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  1. VladimirM

    45kVA transfromer controlled by a contactor

    IMHO that is not very good solution since the transformer will be subjected to frequent inrush currents and hence frequent mechanical stresses. I think it's lifetime will be reduced. Why not to switch the secondary side of the transformer?
  2. VladimirM

    IT earthing on MV and HV systems

    Just for information - in Russia MV networks are 6kV, 10kV and 35kV (50Hz) networks, and almost all of them are isolated from earth. Networks above 35kV (that is 110kV, 220kV, 330kV etc) are so-called "effectively-grounded" - i.e. they are grounded via small impedance, almost solidly. Networks...
  3. VladimirM

    Faults on three-phase motors

    Itsmoked: agree to negative sequence and strongly disagree to 160% and losing its speed. When the load is low or in the idle mode there can't be 160% even if the phase failure occurs. The speed also can't change much in the idle mode since the rotor tends to run after the positively rotating...
  4. VladimirM

    Faults on three-phase motors

    Let us assume the following situation: - a three-phase motor is running with two phases only (one of the phases was opened somehow after it was successfully started) and its speed is approx rated (no starting issues), - its stator current is: Line1 = 100% of FLA, Line2 = 100% of FLA, Line3 = 0%...
  5. VladimirM

    Siemens Robicon perfect harmony

    www.ld-harvest.com is not the only one so similar to Robicon. There are also: www.yaskawa.com www.rxpe.com www.tmeic.co.jp The last one did installed its MV drive in Russia in the city of Toliyatti. I heard there were problems with those drive on the 4th day after start-up due to power cell...
  6. VladimirM

    AC current sensing

    Skogsgurra, thank You for the education.
  7. VladimirM

    AC current sensing

    Hello Slava, VladM is me - I am on www.electrik.org also :-) Best Regards. Volodya
  8. VladimirM

    AC current sensing

    ScottyUK, thanks a lot. Skogsgurra, You mentioned that Rogowski Coil has no leakage reactance. I looked through the operating principle of this device again and I came to conclusions that: 1. Actually there is leakage reactance in the secondary of the Rogowski Coil but since secondary current...
  9. VladimirM

    AC current sensing

    "The CT will struggle below nominal frequency at rated current because of core saturation" That has made a lot of sense to me. I thought through this idea and I had a question to it: does the degree of saturation depends on the secondary circuit ohmic resistance? I mean I came to a conclusion...
  10. VladimirM

    AC current sensing

    No leakage reactance? Wow! I guess I should the operating principle of this Coil more properly. And what can You say about CT?
  11. VladimirM

    AC current sensing

    Yes, but why does CT has only 50/60Hz while RCCS may have (30...6000)Hz or even wider frequency range?
  12. VladimirM

    AC current sensing

    Hello everyone, Would You please explain the following: we have a conventional current transformer (CT) and we have a Rogowski Coil Current Sensor (RCCS). Both use the same principle - Faradey's Law, right? Then why do we have such a narrow frequency range for CT - just 50/60 Hz, while RCCS...
  13. VladimirM

    Siemens Robicon perfect harmony

    I had an experience with ROBICON Perfect Harmony (6kV/1250kW) here in Russia. What can I say? It works exactly as declared by ROBICON. (Now it's SIEMENS, but who cares?) Anyway it seems to me as a very good drive, but the production takes a good deal of time and cost is very high. What exactly...

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