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Mudcat, If the installation is ruled by NFPA the answer is 90 °C. As per NEC 2011 Article 110 (Requirements for Electrical Installations), Part III (Over 600 Volts, Nominal)see the following articles: 110.30 General. Conductors and equipment used on circuits over 600 volts, nominal, shall...

Hello, Sorry for the delay in answering. Davidbeach: No, there is no generation downstream the transformer. Generation is electrically close to the high voltage side (115 kV or 130 kV) PRC: Thank you for the reference. I will read it thoroughly. Actually you recommendation of using filters...

Thanks for your answer PWTRAN, If we consider that the three winding transformer is supplied by a 230 or 115 kV network and the secondary is 34.5 kV I have the following questions based on PWTRAN response: 1. In general a three winding transformer is cheaper than buying a regular two winding...

Hello all, I have few questions about three winding transformers and harmonics that I would like to get some help from you. I have seen three winding transformers wye-wye-delta with the delta not connected to any load; the neutrals of the “wye” are grounded and these transformers are used to...

Hello, Thanks all for your responses. In the system we are dealing with the two transformers are fed from Bus A and Bus B of a 15 kV Switchgear which will normally operate with its tie breaker in open position. The two transformers are not close to each other so the grounding of the neutrals...

Hello all, Currently I am looking at a 3-Phase 4-Wire system (208/120 V) which will be supplied from an Automatic Transfer System (ATS). This ATS does not have the typical Normal and Emergency sources one can find in regular ATS systems: step down transformer (Normal) and the generator...

Hi ivana24, Most manufacturers (Okonite, Prysmian, General Cable, Anixter, etc) will be able to provide this cable, even up to 2500 kcmil. Usually catalogs go up to 1000 kcmil. If you give them a call and ask I am pretty sure they will meet your needs. A 1250 kcmil 28 kV XLPE 133% is not an...

Hi greenelec, Regarding your first question I guess it would be a code violation if you are not able to protect the cable. If the load requires a 1200 A CB, as you said replacing the CB for a 1000 A will not work; maybe a closer look at the load list may justify changing the CB rating to a...

If you are in Canada these standards may help: CSA C68.3 Shielded and Concentric Neutral Power Cables Rated 5 - 46 kV CSA C22.2 No. 0.3 Test Methods for Electrical Wires and Cables Regards

Hi John, Standard CSA C68.3-1997 "Shielded and Concentric Neutral power Cables Rated 5-46 kV, (Reaffirmed 2001)" on Table 11 has DC resistance values for stranded and solid conductors (Al and Cu) in ohm/km @ 25 °C. You can also try the Technical Data PDF (free to download) from Prysmian...

Hello, I have been looking at the Canadian Electrical Code Ampacity Tables for underground circuits, specifically for direct buried installations (Tables D12A to D13B), and I have not been able to find what soil thermal resistivity the calculations are based on. I am working in a project (in...

Hi everyone, The reason I am consulting you is to ask if you know if there is any limitation or restriction given by NFPA 20 or NFPA 70 (NEC) for the power supply configuration of an electrical driven fire pump; I mean if it matters if it is Wye solidly grounded or Wye grounded with a NGR. I...

Hi everyone, I've read a little more about this and as many of you replied, there is no “easy” factor to be applied against the cable’s ampacity. I should study every single cable configuration to determine which is the maximum current that can flow through each cable without harming its...

Hi, Thanks for your response. From the NEC 2008 Table B.310.8 "Ampacities of Three Triplexed Single Insulated Conductors, Rated 0 Through 2000 Volts, Directly Buried in Earth Based on Ambient Earth Temperature of 20°C (68°F), Arrangement per Figure B.310.2, 100 Percent Load Factor, Thermal...

Hi everyone, If I know the ampacity of a given cable directly buried, provided the conductor's temperature, thermal resistivity (RHO), soil temperature, etc, is it possible to calculate a factor in order to determine the new ampacity when only the RHO has changed? The rest of the parameters...

Regarding Slava answer I have a question: If the ANSI 21 function is used as a backup protection, why the first zone should be set with 0 second delay? Shouldn't it be set with enough delay so that other primary protection, such as differential, trips in case of a short circuit? Thanks, Guillermo

Sorry for the delay on responding. I would like to thank everyone for your support. I really appreciate that. Thanks, Guillermo

Hi everyone, I have been doing some research on generator protection and I have found that in some protection schemes the distance function (ANSI 21) is used as a backup protection. I am having trouble to understand its philosophy (e.g. where should CT's be placed: before or after the...

I have a question about the impedance value in percent that is found on transformers under IEC standards. As I understand a 32/40 MVA ONAN/ONAF, 20/6.9 kV with and Z=12%, had its impedance refered to lowest power rating, 32 MVA in this case. For ANSI transformers the previous is true, but I...