Tek-Tips is the largest IT community on the Internet today!

Members share and learn making Tek-Tips Forums the best source of peer-reviewed technical information on the Internet!

Register Log in
  • Congratulations TugboatEng on being selected by the Eng-Tips community for having the most helpful posts in the forums last week. Way to Go!

Recent content by wattyeng

  1. wattyeng

    VFD In-rush current

    Why don’t you enquire with the VSD OEM? - do they have a support Engineer who can go to site and check config? He will likely know within an hour what the problem is and can test output As others have suggested, it’s likely a settings issue in config but best sorted actually stood in front of...
  2. wattyeng

    Determining the Short Circuit Current Rating (SCCR) of an unrated panel that has power and control

    bdn2004 - yes agree - with BSEN61439, if the control panel is small and fits within the exempted criteria, then no S/C withstand needs to be assessed / calculated / tested, provided the supply network at the POC is also less than stated exemption limits - it is not acceptable to install a 10kA...
  3. wattyeng

    Determining the Short Circuit Current Rating (SCCR) of an unrated panel that has power and control

    The panel must be considered in its entirety - the fact it has different internal sections (form types) for power and control is irrelevant for certification, certainly against BSEN61439 Your extract from NEC409 references purely control panels (purely PLC + I/O etc, no power devices such as...
  4. wattyeng

    Determining the Short Circuit Current Rating (SCCR) of an unrated panel that has power and control

    in the UK, Control Panels have to undergo S/C withstand analysis checks too, in accordance with BS EN 61439 (also in the EU generally) Unsure what NEC provisions are, but from a safety point of view, you need to know this panel will safely stand the effects of a short circuit at the point of...
  5. wattyeng

    Do you delay tripping on low oil? How long?

    stevenal - yes, I read your question and answered it - it reads that you are specifying a low level trip delay on a transformer and the OEM who is quoting it, has questioned that function the only persons who can give you that accurate and detailed response is the transformer OEM - they have...
  6. wattyeng

    Do you delay tripping on low oil? How long?

    You would only delay any functional trip application if: > it is safe and reasonable to do so > it is marshalled and presented via SCADA etc to someone who can evaluate the situation > it is part of the design spec Many conditions can momentarily slip out of tolerances or limits during normal...
  7. wattyeng

    How would you calculate the amount of power utilized in a typical coal mining process?

    You would calculate the same as you would for anything - gather all appropriate data and do the maths! I.Eng MIMMM MIET MIPowerE AIOSH
  8. wattyeng

    Transformer sizing

    Your basic analysis shows no, it isn’t from a max load perspective Your new CNC machine will have a design loading profile, which may have diversity and therefore will not take full load, all the time Check the transformer design spec, including the oil - all transformers allow some overloading...
  9. wattyeng

    1/2 Cycle Momentary Symmetrical vs Asymmetrical Fault Current can you clear up the confusion?

    Symmetrical faults have no asymmetry - they are the most onerous RMS currents but in practice are rare Asymmetrical faults are far more common (system fault imbalance) and produce the highest peak values (during the sub transient period) - the extent of asymmetry decay is a product of system...
  10. wattyeng

    1/2 Cycle Momentary Symmetrical vs Asymmetrical Fault Current can you clear up the confusion?

    Symmetrical and asymmetrical are quite different - a symmetrical fault, with no dc component maintains symmetry around the x axis - an asymmetrical fault, with dc component due to X/R, has highest peak during sub transient period (first half cycle) with asymmetry decay in accordance with system...
  11. wattyeng

    Portable generator versus grid. How bad?

    A domestic single phase gen set randomly paralleled to a live grid would result in many scenarios, from no noticeable result to catastrophic failure of the set, dependant upon phase difference at moment of paralleling A large 3 phase set - spectacular 💥 if not synch’d properly! I.Eng MIMMM...
  12. wattyeng

    1/2 Cycle Momentary Symmetrical vs Asymmetrical Fault Current can you clear up the confusion?

    Sub transient component xd” of AC short circuit current is the initial short circuit period - the X/R ratio of system defines the dc component, hence severity of asymmetry and decay - sub transient value xd”, is used to correctly specify switchgear ratings I.Eng MIMMM MIET MIPowerE AIOSH
  13. wattyeng

    Purpose of 87N Circuit

    87N is restricted earth fault protection REF It is restricted to the zone protected - normally transformer LV winding and LV cable feeding the LV switchboard - the NE link and CT will be sited in the LV switchboard incomer, some distance from the transformer I.Eng MIMMM MIET MIPowerE AIOSH
  14. wattyeng

    Transformer In rush current

    Inrush current (worst case) can be calculated and would be used in design spec for core bracing etc There is no IEC60076 requirement to physically test it - there are many variables involved to get WC - it could be done if absolutely required, but unsure why anyone would want to I.Eng MIMMM...
  15. wattyeng

    Size of dc CAP

    Increased voltage rating - ok Increased 10x microfarad rating - depends upon circuit application and config I.Eng MIMMM MIET MIPowerE AIOSH
See more

Part and Inventory Search

Back
Top