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Let me rephase my question: I am to install a STS (static transfer switch), in the upstream we only have one supply and one generator...I am planning to use a 3 pole STS instead of a 4 pole STS...(since we dont need to switch the neutral because there is only one generator)...Am I right...

To do with Tier 1, 2, 3, 4 requirements? When dont you need to switch the neutral??

Hi, Can someone clarify for me...when can we select a 3 pole STS over a 4 pole STS unit? Thanks Allan

Thanks for that..as with naming convention..what is the best/recommended naming of double neutral... e.g 5 *1C 185mm^2 + E (XLPE/PVC) CU cable or e.g 3 *1C + 2N 185mm^2 ...etc

Hi, I am wondering if anyone can give me advice on when to use double netural cables for building services: eg...data centres (with harmonics) is the only one I am thinking about. To take it to the next step...what is the deciding factor of using double netural cable and how you can calculate...

HI, Does anyone have a link to a spreadsheet to sizing swithboards and cables. Thanks

For confirmation: Steady state fault analysis give you the maximum and minimum fault current that can be reached. So what does transient fault analysis give you? Thanks

Is it true that only recently breakers are rated for symmetrical amps and a maximum x/r? Because there are still lot of books still refer to asymmetrical rms values.

Thanks jraef But why whould the manufacture publish symmetrical interrupt ratings and not asymmetrical? Since symmetrical current is found in steady state and asymmetrical is the transeint part in the short circuit currnet with the sum of DC component. Hence asymmetrical is usually bigger then...

Waross, Thanks for you post, however wht you telling me i already know...no need to search the forum. Wht i want to know, which i am still not getting it, is that: By using SKM, I obtained an asymmetrical rms value of 50kA at 0.5 cycles, and then I look at my circuit breaker it tells me Imax...

Hi, I looked at a few circuit breaker catalogs and I want to verify what the catalogs are saying: For a 630A circuit breaker at 11kV network, the Ip or Imax is 50kA. Is this value the rms value or the peak value? Thanks

Can you expand more on the purpose of minimum currents for protection settings. thanks

Hi, I am performing fault analysis to rate protective equipment in one of our stations. Is it necessary to find the minimum fault current? My point is, isnt true that you only want to know the maximum fault current so your protective equipment can be rated above this level. So how does...

Hi, the above question should be made clear as follows: I know that from steady state fault analysis, it gives you the maximum and minimum fault levels which sets a benchmark for rating protective equipments. But how will fault 'transient' analysis help in rating protective equipments.

Hi, I am performing fault analysis using SKM. Books often associate fault methods by finding thenevin equivalent and then using ohms law to find the fault current. And thats what i have been doing. Are the results then steady state values. If so, how would transient analysis come into fault...

Hi given, impedance for a 12.5kV generator z1 = 0.0016 + j0.15 z2 = 0 + j0.18 20 = 0 + 0.1 obviously there is a x/r ratio for z1, but how about z2 and zo. I am using SKM power tools to represent this generator. And it ask for x/r ratio for all impedances? Thanks

Hi, Should the fault results be the same if i use these two methods: 1. bus admittance matrix 2. hand calc by using Thevenin equivalent sequence circuits Thanks

Hi, If the manufacture only provides positive sequence impedance for a 3 winding core type, 12/11/0.415kV transformer with out giving the zero sequence impedance, what approximation can I take? Any links or doc that I can refer to will be very much appreciated. Thanks

Hi, I have performed fault anaylsis using SKM, the results obtained is quite interesting... The biggest initial symmetrical current is LLG 19.5kA followed closely by SLG 19.36kA However the highest asymmetrical current is SLG 47.5kA and 46.6kA for LLG fault. Why is this reverse? Dont know...

Correction... it should be LLG (double phase to ground fault) not LL.... Why is LLG bigger than 3ph fault? Because of low zero sequence impedance from generators and transformers? Thanks