NuMI Horn Test Power Supply Safety Analysis Report

Ken Bourkland

June 5, 2000

**Purpose:** A power supply system has been built for the purpose of
pulsing the prototype NuMI focusing horns. Various field, temperature,
vibration, and life tests will be carried out on the horns using this
equipment. When construction of the operational power supply is
completed, it will replace this unit. The charging source and capacitor
bank, working together, can produce the pulse train as shown in
Figure 1. Continuous operation with a rep-rate of 1 Hz, or less, can be
achieved.

![](media/image1.wmf){width="2.9583333333333335in"
height="1.104861111111111in"}

Figure 1. Output waveform from capacitor bank

The circuit contains a capacitor bank of 80 mF, total, that is charged
by a 240kW PEI power supply configured to provide up to 800 volts. The
capacitor bank is divided into four independent sections. Each section
is isolated from the others and the charging source by diodes, and from
each other and the load by SCRs. A schematic of the equipment is shown
in Figure 2.

![](media/image2.wmf){width="4.531944444444444in"
height="2.4277777777777776in"}

Figure 2. Schematic of PEI charging supply and capacitor bank

**Equipment:** The equipment is installed in the south end of the MI-8
service building. The capacitor bank is constructed within a heavy-duty
enclosure equipped with multiple doors, each secured with latches and
key locks. The PEI is a standard unit but modified to include later
model regulation electronics and a lock on its rear doors. The capacitor
bank is switched with eight parallel SCRs and will be connected to the
horn load via an eight layer, four conductor pair, stripline. A
floorplan of the equipment configuration is shown in Figure 3.

![](media/image3.wmf){width="4.531944444444444in"
height="3.573611111111111in"}

Figure 3. Layout of equipment in the MI-8 service building.

**Hazards:** Certain hazards inherent with high voltage, high current,
and capacitive energy storage exist within this circuit. A list of each
hazard and the mitigation steps for that hazard is as follows.

• [Voltage:]{.underline} The PEI power supply used to charge the
capacitor bank is connected internally to provide up to 800 volts at 300
Amps and will be operated to its full output voltage during horn
testing. The PEI enclosure is fitted with door interlock switches on its
rear doors. This interlock will interrupt operation of the supply if the
door is opened. The rear doors will be locked during operation.

The PEI front doors are locked by the front panel disconnect switch when
it is in the ON position. Shielding panels within the PEI will guard the
120 Vac power and 480 Vac power connections against accidental personal
contact when the front door is open. Additional panels will prevent
access to any electrical bus connected to the capacitor bank load.

The PEI is isolated from the capacitor banks by diodes to prevent any
energy stored in the capacitors from back-feeding into the PEI should
there be a fault internal to the PEI.

The capacitor banks are located in an enclosure separate from the PEI
charging source. All of the doors of the capacitor bank enclosure are
fitted with interlock switches. These switches are connected into the
PEI interlock chain to turn off the charging supply upon entry.

Two high voltage, high current, shorting (Ross) relays with independent
discharge resistors are series connected across each of the capacitor
banks for discharging the capacitors upon turn-off of the charging
supply. The relays close the resistors across the capacitor banks while
in the de-energized state. The dual shorting scheme provides redundancy
for additional electrical safety. The shorting relays are mounted such
that gravity assist is accommodated for fail-safe operation, removing
dependence upon springs for contact closure. Auxiliary contacts on the
shorting relays are connected into the PEI interlock chain to maintain
the charging source in by-pass mode unless both shorting relays are
energized.

• [Current:]{.underline} Each capacitor bank is designed to provide up
to 50kA~Peak~ output into a common horn load via a parallel plate
stripline, providing a total of up to 200kA~Peak~ output current. Each
capacitor bank is configured with copper bus of 1/4\" x 4\" dimension,
equal to 1 in^2^ in cross-section. During 1/2 Hz operation, bus current
will be 725 A~RMS~. At 1 Hz operation, bus current will be 1000 A~RMS~.
2Hz operation, 1414 A~RMS,~ may be possible with additional cooling.

The stripline external to the capacitor bank enclosure will be
constructed with 3/8\" x 12\" aluminum, 6101-T6, electrical bus material
and can operate at 7250 A~RMS~ continuously.

Any access to high current connections requires LOTO procedures to be
followed so that no hazard exists.

• [Stored energy:]{.underline} Each capacitor bank cell, 0.02 Farads,
will store 6.4 kJ when operating at 800 volts. Each diode providing
capacitor cell isolation from the PEI cell is rated for 2.4 kV~PIV~ and
450 A~IF(AV)~. The Eupec SCRs switching the output are rated for 2 kV
VDRM and VRRM. Six different makes/values of capacitors are used in the
circuit and are rated 1.35 kV, 1.5 kV, 2 kV, 2.5, and 5 kV. Case
construction is of a style nominally rated for 20 kJ containment. A
resistive ground stick is provided to discharge the four capacitor
groups. A hard ground stick is also provided for maintaining a ground
while the permanently anchored grounding clip leads can be secured.

• [Induced voltage on Equipment During Faults to Ground]{.underline}:
The PEI enclosure, the capacitor bank enclosure, and the single point
ground bus within the capacitor enclosure are all bonded to the MI-8
building ground system grid via 500 mcm bare copper conductor. All
ground conductors are sized to handle any fault current that may occur.

• [Acoustic:]{.underline} It is not anticipated that the sound levels
will be high enough to be hazardous to building occupants but sound
levels will be measured if so indicated.

• [Hazardous Materials:]{.underline} The capacitors are of six different
models by three different manufactures. They are:

General Electric;

900 uF - 1.35 kV~DC~

Impregnent - Castor Oil. Units labeled \"No PCBs\"

Maxwell Laboratories;

240 uF - 5 kV~DC~

400 uF - 5 kV~DC~

1200 uF - 2 kV~DC~

Impregnent - Castor Oil for all of the above

Westinghouse;

480 uF - 2.5 kV~DC~

1600 uF - 1.5 kV~DC~

> Impregnent - WEMCOL - the Westinghouse capacitors are labeled that

they do not contain PCBs.

MSDSs are on hand for these materials.

No other known hazardous materials exist within the equipment.

The enclosure design is such that it will contain any oil spill or
leakage.

**LOTO:** Due to there being two sources of energy for the PEI, and the
potential for stored energy in the capacitors, a written LOTO procedure
will be necessary. The LOTO procedure describes the steps to safely lock
out energy sources and discharge stored energy.

480 V~AC~ power for the PEI is supplied via a dedicated circuit breaker
in power panel DHP-MI8-1, breaker #17. It is located in the southeast
corner of MI-8.

The circuit breaker for the 120 V~AC~ control power in the PEI is
located in power panel PP-MI8-1A-5-A1, breaker #5.

The circuit breaker for the 120 V~AC~ power for the capacitor bank
enclosure is located in power panel PP-MI8-1A-5-A1, Circuit Breaker #3.
However, all 120 V power in the capacitor bank enclosure is guarded by
utility boxes and guards over terminal strips.

All breakers are fitted with a locking device for LOTO locks.

**Warning Device:** A flashing red warning light is installed on the top
of the capacitor bank enclosure, on the end nearest the horn load. It
will operate at any and all times the PEI charging supply is in the \"DC
ON\" mode.