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Recent content by Gr8blu

  1. Gr8blu

    Motor control via VFD using V/F ratio in Squared mode

    Muthu - Affinity laws. For a given pressure or velocity, we either have k = (power squared) / (speed cubed) OR k = (power) / (speed squared). At half speed (= 0.5 pu), the required power for a typical centrifugal fan is (0.5 * 0.5 = 0.25 pu).
  2. Gr8blu

    NFPA 70E-2018 and IEEE 1584-2018

    The simple answer to that is ... not likely. Usually, the 70E document gets updated in the subsequent (or subsequent plus one) revision cycle - which means it would have to occur AFTER 2018 since the subject IEEE standard was not available UNTIL 2018.
  3. Gr8blu

    Motor control via VFD using V/F ratio in Squared mode

    Muthu The drive acts to limit current - which means it is typically set to maintain a specific value. The copper loss does not change (much) when operating at reduced V/Hz because the CURRENT DOES NOT CHANGE. The POWER at a given speed point changes but that is because the VOLTAGE is changing...
  4. Gr8blu

    IEC world - GCB in Medium Voltage Switchgear, surge capacitors & lightning arresters placement

    A "p5/6" winding means the PITCH of the winding (which is the amount of circumference spanned by a single coil) is approximately 5/6 of the span of one pole, or about 83% of the POLE PITCH. Example: machine has 6 poles and 72 slots. A winding pitch of 100% (i.e. p6/6) would have the top leg of...
  5. Gr8blu

    Looking for IEEE or Industry Standards Supporting Use of Current-Limiting Devices

    The two standards you mentioned (IEEE 242 and 141) DO NOT explicitly recommend using CLP devices. However, they DO provide guidelines for their effective use in terms of how to specify the CLP device and how to implement it appropriately within the electrical system. The reason they do this is...
  6. Gr8blu

    Calculate 3-phase current sum of single-phase loads

    Ryre - read the first line of the post again. As seen by the upstream power source, KW plus KW equals KW, no matter whether the loads are single phase or three phase. The method works REGARDLESS whether the loads are single or three phase. Let's look at your layout again. Four of the five...
  7. Gr8blu

    Heat treatment steel 4140 stress relief.

    absaul02 Our processes use ovens all the time - as in 24 hours a day, 365 days a year. Generally speaking, the volume of a 4m x 4m x 3m oven (properly gas-fired) can reach operating AIR temperatures of 500 C in roughly 70 minutes. The PART temperature takes longer - but for something the size...
  8. Gr8blu

    Calculate 3-phase current sum of single-phase loads

    As seen by the upstream power source, KW plus KW equals KW, no matter whether the loads are single phase or three phase. Current does not behave the same way. You need to first add all KW, divide that result by the phase-to-phase voltage, and divide again by the square root of three, in order...
  9. Gr8blu

    Heat treatment steel 4140 stress relief.

    Agree with mfgenggear. By the way - that is a very poor representation of how the part is designed/actually looks. The right-hand oval should be oriented vertically, not horizontally - or placed above/below the left-hand image if the orientation is not changed. Take a look at "third angle...
  10. Gr8blu

    2400V startup of long idle motors

    If you're going to be testing the machine windings from the panel, you're going to have to disconnect the caps anyway. So, they are already a separate entity. Test caps (in groups, or as individuals) per the steps outlined by Bill (waross). And regrease the bearings. If these machines have...
  11. Gr8blu

    Is stranded wire inferior to solid core wire in this situation?

    I apologize, Bill. I am so used to rating ampacities for high temp environments I automatically derate everything ... you are correct. AWG 12 and 10 are FAR more common in residential construction at these current levels ...
  12. Gr8blu

    Viable masters degree for me?

    Industrial Engineering: engineering that deals with the design, improvement, and installation of integrated systems (as of people, materials, and energy) in industry To be really good at what they do requires that an industrial engineer have at least a working knowledge of the science and...
  13. Gr8blu

    Motor control via VFD using V/F ratio in Squared mode

    Almost all motor-driven process applications fall into one of three possible torque profiles. 1) CP (constant power). The motor produces the SAME power at all speeds. 2) CT (constant torque). The motor produces power that is LINEARLY proportional to the speed. 3) VT (variable torque). The...
  14. Gr8blu

    Is stranded wire inferior to solid core wire in this situation?

    Pulling 15 or 20 A for house wiring means using either AWG #10 or AWG #8, depending on the "safety" factor. For both of these sizes (in North America), the commercially available standard is a 7-strand construction, not single strand. This could be why you are being stuck with a "minimum...
  15. Gr8blu

    Screw pump price research

    A quick internet search gives results anywhere from $US 3500 to just under $US 20 000. The price is directly related to the size of the pump - which means the pressure and flow requirements. A higher pressure and/or more flow means more money. Note that these prices were from eBAY, which may...
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