Office Memorandum: RPC Tech Note 4

SLAC, Power Conversion Department

March 20, 2001


To: Steve St Lorant MS 20

From: Martin Berndt MS 49

Subject: Power for 70D43 Using Existing Supplies



The following is information relevant to the problem of providing power to the old LASS Dipole type 70D43 magnet that will be moved to ESA.


1.- Magnet data as culled from Slim Harris’ (RIP) handy little handbook:

Magnet width 70 inches

Magnet aperture 43 inches

Coil material Aluminum

Winding style Two sets of coils in parallel

Resistance of coil assembly 0.0813 Ohms, at 50^C outlet water temperature

Maximum current/voltage/power 6000 Amperes / 488 Volts / 2.93 MW

Water at maximum power 410 gpm

Temperature rise at max power 27^C



2.- Cable resistance from Building 108 to ESA. Using two existing water cooled cable runs, plus some short dry cable jumpers:

Cabling 1 to 2 milliohm.

This gives a total circuit resistance (magnet plus cable) of about 0.083 Ohms.



3.- Nominal capability of the PB202 and PB203 power supplies in Building 108 (generally called the 1.59MW supplies):

PB202 & PB202 supplies 3000 Amperes / 580 VDC / 1.75 MW each

Two supplies can be operated in parallel. Operation in series not recommended because of insulation voltage limits.



4.- Nominal power capability of the other 6 large supplies in Building 108 (generally called the 567KW supplies):

Six large supplies 2700 Amperes / 240 VDC / 650 KW each

Two of these supplies may be operated in series or in parallel.


1.- The 2 large supplies (PB202 and PB203) may be operated in parallel and should have no trouble delivering at least 5500Amperes total to the 70D43 magnet.

PB202 & PB203 in parallel into 70D43 5500 Amperes / 456 VDC / 2.50 MW


2.- Paralleling should be done at the magnet, using two existing water cooled cable runs between ESA and Building 108.


3.- If 410 gpm of LCW exceeds the water supply capabilities at ESA, a reduction in cooling water requirements could be allowed, if accompanied by proportionally reduced power

Current Magnet Power Cooling Water Requirement

6000 Amperes 2.93 MW 410 gpm

5000 Amperes 2.03 MW 285 gpm

4000 Amperes 1.30 MW 182 gpm


5.- There are some additional operational problems to look out for:

    1. Both power supplies must be operating in the constant current mode, i.e. current regulated, not voltage regulated, when in parallel.
    2. The current set point of the 2 supplies should be controlled individually, each one from its own DAC. The voltage of the two supplies will of course be about the same when in parallel, regardless of the current each one is carrying. It will be best to run both supplies up together so they share about equally, up to just under 3000 Amperes each. Raising the current in sequence, first in one supply, then in the other, should work also, but might result in some transient jumps in the DC current. The problem has to do with ripple current circulating between the output filter capacitors of the two supplies, causing the transductor to produce a false signal near zero DC current.
    3. The total magnet current will simply be the added value of the currents from each supply. This is simpler and less expensive than installing an additional transductor to read the total magnet current.
    4. It could be disastrous for the power supplies if the reversing switches were ever to be in opposite polarities with the supplies in parallel. Therefore it will be best to disable operation of the switches (or blocking the contacts) after initially determining that both supplies have the same polarity.
    5. Magnet interlocks have to turn off both supplies.
    6. It should not be necessary to cross-interlock the two supplies, though it would not hurt to do so. The overload and interlocks for each supply should be sufficient.
    7. It goes without saying that safety will require that both supplies be tuned off and secured whenever access is required to either power supply or to the magnet.





Distribution: Pete Segura MS 49

Tony Donaldson MS 49

John Beach MS 49

Dave Macnair MS 49

Steve Williams MS 75

Peter Bosted MS 44