Jump to content


Photo

Running Bypass For Variable Speed Drives


  • Please log in to reply
4 replies to this topic

#1 EPAMGR

EPAMGR

  • Members
  • Pip
  • 1 posts

Posted 30 July 2009 - 07:35 PM

Involved with using a bypass contactor to take over operation of a vertical turbine centrifugal pump from a drive at full speed. Problem is that, on random occasions, there is a significant 'bang' at the pump when transfer occurs. Suspect this is a result of drive output being significantly out-of-phase with utility. Have resolved control and drive issues, but not this problem!

#2 marke

marke

    Posting Freak

  • Moderator
  • PipPipPipPipPipPip
  • 2,604 posts
  • Gender:Male
  • Location:Christchurch, New Zealand

Posted 30 July 2009 - 07:50 PM

Hello EPAMGR

Welcome to the forum.

Yes, almost definitely, the problem is due to the "auto reclose" effect where you have a motor operating at speed and then disconnect the motor and then reconnect a very short time later.
While the motor is being driven, there is a rotating magnetic field induced in the rotor. When the motor is disconnected, the rotating magnetic field generates a voltage in the stator. When you reclose, you must be in phase with the generated voltage or you will have a very high current and torque transient.
Some drives will synchronise to the supply allowing shunt switching.
You could try connecting to the supply via resistors before the drive is disconnected. This would mean that the motor is never open circuited and should reduce the transients. The resistors would need to be high power rated and sized so that the current from the supply is in the order of 50% motor rated when the drive and supply are 180 degrees out of phase.
Sequence would be 1) drive running on motor, 2) drive running on motor and supply via resistors, 3) drive running on supply via resistors, 4) drive running on supply.
The switching sequence would be reasonably quick to prevent the motor slowing and would essentially be similar to the closed transition star delta starter.
The current through the resistors needs to be significant to resynchronise the flux during the period (3) where the motor is disconnected from the supply and drive.

Best regards,
Mark.

#3 agentyym

agentyym

  • Members
  • Pip
  • 1 posts

Posted 12 March 2010 - 08:18 AM

Hello Marke, I was trying to run a fan 215HP using Inverter-bypass also, but it failed as the MCCB 400A tripped everytime when bypass contactor closed. The time for switching from isolate contactor to bypass contactor is about 1 sec. Do you think I need to try to set the time to below 1 sec??

And for your comment and suggestion above, I am not quiet understand because I am a beginner in this field. Thus, could you sketch a diagram for me? very much appreciated. Thank you.

#4 jOmega

jOmega

    Senior Member

  • Full Member
  • PipPipPipPipPip
  • 254 posts
  • Gender:Male
  • Location:Midwest, USA

Posted 12 March 2010 - 05:48 PM

QUOTE (marke @ Jul 30 2009, 01:50 PM) <{POST_SNAPBACK}>
Hello EPAMGR

Welcome to the forum.

Yes, almost definitely, the problem is due to the "auto reclose" effect where you have a motor operating at speed and then disconnect the motor and then reconnect a very short time later.
While the motor is being driven, there is a rotating magnetic field induced in the rotor. When the motor is disconnected, the rotating magnetic field generates a voltage in the stator. When you reclose, you must be in phase with the generated voltage or you will have a very high current and torque transient.
Some drives will synchronise to the supply allowing shunt switching.
You could try connecting to the supply via resistors before the drive is disconnected. This would mean that the motor is never open circuited and should reduce the transients. The resistors would need to be high power rated and sized so that the current from the supply is in the order of 50% motor rated when the drive and supply are 180 degrees out of phase.
Sequence would be 1) drive running on motor, 2) drive running on motor and supply via resistors, 3) drive running on supply via resistors, 4) drive running on supply.
The switching sequence would be reasonably quick to prevent the motor slowing and would essentially be similar to the closed transition star delta starter.
The current through the resistors needs to be significant to resynchronise the flux during the period (3) where the motor is disconnected from the supply and drive.

Best regards,
Mark.



Hi MarkE,

Curious: Your proposed solution— is it Conceptual or have you experienced it being successful first hand ?

Kind regards


#5 yuri

yuri

    Member

  • Full Member
  • PipPipPipPip
  • 93 posts

Posted 13 March 2010 - 03:48 PM

I expect also a "bang" in the Mark's second stage (if I got the sequence right 1/ motor supplied from inverter 2/ motor supplied from the inverter plus is connected to the supply via resistors 3/ motor only connected to the supply via resistors 4/ motor connected directly to the supply). Better omit the second stage.

But if as he write "some drives will synchronise to the supply allowing shunt switching" I would not risk experimenting and insisted on procuring such a drive.




0 user(s) are reading this topic

0 members, 0 guests, 0 anonymous users