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  1. RalphChristie

    Catenaria and Panto - huge problems.

    Gunnar: I used to work a lot on pantographs - more on haul trucks than on trains - but the same should apply. In the summer-months we operate during quite high temperatures (ambient more than 40˚C easily during the day) but heat-wise we did not really had problems. I would have looked into two...
  2. RalphChristie

    CT Magnetizing current

    Scott: Thanks a lot for your answer. From a field perspective I thought I knew enough, I've tested a lot of CT in my career and I've used a lot of CT information to determine settings for protective schemes (for instance REF-protection when mentioning Class X CTs) - but never really thought...
  3. RalphChristie

    CT Magnetizing current

    Hi After a discussion I've realized I had a lack of knowledge on CTs - any specifically on specifying the magnetizing current of a Class PTX (X) CT, thus an CT been used in the IEC-world. In a class X CT the performance is defined in terms of a knee-point voltage and the magnetizing current at...
  4. RalphChristie

    Substation authorization

    Thanks for the responses, David and Zogzog: To answer your question Zogzog: Voltage up to 66kV present in the yard, although only up to 11kV present inside the buildings. No exposed live parts in the buildings, and outside all exposed live parts are out of reach. Thanks Regards Ralph...
  5. RalphChristie

    Substation authorization

    It is my responsibility to declare people authorized to do work in substations on our mine. Normally it is not a problem, the persons working in the substations is qualified electrical artisans, they do get some training on the safety, the relevant procedures, the operating principles, the...
  6. RalphChristie

    Design of zig zag earthing transformer in an 11kV system

    I am not really familiar with generators or with generator-grounding, but I suppose it might use the same guidelines as applying a zig-zag transformer to a Power transformer. The first step is to decide how much ground fault current you want to allow. If you plan to solidy ground the...
  7. RalphChristie

    SETTING THE BIAS FOR A TRAFO DIFFERENRIAL SCHEME

    gbk: Thanks for the correction. The first setting is indeed not for inrush but for the magnetizing or energizing current. Regards Failure seldom stops us, it is the fear for failure that stops us - Jack Lemmon Make the best use of Eng-Tips.com Read the Site Policies at FAQ731-376
  8. RalphChristie

    SETTING THE BIAS FOR A TRAFO DIFFERENRIAL SCHEME

    The bias setting is used to ensure stability during external faults/conditions while the relay is still sensitive for internal faults. Settings depends on: Type of relay, (electromechanical, static, electronic etc) If a Tapchanger is present or not. (especially for an on-load tapchanger) Type...
  9. RalphChristie

    Design of zig zag earthing transformer in an 11kV system

    Hi Do you want to change an ungrounded system into a grounded system? Regards Failure seldom stops us, it is the fear for failure that stops us - Jack Lemmon Make the best use of Eng-Tips.com Read the Site Policies at FAQ731-376
  10. RalphChristie

    using single-phase transformer in distribution feeder

  11. RalphChristie

    Bus Zone Protection On Open Conductor Site

    Yes, yes, you are quite right - if there is a element on each phase. Although I can't see any real advantages in doing it on such a way. Regards Ralph Failure seldom stops us, it is the fear for failure that stops us - Jack Lemmon Make the best use of Eng-Tips.com Read the Site Policies at...
  12. RalphChristie

    Bus Zone Protection On Open Conductor Site

    That would be the first time I've even heard about a bus zone scheme connected like that. You sure the reversed CTs were not incorrectly marked? Can't see how such a scheme will stay stable, especially when loaded. Regards Ralph Failure seldom stops us, it is the fear for failure that stops us...
  13. RalphChristie

    using single-phase transformer in distribution feeder

    Do a search for SWER (single wire earth return) on this site or on Google. Also check http://www.ruralpower.org/ I mention SWER specific because it is used (many parts of the world) in rural areas with a low population and density. Some advantages and disadvantages of SWER-systems: Advantages...
  14. RalphChristie

    SEF protection

    Slavag: In the new SEL-relays we are using, directionality is an option, but we do not use it. The cables always stay the same length - 1000m - a cable-reel is installed on each machine for propel (travel) issues. Regards Ralph Failure seldom stops us, it is the fear for failure that stops...
  15. RalphChristie

    Secondary concentric neutral terminations

    I also prefer Marmite's method. http://tinypic.com/view.php?pic=4vn0som A picture taken of a damaged 630mm² singe-core cable due to circulating currents. The cable was installed and grounded at both ends, no-one considered circulating currents, and it was probably energized for two weeks...
  16. RalphChristie

    Standby earth fault protection

    I haven't seen standby schemes on solidly grounded transformers before, thanks for the correction. Lesson learned! Raghun: Thanks Regards Ralph Failure seldom stops us, it is the fear for failure that stops us - Jack Lemmon Make the best use of Eng-Tips.com Read the Site Policies at...
  17. RalphChristie

    CT change and accuracy

    The reason for specifying Class PX CTs, are to ensure that the kneepoint and anklepoint voltages are the same. Class PX CTs are used in differential schemes, thus the composite errors will be much smaller than normal Class PR CTs, even at lower ranges. You can use a much lower setting with a PX...
  18. RalphChristie

    Transformer Differantial protection

    Try to determine what was the intentional use for the interposing CTs. Aside from Raghun's comment: Due to the British influence, many of the former British colonies used a combined REF and differential scheme, including interposing CTs, for transformer protection. By taking the interposing CTs...
  19. RalphChristie

    Transformer Diff. Tripping

    Most probably CT-saturation. Do a mag-curve on each CT and compare the results. Can you give a little more info on your system? Old or new installation, type of CTs, type of relay, etc, etc. It is quite difficult to give a meaningful answer with almost no information. regards Ralph Failure...
  20. RalphChristie

    High Resistance Grounding in 15kV Above Application?

    nightfox1925 The highest voltage I have seen using high-resistance grounding was 11kV. I have once come across it in an underground mine. This was a flame-proof mine, and I think this was the reasoning for using such a grounding-system. Another reasons for using high-resistance grounding in...

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