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  1. motorspert

    Frequency conversion for Steam Turbine Generator

    Hi Sakaran, There is one possible solution that hasn't been discussed, a bit off the wall. How about leave the generator as it is and fit a static frequency converter (VFD). A 3MW drive isn't cheap but it will allow your client to deliver an extra 400kW so may pay for itself in time (;provided...
  2. motorspert

    Condensation in explosion proof enclosure

    Hi Mike The enclosure is aluminium and I assume the gland is brass? The moisture is causing galvanic corrosion between the two materials and aluminium being the anode is corroding. There is a galvanic voltage of 0.5V between the two materials. An aluminium gland would solve this problem if such...
  3. motorspert

    Intermittent Generator Differential Fault

    Hi John, Goof question, and I'm not 100% sure, but normally diff CTs just feed a differential relay and phasing shouldn't matter. But for a multifunction relay, I would imagine they should be ok. If you swap all 6, the phase sequence will be the same.
  4. motorspert

    Intermittent Generator Differential Fault

    Hi A quick check (if you are unable to complete the checks suggested by DTR2011 or Hoxton) would be to swap the CT's between B and C phases. If the 'fault' then swaps to B phase, you know its the CT's, if it stays on A phase then it's either the winding (unlikely from your other checks) or the...
  5. motorspert

    Motor water to air heat exchanger tubes - 70/30 or 90/10 CuNi ?

    Hi Edison You don't say why the heat exchanger needs replacing. Assuming it's not a corrosion problem then either material would be ok, I personally would go for the Cu/Ni as it's readily available and relatively inert (90/10 CuNi is specified in the majority of end user specifications. The...
  6. motorspert

    Surge test on generator field coil

    @petronila - thanks for your comments, thats's useful information - they are new coils and this may be a test that some OEM's perform. I will let you know how it goes. @scottyuk et al - we are just proof testing a new set of coils, we normally test for interturn faults bt applying 220V 400Hz...
  7. motorspert

    Surge test on generator field coil

    Thanks guys All useful info. We will do them away from the rotor, so that sounds like it could work. I share your nervousness electricpete but am also keen to experiment! So, we will take it slowly. Luckily it's bare copper so we can put a scope on pretty easily.
  8. motorspert

    Commutator Undercutting and Chamfering

    With regards brush seating grit, we have always been told to use 100 grit if the surface is highly polished. A wise old engineer once told me that too highly polished surface causes problems building a skin on the surface which can lead to high brush wear. We work to an ideal surface finish is...
  9. motorspert

    Surge test on generator field coil

    Hi We have been asked to perform a surge test on some salient pole field coils at 1500V. I am familiar with voltage drops using an AC supply at 50/60hz. Also aware of tests at higher frequencies (400Hz). But should I be concerned that user a standard surge tester (Baker type) we will overstress...
  10. motorspert

    Dilemma about the rotation of GEC dc motor

    Hi jog reverse means rotating in small increments in the revers direction ie iF you had a crane motor jog reverse would be used to move the crane in small steps (jog) when close to the object. I am afraid this doesn't tell us what the direction of rotation is unfortunately.
  11. motorspert

    Submerged Motor

    Search for submersible motors, some are designed as 'wet type' and run in water http://m.youtube.com/watch?v=2mVteXOBo0Y
  12. motorspert

    magnetic wedges against efficiency

    How old is the machine? You may find a modern insulation system allows more copper to be used and this would be more beneficial than the mag wedges. Its difficult to quantify without knowing generator details. Why the need for a rewind? IS the core ok?
  13. motorspert

    Sealed winding conformance test / submersion test

    Hi Pete I have been involved a few times (as a vendor). If its VPI and has been well impregnated it should be ok. Main problem area was the cable exits from the coil ends water seeps in the joints and fizzzzzzz. The otehr problem we had (a long time ago) was rust at back of core - make sure...
  14. motorspert

    AC Motor Supply Wye Delta

    jlamann Firstly, the harmoncs are internal, they will not be seen outside the motor and you will not need any filters - apolgies if I have mislead you. The effect will be second order in terms of temperature rise and motor efficiency, the motor designer will incorporate this into the design...
  15. motorspert

    AC Motor Supply Wye Delta

    I think the motor vendors would prefer three wire star connected. When connected in delta there will be third harmonic currents circulating which need to be considered in the design. If star connected, these currents cancel out and can be ignored. These affects are negligible on smaller motors...
  16. motorspert

    66kV VT connection

    Hi We are trying to connect a cable from a 66kV bushing to a VT bushing. The clearances to earth are considerable and so a bare uninsulated copper bar or cable would suffice. But as the installation is outdoors and coastal we thought we would offer some environmental protection for the cable and...
  17. motorspert

    Sizing unit transformer

    I think I agree with Scotty, the transformer losses wouldnt be as high as 5%. I would specify 7.5MVA though, seems a good size. But tell the Tx manufacturer what the starting regime is, starting current, duration of start and frequency of starts etc. If the power factor is really going to...
  18. motorspert

    UK embedded generator neutral earthing

    http://www.energynetworks.org/spring/indexpages/enaindex_ndate.asp Electrical netwoks association, they used to be part of the CEGB once upon a time, now they issue the G59 G5/4 pubilcations etc
  19. motorspert

    UK embedded generator neutral earthing

    In my opinion, you are right. If you earth the two neutrals then you will have circulating third harmonic currents which will overheat the NERs and the generator windings. If your colleagues ar unconvinced, then there are a numer of power books that may be of use. There may be some papers on...
  20. motorspert

    Water Cooled Machine IC81W

    If the generator is at full load the losses are 44kW. My experience 90% of that will be taken by the water. leaving around 4-5kW loss into the room. I was once told a rule of thumb that the heat loss was the centre height (in mm)/100. ie for a 710 machine it is approx 7.1kW. Its arbitrary and...

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