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**Fermilab**

March 3, 2003

**To:** Nancy Grossman, Burce Baller

**From:** George Krafczyk, Dan Wolff, Steve Hays

**Subject:** Pulsed Power loading at MI_60N, MI_62 and MI_65

As we talked Wednesday, EE Support has finished going over the NuMI
magnet loads with a look at transformer loading at NuMI Service
Buildings MI_60N, MI_62 and MI_65. The loads that are located in each
building are generally ramped from some low value of holding current up
to the required current for NuMI beam extraction. In sizing the
transformers for these ramped loads, EE Support's experience suggests
that the proper rating is very near ½ the way between the RMS
transformer load and the peak transformer load. This is a compromise
solution that allows for a smaller kVA rated transformer in pulsed
situations. Another solution would be to size the transformer for the
peak power of the load and thus get a transformer that is rated for the
forces involved with the peak load and an overkill for the RMS heating
of the load. EE Support requires (by our pulsed power transformer
specification) cylindrical copper windings and thus when the windings
are subject to cyclical loads the windings are under hoop stress and
better able to handle fatigue. With the above argument in mind, I will
be quoting three numbers at each building to represent the transformer
rating. (RMS kVA / Peak kVA / Transformer kVA Rating) The results of our
investigation are as follows.

# MI_60N

5 Bend circuits (E:LAM60, E:LAM61, E:V100, E:HV101 and E:H104) and 6
quadrupole circuits (E:Q101, E:Q102, E:Q103, E:Q104, E:Q105 and E:Q106)
are located at this service building. Four of the bend supplies are
ramped and E:V100 plus all of the quad supplies are DC. The ramped
supplies are PEI/500kW and all others are PEI/20kW units run in DC. The
ramps used for all calculations have a period of 1.867 seconds and a
flattop of 0.1 seconds. (Changing the flattop value to as little as 0
seconds is only a 10% decrease in RMS current and thus a 5% decrease in
transformer rating.) All supplies at MI_60N are planned to be powered
from the 1.5MVA transformer installed on the 95/96-beamline feeder.

**The load on the MI_60N transformer is 1,288kVA/2,324kVA/1,806kVA**

**EE Support sees this as a problem that could be solved in one of
several ways. 1) A second 1.5MVA transformer could be purchased and
installed splitting the load between the two transformers. 2) The
existing 1.5MVA could be de-installed and added to the spares inventory
and a 2MVA transformer could be purchased under our pulsed power
transformer specification. The transformer would have to have a foot
print that allows it to be installed on the existing pad. 3) Part of the
MI_60N load could be moved to the MI_62 service building.**

**While solution #1 gives the best possibility for expansion in the
future, solution #2 may be the most cost effective for NuMI especially
if NuMI could get reimbursed for the spare added to inventory.**

# MI_62

6 Quadrupole circuits (E:Q107, E:Q108, E:Q109, E:Q110, E:Q111 and
E:Q112) are installed on the 1.5MVA transformer off the 95/96-beamline
feeder at this building. Each circuit is powered by a single PEI/20kW
power supply and all supplies together represents approximately 68kVA
additional loading for the transformer. Since the PEI 20kW supplies will
not be ramped this will be the RMS/Peak/transformer rating used.
Remember that the Main Injector installed this transformer for A1 line
transfers. The NuMI load at this location represents a very small
increase in transformer loading.

Also located at this building is the E:V108 magnet power supply. Some
time ago this supply was upgraded from 4 PEI/500kW supplies in series
(which would have taken power from this 1.5MVA transformer) to a single
MR style power supply which gets its primary power directly from the
13.8kV feeder. Although this string represents an additional load to the
95/96-beamline feeder no power is used from the 1.5MVA transformer.

**The added rating for the MI_62 transformer is 68kVA/68kVA/68kVA**

**The added load to the 95/96-feeder at MI_62 is
965kVA/1,753kVA/1,359kVA**

**EE Support sees NO problem with the MI_62 Pulsed Power Transformer.**

# MI_65

2 Bend circuits (E:H117 and E:V118), 9 quads (E:Q113, E:Q114, E:Q115,
E:Q116, E:Q117, E:Q118, E:Q119, E:Q120 and E:Q121) and the Horn Power
Supply are located at MI_65. All of these supplies are planed to be
installed on the 1.5MVA transformer off the 95/96-beamline feeder at
this building. The bend load (E:V118) is powered by 3 -- PEI/500kW
supplies. The Horn load is powered by 2 -- PEI/240kW supplies. And
finally all other loads (1 bend and 9 quads) are powered by PEI/20kW
supplies.

**The load on the MI_65 transformer is 1,403kVA/2,191kVA/1,797kVA**

**EE Support sees this as a problem that could be solved in a couple
ways. 1) A second 1.5MVA transformer could be purchased and installed
splitting the load between the two transformers. 2) The existing 1.5MVA
could be de-installed and added to the spares inventory and a 2MVA
transformer could be purchased under our pulsed power transformer
specification. The transformer would have to have a footprint that
allows it to be installed on the existing pad.**

**In this case solution #1 would be our preferred solution since we have
been shown expansion plans at the target area that would increase the
power to 3MVA.**

If 2MVA transformers are in NuMI's future, perhaps a 1.5MVA spare could
be used for the 6 months needed to replace a failed unit in the future.
Of course the footprint would have to fit.

My guess is that a 1.5MVA and adding a 500kVA transformer (built to the
pulsed power specification) with its pad, duct bank, etc. would be a
larger cost than a single 2MVA transformer.