Re: Kicker overcurrent

[Brendan Kiburg <kiburg@npl.uiuc.edu>]

Dear Mike,
  We double checked the connections and polarity and have found the
following:
1) The NEG1 signal is connected to optical fiber that goes to the HV1-down
cabinet.
2) The HV1 cabinet has negative polarity and HV2 has positive polarity.
3) We wish to clarify the exact nature of the overcurrent that occurred
last night.
   a) We began turning up HV1 and HV2 at the same time
   b) There was no current drawn on either supply unit until HV1 reached
about 2 kV.
   c) Then HV1 current regulated and the display read -0.4 kV and 112 mA.
   d) We ramped down the voltage to 0.
   e) We tried ramping up but immediately saw an increasing current (as
opposed to earlier, when there was no current until the breakdown.
   f) We turned off the HV supplies, the MV1 supply as well as all of the
fans.
   g) We inspected inside cabinet HV1 and cleaned with compressed air (all
cards).
   h) We turned on the fans, MV1 and tried to ramp again.
   i) At first there was no current drawn and we reached 2 kV.  Suddenly
the current regulation light came on and the display read -0.4 kV and 112
mA, as in step b.

4) With respect to the operating conditions last night,
   a) HV1 and MV1 were on negative polarity
   b) The frequency of the kick signal was quite low (<1 Hz) coming from
our entrance counter, which was not seeing the beam as we were in the
area.
   c) The duration of the pulse was 26 microseconds, as determined by the
muon on request logic documented by Peter.
   d) We then inserted a fixed frequency pulser (between steps 3g and
3h) that had been used in previous tests with Francoise.  This pulser had
a kick of 5 microseconds with a 1 kHZ rate.

We will now go and inspect the kicker cabinet and connections for
potential short circuits.  Please let us know if we can give more
information concerning last evening.

Regards,
  Peter and Brendan


On Tue, 29 Nov 2005, Michael Barnes wrote:

> Dear Peter,
> 
> Further to my email of earlier today, I have had a chance to further 
> think about the problem. I am now fairly well convinced that item "2" 
> and item "3" in my earlier email canNOT result in what you are seeing. 
> For example, for my item 3 a false signal back from the overcurrent 
> protection would result in the appropriate LED on the TTL splitter being 
> lit and the appropriate (pull-up or pull-down) stack would be turned 
> continuously: however this cannot result in the HV power supply seeing 
> an overcurrent unless there is a short circuit, e.g. on the output of 
> the stacks. A similar argument applies to my item "2", a faulty 
> interlock can trip the system and cause either the pull-up or pull-down 
> stack to be turned on; however, again, this cannot result in the HV 
> power supply seeing an overcurrent unless there is a short, e.g. on the 
> output of the stacks
> Hence I am sure that there must be a breakdown problem  (or short 
> circuit) associated with HV1 cabinet (e.g. deflector plates, feed-thru, 
> output of stacks ....).
> When you tried starting up the kicker last night, at voltages of say 1kV 
> on both HV power supplies were the currents drawn from the 2 HV supplies 
> more or less identical or was HV1 higher current than HV2?t. What were 
> the operating conditions (polarity of HV1 & MV1, approximate frequency 
> and pulse duration).
> 
> Cheers,
> Mike
> 
> >Dear Peter,
> >
> >There sounds as thought there is a problem with an electrical breakdown in
> >one of the NEG cabinets: the 'NEG 1' LED identifies an over current fault.
> >However I cannot recall which cabinet 'NEG 1' is (i.e. HV1 or MV1,
> >although I think it is probably HV1) -- it depends on how the fiber optic
> >cables have been connected back to the TRIUMF splitter box. NEG indicates
> >the bottom stack in the cabinet. What polarity is HV1 supply (negative I
> >assume)?.
> >
> >2kV is probably the lowest voltage that the over current circuit can
> >indicate a fault (approx. 8A of current = 2kV/((19R*9)+17R)). But this
> >fault current must be flowing to ground through only the one stack.
> >
> >I agree with Gary that this cannot be caused by a problem with a single
> >card. Instead there is either:
> >1) a conductor (e.g. wire or grounding rod) or a real fault/breakdown near
> >the output to the deflector plates;
> >2) a problem with an interlock (which, depending on the interlock, would
> >cause the controls to switch on all the cards to short the stacks to
> >ground) -- but I doubt this as the fault current must be flowing though
> >only one stack for the fault to be indicated at only 2kV;
> >3) A problem with the fiber optic signal from the over current circuit in
> >the lower stack.
> >
> >I will have to give some thought to the best way of diagnosing this -- so
> >I will email you again later. In the meantime please let me know the
> >polarity of HV1 and have a look for any obvious clearance problems.
> >
> >Good luck,
> >Mike
> >
> 
> 
> Winter Peter wrote:
> 
> > Dear Mike,
> >
> > this evening we were trying to start the kicker again after it wasn 
> > running on HV the last days. While trying to ramp the HV up, we had a 
> > current regulation on the HV1 side. We could go up until 2kV and then 
> > suddenly the current went to 112mA and the voltage dropped to 0.41kV. 
> > There was a red LED on the small black box at the 'NEG 1'. We reset 
> > the kicker and went up with the HV on the HV2 side without problems. 
> > Then we tried slowly to ramp the HV1 side again and at 1.4kV we could 
> > see the red LEDs being on. The current was ~75mA and therefore still 
> > below 112mA but higher than usual. We then noticed that on the lower 
> > stack of the cards in HV1 the card DOWN-13 didn show a red LED.
> >
> > With the online help of Francoise we took out this card and checked 
> > the resistance. It showed 1.6MOhm in one direction (similar to one of 
> > the spare cards). Then we put it back and bypassed the door interlock 
> > in order to measure the voltage on the resistor C13. That measurement 
> > gave 15.1 V while the two neighbouring cards had 14.9 and 15.06 V for 
> > this resistor. According to what I learned from Francoise, this card 
> > might not be a problem.
> >
> > Now we don want to switch on this half of the kicker before we have 
> > some advice what to do next. Do you have any suggestions / ideas for 
> > the high current? In principle we could exchange the card with a spare 
> > one and test the kicker again but we rather wait for your answer.
> >
> > Looking forward for any suggestions,
> > best greetings
> > Peter
> >
>