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Wonderful link dpc. Thank you for sharing.

Thank you very much Scottf.

Hello, When several sets of current transformer are mounted on a bushing I have seen them marked as X, Y,(Z, W ...). However it is unclear to me what is what are the relative position of these marking within the bushing. That is: I have seen manufacturer drawings (for CBs with bushing CTs) where...

Thank you very much for your feedback cranky108 and bacon4life. Based on these replies and what I have read elsewhere I think that I will have to seek confirmation of the breaker capabilities from the supplier anytime I encounter a reclosing sequence that exceeds two shots. Thanks again for the...

Hello, I can see that the standard duty cycle for circuit breakers is well documented and can be found for example on the breaker nameplate. However this standard rating appears to cover two closing operations. What is unclear to me is what happens when we reach the last "open" of the sequence...

Thank you very much. That is very helpful information.

Hi, I am trying to replace an old analog voltmeter installed in a synch panel. The reason for doing so is that the ratio of the VT connected to this device has changed. I would like to replace it by another one as similar as possible to the original. Going through different catalogs of analog...

Thank you very much for the all the info. It is very helpful.

Thank you very much cranky108 and waross for the great feedback. What we are trying to achieve in our case is to segregate a trip branch so that we can monitor it. I think the sketch will clarify more than my words: What we are trying to do is to "Monitor" the operation of Tripping Contact...

Hi, I would appreciate it very much to know your opinions on the following subject: We are modifying an existing electromechanical busbar tripping circuit, and we would like to segregate the new trip contacts by means of a blocking diode. The control voltage is 125Vdc. The new tripping branch we...

Hi, In some of the projects I have been involved, our customer has advised us to use another factor when rating bushing CTs using a tap less than its maximum. The formula they have asked us to use is: CT Thermal Rating = Rating_tap_used x (sqrt(Rating_max_tap / Rating_tap_used)) x RF That is: If...

Hi, Recently I did a bit of research on that subject. I came across a couple of interesting papers that might be of help: https://www.pes-psrc.org/kb/published/reports/Protection_of_PAR_Transformers_Report.pdf...

Hi Interesting. That's something I hadn't considered. Thank you very much for the feedback.

jwatty, cranky108 and davidbeach, Thank you very much for the feedback! I am curretly studying the loadability of a line where the utility is using a zone 2 POTT scheme with no delayed tripping (step distance). The scheme is intended as a backup for other prot. functions (such as line diff) and...

Hi I am trying to understand how to calculate the loadability of a distance scheme that uses a basic POTT (permissive overreach, looking into the forward direction with no modifications such as echo, weak infeed logic etc) scheme. I am focusing on a simple case of a two ended line with no taps...

jwatty: your indications make perfect sense. Thank you very much. protoslash: you are right in your last comment. The reason for the 125% is to avoid overreaching due to any error in calcs, relays, cts, etc. Thank you both very much for your feedback.

Hi, I would appreciate very much to have your opinion on the following: I am trying to set a directional ground instantaneous element (34.5kV Line Prot. Application). The utility policy on this regard is that it should be set as "1.25 x 3Io for the maximum line end fault, with the remote end...

Hi, If I am not missing something (which is very likely) I would use the following approach to calculate the neutral current. a) Assume line infinite source (that is Zs = 0). b) Calculate voltage at the neutral point directly using the Millman theorem. c) Compute the neutral as the addition of...

Thank you very much for the very helpful feedback. It is much appreciated!

Hi! I need to specify a current transformer that is to be connected to the neutral of an existing 34.5kV : 4.16kV (delta - wye) power transformer. The CT is intended for installation at the wye neutral connection (4.16kV side) which is directly connected to ground. In principle I was thinking...