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  1. dkle40h

    Synchronous Motor Protection

    Thank you for the comments. It would appear after my investigations that the majority of the top-end motor protection relays offer very similar protection features. Still remain at a loss to successfully adjudicate the best relay in terms of protection features, ease of programming...
  2. dkle40h

    Synchronous Motor Protection

    Hi, I am busy with a project to install new switchgear to supply two 2500HP, 6300V Synchronous Motors. As part of the project I thought of including a motor protection relay to provide stator protection for the motors, to complement the Multilin SPM (Synchronous Motor Protection) relays...
  3. dkle40h

    Maximum Voltage across CB Contacts?

    Thank you for the comments and my apologies for the delayed response. I was referring to the maximum system voltages that can develop across the single phase contacts of a three phase breaker. For a phase to phase short circuit, two sets of contacts are in series so as they open to clear the...
  4. dkle40h

    Maximum Voltage across CB Contacts?

    Hi, What is the maximum voltage that can develop across the contacts of a three phase circuit breaker? This may seem like a trivial question at first but please give it some thought. Assume the circuit breaker feeds a load from the secondary side of a three phase, 11kV/550V, delta-star...
  5. dkle40h

    Siemens circuit breaker 315 A,400 V

    hi, I would like a to ask for a little more information. Are you using the circuit breakers in a TN earthing system (solid earth) or an IT system, where the star point is earthed through a high impedance? Does the fault appear to be on a single phase? Regards
  6. dkle40h

    Proximity of O/head line to Water Pipeline

    Hi, Does anyone know how to quantify the effects of an o/head power line running adjacent to a pipeline? I have heard that the power line can change the corrosion patterns of the pipeline. I am busy designing an overhead line and was hoping to run the servitude adjacent to the servitude of...
  7. dkle40h

    Induction Motor Protection

    ESW, thanks for your comments. I will look into the stiffness of the supply - good point. The procedure is to use the first pump to unblock the line with water only, to loosen the slimes, and only once it is running do they start the second and then finally the third pumps. I have requested...
  8. dkle40h

    Induction Motor Protection

    Sorry, I must mention that the motor manufacturer's have recommended that we use DOL starting, rather than star/delta?! Their reasoning is that the on switch-over the stator field momentarily weakens, and then when connected to a higher voltage (line voltage with Delta) the motor experiences...
  9. dkle40h

    Induction Motor Protection

    Hi GordS. Yes, the numbers given are correct. We expect a starting current of 6.9 times FL (290A) for the majority of the starting period. Given the difficulty to clear the line the motor is heavily loaded during this time. My opinion is that the protection should be set so that the...
  10. dkle40h

    Induction Motor Protection

    I would appreciate any information on motor protection, right back to the basics. We have recently blown our second 220kW, squirrel cage induction motor in a slimes pumping operation. We have three pumps running in series to generate the required pressure head. When the slimes settle it is...
  11. dkle40h

    Insulator Pollution Flashover Problems

    Thanks for your responses Cuky, I have found them very useful. Our system voltage is 66kV. I am still of the opinion that I will have to do a thorough analysis of the faults in terms of climatic conditions at the time of flashover, which phase (left, centre, right), time of day, location...
  12. dkle40h

    Insulator Pollution Flashover Problems

    Thank you all for your comments and advice. I have looked into a number of avenues and am going to analyse our flashovers, looking for any trends to confirm a particular problem, and then tackle a costing exercise. Do they use similar methods to combat the carbon deposits on insulators in and...
  13. dkle40h

    Insulator Pollution Flashover Problems

    I am experiencing polluion flashover problems across substation bushings and line insulators. The HT components are situated in a mist belt, on the coast, in a dry windy, semi desert environment - certainly not the best conditions. I am considering "live" spray washing but am...

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