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  1. Parchie

    Short circuit current calculation at MV bus (34.5kV), Tesla Megapack

    @adi 3291, Sorry for the late reply. IEEE has a document on that but IIRC, grid-forming IBRs run around 2 to 3 pu Isc contribution. For grid-following IBRs, that is what I mentioned to be 1.2 to 1.5 pu. LINK
  2. Parchie

    Short circuit current calculation at MV bus (34.5kV), Tesla Megapack

    @adi 3291, IDK if the data you've provided changed. Having 4 megapacks connected to a 4.4 MVA inverter transformer requires you to have 300/4.4 = 75 inverter transformers, not 78. 78 inverter transformers with 4 megapacks per transformer will require 4 X 78 = 312 megapacks, not 310! Still, any...
  3. Parchie

    Short circuit current calculation at MV bus (34.5kV), Tesla Megapack

    At the battery terminals, the short circuit current is only limited by the internal resistance of the battery. At 480VDC and an internal resistance of 20 milli-ohms, you'll have 24 kA. Available short circuit currents from inverters (at the AC side) are in the range of 1.2 to 1.5 times the rated...
  4. Parchie

    capacitor banks and passive filters

    @unnikri57 (Electrical) Please share with us some details like voltage level, prevalent harmonics detected, size and capacity of PCC panel versus cap bank MVA. Gr8blu is correct, reactor in series with a cap will have the effect of filtering harmonics present in the POCC. Whether you need those...
  5. Parchie

    500 RPM 8000 kW hydro generator dimensions

    Too few inputs. Please complete your generator specs. You could find better luck if others will be given ideas about voltage, winding preference, pitch, local environment, etc.
  6. Parchie

    Motor kW Reading

    @Pandit, Correct. If the VFD panel displayed 114.5 kW, it means the power transmitted by the VFD to the motor. Subtract the VFD losses and you'll get the actual power delivered by the VFD to the motor. To consider @FacEngrPE's idea on finding the power delivered at the motor shaft, one has to...
  7. Parchie

    Equipment to solve phase unbalance

    YKC, Please see it this way: if your load amps differ in every phase, naturally the voltage drop in each of the supply line will differ. Even if the source is balanced, the resulting terminal voltage at the point of common coupling at your location will not be equal. That is what @stevenal is...
  8. Parchie

    Harmonic Distortion Limit and Neutral Cable Sizing

    @che12345, Goggle is friend. It could be your too. Go figure. @Edelma_1, The best way to go is hire the services of a third party doing harmonics frequency sweep on your system. We did that. That neutral to phase current ratio hold true if the dominant harmonics in your system is the 3rd...
  9. Parchie

    PFC equipment not registering current use despite working

    Assume that the meter is fine. Check if the PFC unit is really "working". My experience in my other life was that the PFC unit was set wrongly; the PFC unit inserted more capacitors for a certain power factor resulting to over-correction. Then, the contactors were pulling in and then dropping...
  10. Parchie

    DIY Circuit Breaker Current Injection Testing Kit

    Y'all. The power draw should be the amount of power required when connecting the equipment under test plus the test lead resistance plus the load resistance. E.g. a 100A thermal overload relay with have a resistance per pole of about 0.378 milli-ohms, Using a 38 mm2 x 1 meter cable with a...
  11. Parchie

    Harmonic Distortion Limit and Neutral Cable Sizing

    @EdeLma_1, The formula I got is In/Ip = 3 X (per unit THD)/(sqrt(1+(per unit THD)^2) for circuits laden with 3rd harmonics. In = neutral current, and Ip = phase current. I got 45% with 15% THD
  12. Parchie

    level sensors

    OP believes it is best to test the sensor in-situ. That's the main problem. Unless he thinks out of that box, he'll never see that are many ways to do it.
  13. Parchie

    11KV Busbar Sizing

    @SK07, Your 3150A busbar rating @ 50 deg C rating is an overkill, IMO (if there are no future expansions being contemplated). Your expected full load is just half of that. If the install is still on the drawing board, I recommend you downgrade to 2300A (1/2" x 4") or 2750A (1/2" x 5"). The rule...
  14. Parchie

    11KV Busbar Sizing

    @SK07, You haven't posted the temperature at which your installation is designed for. Can you specify if it's for 30 degrees, 50 or 65 degrees C?
  15. Parchie

    Overhead line structure footing resistance measurements

    @KillBill7, We have the same problem in my other life. What we did was drive additional ground rods at our transmission towers. We measured earth resistance after each activity and make sure our earth resistances don't exceed 25 ohms. Also, we found out those copper conductors we used were like...
  16. Parchie

    What happens when two sources are paralleled into one bus and the 15kV voltages are off by 400V ?

    @bdn, Don't overthink it. There will always be slight differences in voltages. Just let the synchronizer do the job. You won't get synchronized if the differences are too big for the control equipment.
  17. Parchie

    transition starter from star to delta

    @che, The only way you can be sure the motor is very near it's rated speed is to do a motor acceleration time simulation. There are softwares that offer to do those. But you can calculate yourself using the well-extablished motor equations.
  18. Parchie

    transition starter from star to delta

    We did have lots of damaged contactors that were traced to wrong setup of transition timing. The worst situation was when the arc chutes themselves helped in the destruction, the chutes accumulated previous debris, the contact arc sustained when switching happened.
  19. Parchie

    transition starter from star to delta

    @cr, Please take note of the use of the word "like". That means, it is not the thing, it is just "like" in plain English.
  20. Parchie

    6.9 kV or 13.8 kV to feed big synchronous motors?

    As an example, we have a 2.6 MW ball mill that is supplied with 13.8 kV from our on-site generator. The difference I think is ours is a WRIM, not synchronous motors. The motor is also controlled using liquid resistor on starting.

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