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  1. jraef

    Currant imbalance submersible pump

    Differing amounts of cable capacitance due to the uneven arrangement of the flat cables. I'm going to guess the "blue" phase is the center wire on the flat cable.
  2. jraef

    VFD increasing the motor winding temperature

    Harmonics on the output of a VFD is generally not corrected by the VFD, so it absolutely increases the motor temperature. This is why, on NEMA based inverter duty motors, you often see a Service Factor of 1.15, but a note saying that the SF is 1.0 if run on an inverter. The inverter output...
  3. jraef

    VFD(VSD) on sluice gates

    There is a special “voltage doubler” circuit added to the front end of the drive that boosts the DC from 165VDC to 330VDC. So as far as the inverter portion does, it’s no different. The voltage doubler is typically limited to about 1-1/2HP max, but only because after that, it becomes...
  4. jraef

    VFD(VSD) on sluice gates

    Also, simple reversing, which is more complex with single phase motors. With a VFD on a 3 phase motor, you just give it a reverse command, no contactors involved. With Sensorless Vector Control, which is standard on most VFDs now, you can get full torque at the outset, you no longer need to use...
  5. jraef

    120/240V 1P-3W, 100A Service to Very Remote Building

    I don’t understand the objection by the electrician to the step-up transformer… Is someone thinking of using only 2 legs of a 3 phase 240 to 600V transformer? Because I can see that possibly being a problem, but just use a single phase transformer and it’s not a problem at all.
  6. jraef

    IP65 PROTECTION CLASS FOR NON ELECTRICAL EQUIPMENT

    Since it is fully pneumatic, it implies you have air available. If you want to continue on with this silliness, you could put the valve into an IP65 enclosure, then use the air feed to provide a “purged air system” for the enclosure, which keeps a positive air pressure on the enclosure when the...
  7. jraef

    Pump Automation

    These are contracting statements. The term “self priming” means it does NOT need to have a priming case filled in advance if starting. You do not have a self priming pump, which is a poor choice for a sump pump. The easiest solution is it INSTALL an actual self priming sump pump. Ah, after...
  8. jraef

    Star delta

    That would be pointless with a VFD. The Star current would be less, but the torque would be severely limited. The VFD can achieve the same reduction in current without losing torque. So the Star-Delta would be pointless in that regard. If the S-D is still connected and active (meaning not just...
  9. jraef

    Excitation current on induction motor as a generator via VFD

    At this point they are not connecting to the grid, and I have warned them that using VFDs will not allow that because no VFDs I know of have UL-1741 listing, which is necessary to get a NEM contract with a utility. Thanks everyone for the info and help.
  10. jraef

    Excitation current on induction motor as a generator via VFD

    Hey fellow drive gurus, I have one that I have never come across before. I have a client wanting to use an 40HP (30kW) 460V induction motor on a water turbine pump and have the water overhaul it to turn it into an induction generator. So far so good, I’ve done that before. But the new twist is...
  11. jraef

    What is a Package Starter (PS)?

    It is an uninformed mechanical engineer’s term for a combination starter, ie one that comes in a box with a breaker, control switches and lights. As in “all in one package”. I’ve run across this before, it’s an HVAC thing.
  12. jraef

    Auxiliary Motor Speed Impact on Transient Undervoltage?

    I’m not sure about the torque increase part being 200%. The REASON the slip will increase is because there is already a LOSS of torque with the voltage sag, close to directly proportional to the magnitude of the voltage sag when the motor is already running (it’s worse if the motor has to start...
  13. jraef

    Starting and load sharing between VFD and soft-starter

    The way load sharing is usually done with two VFDs is to make one of them a speed follower, the the second drive is set as a torque follower to the first drive. In your case you have no control of the one on the soft starter so there will be no speed control, only torque control on the one that...
  14. jraef

    How to use the Variac

    With the clear plastic covers allowing you to see the wiring inside, I would suspect this was from a classroom somewhere.
  15. jraef

    open delta 3 phase voltages - 2 single phase transformers

    That looks to be a transformer configured for an open delta 240/120 3 phase 4 wire “high leg” system, where one pot is center tapped to provide 120/240 single phase for lights and outlets, then the other pot is straight 240, with the open delta providing 240V 3 phase for motors. Generally in...
  16. jraef

    1000volt deep well motors

    A bespoke VFD “modified” to handle 1000V would be a nightmare in terms of spares, replacements and repairs. Low voltage drives stop at 690V, 1000V is considered medium voltage (for drives), ehere designs typically start at 2300V. So to handle 1000V, there would have to be a custom design of a...
  17. jraef

    Single VFD running two motors - One motor temperature much hotter.

    Also better ability for the motor to cool itself at lower speeds. As to the V/Hz issue, yes, in V/Hz mode the drive is NOT doing all the stuff I said above. My assumption was that if someone was doing an ID Run, it was because they were using vector control of some sort, and that just isn’t...
  18. jraef

    Single VFD running two motors - One motor temperature much hotter.

    A drive, running ONE MOTOR in any type of vector control mode, is watching the performance of the motor and adjusting the PWM pattern going to it in order to correct any “error” between what it is being told to run the motor at, and what the sensors tell it the motor is doing. What it is...
  19. jraef

    1957 115v motor draws massive current

    Most likely degraded insulation and shorted turns. A bad cap generally means it doesn’t start turning, it will just sit there and vibrate back and forth until something trips. Shorted windings, especially turn-to-turn, means less impedance and thereby higher current. If you have a Megger, you...
  20. jraef

    Low Frequency (1 Hz to 60 Hz) ammeters, voltmeters and CT's - Any suppliers / OEM's?

    CTs, you probably can’t use, but you can get transducers that use Rogowski Coils as the sensing elements that will work at low frequencies. They work down to <1Hz and up to I think 400 Hz. Voltage measurements at low frequencies like 1Hz is an entirely different situation. I have never seen any...

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