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    Robert Gift's Avatar
    Robert Gift Posts: 100, Reputation: 3
    Junior Member
    		  
    #1

    Apr 16, 2010, 07:29 PM
    Can I slow speed-up of three-phase siren?
    My Federal Signal 2t22A air raid siren (now tornado siren) attains peak speed, 3,450 rpm, very quickly.
    10 hp, 208-240/480.
    It is running on 240 V. at a small sewage plant next to my fire station.
    At 5,300 feet and low humidity, I assume the air does not impose the load on the rotors that it would at lower elevations and higher humidity.

    If I mount the siren on the fire station roof and size the wire to produce a voltage drop to 200 Volts, would that safely slow the acceleration?
    Federal Signal states that within 10% of operating voltage is acceptable.

    Thank you.

    Robert
    KISS's Avatar
    KISS Posts: 12,510, Reputation: 839
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    #2

    Apr 16, 2010, 07:56 PM

    Why would you need to slow the acceleration?

    I seriously doubt that sizing the wire to 200 V would:
    a) be code compliant
    b) work effectively

    You can do it with a variable speed drive that has a custom ramp control. If it doesn't try a PLC to generate the ramp control. Be warned that you also may need a speed sensor.

    Another possibility is to use a soft-starter.
    Robert Gift's Avatar
    Robert Gift Posts: 100, Reputation: 3
    Junior Member
    		  
    #3

    Apr 16, 2010, 09:17 PM

    Thanks, KISS.
    The siren would be easier to notice with slightly slower speed-up.
    If I must supply wire, I might as well make it a less expensive smaller gauge AND supply 190 volts at the siren.
    Can't afford and would not want a VFD at my VFD.
    Would 190 Volts rather than 240 Volts cause a slightly slower acceleration?
    208 volt is design voltage +/- 10%= 188.
    KISS's Avatar
    KISS Posts: 12,510, Reputation: 839
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    #4

    Apr 16, 2010, 09:27 PM

    In an AC motor frequency really determines speed and not so much voltage. Lower voltage isn't good for the motor long term.

    A soft-starter would be the best solution. http://www.danfos.info/content/files...controller.pdf

    Older solutions basically added resistors in the line for a short time for start up. That's another way it can be done.
    Robert Gift's Avatar
    Robert Gift Posts: 100, Reputation: 3
    Junior Member
    		  
    #5

    Apr 16, 2010, 09:36 PM

    Yes, the 60 Hz determines final rpm, 3,600 - (minus) "slippage"? (What's the term?)
    I just want it to achieve its peak 3,450 rpm a little more slowly.
    On Youtube, I have heard other 2t22s and they were slower. But maybe they were single-phase. Someone also put my siren on Youtube.

    The 2t22A is actually two sirens on a dual-shaft motor.
    One rotor/stator has 10 ports (openings) and the other 12. At 3,450 rpm it produces musical pitches D5 and F5, a "pure" or "perfect" minor third which creates a B-flat2 Resultant.

    Standing near the siren holding my ears, I can feel my chest vibrate.
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