or calculate impedance? There are formulas for calculating impedance. Varies depending on the data you have.

rysiu.e · Answer

I would like to calculate but I found nothing concrete. How can you Stomat give the formulas I would be really grateful.

sq9jjh · Answer

Hello. Root of the sum of the squares of R and X. Google it and you will find it. Greetings.

Łukasz-O · Answer

Understands that you have measured short circuit loops and want to calculate allowable impedance? That's what you mean? Zdop = Uf / k * Ibezp where: Zdop - admissible impedance Uf - phase voltage k - correction factor I - nominal fuse current greetings

rysiu.e · Answer

I do not have such a measure and I would like to calculate it from the formula.

Łukasz-O · Answer

If you want to evaluate the protection against electric shock, unfortunately, you will not be able to do without a meter. You can, of course, theorize. If you have an ordinary voltmeter and ammeter, you can try to approximate calculations - rather just for fun: Zs = Uo-U / I Ik = Uo / Zs where: Zs - fault loop impedance Uo - idle phase voltage U - phase voltage under load I - load current Ik - short-circuit current I also recommend google and Wikipedia, just like my colleague sq9jjh there you will learn about basic formulas. Unfortunately, complex numbers will also be needed. I wish you perseverance Greetings.

rysiu.e · Answer

Thanks for your interest helped.

sq9jjh · Answer

In the past, it was all on foot, but nowadays there are a lot of computational support programs. If someone wants to, he can download the demo version of the obl 2002 program from the net. I have and know this program for pain, and it's pretty decent. The full version is paid, of course, but in my opinion it is the best I have ever found for TN and TT networks. Greetings.

Łukasz-O · Answer

Calculate it, but you must have data

sq9jjh · Answer

Sure he will. He knows the cross-section and length, he will find formulas, he will also find tables with data, it is not easy to want to be able to do so. Best regards to my colleague Łukasz-O.

pawelo220v · Answer

And if you have a friend of an electrician who has a short circuit loop impedance meter, let him tell you or measure it himself as a friend (because it normally costs a few zlotys.

lukaszu6 · Answer

Tell me what is the acceptable short circuit loop impedance? As I measured with the meter recently, it was 0.58 ohm. It's good or bad

modlinp · Answer

It is very difficult to give a correct answer to this question. The impedance value should be small, i.e. single ohms and less (in your case the value is correct, but you can find a case where this value could still be too high ). Is the value correct, it is necessary to check the effectiveness of the automatic power off (and this depends on the used protection and network system)

sq9jjh · Answer

Hello. Good questions! If you asked in practice why we measure the short circuit loop impedance, you would not have such dilemmas now. Greetings.

Spiced91 · Answer

Hello,
I would like to check the effectiveness of the applied protections in the LV switchgear (measuring junction) during a short-circuit. The circuit from the junction is routed through a cable line in the ground, approx. 100 m, then enters the pole and then runs along the overhead line for approx. 150 meters to the RSA type longitudinal switch disconnector.
I want to check the effectiveness of the automatic power cut-off in 5 seconds. and the question is whether to check it for a circuit whose entire length is 250m? Is this the worst case? Or should I also check for a shorter circuit, e.g. when the cable enters a pole? I would like to ask for your support.

CYRUS2 · Answer

Not true. IPZ cannot be calculated. Because the IPZ covers everything - right down to the way. What colleague Łukasz wrote in post # 7 is IPZ measurement using the technical method.

stonefree · Answer

And yet the designers calculate the performance conditions using the SWZ, and this even coincides with the measurements.

CYRUS2 · Answer

The power supply cable to the building is protected by a fuse in the connection - not in the switchgear. Because they have measured input data. This calculation can only be used to make a project. It cannot substitute for a control measurement.

Fault loop impedance. Is there a formula to calculate the impedance?

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