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  1. Drivesrock

    Large Generator Exciter Air gap

    Thanks everyone for the replies so far. The AVR is a 20Amp nominal unit, with thyristor rectifier for a brushless generator. The operating power is from a PMG. The unit that was seen to have the internal flashover was opened and had a thyristor snubber resistor (R-C circuit) with a small burn...
  2. Drivesrock

    Large Generator Exciter Air gap

    Hi guys, thanks for the replies. With regards to the AVR: The generator can run in parallel and the loads are very constant. It behaves ok with the VAr loadsharing voltage raise/lower pulses for many hours. BUT, when a large load is started - like a 4.5MW compressor motor - the AVR fails. I...
  3. Drivesrock

    Large Generator Exciter Air gap

    Hi all. Has anyone had any (bad) experiences with an irregular exciter air gap of a synchronous generator? Generator in question: 31.2MVA/25MW, 13.8kV, 60Hz; Brushless Exciter 76V, 9.8Amps. The exciter air gap was measured by the original manufacturer and was 4.3mm, 2.7mm, 0.95mm, 3.0mm at...
  4. Drivesrock

    Fuji Hirex 80 AVR Manual

    Hi Petronila. Thanks for the message. Alangstore say they only supply 'machinery', so no manuals unfortunately. Best Regards Drivesrock
  5. Drivesrock

    Fuji Hirex 80 AVR Manual

    Dear all, has anyone a manual for the Fuji Electric Hirex 80 AVR, (DC135V, 15A)? I have searched online to no avail so far. Thanks
  6. Drivesrock

    VFD for a 100 Amps, 1500 Hz application

    Hi Muthu. Danfoss-Vacon NXP drives with special firmware, they say, can reach 7500Hz. What do you need 1500Hz in this 3 phase inductor for? A special application? Remember that the voltage will not be sinusoidal - it's PWM and probably quite a low PWM frequency to obtain the 1500Hz...
  7. Drivesrock

    ESP/VFD Issues

    The generator voltage rising makes me think that the generator AVR may well be being affected by the VFD 6 pulse input current harmonics causing enough voltage distortion that the AVR is seeing for the voltage feedback. What is the AVR make and model? What is the rating of the generator? Where...
  8. Drivesrock

    Isochronous load sharing lines for generators in parallel (Island system)

    Also note that if there are any main bus interconnectors/bus-ties (and also ring connection) that separate (reconfigure) the online generators, the status of these must be connected to the controllers or droop CT / cross compensation circuit so that only the parallel generator sets kW and VAr...
  9. Drivesrock

    95i Inrush Blocking Function - Symap Protection Relay

    Feedback Thanks for your comments wcaseyharman The Fluke PQM read only some maximum 0.5% 2nd harmonic but the relay records from 5% to 8% when it fills the event log. 5% being the threshold setting to start the 95i blocking function - which is used only in the 87 Differential protection...
  10. Drivesrock

    95i Inrush Blocking Function - Symap Protection Relay

    Hi all. A Dynamic Postioning drilling rig I'm on has 5 x 5.1 MVA generators per 11kV bus (2) and bus-tie open. Mostly, only two generators run in parallel at a time per bus. This is minumum requirement. The generators have the Symap BCG Protection relays and 95 i Inrush Blocking Relay function...
  11. Drivesrock

    dv/dt filters or sinus filters for motor with cable length of 60 meters/200 ft?

    Hi Muthu I've seen these faults before with this type of motor where the cooling sea air is blown through the inside of the motor. Not Reliance motors though. The salt builds-up internally and the motors soon fail. These were the drawworks motors and mounted at drilling platform level and drew...
  12. Drivesrock

    Allen Bradley 1407CGCM showed up (CGCM fault) on HMI

    Hello newelecteng. Did you get anywhere with this? These AB CGCMs require connecting to with the Rockwell Studio 5000 S/W. Maybe that way you can find out what the fault alarm is? Let us know how you got on.
  13. Drivesrock

    VFD starting several motors

    Hi Petronila. Can you tell us what the failures of the motors have been - the reports by the repair shops? Also, what is the application? If there is not a synchronizing of the VFD output frequency and phase with the mains supply with paralleling of VFD output with the mains for a short time...
  14. Drivesrock

    Manual separate controls of V and F in VFD's

    Hi Muthu. The initial boost voltage stays on and may just slightly increase as the frequency increases but not at the same rate as would be the normal V/f ramp. So, at some frequency the boosted voltage will be at the same value as the normal V/f ramp voltage would be and then the normal curve...
  15. Drivesrock

    Manual separate controls of V and F in VFD's

    Hi Muthu. What you describe as higher V/Hz at start sounds like the voltage boost function at 0Hz that most (if not all) VFDs have to enable the motor to 'break away' or overcome the winding resistance effects (voltage drop) at this low frequency and low applied voltage. There is fixed boost...
  16. Drivesrock

    Will increasing the copper area of AC motor winding affect its VFD operation?

    Depending on the VFD there may be several types of control available - simple scalar to a flux vector control, (however the different manufacturers call theirs). Two or more motors in parallel with flux vector control is possible as long as the motors are 'the same'. Same rating motors may vary...
  17. Drivesrock

    Overvoltage during a VFD start

    With a true active front end drive there should be a large input inductor, of around 10% impedance (Z) and there may be a PWM filter in there too - parts of the "secret sauce". The active front end control must 'know' (be programmed with) the correct value of that inductor else the voltage...
  18. Drivesrock

    Unitrol M AVR - Extender card

    Hello to all. Can anyone point me in the direction of where I can get hold of the Unitrol M AVR pcb extender-card - site, part-number, other suggestion? I would make an extender-card so that I can hang a scope or multimeter lead off a component or test point and test some of the pcbs poking...
  19. Drivesrock

    VFD for Conical Rotor Motor

    Hi all. We have a customer with an overhead travelling crane with a conical rotor motor on the main hoist. This was a recente upgrade. The motor is DOL and when energised, the rotor aligns and opens the integral brake but the inrush current is causing voltage dips in his factory. Especially...
  20. Drivesrock

    Vibration spikes on 8.5 MW motor in start or during large load switching on same Bus

    Hi Yasit. The insulated stud looks like it has suffered heat damage - slightly loose connection? Incorrect torquing of the bolts? I have been investigating a vibration spike issue recently on a large gas compressor - electrical/power side - at start of one other equipment, every time. But in...

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