[Sneap] GVM needed for General IonX Tandetron

[Nicholas Pastore]

Howard,

 If your GVM is near the top of your tank, you might consider equalizing the
pressure of the SF6 and capping the flange after removing the GVM.  Since
SF6 is a heavy gas it should remain in the tank.  This will save you from
losing any by doing a full pump-out and backfill.  We did this recently when
we removed our GVM and it saved us from having to buy extra gas.
Hope I'm not too late.
Nick

______________________
Nicholas Pastore
Operations Manager
Louisiana Accelerator Center
UL Lafayette
______________________


Message: 2
Date: Thu, 17 Jan 2008 13:54:11 -0500
From: "Howard Evans" <hevans at ues.com>
Subject: Re: [Sneap] GVM needed for General IonX Tandetron
To: "Symposium of Northeastern Accelerator Personnel"
	<sneap at tunl.duke.edu>
Message-ID:
	<B84AFF61D8923049985797D281D4E81702F008 at uesserver1.ues.com>
Content-Type: text/plain; charset="iso-8859-1"

Klaus,
 
Indeed, it did help. I was just about to recover the SF6 from the tank
without first checking the obvious things you mentioned. Except for
mechanically checking the bearing, all of the things you mentioned can be
electrically tested on the air side of the motor without opening the tank.
 
The phase-shifting capacitor is the most logical component to fail. On large
split-phase motors delivering significant power to a rotating load, this
capacitor will have a lot of current and high voltage stress. This is known
to cause overheating and subsequent dielectric failure if the capacitor
isn't properly sized and rated for this type of motor service. Fortunately,
for the GVM application, there is only a small "windage" load so the
capacitor is only lightly stressed. Alas, it measures 4.27 microfarads using
my BK Precision Model 5360 DVM and has no measurable DC leakage resistance
using the same meter. So, I conclude the capacitor is probably still in good
condition.
 
The motor windings are another story. This motor has four wires coming
through the bulkhead fitting. One of these is a "shield" that is connected
to one of the four mounting screws securing a 4-pin Amphenol circular
MIL-style bulkhead connector. This connector brings in two of the three
phases plus neutral to power the motor and the electronics in the GVM. Two
of the other three motor wires connect across phase A and phase B of the
three-phase 208/120 VAC wye feed from the Tandetron. The third motor wire
connects to one side of the phase-shifting capacitor, and the other side of
the capacitor connects to phase A. One would expect to measure motor winding
resistance between any two of these three wires, but each wire indicates an
open circuit to the other two. One wire, connected to phase A, measures
about eighty ohms resistance to ground. So, not only are the windings open,
one of them has shorted to the case. The outer shell of the GVM gets quite
warm when the AC power conne
 
 ctor is plugged in. I don't recall it ever heating up during normal
operation, but my memory could be faulty.
 
Well, on with the task of removing as much SF6 as I can using the liquid
nitrogen sublimation process... 
 
Thanks to everyone who has offered help so far. I sure hope I find a Rotron
motor inside that has a modern replacement!
 
Howard