[SBE] Phasor current draw

[Mike Langner]

Hello folks !

The closure of momentary-powered changeover contactors is, in old plants
(old guy speaking) often controlled by latching switches.  The changeover
contactors are then powered until the contactor arm moves across the
contactor air space and operates the microswitch that indicates completed
movement of the armature.

This is good and bad.  It helps insure that the contactor armature doesn't
stop halfway across the movement area.

It also helps burn out the armature coil if the microswitch doesn't "make
up."

When I "re-did" an old 5 kW DA/N array, I put in a "homebrew" contactor
controller that applied power to each contactor for a couple of seconds, and
then if any individual contactor reported not being "seated," pulsed the
contactor 10 times before it gave up and stopped trying.

I also threw away the pile of burned-up armature coils I found on the shelf!

These old arrays are often very "creatively wired!"

Good luck !!

Mike Langner, CPBE
Albuquerque, NM

  -----Original Message-----
  From: sbe-bounces at sbe.org [mailto:sbe-bounces at sbe.org]On Behalf Of Edwin
Bukont
  Sent: Monday, July 13, 2009 3:18 PM
  To: sbe
  Subject: Re: [SBE] Phasor current draw


  Cris

  the bizzareness is that the Tx and DA modes are controlled by momentary
closures,,,but the DA/NDA is a rotary 4P latching switch.  Thus I figure I
need a latching relay that can handle the total current rather than a simple
actuator paralleled.

  The fun of old plants and no plans.

  Edwin Bukont CSRE, DRB, CBNT
  V- 240.417.2475; F- 240.368.1265








----------------------------------------------------------------------------
--
  From: crisa at crawfordbroadcasting.com
  To: sbe at sbe.org
  Date: Mon, 13 Jul 2009 14:29:39 -0600
  Subject: Re: [SBE] Phasor current draw


  Edwin:

  If those are the solenoid-type RF contactors, at 250 volts you can expect
about 6-7A current draw per switch nominal, but the inrush current may be
considerably more. So with five towers, it seems that a 30A relay would be
boderline.

  You should be able to jeep some 24V relays in there to control the phasor
remotely. Just hang the NO contacts of a 24V-coil relay across the actuator
lines for each mode.

  ______________________________
  Cris Alexander, CPBE, AMD, DRB
  Crawford Broadcasting Company
  Denver, Colorado
  (303) 433-0104
  (303) 433-0905 Fax
  Assoc. Member AFCCE



----------------------------------------------------------------------------
--
  From: sbe-bounces at sbe.org [mailto:sbe-bounces at sbe.org] On Behalf Of Edwin
Bukont
  Sent: Monday, July 13, 2009 2:06 PM
  To: sbe
  Subject: [SBE] Phasor current draw


  I am trying to create a DA/NDA remote control for a 3-tower phasor system.
The system has remote for choosing transmitters and Day or Nite. It does not
have remote for choosing DA/NDA.

  Currently, someone has brought out the Tx and D/N to 240VAC relays with
30A contacts.  Is this really necessary?

  The mode change itself appears to throw maybe 5 contactors including the
towers.  I realize that in the DA mode it has to support the current
involved with switching of Day and Night.

  I want to do my additional control with a 24VDC coil and contacts rated at
15A/250VAC.

  Am I missing something here.  Do I really need those big power relays or
will something smaller suffice.  I do not know what the current draw is,,and
it would be difficult to amp clamp.

  Anybody have any ideas what a 30-40 year old three tower, 3 modes Phasor
array might draw in Amps at 250VAC during switching?

  Thanks

  Edwin Bukont CSRE, DRB, CBNT
  V- 240.417.2475; F- 240.368.1265



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