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  • Users: ZeroSeq
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  1. ZeroSeq

    3C Teck Cable Shield Ground

    Hello, Recommended practices and calculations for cable shield grounding and induced voltages are readily available for single conductor cables. However, I'm finding a difficult time in finding a similar reference or standard for 3-Conductor or trefoil cable arrangement (e.g. Teck). Does anyone...
  2. ZeroSeq

    11th Harmonic Only

    Hello, I have an interesting current waveform at an industrial facility that appears to be quite sporadic (potentially occurring only once or twice a week), which very clearly has high harmonic content. This oscillography is only captured as there are fairly sensitive alarm elements programmed...
  3. ZeroSeq

    Y-Yg with buried Delta tertiary - Secondary Ground Fault

    Hello, For a Y-Yg transformer (primary floating, secondary solidly grounded), a secondary ground fault will have no current flow as there is no path on the primary windings for the necessary congruent current to flow. However, will this still be the case for a transformer with a buried delta...
  4. ZeroSeq

    Mudjacking leading to significant shift

    Hello, Two years ago, I had a part of the slab of my house hydraulically jacked based on a recommendation of my contractor who was constructing a new bathroom. The following year, we had a significant amount of rain, resulting in a raising of the slab by over 2". Aside from the obvious...
  5. ZeroSeq

    Stamp / Seal on Study Work

    Hello, I'm wondering if anyone knows off the top of their head or can point to the specific engineering act clause stating what work *specifically* requires the seal of a professional engineer. The work I'm looking for clarification on is some technical study work not related to any type of...
  6. ZeroSeq

    Transformer Saturation Margin

    Hello, I have scoured my technical documents regarding transformers and have not been able to find an answer to the below question. I am wondering if anyone would have an answer or direction to the following: For distribution transformers (~20-50MVA base), how close to the knee point is design...
  7. ZeroSeq

    UL 508A short circuit calculation

    Hello, I am looking to provide a rating for an industrial control panel with solid state relays (using UL 508A Supplement SB). I've been unable to find a reference to which standard the "available short circuit current" must be calculated. When rating gear and breakers, it is obvious - ANSI...
  8. ZeroSeq

    Time-Variant Current w/ 51 Element

    Hello, I have a question regarding a typical 51 element's response to a decaying AC current. If I were to have a decaying AC (no DC or asymmetrical component) current and a standard ANSI inverse overcurrent element, would you assume the best way to calculate the time to trip is using an...
  9. ZeroSeq

    SCIM dynamics during loss of utility

    Hello everyone, I've been pondering the following scenario, and after modeling it in ATPDraw, I'm not exactly trusting my results: Immediately following a utility outage at an industrial facility, will a squirrel cage induction motor's stator voltage (air gap flux) and its slip (rotor speed)...
  10. ZeroSeq

    LV Breaker "Current Sensors"

    Hi everyone, I have searched this topic far and wide and have been unfortunately unable to acquire it, even directly from the manufacturer: Does anyone happen to know the technical specs (ratio, excitation, burden, voltage rating, etc.) of the "current sensors" which are used for the...
  11. ZeroSeq

    Future of oil and gas industry in Canada (specifically Alberta)

    So being an Albertan and an engineer in the oil and gas sector, I thought I would probe eng-tips to get everyone's take on the future of the O&G industry in Canada. We've seen these downturns many times before, and usually the recovery begins just a few years after, with the good boom times...
  12. ZeroSeq

    Circuit unbalance code stipulation

    Hello all, I have a basic question regarding low voltage branch circuiting. (moved from Motors section) Would anyone be able to point me to a code stipulation (NEC) which requires a minimum amount of balance within a three phase branch circuit? For example, if I had a three phase branch...
  13. ZeroSeq

    Motor cooling as function of speed

    Hello all, I have been scouring the internet including as many threads as I could find in relation to motor cooling as a function of speed/frequency. I cannot find it in any motor protection standard or white paper across multiple manufacturers (including IEEE stds, GE industrial practice...
  14. ZeroSeq

    Incorrect Ground Current Measurement

    Hello, I've had a ground fault in my system for which an event recorder (SR750) is giving me ground currents that are not possible. This is a 6900V delta system with a 400A (10ohm) neutral grounding resistor. The phase and ground currents shown from the recorder are as follows: A = 2810A B =...

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