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  1. jimmy2times

    failure of compensation cable wiring insulation

    The insulation is supposedly meant to be good for up to 150degC. I was reading elsewhere that moisture at the thermocouple junction remote end can affect insulation throughout the whole cable length? It was only a reference in passing though and no further references elsewhere saying same thing
  2. jimmy2times

    failure of compensation cable wiring insulation

    does any one have a view of the reason for insulation failure of compensation cable in photo attached. analogue input module with k type compensation cable. insulation seems to be failing in many cores in random places.
  3. jimmy2times

    Single Point Failure Modes

    Not saying it’s perfect but your could look to offshore dynamic positioning vessels to see how / how not to design when operating a closed bus system. More savvy vessel owners will demand verification of things like short circuit testing of main bus, simulated failures etc. each year vessels...
  4. jimmy2times

    Generator OV trip

    We have two identical MV generators on ship, 9MW each, after long period of maintenance we return to service. On paralleling they both trip on over volts. Then we test one on its own, sometime it trips on over voltage when energise mv/lv transformer (no other load on generator or secondary of...
  5. jimmy2times

    Transformer energisation restriction

    There is next to no information on the pre-mag transformer, I’m still trying to search if anything exists. I will get back in touch with supplier next week to see if they have history on it
  6. jimmy2times

    Transformer energisation restriction

    Hi prc, I've now obtained copy of C.57-142 2010. I see it states "Users of switching devices switching transformers that are inductively loaded (that is reactor loads, or stalled or accelerating motors) or those operated on a frequent basis (daily or weekly) should strongly consider transient...
  7. jimmy2times

    Transformer energisation restriction

    Surge arresters are fitted at MV switchboard feeder, in cable compartment
  8. jimmy2times

    Transformer energisation restriction

    Thanks gents Yes switchgear is VCB The transformer is insulation AC20kV and LI 60kV Prc, I looked at part 11 of IEC60076 and could not find anything further than what you already quoted in the standard. What would be the transformer manufacturers response to a purchase order inquiry that...
  9. jimmy2times

    Transformer energisation restriction

    Itsmoked, that’s what I was planning to do next. Take transformer offline, let it cool down to ambient and then energise (without pre-mag transformer). Then shut down after 1min. And see what the temperature profile looks like. Then I was going to try and load transformer to as high as...
  10. jimmy2times

    Transformer energisation restriction

    Yes, winding RTDs fitted Good thinking on using pre-mag system regardless what spinning capacity is on line. Surely better for transformer life anyway
  11. jimmy2times

    Transformer energisation restriction

    Sorry, I should have said upfront. Transformer is dry type
  12. jimmy2times

    Transformer energisation restriction

    Pre-mag transformer has S2 intermittent duty, Specification states:- On 10ecs Isec = 150A, then On 15secs Isec = 10A Off 215secs Then follow by break at least 15mins
  13. jimmy2times

    Transformer energisation restriction

    It’s a ship’s distribution transformer. 6.6/0.45kv, feeds general ships loads. Part of redundant pair, one feeds port bus, the other starboard bus. so typically each transformer carries less than 50% load. If one transformer were to fail, other could supply both port and starboard bus loads...
  14. jimmy2times

    Transformer energisation restriction

    I’ve picked up an operating procedure implemented some years ago that recommends a period of 12hrs before a transformer is re-energised after in has been shut down. Nobody knows why this restriction is in place, I contacted manufacturer also they didn’t have any restrictions on how often and...
  15. jimmy2times

    decay time to safe touch voltage

    thanks. yes I was setting myself up for some of those flippant remarks!!! ha! extract of a paper i have, can't share sorry, suggests charge could stay trapped in capacitance of transformer winding for days. The short time constant set up by the body's resistance (at point in time, worst case...
  16. jimmy2times

    decay time to safe touch voltage

    how would you calculate the time for a MV conductor to decay to voltage that is safe to touch, i.e. extra low voltage. i'm aware that all circuits must be earthed and proven dead before maintenance/work can take place. but if a feeder circuit breaker were to be opened and not its circuit earth...
  17. jimmy2times

    Brine tank load testing

    Well everyday you learn something new as they say. Today for me was brine tank load testing. I remember when I was younger I listened to an old sea dog telling me how he could replicate fast acting action of a semi-conductor fuse with bucket of water of section of copper wire. Today someone...
  18. jimmy2times

    in situ motor testing

    I’ll have to check with technicians whether they meggered from the switchboard end or whether they dropped cables off at motor terminal box. I think the maintenance task requires cables to be dropped off at motor terminal box but I’ll check with them tomorrow. By in-situ I was referring to...
  19. jimmy2times

    in situ motor testing

    we have 6.6kv induction motor for bow thruster of ship (1.4MW), difficult access for cleaning and removal. we conduct PI insulation resistance measurements and have low PI reading ratio. 1min IR reading is just over 100Mohm though (102Mohm) so not awful by any means. We ran anti condensation...
  20. jimmy2times

    2 speed transition

    So update on above. Introduced dwell timer. Incremental in 0.1secs steps. Residual motor component found to decay to almost zero in 1,25secs. During tests Set timer from anywhere from o.1 up to 2secs. On this particular fan we did not trip circuit breaker in any transitions to high speed (and...

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